8/14/2019 Definition of Iron, Steel, And Cast Iron

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Definition of Iron, Steel, and Cast Iron

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Iron. Chemical symbol "Fe".

Iron is a general word used to describe metals that have pure iron as their main

constituent. Sometimes the word iron is used as simile of something hard like

an "iron lady".

Most iron wares around us are not made of chemically pure iron but are alloys,

the most important of which is Carbon. Carbon is a big factor in understanding

the difference between Iron, Steel and Cast iron. Adding some carbon to

chemically pure iron makes steel. Add even more and you'll make cast iron

Iron 

Technically, iron means just that, chemically pure iron. Without carbon, iron is

very soft and ductile.

Iron become softer upon heating. So a smith can change its shape by

hammering but it can never be hardened by heat treatment.

Steel 

Steel is an alloy of iron and carbon. The amount of carbon dictates whether a

steel is hard or it is tough.

Adding Carbon makes the iron harder. The more carbon the harder the steel.

Carbon content in steel usually falls a range between 0.3 ~ 1.5 % by volume.

Iron /carbon alloys within this range are called steels.

Steels can be forged and hardened by heat treatment. The high carbon steel is

harder than the low carbon steel. Because carbon content is critical to

hardening, the effect of heat treatment is big on high carbon steel, and small on

low carbon steels.

In other words, high carbon steels are more sensitive to tempering work. High

carbon steels undergo structural changes when heated and cooled rapidlymaking them useful for items that require degrees of hardness.

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High carbon steels appear some different phases that come from the difference

of the situation in tempering work. The result of relation between sensitive steel

and good tempering work makes subtle appearances on blade surface.

 Cast Iron 

Carbon content over 1.5 % make iron alloys brittle, non-ductile and unable be

worked by hammering. Also these alloys can't be hardened by heat treatment.

Such metals are easy to melt, and easy to break by hammering. Therefore they

are used only for casting work.

Therefore we can see that iron, steel, and cast iron form a family based on the

absence or degree of carbon content.

Although iron is not used for blades it can be used for tsuba and other fittings

like fuchi/kashira, kuirikata, and kojiri etc.

Low carbon steel is used for various kinds of tools and arms.

Most good tsubas are made of low carbon steel. Some "dubious" tsuba are

made of cast iron.

High carbon steel is used for cutting edges of blades and tools.

Usually a blade is made of combination with some kinds of steel.

Sword smiths can use either iron or cast iron as ingredients to produce their 

own steels. They control the carbon content of the steel using their forge. We

call this home-made steel "Oroshi-gane".

Purity of materials for making blades and tsuba 

In the modern age there are numerous kinds of alloy steels. Other metals are

added to the iron to produce special properties for example stainless steel. We

call these steels "alloy steels" to differentiate them from "pure carbon steels".

(Although this term is strange in exact meaning of the word, I will use it. Please

see note at bottom.)

Even commercial Carbon steels have trace amounts of other metals, that is why

we don't call them "pure" carbon steels. Japanese swordsmiths never use these

modern steels for blades or tsuba and a Japanese blade can not be made with

these metals.

TAMA-HAGANE is the main material used in making a Japanese blade. It is a

primitive and pure steel made using a traditional Japanese furnace, the

TATARA.

The materials for OROSHI-GANE must also be pure of course.

The next step, fold welding, can remove slags and bubbles, but can't removemetal contamination.

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Therefore the materials must be as pure a steel as possible.

A Japanese blade must be made from this "pure" steel. Pure steel, simply iron

and carbon is a reflection of the beauty of nature.

The value of the Japanese blade lies in its purity.

Some other terms about iron/steel 

pure iron = the most pure iron we can get by the top technology today. It can

be one of the materials for oroshigane.

sponge iron = one form of pure iron. It looks like a sponge because it has

many bubbles inside of it.

electrolytic iron = another kind of pure iron. It is made by electrolysis from iron

salts.TETSU = iron

HAGANE = carbon steel

ZUKU = cast iron

IMONO = cast iron ware

TAMA-HAGANE = a pure steel made by TATARA method.

OROSHI-GANE = a pure steel that is made by sword smith themselves.