The Processes of Iron and Steel Making

This page has been constructed to give the reader a more in-depth insight into the processes carried out at the Wortley Forges, associated and similar works. You will find some descriptions are duplicated on other pages in this site.

Iron Mining

The Bloomery Iron Making Process

The Finery & Chafery Iron Making Process

Iron Making by Blast Furnace

The Puddling Process

Making Cementation Steel

Making Crucible Steel

Making Bessemer Steel

Making Steel by the Siemens Process

Magazine Article explaining iron making

Iron Mining

The availability of Iron Ore was the key to the early iron industry. Even today (and more conspicuously up to the 1970s) a number of steelworks sites were directly a results of a furnace and later a works built were iron ore was available, although some sites are a result of water power, transport, fuel and other economic pressures.

Iron is very common on the planet earth and the British Isles are no exception, however only where the iron content of the ore is quite high is the ore worth exploiting. This is one reason why almost all iron ore is now imported into the U.K. from the likes of Africa and Australia.

It seems that iron ore was mined in many areas across the country, but these area progressively reduced as the demand increase and larger scale operations became more common. The important iron mining areas were to the south of Cumbria (near Barrow in Furnace), South Teeside, North Lincolnshire and a band across the midlands from Lincolnshire to Oxfordshire.

Iron Ore, be worth working, must be high in Iron & Oxygen, but will also include such unwanted impurities as Phosphorus.

Return to Top of Page

The Bloomery Iron Making Process

This is the process that started the Iron Age. It seems most likely that a lump of Iron Ore in a particularly hot fire lead to a strange material left in the embers of the fire. From this, the Bloomery Furnace developed, in this a mixture of Iron Ore and Charcoal was burnt with the help of a blast of air from hand worked bellows.

The Output was typically a small lump of Wrought Iron of poor quality, but even this was enough to make an impact on history.

Return to Top of Page

The Finery & Chafery Iron Making Process

Return to Top of Page

Iron Making by Blast Furnace

How the tower of the first Blast Furnace was developed may never be known but the associated process of iron making increase the volume of iron that could be smelted while also reducing the price. The first record of a Blast Furnace in the U.K. is in 1496.

Early furnaces were best located on sloping ground, close to a reliable stream. Water was used to drive the early bellow to create the drought, while the slope helped to provide a near level roadway onto the top of the furnace.

The key to the process is the removal of the oxygen from the iron ore at the same time as separating as many of the other impurities as possible.

A blast furnace works on a continuous process lasting weeks, months, or in modern times, years and it will be assumed that the furnace is in the middle of a campaign and so the lighting the furnace (blowing in) can be ignored.

Clean carbon (Charcoal or later Coke), Iron Ore and Limestone are added to the top of the furnace. Little and often is best as it has the least affect on the burning of the furnace. Also important is that the charge material is alternated (e.g.. Iron Ore, then Coke, then Limestone, and then more Iron Ore).

At the top of the furnace the charge is heated and dried by the hot gases being blown through the furnace. Lower down, the iron ore melts as the carbon starts to burn and from just below the middle of the furnace, molten iron drips down through the remaining carbon fuel onto the hearth at the very bottom of the furnace.

As there is insufficient oxygen in the air blast to properly burn the carbon fuel oxygen is captured from the iron ore, however, in spite of this, the majority of the gas produced is still Carbon Monoxide.

In the lower part of the furnace, the limestone acts as a flux and draws together many impurities together into a layer of slag that floated onto of the molten iron.

The molten iron and slag is drawn off periodically.

The air blast is introduced a little way above the hearth and must be strong enough to stop the burning contents of the furnace stack dropping into the hearth, but must also not be so strong as to blow the contents out of the top.

Until the introduction of the Blast Furnace cast iron had not existed and iron had never been seen as a liquid in any great volume.

Since the start of the 18th Century the Blast Furnace has developed in a number of ways. Firstly Coke was introduced as a fuel in place of charcoal, allowing the size of furnace to be increase (charcoal would collapse under the extra weight from a large furnace). This was famously pioneered by Abraham Darby at Coalbrookdale in 1709 and was almost universal within 100 years, however a few charcoal furnace carried on until as late as 1921! Secondly the blast air was heated using heat recovered from the exhaust gases (energy conservation is not that new). Lastly, the Coke and Iron Ore are now mixed and heated, producing sinter, before they are charged into the furnace. Interestingly, you can tell from the texture and colour of the slag whether or not a furnace has had a hot or cold blast.

Modern Blast Furnaces can be 35m (120ft) high, 14m (45ft) diameter and can produce 10,000 tons per day.

The Iron produced by a Blast Furnace is always call 'Pig Iron'. The title of 'Cast Iron' is only generally used after the iron has been cast into a finished product.

Early furnaces producing small quantities of iron could be used to cast products directly and some furnaces, such as Rockley Furnace, had casting pits for large items such as Cannon. With larger furnaces, all iron was cast into pigs and was remelted but from the 1850s molten iron was charged into other types of furnace, mixer or converter. Little if any iron is now cast into pigs in the U.K., as steel making plants are incorporated into the same works as the Blast Furnaces.

Return to Top of Page

The Puddling Process

In 1784 Henry Cort devised a method of producing Wrought Iron from Cast Iron using a Coal fired Reverberatory Furnace. Solid Cast Iron was heated within an enclosed furnace.

A Reverberatory Furnace is a long low structure built out of fire bricks. The coal fire was at one end with the hearth between the fire and the chimney. The hearth was slightly dished with a roof that directed the smoke and flame from the fire well above the iron. By keeping the smoke and flame above the iron, no carbon from the fire came in contact with the iron.

Solid Pig (Cast) Iron was heated vigorously in the hearth until it was all molten. The fire was then damped down and the iron stirred so as to bring as much as possible in contact with the air. As wrought Iron has a higher melting point than Cast Iron, if the temperature in the furnace was correct the iron began to solidify as the carbon was removed. Eventually the Wrought Iron could be worked into a single lump of iron in the centre of the Hearth. Although in theory this was Wrought Iron it was not usable in this form because of the slag within the lump.

For the Wrought Iron to be made usable, it was lifted from the furnace and forged using a 'Shingling Hammer'. Finally it was rolled into bars or sheet. As most of the slag was squeezed out of the iron under the Shingling Hammer this could be a dangerous job, with each drop of the hammer white hot slag would be strayed out across the forge. As the workmen had to hold and move the iron during the forging, there was no option other than for them to dress in heavy protective clothing.

An improvement to Cort's puddling process came from Joseph Hall in 1816. Hall added mill scale (iron oxide formed and broken off during the forging and rolling) to the Cast Iron at the start of the Puddling process. Once the iron had melted, the carbon monoxide formed by the mill scale bubbled up through the iron giving the impression of boiling, thus the common name for this refinement 'Pig Boiling'.

Return to Top of Page

Making Cementation Steel

Standard Wrought Iron bars were placed in the Cementation Furnace for conversion into Cementation or Blister Steel. The furnace was constructed from sandstone in the from of a large chest with a lid and was loaded with the iron bars placed in layers inter spaced with large quantities of high quality Charcoal. When fully loaded, the lid was put in place and mortar use to seal the chest. Heating was applied from a fire below the furnace where a coal fire was maintained from a pit. Heat was maintained for up to a week and a further week was taken for the chest to cool before being opened, emptied, and reloaded.

The common design for cementation furnaces had two chests side by side with a fire hole in the centre of the two and the whole lot contained within a bottle shaped structure, similar to 'glass cones' and 'pottery kilns', that sheltered the furnaces from the weather and acted as a chimney. The placing of two furnace chest together would allow the one fire to heat the first chest while the second was cooling and being reloaded.

During the long slow heating carbon from the charcoal was absorbed into the iron bars.

When removed from the furnace, the steel had a blistered appearance (thus the alternative name). These blisters contained steel with a high carbon content while the centre of the bars were still Wrought Iron with very little carbon, thus Blister Steel was of little if any use until it had been processed further.

Before Crucible Melting the Blister Steel was heated and forged under a hammer such that the bar was folded over on its self. This resulted in 'Shear Steel', a second round of folding and hammering produced a steel known as 'Double Shear', a better quality produce, further rounds of folding and hammering produced still higher grades of steel.

Return to Top of Page

Making Crucible Steel

When Benjamin Huntsman tried to produce small clock springs from steel he found that even the supposed high quality steel made by repeatedly forging Cementation Steel was still too crude and inconsistent to be used for his minute products.

He set out to produce truly high quality steel that was totally consistent throughout.

In order the Cementation Steel be made into this high quality steel, it needed to be melted and cast into ingots. This required a high temperature, in order to melt the steel, and isolation from the fire, so that the carbon content did not change. The solution was to break the Blister Steel bars into small lengths and to place them into a small cylindrical vessel made of fireclay, the Crucible. After being fitted with a lid, the crucible was placed into a coke fire until the steel had completely melted.

When removed from the fire, the crucible was tipped to empty the contents into molds.

While Crucible steel was very high quality, it was also expensive, however a sign of the quality was the use of crucible steel into the 1950s for specialist uses.

The Bessemer Process brought about the end of Crucible steel for the less critical uses.

Return to Top of Page

Making Bessemer Steel

A Bessemer Converter is a large steel vessel that is supported on pivots. It has only one opening, in the top in the form of a spout. The flat bottom of the converter has a number openings through which air was blown during the conversion process.

For charging (filling) the converter was tipped onto its back and molten iron poured in through the upturned spout. Scrap iron and steel were also added in solid form. Then with a small air pressure applied to the converted it could be rotated to the upright working position. In this position the spout was aligned to a duct or chimney to carry the smoke and fumes out of the building. The conversion process could now begin by increasing the air pressure applied until it was forced vigorously through the molten iron. Each batch took about 30 minute to process.

Oxygen from the air blast combined with the carbon to form carbon monoxide, but the most impressive feature was the jet of sparks and flame shooting out of the spout.

The process could, with be experience, be judged very accurately just by the size and colour of the flames thrown out. The oxidisation of the carbon released heat, resulting in the Steel being considerably hotter than the iron that was originally charged. Adding the solid scrap at the beginning of the process helped to keep the temperature under control.

When ready, the blast was reduced as the furnace was tilted for teaming (emptying).

A major achievement was the 'Basic Bessemer Process' in which phosphorous was removed from the iron by using an Alkali (Basic) lining in the vessel. This allowed the wide use of lower quality iron ores in producing steel for general and specialist use.

The Bessemer Converters increased in size from 5 tons to 30 tons, but the process was quickly rivalled by the Siemens process and was finally superceded in the U.K. in 1974 by the use of the 'Basic Oxygen Steelmaking' Process.

Return to Top of Page

Making Steel by the Siemens Process

Return to Top of Page

Return to Contents Page

A Brief History of SteelThis is a much embellished translation of an earlier version written in German (it can be found in the Hyperscript "Matwiss I") and with some footnotes added later.

In order to make steel not accidentally, but conscientiously, you obviously first need to make iron. In contrast to the noble metals like gold, silver or platinum (and the occasional find of pure copper), iron is never (?) found as an element but practically always as an oxide.

However, in contrast to other metals found as oxides (especially Cu and Sn oxides needed to make bronze), the temperature of a "normal" fire is not sufficient to reduce iron oxide and to make the elemental iron liquid - the melting point of iron is Tm(Fe) = 1535 0C; far above the (1000 - 1100) 0C that the ancients could produce (?).

For Copper (Cu), e.g., it is different - its melting point is Tm(Cu) = 1083 0C. Throw some copper minerals in a nice hot fire made with plenty of charcoal (producing CO which is great for reducing oxides), and liquid copper will result almost automatically.

This happened and was noticed probably a good 6000 years ago, when early potters tried to adore their pottery with nice green malachite - a copper mineral known in antiquity and used as a gem stone. What a surprise, when one day in a particularly hot fire, instead of decorated pots they found an ingot of pure - and then extremely precious - copper in their oven. Copper was otherwise only found in small quantities (much less frequent then the (then) ubiquitous gold) in mountain ranges and river beds.

This was a decisive discovery for mankind: Precious and shiny metals could be made from dull stones. Things could be changed from one, seemingly immutable form into a completely different one - alchemy has its roots right here, and the yearning for "transmogrification" has never stopped since.

Early metal industry and the short-lived "copper age" began to be replaced rather soon by the bronze age (Cu + (5 - 10)% Sn and often some As); and the bronze age lasted more than 2000 years (it was not abruptly replaced by the iron age, but coexisted for about 1000 years).

From the "Kieler Nachrichten", front page, one day after after I wrote this paragraph. It says:On the Track of CharcoalersUp to the 16th century, Schleswig-Holstein was woodland. Then the trees were felled to produce charcoal (among other things). How that is done will be demonstrated by Stefan Brocke in the Loher woods.

Here we first encounter the importance of impurities: A little bit of As as an impurity atom makes bronze "harder", it doesn't deform so easily any more. Of course, nobody knew this. All that was probably known was that some sources of copper and tin ore, together with all kinds of tricks (including some magic or prayers, of course) produced superior bronze.

It is quite natural that tin and other metals were discovered shortly after the momentous discovery of copper smelting. Once you saw that precious copper could be made from some kind of rock, everybody not completely stupid would of course try what you could get with other rocks.

We also have the beginnings of an environmental disaster, because for metal smelting you need tremendous quantities of charcoal. First to obtain high temperatures, but, just as important, for reducing the metal oxide according to

MeO + C Me + CO

About 100 kg charcoal are needed to smelt 5 kg of copper.

Besides shipbuilding, charcoal production is responsible for the disappearance of large parts of European forests (the disappearance of yew trees (which were ubiquitous in antiquity) from present day forests, by the way, is due to the middle age bow-and-arrow industry - nothing beats a yew bow!). Charcoal production was a major industry and the source of the many charcoaler ("Köhler") stories in fairy tales and folklore.

Beside Cu and Sn, Pb, Hg, Ag, and of course Au, were known and produced on an industrial scale - especially by the romans. But the romans (and the Chinese, and the Indians, and the ...) had also Fe - but still no fire hot enough to melt it.

Early experience with the smelting and melting of other metals did not help in producing iron - it first came into use about 1000 years later than bronze. This must have been a kind of puzzle, because the ancients did know that iron existed. It was extremely rare and precious - because it fell from the sky in exceedingly small quantities.

King Tut, matter of fact, had a little iron dagger made from meteorite iron right on his breast - obviously his most precious object. In old Sumeria, iron was called "sky metal" and the pharaohs in old Egypt knew it as "black copper from the sky".

The Eskimos in Greenland, matter of fact, made their iron tools for hundred of years from a large (30 tons) meteorite.

Some American explorer (Admiral R. Peary) finally stole it (he wouldn't have expressed it that way, though) in the 1890s and had a hard time to transport it to the

Natural History Museum in New York. Here it is:

We may safely assume that the old materials scientists tried everything to smelt iron from suitable stones. They did have tricks to raise the temperature of a fire - in a 4500 old mastaba in Egypt, I took a picture of a relief showing six gold smiths (probably rather their Ph.D. students) blowing into the fire with hollow reeds. But just blowing with lung power will not do - maybe you get 1200 oC, but that's it.

So you do not get liquid iron - but you do get solid iron because reduction does take place - in a solid state reaction. What you get is an iron bloom ("Eisenblüte" in German), a mixture of fine iron particles, unreacted iron oxide, slag and charcoal residue. Here is an actual picture of some ancient bloom (from around 600 AD; I actually "found" this myself (in some museum).

The iron in the bloom was rather pure (and thus comparatively soft) because a solid state reaction produces only iron - carbon or other impurities have to diffuse in from the outside (if the iron would be liquid, it would just dissolve the dirt up to the solubility limit).

The early iron smiths (probably being Hethites of some form) could "wring" the iron from this bloom by separating the iron from the rest mechanically and repeatedly hammering together what was left at high temperatures (about 800 oC; some of the slag

then is liquid and gets squeezed out) with, no doubt, proper prayers to the respective gods and many (magical) tricks.

What they finally obtained was "wrought iron" ("Schmiedeeisen"), i.e. a lump of rather pure iron consisting of small pieces welded together, with plenty of small inclusions (small, because of the hammering that breaks up large pieces of slag).

Extreme care was necessary - from the selection of the iron ore, the reduction process and the hammering business. If you were careless, the iron oxidized again (it really "burns" at temperatures in excess of about 800 oC), and if you kept your reduction process going too long, carbon diffuses in and you may end up with cast iron (C content about 3% - 4%; melting point as low as 1130 0C). Then you actually got it liquid - "casting" was possible - but cast iron is brittle and useless (for weapons, that is).

Somewhat later, with larger furnaces and increased experience, the bloom obtained may have contained some high-carbon melted parts on its top layer. It then consisted of a whole range of iron-carbon alloys - from rather pure wrought iron to cast iron with good steel - say 0,5 % - 1,5% carbon - in between. The art of the smith than included to pick the right pieces. This was a highly developed skill, we know about it especially from Japan; but that does not mean that the Kelts or others did not do it just as well.

But beware. The art of making iron and steel, developed over 2000 years in many civilizations, cannot be contained in a few lines, not to mention that very little is known about that story - iron, after all, rusts (see the link showing an old sword), and not much has been found that gives detailed knowledge about how the old romans, Indian, Chinese, etc. made their steel and iron products.

Nevertheless - the early smiths, starting with the Greek god Hephaistos (the roman Volcanos) and containing many fabulous figures like the Nordic "Wieland the smith" or "Mime" in Wagners "Ring des Nibelungen", could produce articles, especially swords, from the iron bloom that were much better than the customary bronze stuff (and than of course "Magical" swords). In other words, they sometimes succeeded in making good steel.

What was their secret? It is rather simple - looking at it retrospectively: You need the proper concentration of C in the Fe bcc lattice at room temperature (some other impurities are helpful, too; while others - especially S and P - were harmful). Raising the about 0,1% C in wrought iron to an optimal 0,7 -0,9%, raised the hardness (or better the yield point) threefold! But if you got too much - say 2% - you were on the road to brittle cast iron not useful for swords.

Not being able too melt iron (and thus not being able to throw some magical stuff into the brew) the only way to get carbon (or on occasion N which also "works") into the Fe lattice was diffusion via the surface. What you needed to do was to "roast" you iron (possibly the whole sword) for the right time at the right temperature in a charcoal fire. Magic and praying helped - it did indeed: How do you keep track of the

time without a watch? You utter a long prayer that you learned from your master - the right ones "worked"! The rest of the magical ritual was helpful in providing reproducible conditions.

Of course the old practitioners had no idea of what the really were doing; if they thought about it, they felt that were purifying the iron in the (more or less holy) fire. This erroneous believe (like so many others) goes back to the (from a materials science point of view somewhat questionable) philosopher Aristoteles who certainly asked the right questions about life the universe and so on, and is righteously famous for that. His answers, however, were invariably wrong - even in the few instances where he could have known better.

Well, we have made but the first step to steel. We now must make a few more steps for good homogeneous steel - or we delve into a fascinating world of its own, the various damascene techniques, one of which is blending different kinds of steel into a compound material. More to that in the link.

Here we look first a bit on what happens in heating up and cooling down your material. We know, after all, that going up in temperature, iron changes at 910 0C from the bcc ferrite phase to the fcc austenite phase.

Carbon feels much more at home in austenite - its solubility is higher than in ferrite. If the smith kept his iron in a good fire very long, he now might have had a rather carbon rich austenite in the outer layers of his sword. So what happens upon cooling down?

Well, it depends. If the iron cools down s l o w l y, the carbon rich austenite will change to carbon rich ferrite. If there is more carbon in the austenite than the ferrite can dissolve, carbon will precipitate, forming a new Fe - C phase called cementite (with a quite complicated lattice). We now have cementite particles in fcc ferrite; usually in a very typical structure - both phases appear like a stack of plates. This kind of structure is called perlite because, looking at it under a microscope, it has a luster like pearls..

Perlite, the mixture of ferrite and cementite, however, is not much better than bronze as far as its mechanical properties are concerned. So you must prevent the phase change from austenite to perlite if you want to keep your sword "magic"! In other word, you must not allow enough time for the carbon atoms to diffuse around during cooling as would be necessary for forming precipitates. In other words: You must cool down rapidly (hopefully you did the proper exercise for calculating how fast you must cool down).

Here we have the next big trick - after making bloom, extracting wrought iron, and carburization: Quenching - often the big secret of master smiths (there is a whole Japanese mythology to this subject). The hot sword is stuck in a liquid for some time and thus quenched - and only very unimaginative smiths would have taken common water at room temperature for that.

If the cooling time was too short to allow Fe-C precipitate formation, we now have a

supersaturation of C in the ferrite phase which then will have a strongly disturbed lattice structure. A kind of mixture between fcc and bcc phases will prevail which has its own name: "Martensite".

Now you did it: Martensite has the fivefold "strength" of wrought iron!

Unfortunately - if you got martensite at all, it tends to be brittle! Now the next bag of tricks is needed: Heat up your sword again - but keep the temperature moderate.

Some of the defects that make martensite brittle anneal out and its ductility goes up. Bang it (i.e. deform it plastically), and you produce dislocations (hey, that's were we started from some time back!). Now you are manipulating a second kind of defect for optimizing mechanical properties!

But now we stop (so does the smith). If you really want to know much more about this, use this link.

HowStuffWorks Search HowStuffWorks and the web

And don't think that an increase in strength by a factor of 4 - 5 is not all that much. The old Gauls, Asterix and Obelix notwithstanding, were conquered by the Romans not least because their swords bent and needed straightening (over your knee) after a forceful blow - something the Roman swords did not need. (Haha - don't you believe all this roman propaganda!)

HowStuffWorks

Search HowStuffWorks and the web

Video | RSS | Random

Home Adventure Animals Auto Communication Computer Electronics Entertainment

Submit

Submit

Food Geography Health History Home & Garden Money People Science

Awards and Organizations Earth Science Engineering Everyday Science Life Science Military Physical Science Space Supernatural Science

Home

>

Science

>

Engineering

>

Materials Science

How Iron and Steel Work

by Marshall Brain and Robert Lamb

Browse the article How Iron and Steel Work

Introduction to How Iron and Steel Work

English School/The Bridgeman Art Gallery/Getty Images These daggers are an example of the kind of superior weaponry that Iron Age civilizations were able to

craft.

If you were to follow humanity's genetic trail back through the millennia, you'd find primitive creatures fumbling for a foothold on a primeval Earth. Lacking the natural, physical advantages of other animals, it's a marvel humans were able to claw their way out of the Cenozoic era at all. Of course, Homo sapiens had one advantage over all the other animals: the ability to make and use tools. While they lacked a lion's teeth and claws or a deer's defensive antlers, they learned to craft their own weapons from the world around them.

The oldest known tools date back 2.6 million years, to a time when humans used shaped stone to carry out a variety of tasks [source: Encyclopaedia Britannica]. After all, a sharpened rock can potentially slice, stab, scrape, pound and bludgeon. In time, humans began to specialize their tools, creating everything from arrowheads to pestles for grinding grain. Yet stone is a brittle, inflexible medium. Eventually, they were able to pinpoint more durable and malleable elements and their alloys: first copper, then bronze and iron. Instead of flaking or fracturing under blunt force, they proved malleable.

Up Next

Iron Quiz How Skyscrapers Work Discovery.com: Steel-melting Mirror

If you had to name the technologies that had the greatest effect on modern society, the refining of the heavy metal element iron would have to be near the top. Iron makes up a huge array of modern products. especially carbon-rich, commercial iron, which we call steel. Cars, tractors, bridges, trains (and their rails), tools, skyscrapers, guns and ships all depend on iron and steel to make them strong. Iron is so important that primitive societies are measured by the point at which they learn how to refine it. This is where the "Iron Age" classification comes from.

Have you ever wondered how people refine iron and steel? You've probably heard of iron ore, but how do we turn a slab of rock into a set of stainless steel surgical instruments or a locomotive? In this article, you'll learn all about iron and steel.

Your Browser Does Not Support iFrames

The Advantages of Iron

Dex Image/Dex Image/Getty Images A skilled blacksmith can work heated iron into just about any shape imaginable.

Iron is an incredibly useful substance. It's less brittle than stone yet, compared to wood or copper, extremely strong. If properly heated, iron is also relatively easy to shape into various forms, as well as refine, using simple tools. And speaking of those tools, unlike wood, iron can

handle high temperatures, allowing us to build everything from fire tongs to furnaces out of it. In contrast to most substances, you can also magnetize iron, making it useful in the creation of electric motors and generators. Finally, there certainly aren't any iron shortages to worry about. The Earth's crust is 5 percent iron, and in some areas, the element concentrates in ores that contain as much as 70 percent iron.

When you compare iron and steel with something like aluminum, you can see why it was so important historically. To refine aluminum, you need access to huge quantities of electricity. Furthermore, to shape aluminum, you have to either cast it or extrude it. Iron, however, is much easier to manipulate. The element has been useful to people for thousands of years, while aluminum really didn't exist in any meaningful way until the 20th century.

Aluminum: The Precious Metal

Ease of production plays a huge role in defining a material's worth. The 10-inch (25-centimeter) pyramid at the tip of the Washington Monument is actually made of aluminum rather than gold, because gold was less valuable than aluminum in 1884.

Fortunately, iron can be created relatively easily with tools that were available to primitive societies. There will likely come a day when humans become so technologically advanced that iron is completely replaced by aluminum, plastics and things like carbon and glass fibers. But right now, the economic equation gives inexpensive iron and steel a huge advantage over these much more expensive alternatives.

The only real problem with iron and steel is rust. Fortunately, you can control rust by painting, galvanizing, chrome plating or coating the iron with a sacrificial anode, which corrodes faster than the stronger metal. Think of this last option as hiring a bodyguard to take a bullet for the president. The more active metal has to almost completely corrode before the less active iron or steel begins the process.

Humans have come up with countless uses for iron, from carpentry tools and culinary equipment to complicated machinery and instruments of torture. Before iron can be put to any of these uses, however, it has to be mined from the ground.

Iron Ore

© iStockphoto.com/Susan DanielsIt may not look like much, but this lump of iron ore is the starting point of everything from precision

surgical equipment to reinforced skyscrapers.

Before many ancient civilizations began to transition from their bronze age to an iron age, some toolmakers were already creating iron implements from a cosmic source: meteorites. Called 'black copper" by the Egyptians, meteoric iron isn't the sort of substance one finds in huge, consolidated locations. Rather, craftsmen found bits and pieces of it spread across great distances. As such, this heavenly metal was mostly used in jewelry and ornamentation. While blacksmiths occasionally used meteoric iron to craft swords, these prized weapons were usually relegated to men of great power, such as the seventh century Caliphs, whose blades were said to have been forged from the same material as the Holy Black Stone of Mecca [source: Rickard].

The majority of Earth's iron, however, exists in iron ore. Mined right out of the ground, raw ore is mix of ore proper and loose earth called gangue. The ore proper can usually be separated by crushing the raw ore and simply washing away the lighter soil. Breaking down the ore proper is more difficult, however, as it is a chemical compound of carbonates, hydrates, oxides, silicates, sulfides and various impurities.

To get to the bits of iron in the ore, you have to smelt it out. Smelting involves heating up ore until the metal becomes spongy and the chemical compounds in the ore begin to break down. Most important, it releases oxygen from the iron ore, which makes up a high percentage of common iron ores.

The most primitive facility used to smelt iron is a bloomery. There, a blacksmith burns charcoal with iron ore and a good supply of oxygen (provided by a bellows or blower). Charcoal is essentially pure carbon. The carbon combines with oxygen to create carbon dioxide and carbon monoxide (releasing lots of heat in the process). Carbon and carbon monoxide combine with the oxygen in the iron ore and carry it away, leaving iron metal.

In a bloomery, the fire doesn't get hot enough to melt the iron completely. Instead, the iron heats up into a spongy mass containing iron and silicates from the ore. Heating and hammering this mass (called the bloom) forces impurities out and mixes the glassy silicates into the iron metal to create wrought iron. Wrought iron is hardy and easy to work, making it perfect for creating tools.

Tool and weapon makers learned to smelt copper long before iron became the dominant metal. Archeological evidence suggests that blacksmiths in the Middle East were smelting iron as early as 2500 B.C., though it would be more than a thousand years before iron became the dominant metal in the region.

To create higher qualities of iron, blacksmiths would require better furnaces. The technology gradually developed over the centuries. By the mid-1300s, taller furnaces and manually operated bellows allowed European furnaces to burn hot enough to not just soften iron, but actually melt it.

Creating Iron

China Photos/Getty Images News/Getty Images A worker covers the steel slag poured on the ground with sandy soil at a stainless steel factory.

The more advanced way to smelt iron is in a blast furnace. A blast furnace is charged with iron ore, charcoal or coke (coke is charcoal made from coal) and limestone (CaCO3). Huge quantities of air blast in at the bottom of the furnace, and the calcium in the limestone combines with the silicates to form slag. Liquid iron collects at the bottom of the blast furnace, underneath a layer of slag. The blacksmith periodically lets the liquid iron flow out and cool.

At this point, the liquid iron typically flows through a channel and into a bed of sand. Once it cools, this metal is known as pig iron. To create a ton of pig iron, you start with 2 tons (1.8 metric tons) of ore, 1 ton of coke (0.9 metric tons) and a half ton (0.45 metric tons) of limestone.

The fire consumes 5 tons (4.5 metric tons) of air. The temperature at the core of the blast furnace reaches nearly 3,000 degrees F (about 1,600 degrees C).

Iron Advantage

Between the 15th and 20th centuries, some countries had an industrial leg up on the competition due to the availability of iron ore deposits. For example, China, India, England, the United States, France, Germany, Spain and Russia all have substantial iron ore deposits. When you think of the historical importance of all of these countries, you can see the correlation!

Pig iron contains 4 to 5 percent carbon and is so hard and brittle that it's almost useless. If you want to do anything with it, you have three options. First, you can melt it, mix it with slag and hammer it out to eliminate most of the carbon (down to 0.3 percent) and create strong, malleable wrought iron. The second option is to melt the pig iron and combine it with scrap iron, smelt out impurities and add alloys to form cast iron. This metal contains 2 to 4 percent carbon, along with quantities of silicon, manganese and trace impurities. Cast iron, as the name implies, is typically cast into molds to form a wide variety of parts and products.

The third option for pig iron is to push the refining process even further and create steel, which we'll examine on the next page.

Creating Steel

Sean Gallup/Getty Images News/Getty Images A ladle filled with molten iron approaches a blast furnace that will convert it to liquid steel.

Steel is iron that has most of the impurities removed. Steel also has a consistent concentration of carbon throughout (0.5 to 1.5 percent). Impurities like silica, phosphorous and sulfur weaken

steel tremendously, so they must be eliminated. The advantage of steel over iron is greatly improved strength.

The open-hearth furnace is one way to create steel from pig iron. The pig iron, limestone and iron ore go into an open-hearth furnace. It is heated to about 1,600 degrees F (871 degrees C). The limestone and ore form a slag that floats on the surface. Impurities, including carbon, are oxidized and float out of the iron into the slag. When the carbon content is right, you have carbon steel.

Another way to create steel from pig iron is the Bessemer process, which involves the oxidation of the impurities in the pig iron by blowing air through the molten iron in a Bessemer converter. The heat of oxidation raises the temperature and keeps the iron molten. As the air passes through the molten pig iron, impurities unite with the oxygen to form oxides. Carbon monoxide burns off and the other impurities form slag.

However, most modern steel plants use what's called a basic oxygen furnace to create steel. The advantage is speed, as the process is roughly 10 times faster than the open-hearth furnace. In these furnaces, high-purity oxygen blows through the molten pig iron, lowering carbon, silicon, manganese and phosphorous levels. The addition of chemical cleaning agents called fluxes help to reduce the sulfur and phosphorous levels.

A variety of metals might be alloyed with the steel at this point to create different properties. For example, the addition of 10 to 30 percent chromium creates stainless steel, which is very resistant to rust. The addition of chromium and molybdenum creates chrome-moly steel, which is strong and light.

When you think about it, there are two accidents of nature that have made it much easier for human technology to advance and flourish. One is the huge availability of iron ore. The second is the accessibility of vast quantities of oil and coal to power the production of iron. Without iron and energy, we probably would not have gotten nearly as far as we have today.

Explore the links on the next page to learn even more about iron and steel.

Lots More Information

Related HowStuffWorks Articles

Iron Quiz How Skyscrapers Work How Bridges Work How Flintlock Guns Work How Sword Making Works Why do tools have "Drop Forged" stamped on them? What is drop forging? What does "Case Hardened" mean when it's stamped on a piece of metal? How Aluminum Works How can adding iron to the oceans slow global warming?

More Great Links

Iron Ore Statistical Compendium Alegria Iron Ore Mine, Brazil

Sources

"Hand Tool." Britannica Online Encyclopædia. 2008. (Dec. 22, 2008)http://www.britannica.com/EBchecked/topic/254115/hand-tool

Rickard, T.A. "The Use of Meteoric Iron." Royal Anthropological Institute of Great Britain and Ireland. 1941. (Jan. 6, 2009) http://www.jstor.org/pss/2844401

"Steel Works Glossary." American Iron and Steel Institute. 2008. (Dec. 22, 2008)http://www.steel.org/Content/NavigationMenu/LearningCenter/SteelGlossary/Steel_Glossary.htm

Tripathi, Vibha. "Iron Technology and Its Legacy in India (From the Earliest Times to Early Medieval Period)." Infinity Foundation. (Jan. 6, 2009)http://www.infinityfoundation.com/mandala/t_pr/t_pr_tripa_iron_frameset.htm

Young, Suzanne M.M. et al. "The earliest use of iron in China." Metals in antiquity. 1999. (Jan. 6, 2009)http://www.staff.hum.ku.dk/dbwagner/earfe/earfe.htm

Home | Adventure | Animals | Auto | Communication | Computer | Electronics | Entertainment | Food | Geography | Health | History | Home & Garden | Money | People | Science

Company Info | Advertise With Us | Newsletter | Careers | Privacy | Contact Us | Help | Visitor Agreement |

RSS | HSW Tools

HowStuffWorks | HSW Brazil | HSW China

© 1998-2010 HowStuffWorks, Inc.

Video Center | Maps | Consumer Guide Auto | Consumer Guide Products | Make HSW your homepage

Discovery Communications, LLC | Discovery Channel | TLC | Animal Planet | Discovery Health | Science Channel | Planet Green | Discovery Kids

Petfinder | TreeHugger | Military Channel | Investigation Discovery | HD Theater | FitTV | Turbo | Discovery Education

ATTENTION! We recently updated our privacy policy. The changes are effective as of Thursday, October 30, 2008.

To see the new policy, click [here]. Questions? See the policy for the contact information.

The Topic:

Iron & Steel

Easier - Iron is a chemical element. It is a strong, hard, heavy gray metal. It is found in meteorites. Iron is also found combined in many mineral compounds in the earth's crust. Iron rusts easily and can be magnetized and is strongly attracted to magnets. It is used to make many things such as gates and railings. Iron is also used to make steel, an even harder and tougher metal compound. Steel is formed by treating molten (melted) iron with intense heat and mixing it (alloying) with carbon. Steel is used to make machines, cars, tools, knives, and many other things.

Harder - The exact date at which people first discovered how to smelt iron ore and produce usable metal is not known. Archaeologists have found early iron tools that were used in Egypt from about 3000 bc. Iron objects of ornamentation were used even earlier. By about 1000 BC, the ancient Greeks are known to have used heat treatment techniques to harden their iron weaponry. These historical iron alloys, all iron alloys produced until about the fourteenth century ad, were forms of wrought iron.

Wrought iron was made by first heating a mass of iron ore and charcoal in a forge or furnace using a forced draft of air. This generated enough heat to reduce the iron ore to a hot, glowing, spongy mass of metallic iron filled with slag materials. The slag contained metallic impurities and charcoal ash. This iron sponge was then removed from the furnace and while still glowing hot, it was pounded with heavy sledges to separate the slag impurities and to weld and form the purer mass of iron. The iron produced in this way almost always contained slag particles and other impurities, but occasionally this technique of small batch iron making yielded a true steel product rather than wrought iron. These early iron makers

also learned to make steel by reheating wrought iron and charcoal in clay boxes for several days, until the iron absorbed enough carbon to become a true hardened steel.

By the end of the fourteenth century, iron furnaces used in smelting were becoming larger with increased draft from large bellows being used to force air through the “charge” (mixture of raw materials). These larger furnaces first freed the molten iron in its upper levels. This metallic iron then combined with higher amounts of carbon because of the heated combustion blast produced by the air forced up through the furnace. The product of these furnaces was pig iron, an alloy that melts at a lower temperature than steel or even wrought iron. Pig iron was then further processed to make steel.

Today, giant steel mills are essential for producing steel from iron ore. Steel making still uses blast furnaces that are merely refinements of the furnaces used by the old ironworkers. Improvements in the refinement of molten iron with blasts of air was accomplished by the 1855 Bessemer converter. Since the 1960s, electric arc furnaces have also been producing steel from scrap metal.

How Iron & Steel Work (Part 1 of 6) by M. Brain from Howstuffworks

http://science.howstuffworks.com/iron.htm

Have you ever wondered how people refine iron and steel? You probably have heard of iron ore, but how is it that you extract a metal from a rock? Here you can learn all about iron and steel.

Related Websites from Howstuffworks:

2) How does Rust Work? by M. Brain http://science.howstuffworks.com/question445.htm

3) What does Case Hardened Mean When It's Stamped on a Piece of Metal? http://home.howstuffworks.com/question196.htm

4) Why do Tools have Drop Forged Stamped on Them? What is Drop Forging?

http://science.howstuffworks.com/question376.htm

Iron And Steel Making Industry from Science, Technology and Engineering

http://www.enged.com/students/matcom/matcom67.html

The 18th century use of coke instead of wood as the fuel marked the beginning of the iron and steel making industry that became so important over the next two centuries.

Related Sections at Science, Technology and Engineering:

2) Casting Metal http://www.enged.com/students/matcom/matcom68.html

3) From Ore To Metal - Part 1 http://www.enged.com/students/matcom/matcom52.html

4) From Ore To Metal - Part 2 http://www.enged.com/students/matcom/matcom56.html

5) From Ore To Metal - Part 3 http://www.enged.com/students/matcom/matcom57.html

6) Machining Metals http://www.enged.com/students/matcom/matcom69.html

7) Metal http://www.enged.com/students/matcom/matcom02.html

Medieval Iron and Steel -- Simplified by B. Hall from ORB (Online Reference Book for Medieval Studies)

http://orb.rhodes.edu/encyclop/culture/scitech/iron_steel.html

Iron is one of the most useful metals ever discovered, but it is also one of the more difficult metals to understand in history, especially in medieval history. Iron comes in several forms, and the complications involved in producing each of them fosters further confusion. Here you find a layman's guide to medieval iron.

Related Websites:

2) Ferrous Metals and their Properties from UK Technology Education Centre

http://atschool.eduweb.co.uk/trinity/projects/material/ferrous.html

3) Iron http://www.minerals.org.au/downloads/pdf/Iron.pdf

4) Iron Downunder http://www.ga.gov.au/education/minerals/ironfact.html

5) Iron and Steel http://www.geo.msu.edu/geo333/ironsteel.html

6) Iron Working from Anglo-Saxon and Viking Crafts http://www.regia.org/ironwork.htm

7) Irons and Steels by H. Jack http://claymore.engineer.gvsu.edu/eod/material/material-7.html

8) Steel - 2000 Million Years in the Making http://www.library.unisa.edu.au/infores/steel/steel.htm

Virtual Steel Works by G.D. Yaros

http://ourworld.compuserve.com/homepages/DYaros/vsteel.htm

Steel has been part of some of the greatest achievements in history; it was the "iron horse" and steel rails that helped carve a nation out of the frontier. Steel is the backbone of bridges, the skeleton of skyscrapers, the framework for automobiles. And at the dawn of the 21st century, it's still revolutionizing the way we live. Here you can find detailed information on how steel is made.

Related Websites:

2) All About Steel http://www.ltvsteel.com/htmfiles/about.htm

3) Chemistry of Steelmaking from Corus http://www.schoolscience.co.uk/content/4/chemistry/steel/index.html

4) History of Steel from Sun Belt Steel http://www.steelrep.com/News___Info/HISTOR_1/histor_1.HTM

5) How Steel is Made from UK Steel http://www.uksteel.org.uk/stmake.htm

6) Iron and Steel: A Trip Inside a Steel Mill http://www.geo.msu.edu/geo333/steel_mill.html

7) Iron and Steel Production to 1945 http://www.uow.edu.au/commerce/econ/modbusiness/Iron%20&%20steel.pdf

8) Making of Steel http://www.geocities.com/SoHo/6570/steel.html#making

9) Making Steel from Muggah4Kids http://www.muggah4kids.org/whatHappened/theStory_4.asp

10) Making of Steel: Production of Molten Steel http://www.steel.org.uk/makstl.html

11) Physics of Steelmaking from Corus http://www.schoolscience.co.uk/content/4/physics/corus/index.html

12) Processes of Iron and Steel Making http://www.topforge.co.uk/Processes.htm

13) Retrospective of Twentieth-Century Steel from New Steel http://www.newsteel.com/features/NS9911f2.htm

14) Steel Learning Center from American Iron and Steel Institute http://www.steel.org/learning/

15) Steel Learning Centre from Steel Authority of India http://www.sail.co.in/learning/learning.htm

16) Steel Making from SteeleMart http://www.steelemart.com/steelmak.asp

17) Steel Making Industry http://www.wmrc.uiuc.edu/main_sections/info_services/library_docs/manuals/primmetals/ch . . .

18) Steel Manufacturing from Ball State University http://www.bsu.edu/web/acmaassel/steel.html

19) Steel Matter http://www.matter.org.uk/steelmatter/

20) Types of Steel http://engr.bd.psu.edu/rcv/470/steeltypes.pdf

After visiting several of the websites and learning about iron and steel, complete one or more of the following activities . . .

Complete An Iron & Steel WebQuest. Adapt or follow the directions found at the following webQuest site:

Wanna Write a Recipe for Steel? by W. Macala http://www.kn.pacbell.com/wired/fil/pages/websteelmakwe.html

Was There A Iron Furnace In Your Region? Many small iron furnaces were operated in early America. Some remains of those operations can be found in many different locations. Find out if there were ever an iron furnace operating nearby. Research and learn as much as possible about its use. See if you can locate any records and photographs related to the operation. Share all your findings.

Identify Iron And Steel Products. How many types of iron and steel products can you identify? Can arrange or group them into categories? Use a software graphic tool (Inspiration, MS Excell) to organize and display your items. Include illustrations.

Construct A Iron & Steel Timeline. Build a timeline that includes the important developments with iron and steel throughout history. Display and share your finished project.

Compare And Contrast Steel With Another Material. Pick one - - choose another material that is used

to manufacture or construct things: stone, plastic, wood, another metal (lots to choose from), a composite, a fiber, whatever. Then compare and contrast the charateristics and properties of the two, steel and the other material.

Write A Story About Life Without Iron Or Steel. Imagine what life would be without iron or steel metals. What would happen if you woke up one day and found that iron and steel no longer existed? Write a science fiction story that embraces that concept. Share your story.

Log Your Use Of Iron And Steel. In your journal, keep a log of each use of an iron or steel product. Be sure to include an account of all items that you discard or dispose of during the time period as well as those new items that are acquired. See if you can maintain the record for at least one week. At the end of the period, summarize your findings and reflect on what you learn.

Websites By Kids For Kids

Sir Henry Bessemer: Bessemer Steel Project by L.B. Khan & A.S. Khan

http://web.isoi.edu.pk/Student_Projects/Inventor and Inventions/Henry Bessember.rev/He . .

Sir Henry Bessemer, a British inventor, developed the Bessemer steel process along with his American counterpart, William Kelly. It was a very refined and cost effective innovation for the production of steel.

More Websites for Iron and Steel

American Iron and Steel Institute (AISI)

http://www.steel.org/

This organization's mission is to promote steel as the material of choice and to enhance the competitiveness of the North American steel industry and its member companies.

Related Organizations:

2) American Iron Ore Association (AIOA) http://www.aioa.org/

3) AISE (Association of Iron and Steel Engineers) http://www.aise.org/

4) International Iron and Steel Institute http://www.worldsteel.org/

5) Iron and Steel Society (ISS) http://www.iss.org/

6) Minnesota Iron Mining http://www.taconite.org/

7) Steel Recycling Institute http://www.recycle-steel.org

8) UK Steel Association http://www.uksteel.org.uk/index.html

Other Organizations:

9) American Foundry Society http://www.afsinc.org/

10) American Welding Society http://www.aws.org/

Bessemer Process from Wikipedia

http://www.wikipedia.org/wiki/Bessemer_process

The Bessemer process was the first industrial process for inexpensively producing steel from molten pig iron.

Related Websites:

2) Basic Oxygen Steel (BOS) Making Process http://wwwchem.uwimona.edu.jm:1104/courses/BOS.html

3) Bessemer Steel Process by J. Walton http://webpub.alleg.edu/employee/m/mmaniate/pittprogress/walton.html

4) History of the Bessemer Process http://helium.vancouver.wsu.edu/~meeker/steel/history.htm

5) Kelly's Converter by J.H. Lienhard http://www.uh.edu/engines/epi762.htm

Blast Furnace from BBC History

http://www.bbc.co.uk/history/games/blast/blast.shtml

Up to 1709, furnaces could only use charcoal to produce iron. However wood was becoming expensive as the forests were being cleared for farmland and timber. This site houses an animation of the blast furnace process that utilized coke as a fuel.

Related Website:

2) How a Blast Furnace Works from American Iron and Steel Institute

http://www.steel.org/learning/howmade/blast_furnace.htm

3) How It Works: The Blast Furnace by J.A. Ricketts http://www.netcentral.co.uk/steveb/shelton/blast_furnace.htm

4) Introduction to Blast Furnace Technology from ATSI Engineering Services

http://atsiinc.com/BF/BF_Index.htm

Dictionary of Metal Terminology from Metalmart, Inc.

http://www.metal-mart.com/Dictionary/dictlist.htm

Here is an extensive dictionary that covers every term you can think of . . .

Electric Arc Furnace Steelmaking by J.A.T. Jones from American Iron and Steel Institute

http://www.steel.org/learning/howmade/eaf.htm

The electric arc furnace operates as a batch melting process producing batches of molten steel known "heats".

Related Websites:

2) Electric Arc Furnace http://www.steel.org.uk/makstlc.html

3) Electric Arc Furnace http://www.nedians.8m.com/eaf.html

4) Electric Arc Furnace from Steel Authority of India (Sail) http://www.sail.co.in/learning/learning7.htm

5) Electric Arc Furnace: Process Description http://www.energysolutionscenter.org/HeatTreat/MetalsAdvisor/iron_and_steel/process . . .

6) Steel Making with Electric Arc Furnace http://www.arcfurnace.com/electric_arc_furnaces.html

7) Video: Electric Arc Furnace (EAF) http://www.matter.org.uk/steelmatter/steelmaking/eaf.htm

History of Thermal Joining by M.E. Sapp

http://www.weldinghistory.org/

This site contains two related sections: (1) history of welding and (2) history of brazing.

Related Websites:

2) Brazing Book http://www.handyharmancanada.com/TheBrazingBook/contents.htm

3) Trends in the Welding Industry http://www.pro-fusiononline.com/feedback/fc-mar99.htm

4) Welding and Joining Technologies (Links-site) from Vocational Information Center

http://www.khake.com/page89.html

Manufacturing Engineering and Technology Homepage

http://industrialtech.freeservers.com/newpage1.htm

This website covers metal casting, forming and shaping, material removal, joining, surface treatment, and advanced manufacturing techniques for metal.

Other Websites on Steel Fabrication:

2) Machining Resources (Links-site) from Vocational Information Center http://www.khake.com/page88.html

3) Making Tracks from Corus Steel http://www.coruseducation.com/RailWebRun/index1.html

4) Making of Wire by D. Trew http://www.barbwiremuseum.com/makingwire.htm

Minnesota Iron Mining

http://www.taconite.org/

Minnesota’s six iron mining and processing operations produce two-thirds of the iron ore used to make steel in the United States.

Related Website:

2) Iron Mining http://www.geo.msu.edu/geo333/iron-2.html

3) Iron Mining from Mining in Michigan

http://www.sos.state.mi.us/history/museum/explore/museums/hismus/prehist/mining/

iron.html

4) Iron mining 2002 by B. Kelleher from Minnesota Public Radio

http://news.mpr.org/features/200212/30_kelleherb_ironyearender/

5) Mining from Iron Range Resources & Rehabilitation Agency http://www.irrrb.org/mining.php

6) Mining Tour from National Steel Pellet Company http://www.nspellet.com/nsp/nsp_animation.html

7) Taconite from Minnesota Department of Natural Resources http://www.dnr.state.mn.us/education/geology/digging/taconite.html

Muggah4Kids

http://www.muggah4kids.org/index.htm

Tar ponds and coke ovens are part of the Muggah Creek watershed. This area surrounds the steel plant in Sydney, Nova Scotia, Canada. For 100 years, waste from the steel plant and the community was dumped there. Learn how local people and government are working together to clean up the area.

Profile of the Iron and Steel Industry (1995) from U.S. Environmental Protection Agency's Notebook Series

http://www.epa.gov/compliance/resources/publications/assistance/sectors/notebooks/iron.html

This profile report includes industrial process information, pollution prevention techniques, pollutant release data, regulatory requirements, compliance/enforcement data, history government and industry partnerships, innovative programs, contact names, bibliographic references, and a description of the research methodology.

Related Reports from the U.S. Environmental Protection Agency's Notebook Series:

2) Profile of the Metal Castings Industry (1997) http://www.epa.gov/compliance/resources/publications/assistance/sectors/notebooks/casting.html

3) Profile of the Metal Fabrication Industry (1995)

http://www.epa.gov/compliance/resources/publications/assistance/sectors/notebooks/

fabric.html

4) Profile of the Metal Mining Industry (1995)

http://www.epa.gov/compliance/resources/publications/assistance/sectors/notebooks/mining.html

Steel Manufacturing from U.S. Department of Labor's Bureau of Labor Statistics

http://www.bls.gov/oco/cg/cgs014.htm

This site provides a summary of the nature of the industry, its working conditions, employment and occupations in the industry, and more.

Steelynx

http://www.steelynx.net/

This searchable database connects to more than 7,500 links for steelmaking and steel-related technologies.

Related Links-site:

2) Steel Resources on the Internet http://www.geocities.com/SiliconValley/5978/steelm.html

Steel News

http://www.steelnews.net/

This is the source for daily news in the flat rolled steel market.

Related Websites:

2) Key to Steel Articles from Key to Metals Task Force & INI International

http://www.key-to-steel.com/Articles.htm

3) New Steel http://www.newsteel.com/

More on the History of Iron and Steel

Age of Iron by R. Cowen

http://www-geology.ucdavis.edu/%7EGEL115/115CH5.html

This site outlines the possible discovery and production of iron by early world civilizations.

Related Sites:

2) Ancient African Iron Production by P.R. Schmidt and S.T. Childs from American Scientist

http://www.sigmaxi.org/amsci/articles/95articles/pschmidt.html

3) Furnace with Drip-Pit Exposed in Gully near Sokoto (Nigeria)

http://apollo5.bournemouth.ac.uk/consci/africanlegacy/iron_smelting.htm

4) In Praise of Smiths by R. Cowen

http://www-geology.ucdavis.edu/%7EGEL115/115CH9.html

5) Iron and Steel -- Or Magic? http://myron.sjsu.edu/romeweb/ENGINEER/art10.htm

6) Iron-working in Roman Britain http://www.clyes.clara.net/essays/ferrum.html

Iron and Steel from Appalachian Blacksmiths Association

http://www.appaltree.net/aba/iron.htm

This site provides a view of historic methods for producing and working iron and steel.

Related Websites:

2) About Joanna Furnace from Hay Creek Valley History Association (PA) http://www.haycreek.org/about.htm

3) Blacksmith from Colonial Williamsburg Teacher Resource

http://www.history.org/History/teaching/blksmith.cfm

4) Catoctin Iron Furnace from National Park Service

http://www.nps.gov/cato/culthist/furnace.htm

5) Experiments in Historic Iron Making by D.J. Berry

http://www.geocities.com/duncanjberry/index.html

Andrew Carnegie: The Richest Man in the World from PBS's American Experience

http://www.pbs.org/wgbh/amex/carnegie/

Andrew Carnegie's life embodied the American dream: the immigrant who went from rags to riches, the self-made man who became a captain of industry, the king of steel.

Related Websites:

2) Andrew Carnegie http://www.spartacus.schoolnet.co.uk/USAcarnegie.htm

3) Andrew Carnegie http://econ161.berkeley.edu/TCEH/andrewcarnegie.html

4) Andrew Carnegie http://voteview.uh.edu/carnegie.htm

5) Andrew Carnegie: American Hero of Social Responsibility by L.D. Ledger

http://www.liberalartsandcrafts.net/contentcatalog/charity/carneg.shtml

6) Andrew Carnegie: A Tribute from the Carnegie Library of Pittsburgh

http://www.carnegielibrary.org/exhibit/carnegie.html

7) Life of Industrialist and Philanthropist: Andrew Carnegie (1835 - 1919) http://andrewcarnegie.tripod.com/acbio.html

8) Meet Andrew Carnegie from Carnegie Corporation's Carnegie for Kids

http://www.carnegie.org/sub/kids/carnegie.html

Henry Bessemer, Man of Steel from Science and Technology

http://www2.exnet.com/1995/09/27/science/science.html

Most people, if they remember him at all, remember Henry Bessemer as a British steel man, the man who invented the Bessemer Converter, which could make 30 tons of high-grade steel in half an hour. But Henry was a far more ingenious man than is generally realized...

Related Websites:

2) Henry Bessemer - The Steel Man http://inventors.about.com/library/inventors/blsteel.htm

3) Man of Steel: Henry Bessemer and the Converter http://www.angelfire.com/va3/metallurgy/bessemer.html

4) Sir Henry Bessemer, F.R.S: An Autobiography

http://www.history.rochester.edu/ehp-book/shb/

Homestead and its Perilous Trades- Impressions of a Visit by H. Garland from McClure's Magazine

http://www.history.ohio-state.edu/projects/steel/June1894-Garland_Homestead.html

This 1894 article provides the author's impression of a visit to a steel town.

Related Articles:

2) Making Steel and Killing Men (1907) by W. Hard from Everybody's Magazine

http://www.history.ohio-state.edu/projects/steel/MakingSteel/

3) Steel Workers (1909) by J.A. Fitch, 1909 from The Pittsburgh Survey

http://www.history.ohio-state.edu/projects/PittsburghSurvey/SteelWorkers/

4) Wage-Earning Pittsburgh (1909) from The Pittsburgh Survey

http://www.history.ohio-state.edu/projects/PittsburghSurvey/Pittsburgh/

5) Homestead: The Households of a Mill Town (1909) by M. Byington from The Pittsburgh

Survey http://www.history.ohio-state.edu/projects/PittsburghSurvey/Homestead/

“I Witnessed the Steel Strike”: Joe Rudiak Remembers the 1919 Strike by J. Rudiak & P. Gotlieb from History Matters

http://historymatters.gmu.edu/d/106/

Though the Great Steel Strike of 1919 failed in its immediate aims, it left a legacy in the steel regions of the United States that lasted for decades. In 1974 when historian Peter Gotlieb asked former steelworker Joe Rudiak, the son of Polish immigrants, about his participation in unionization struggles in the 1930s, he started by recalling his memories of the 1919 steel strike as a young boy. Here, Rudiak told how his father was blacklisted for acknowledging his support of the union. From such experiences, he explained, unionism got “embedded in you.” The site links to several related articles.

Related Websites:

2) Chapter XXIV: The Steel Strike of 1919 from the Autobiography of Mother Jones

http://womenshistory.about.com/library/etext/mj/bl_mj24.htm

3) Fitzpatrick and Foster: Behind America's Steelworkers from Illinois Periodicals Online

http://www.lib.niu.edu/ipo/ihy971207.html

4) Senate Hearings into 1919 Strike http://www.assumption.edu/users/McClymer/his261/SteelTestimony.html

5) Society: Steel from Birmingham Pittsburgh Traveler http://www.northbysouth.org/2000/Fraternal/steel%20page.htm

Nation of Steel by T.J. Misa (1995) Johns Hopkins University Press

http://www.iit.edu/~misa/NOS/index.html

This published book links the industrial age steel making developments with the expansion of railroads. This site contains the first five chapters of the text.

Saga of New Zealand Steel

http://www.techhistory.co.nz/pages/Iron1.htm

New Zealand is well endowed with deposits of iron sands along the western beaches of both main islands, but many attempts to establish an iron and steel industry foundered on the high titanium content of the ore.

U.S. Steel Gary Works Photograph Collection, 1906-1971 from the Indiana University Digital Library Program (DLP)

http://www.dlib.indiana.edu/collections/steel/

This collection contains over 2,200 photographs of the Gary Works steel mill and the corporate town of Gary, Indiana. In images of compelling diversity, historians and the general public can view all aspects of this planned industrial community: the steel mill, the city, and the citizens who lived and worked there.

Websites For Teachers

Changing Role of the Iron Range (Grades 4-5) by S.M. Loerts from AskERIC

http://www.askeric.org/cgi-bin/printlessons.cgi/Virtual/Lessons/Social_Studies/Geography/. . .

This lesson teaches students about mining, natural resources, and economies. The iron range is used as a case study with learners tracking ore mining to taconite to tourism. Children examine the changing economic function of the iron range.

Hopewell Furnace: A Pennsylvania Iron-making Plantation by R.G. Koman

http://www.cr.nps.gov/nr/twhp/wwwlps/lessons/97hopewell/97hopewell.htm

Using the Hopewell Furnace as its focus, this lesson has students describe how natural resources influenced the location and development of the early American iron-making industry and identify the steps in making iron and iron products.

Taconite Rocks! (Grade 6) from Minnesota Iron Mining

http://www.taconite.org/pdfs/curriculum.pdf

This comprehensive curriculum was developed by educators on Minnesota's Iron Range. It offers a number of modules combining science, language arts, mathematics, and social studies that can be used in a variety of classroom settings.

Steel in Pittsburgh from Houghton Mifflin

http://www.eduplace.com/ss/hmss/3/laag/9.2.html

Student's examine why Pittsburgh was an ideal location for steel production.

Teacher's Guide (Grades 4-12) U.S. Steel Gary Works Photograph Collection, 1906-1971 from Indiana University Digital Library Program (DLP)

http://www.dlib.indiana.edu/collections/steel/tg/index.html

Site houses a collection of lesson plans, learning objectives, and online activities for use in the classroom.

iron recycle blast furnace magnet stainless ferrous

steel drum Fe forge alloy mining carbon

taconite bridge smelting magnetic rustelectric arc

furnace

welding ductility elasticity metal mild steel brittleness

steel drum Iron Age "iron road" casting charcoal labor movement

Bessemer converter

conductivity cast iron "iron age" pig iron metallurgy

tool steel iron oxide wrought iron foundry recyclingindustrial revolution

slagBrinell hardness

testindustrial

archaeologylimestone hardness "pig-iron"

quench anneal malleabilitymeteoritic

ironmetallic

structureheat treat

hematite temper coke smelting iron ore molten steel

Created by Annette Lamb and Larry Johnson, 3/03.

BingBeta

Beta

Web Images News More

MSN Hotmail

Sign in | Malaysia | Preferences

Bing

ALL RESULTS Reference

MORE ARTICLES

view all reference results for this query

REFERENCE » WIKIPEDIA ARTICLESElectric arc furnace

Electric arc furnace

view original wikipedia article

Please let us know what is wrong with this page:

Cancel

In this article:

Locations

electric arc Submit

FDNF

Submit

Images

From the web:

Images

Videos

Electric arc furnace

This article needs additional citations for verification.Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (January 2010)

Engineering portal

An electric arc furnace (EAF) is a furnace that heats charged material by means of an electric arc.

Arc furnaces range in size from small units of approximately one ton capacity (used in foundries for producing cast iron products) up to about 400 ton units used for secondary steelmaking. Arc furnaces used in research laboratories and by dentists may have a capacity of only a few dozen grams. Electric arc furnace temperatures can be up to 1,800 degrees Celsius. Arc furnaces differ from induction furnaces in that the charge material is directly exposed to an electric arc, and the current in the furnace terminals passes through the charged material.

History

Steel mill with two arc furnaces

In the 19th century, a number of men had employed an electric arc to melt iron. Sir Humphry Davy conducted an experimental demonstration in 1810; welding was investigated by Pepys in 1815; Pinchon attempted to create an electrothermic furnace in 1853; and, in 1878 - 79, Sir William Siemens took out patents for electric furnaces of the arc type.

The first electric arc furnaces were developed by Paul Héroult, of France, with a commercial plant established in the United States in 1907. Initially "electric steel" was a specialty product for such uses as machine tools and spring steel. Arc furnaces were also used to prepare calcium carbide for use in carbide lamps. The Stessano electric furnace is an arc type furnace that usually rotates to mix the bath. The Girod furnace is similar to the Héroult furnace.

While EAFs were widely used in World War II for production of alloy steels, it was only later that electric steelmaking began to expand. The low capital cost for a mini-mill - around US$140-200 per ton of annual installed capacity, compared with US$1,000 per ton of annual installed capacity for an integrated steel mill - allowed mills to be quickly established in war-ravaged Europe, and also allowed them to successfully compete with the big United States steelmakers, such as Bethlehem Steel and U.S. Steel, for low-cost, carbon steel 'long products' (structural steel, rod and bar, wire and fasteners) in the U.S. market.

When Nucor - now one of the largest steel producers in the U.S.[1] - decided to enter the long products market in 1969, they chose to start up a mini-mill, with an EAF as its steelmaking furnace, soon followed by other manufacturers. Whilst Nucor expanded rapidly in the Eastern US, the companies that followed them into mini-mill operations concentrated on local markets for long products, where the use of an EAF allowed the plants to vary production according to local demand. This pattern was also followed globally, with EAF steel production primarily used for long products, while integrated mills, using blast furnaces and basic oxygen furnaces, cornered the markets for 'flat products' - sheet steel and heavier steel plate. In 1987, Nucor made the decision to expand into the flat products market, still using the EAF production method[2].

Construction

An electric arc furnace used for steelmaking consists of a refractory-lined vessel, usually water-cooled in larger sizes, covered with a retractable roof, and through which one or more graphite electrodes enter the furnace. The furnace is primarily split into three sections:

the shell, which consists of the sidewalls and lower steel 'bowl'; the hearth, which consists of the refractory that lines the lower bowl; the roof, which may be refractory-lined or water-cooled, and can be shaped as a section

of a sphere, or as a frustum (conical section). The roof also supports the refractory delta in its centre, through which one or more graphite electrodes enter.

The hearth may be hemispherical in shape, or in an eccentric bottom tapping furnace (see below), the hearth has the shape of a halved egg. In modern meltshops, the furnace is often raised off the ground floor, so that ladles and slag pots can easily be maneuvered under either end of the furnace. Separate from the furnace structure is the electrode support and electrical system, and the tilting platform on which the furnace rests. Two configurations are possible: the electrode supports and the roof tilt with the furnace, or are fixed to the raised platform.

A typical alternating current furnace has three electrodes. Electrodes are round in section, and typically in segments with threaded couplings, so that as the electrodes wear, new segments can be added. The arc forms between the charged material and the electrode, the charge is heated both by current passing through the charge and by the radiant energy evolved by the arc. The electrodes are automatically raised and lowered by a positioning system, which may use either electric winch hoists or hydraulic cylinders. The regulating system maintains approximately constant current and power input during the melting of the charge, even though scrap may move under the electrodes as it melts. The mast arms holding the electrodes carry heavy busbars, which may be hollow water-cooled copper pipes carrying current to the electrode holders. Modern systems use 'hot arms', where the whole arm carries the current, increasing efficiency. These can be made from copper-clad steel or aluminium. Since the electrodes move up and down automatically for regulation of the arc, and are raised to allow removal of the furnace roof, heavy water-cooled cables connect the bus tubes/arms with the transformer located adjacent to the furnace. To protect the transformer from heat, it is installed in a vault.

The furnace is built on a tilting platform so that the liquid steel can be poured into another vessel for transport. The operation of tilting the furnace to pour molten steel is called "tapping". Originally, all steelmaking furnaces had a tapping spout closed with refractory that washed out when the furnace was tilted, but often modern furnaces have an eccentric bottom tap-hole (EBT) to reduce inclusion of nitrogen and slag in the liquid steel. These furnaces have a taphole that passes vertically through the hearth and shell, and is set off-centre in the narrow 'nose' of the egg-shaped hearth. It is filled with refractory sand, such as olivine, when it is closed off. Modern plants may have two shells with a single set of electrodes that can be transferred between the two; one shell preheats scrap while the other shell is utilised for meltdown. Other DC-based furnaces have a similar arrangement, but have electrodes for each shell and one set of electronics.

AC furnaces usually exhibit a pattern of hot and cold-spots around the hearth perimeter, with the cold-spots located between the electrodes. Modern furnaces mount oxygen-fuel burners in the sidewall and use them to provide chemical energy to the cold-spots, making the heating of the steel more uniform. Additional chemical energy is provided by injecting oxygen and carbon into the furnace, historically this was done through lances in the slag door, now this is mainly done through multiple wall-mounted injection units.

A mid-sized modern steelmaking furnace would have a transformer rated about 60,000,000 volt-amperes (60 MVA), with a secondary voltage between 400 and 900 volts and a secondary current in excess of 44,000 amperes. In a modern shop such a furnace would be expected to produce a quantity of 80 metric tonnes of liquid steel in approximately 60 minutes from charging with cold scrap to tapping the furnace. In comparison, basic oxygen furnaces can have a capacity of 150-300 tonnes per batch, or 'heat', and can produce a heat in 30-40 minutes. Enormous variations exist in furnace design details and operation, depending on the end product and local conditions, as well as ongoing research to improve furnace efficiency - the largest scrap-only furnace (in terms of tapping weight and transformer rating) is in Turkey, with a tap weight of 300 metric tonnes and a transformer of 300 MVA.

To produce a ton of steel in an electric arc furnace requires approximately 400 kilowatt-hours per short ton of electricity, or about 440kWh per metric tonne; the theoretical minimum amount of energy required to melt a tonne of scrap steel is 300kWh (melting point 1520°C/2768°F). Therefore, the 300-tonne, 300 MVA EAF mentioned above will require approximately 132 MWh of energy to melt the steel, and a 'power-on time' (the time that steel is being melted with an arc) of approximately 37 minutes, allowing for the power factor. Electric arc steelmaking is only economical where there is plentiful electricity, with a well-developed electrical grid.

Operation

Scrap metal is delivered to a scrap bay, located next to the melt shop. Scrap generally comes in two main grades: shred (whitegoods, cars and other objects made of similar light-gauge steel) and heavy melt (large slabs and beams), along with some direct reduced iron (DRI) or pig iron for chemical balance. Some furnaces melt almost 100% DRI.

The scrap is loaded into large buckets called baskets, with 'clamshell' doors for a base. Care is taken to layer the scrap in the basket to ensure good furnace operation; heavy melt is placed on top of a light layer of protective shred, on top of which is placed more shred. These layers should be present in the furnace after charging. After loading, the basket may pass to a scrap pre-heater, which uses hot furnace off-gases to heat the scrap and recover energy, increasing plant efficiency.

The scrap basket is then taken to the melt shop, the roof is swung off the furnace, and the furnace is charged with scrap from the basket. Charging is one of the more dangerous operations for the EAF operators. There is a lot of energy generated by multiple tonnes of falling metal; any liquid metal in the furnace is often displaced upwards and outwards by the solid scrap, and the grease and dust on the scrap is ignited if the furnace is hot, resulting in a fireball erupting. In some twin-shell furnaces, the scrap is charged into the second shell while the first is being melted down, and pre-heated with off-gas from the active shell. Other operations are continuous charging - pre-heating scrap on a conveyor belt, which then discharges the scrap into the furnace proper, or charging the scrap from a shaft set above the furnace, with off-gases directed through the shaft. Other furnaces can be charged with hot (molten) metal from other operations.

After charging, the roof is swung back over the furnace and meltdown commences. The electrodes are lowered onto the scrap, an arc is struck and the electrodes are then set to bore into the layer of shred at the top of the furnace. Lower voltages are selected for this first part of the operation to protect the roof and walls from excessive heat and damage from the arcs. Once the electrodes have reached the heavy melt at the base of the furnace and the arcs are shielded by the scrap, the voltage can be increased and the electrodes raised slightly, lengthening the arcs and increasing power to the melt. This enables a molten pool to form more rapidly, reducing tap-to-tap times. Oxygen is also lanced into the scrap, combusting or cutting the steel, and extra chemical heat is provided by wall-mounted oxygen-fuel burners. Both processes accelerate scrap meltdown.

An important part of steelmaking is the formation of slag, which floats on the surface of the molten steel. Slag usually consists of metal oxides, and acts as a destination for oxidised impurities, as a thermal blanket (stopping excessive heat loss) and helping to reduce erosion of the refractory lining. For a furnace with basic refractories, which includes most carbon steel-producing furnaces, the usual slag formers are calcium oxide (CaO, in the form of burnt lime) and magnesium oxide (MgO, in the form of dolomite and magnesite). These slag formers are either charged with the scrap, or blown into the furnace during meltdown. Another major component of EAF slag is iron oxide from steel combusting with the injected oxygen. Later in the heat, carbon (in the form of coke or coal) is lanced into this slag layer, reacting with the iron oxide to form metallic iron and carbon monoxide gas, which then causes the slag to foam, allowing greater thermal efficiency, and better arc stability and electrical efficiency. The slag blanket also covers the arcs, preventing damage to the furnace roof and sidewalls from radiant heat.

Once flat bath conditions are reached, i.e. the scrap has been completely melted down, another bucket of scrap can be charged into the furnace and melted down, although EAF development is moving towards single-charge designs. After the second charge is completely melted, refining operations take place to check and correct the steel chemistry and superheat the melt above its freezing temperature in preparation for tapping. More slag formers are introduced and more oxygen is lanced into the bath, burning out impurities such as silicon, sulfur, phosphorus, aluminium, manganese and calcium and removing their oxides to the slag. Removal of carbon takes place after these elements have burnt out first, as they have a greater affinity for oxygen. Metals that have a poorer affinity for oxygen than iron, such as nickel and copper, cannot be removed through oxidation and must be controlled through scrap chemistry alone, such as introducing the direct reduced iron and pig iron mentioned earlier. A foaming slag is maintained throughout, and often overflows the furnace to pour out of the slag door into the slag pit. Temperature sampling and chemical sampling (in the form of a 'chill' - a small, solidified sample of the steel) take place via automatic lances.

Once the temperature and chemistry are correct, the steel is tapped out into a preheated ladle through tilting the furnace. As soon as slag is detected during tapping the furnace is rapidly tilted back towards the deslagging side, minimising slag carryover into the ladle. During tapping some alloy additions are introduced into the metal stream. Often, a few tonnes of liquid steel and slag is left in the furnace in order to form a 'hot heel', which helps preheat the next charge of scrap and accelerate its meltdown. During and after tapping, the furnace is 'turned around': the slag door is cleaned of solidified slag, repairs may take place, and electrodes are inspected for damage or lengthened through the

addition of new segments; the taphole is filled with sand at the completion of tapping. For a 90-tonne, medium-power furnace, the whole process will usually take about 60-70 minutes from the tapping of one heat to the tapping of the next (the tap-to-tap time).

An arc furnace pouring out steel into a small ladle car. The transformer vault can be seen at the right side of the picture. For scale, note the operator standing on the platform at upper left. This is a 1941-era photograph and so does not have the extensive dust collection system that a modern installation would have, nor is the operator wearing a hard hat nor dust mask.

Advantages of electric arc furnace for steelmaking

The use of EAFs allows steel to be made from a 100% scrap metal feedstock, commonly known as 'cold ferrous feed' to emphasise the fact that for an EAF, scrap is a regulated feed material. The primary benefit of this is the large reduction in specific energy (energy per unit weight) required to produce the steel. Another benefit is flexibility: while blast furnaces cannot vary their production by much and are never stopped, EAFs can be rapidly started and stopped, allowing the steel mill to vary production according to demand. Although steelmaking arc furnaces generally use scrap steel as their primary feedstock, if hot metal from a blast furnace or direct-reduced iron is available economically, these can also be used as furnace feed.

A typical steelmaking arc furnace is the source of steel for a mini-mill, which may make bars or strip product. Mini-mills can be sited relatively near to the markets for steel products, and the transport requirements are less than for an integrated mill, which would commonly be sited near a harbour for access to shipping.

Environmental issues

Although the modern electric arc furnace is a highly efficient recycler of steel scrap, operation of an arc furnace shop can have adverse environmental effects. Much of the capital cost of a new installation will be devoted to systems intended to reduce these effects, which include:

enclosures to reduce high sound levels Dust collector for furnace off-gas Slag production Cooling water demand

Heavy truck traffic for scrap, materials handling, and products Environmental effects of electricity generation

Because of the very dynamic quality of the arc furnace load, power systems may require technical measures to maintain the quality of power for other customers; flicker and harmonic distortion are common side-effects of arc furnace operation on a power system.

Other electric arc furnaces

For steelmaking, direct current (DC) arc furnaces are used, with a single electrode in the roof and the current return through a conductive bottom lining or conductive pins in the base. The advantage of DC is lower electrode consumption per ton of steel produced, since only one electrode is used, as well as less electrical harmonics and other similar problems. However, the size of DC arc furnaces is limited by the available electrodes and maximum allowable voltage. Maintenance of the conductive furnace hearth is a bottleneck in extended operation of a DC arc furnace. However, Danieli - makers of steel plant equipment - are preparing to install a 420-tonne DC furnace, powered by two 160 MVA transformers, in a Japanese steel mill. Instead of an upper graphite electrode and a lower conductive hearth, this EAF would have two upper graphite electrodes.

In a steel plant, a ladle furnace can be used to maintain the temperature of liquid steel during processing after tapping from the scrap-melting furnace. This also allows the molten steel to be kept ready for use in the event of a delay later in the steelmaking process. The ladle furnace consists of only the refractory roof and electrode system of a scrap-melting furnace, but it has no need for a tilting mechanism or scrap charging.

Electric arc furnaces are also used for production of ferroalloys and other non-ferrous alloys, and for production of phosphorus. Furnaces for these services are physically different from steel-making furnaces and may operate on a continuous, rather than batch, basis. Continuous process furnaces may also use paste-type (Soderberg) electrodes to prevent interruptions due to electrode changes. Such a furnace is known as a submerged arc furnace because the electrode tips are buried in the slag/charge, and arcing occurs through the slag, between the matte and the electrode. A steelmaking arc furnace, by comparison, arcs in the open. The key is the electrical resistance, which is what generates the heat required: the resistance in a steelmaking furnace is the atmosphere, while in a submerged-arc furnace the slag or charge forms the resistance. The liquid metal formed in either furnace is too conductive to form an effective heat-generating resistance.

Amateurs have constructed a variety of arc furnaces, often based on electric arc welding kits contained by silical blocks or flower pots. Though crude, these simple furnaces are capable of melting a wide range of materials and creating calcium carbide etc. An example is shown here.

Plasma arc furnace (PAF)

Plasma arc furnace is very much similar to a conventional arc furnace, however instead of graphite electrodes, plasma torches are installed. A plasma-arc furnace comprises a casing with water cooled plasma torches (plasmatron), installed in symmetrical relationship relative to the vertical axis . Each of these torches consists of a casing provided with a nozzle and an axial tubing for feeding a plasma-forming gas (either nitrogen or argon), and a burnable cylindrical graphite electrode located within the tubing.

Vacuum arc remelting

Main article: Vacuum arc remelting

Vacuum arc remelting (VAR) is a secondary remelting process for vacuum refining and manufacturing of ingots with improved chemical and mechanical homogeneity.

In critical military and commercial aerospace applications, material engineers commonly specify VIM-VAR steels. VIM means Vacuum Induction Melted and VAR means Vacuum Arc Remelted. VIM-VAR steels become bearings for jet engines, rotor shafts for military helicopters, flap actuators for fighter jets, gears in jet or helicopter transmissions, mounts or fasteners for jet engines, jet tail hooks and other demanding applications.

Most grades of steel are melted once and are then cast or teemed into a solid form prior to extensive forging or rolling to a metallurgically sound form. In contrast, VIM-VAR steels go through two more highly purifying melts under vacuum. After melting in an electric arc furnace and alloying in an argon oxygen decarburization vessel, steels destined for vacuum remelting are cast into ingot molds. The solidified ingots then head for a vacuum induction melting furnace. This vacuum remelting process rids the steel of inclusions and unwanted gases while optimizing the chemical composition. The VIM operation returns these solid ingots to the molten state in the contaminant-free void of a vacuum. This tightly controlled melt often requires up to 24 hours. Still enveloped by the vacuum, the hot metal flows from the VIM furnace crucible into giant electrode molds. A typical electrode stands about 15 feet (5 m) tall and will be in various diameters. The electrodes solidify under vacuum.

For VIM-VAR steels, the surface of the cooled electrodes must be ground to remove surface irregularities and impurities before the next vacuum remelt. Then the ground electrode is placed in a VAR furnace. In a VAR furnace the steel gradually melts drop-by-drop in the vacuum-sealed chamber. Vacuum arc remelting further removes lingering inclusions to provide superior steel cleanliness and further remove gases such as oxygen, nitrogen and hydrogen. Controlling the rate at which these droplets form and solidify ensures a consistency of chemistry and microstructure throughout the entire VIM-VAR ingot. This in turn makes the steel more resistant to fracture and/or fatigue.

This refinement process is essential to meet the performance characteristics of parts like a helicopter rotor shaft, a flap actuator on a military jet or a bearing in a jet engine.

For some commercial or military applications, steel alloys may go through only one vacuum remelt, namely the VAR. For example, steels for solid rocket cases, landing gears or torsion bars for fighting vehicles typically involve the one vacuum remelt.

Vacuum arc remelting is also used in production of titanium and other metals which are reactive or in which high purity is required.

See also

Flodin process

References

1. ↑ www.worldsteel.org 2. ↑ Preston, R., American Steel. Avon Books, New York, 1991

Further reading

H. W. Beaty (ed), "Standard Handbook for Electrical Engineers,11th Ed.", McGraw Hill, New York 1978, ISBN 0-07-020974-X

J.A.T. Jones, B. Bowman, P.A. Lefrank, Electric Furnace Steelmaking, in The Making, Shaping and Treating of Steel, R.J. Fruehan, Editor. 1998, The AISE Steel Foundation: Pittsburgh. p. 525-660.

Thomas Commerford Martin and Stephen Leidy Coles, The Story of Electricity, New York 1919, no ISBN, Chapter 13 The Electric Furnace, available on the Internet Archive

External links

Recognition of first foundry as historical site Home made small scale arc furnace using a welder (Caution with experiments!) Electric Arc Furnace module at steeluniversity.org , including a fully interactive simulation Process models demonstrate the EAF operation and control (MPC) YouTube video of a small EAF in New Zealand

Categories: Articles needing additional references from January 2010

|

All articles needing additional references

|

Steelmaking

|

Industrial furnaces

|

Electric arcs

History

View article history All Wikipedia content is licensed under the GNU Free Document License or the Creative Commons CC-BY-SA license or is otherwise used here in compliance with the Copyright Act

Electric_arc_furnace

electric arc furnace

Electric arc furnace

reading mode

return to top

Overview Outline Images Locations Twitter

highlighter

Click on or highlight sentences in the article.When you are done, save or clear.

done clear

To share this highlighted page press copy and paste it in an email or IM. You can also bookmark this page now.

copy clear

Electric arc furnace

History

Construction

Search this Submit

Operation

Advantages of electric arc furnace for steelmaking

Environmental issues

Other electric arc furnaces

Plasma arc furnace (PAF)

Vacuum arc remelting

See also

References

Further reading

External links

2 Locations

United States, France

view all

Images

view all 24

Videos

view all 15

Go to Bing in the United States

© 2010 Microsoft | Privacy | Legal | Help