LECTURE 4.2LECTURE 4.2

OUTLINEOUTLINE

Steel, Cast Iron and Wrought IronSteel, Cast Iron and Wrought IronThe Early Iron AgeThe Early Iron AgeGeorgius Agricola and the HooversGeorgius Agricola and the HooversThe Bessemer ConverterThe Bessemer Converter

Monumental BuildingMonumental Building

CAST IRONCAST IRON

Cast iron usually contains Cast iron usually contains between 2% and 6% carbon.between 2% and 6% carbon.

Cast irons are usually used in Cast irons are usually used in the “cast” condition.the “cast” condition.

Cast irons consist of virtually Cast irons consist of virtually pure iron (the light phase), pure iron (the light phase), graphite (the black constituent) graphite (the black constituent) and “pearlite” (the grey and “pearlite” (the grey regions), themselves a mixture regions), themselves a mixture of an iron carbide (called of an iron carbide (called cementite) and “pure” iron.cementite) and “pure” iron.

Cast irons tend to be brittle!!Cast irons tend to be brittle!!

200µm

WROUGHT IRONWROUGHT IRON

Wrought iron is a Wrought iron is a composite of virtually composite of virtually pure iron, together pure iron, together with slag inclusionswith slag inclusions

Historically, wrought Historically, wrought iron was produced iron was produced without the iron ever without the iron ever being molten.being molten.

Wrought irons contain Wrought irons contain little or no carbon.little or no carbon.

200µm

STEELSTEEL

Steel is an alloy of iron Steel is an alloy of iron and carbon.and carbon.

Typically the carbon Typically the carbon content is less than1%content is less than1%

The microstructure The microstructure consists of virtually pure consists of virtually pure iron (the white regions), iron (the white regions), and “pearlite”, which is a and “pearlite”, which is a mixture of virtually pure mixture of virtually pure iron, together with the iron, together with the compound, cementite, compound, cementite, Fe3CFe3C

200µm

THE CATALAN FORGETHE CATALAN FORGE

The Catalan Forge The Catalan Forge produced a “bloom” or produced a “bloom” or “loupe” of virtually pure “loupe” of virtually pure iron, intimately mixed with iron, intimately mixed with slag particles, This “bloom” slag particles, This “bloom” would be converted to: would be converted to:

WROUGHT IRONWROUGHT IRON The wrought iron was The wrought iron was

never molten.never molten. Excess slag had to be Excess slag had to be

hammered out of the pasty hammered out of the pasty iron at the blacksmith’s iron at the blacksmith’s forgeforge

a

TuyereSlagBloom or LoupeCharcoalOre

SMELTING AND SLAGGING SMELTING AND SLAGGING REACTIONSREACTIONS

2Fe2O3 + 3CO 4Fe + 3CO2 2Fe2O3 + 2SiO2 2Fe2SiO4 + O2

Melting Temperature Slagging Temperature Reduction Temperature.1538˚C 1180˚C 800˚C

STEELING IRONSTEELING IRON

Sheets of wrought iron Sheets of wrought iron would be surface would be surface carburized to produce carburized to produce hard, steel, surface regionshard, steel, surface regions

The interior of the piece The interior of the piece would remain as a tough would remain as a tough “iron”“iron”

Strips of the surface Strips of the surface carburized material would carburized material would be hammer-welded to be hammer-welded to create a strong, yet tough create a strong, yet tough finished product.finished product.

a

a)b)

STEELING IRONSTEELING IRON

CHINESE BLAST FURNACE CHINESE BLAST FURNACE TECHNOLOGYTECHNOLOGY

CHINESE BLAST FURNACE CHINESE BLAST FURNACE TECHNOLOGYTECHNOLOGY

Figure 6.8. Reconstruction of 2nd century BC, Chinese lantern bellows. The two Chinese metalworkers in Figure 6.7aare operating lantern bellows of the form described here. The lantern bellows allowed for a continuous stream of air tothe blast furnace (See text for details). Figures are modified from "Technology in the Ancient World", Henry Hodges.Barnes and Noble Books. New York, NY. (1970)

THE SLAGGING TEMPERATURE OF THE SLAGGING TEMPERATURE OF LIMESTONE-FLUXED FURNACESLIMESTONE-FLUXED FURNACES

Limestone is added to iron-Limestone is added to iron-smelting furnaces to combine smelting furnaces to combine with e.g., the silica to form a with e.g., the silica to form a siliceous slag.siliceous slag.

As the amount of limestone As the amount of limestone increases, then so does the increases, then so does the slagging temperature.slagging temperature.

The limestone is not added to The limestone is not added to reduce the slagging reduce the slagging temperature: rather it prevents temperature: rather it prevents much of the iron from ending much of the iron from ending up in the slag!up in the slag!

DE RE METALLICADE RE METALLICA

DE RE METALLICADE RE METALLICA

PARTINGTON STEEL AND PARTINGTON STEEL AND IRON CO. 1917IRON CO. 1917

THE BESSEMER CONVERTERTHE BESSEMER CONVERTER

MONUMENTAL BUILDINGMONUMENTAL BUILDING

POST AND BEAM POST AND BEAM CONSTRUCTIONCONSTRUCTION

CONSTRUCTION MATERIALSCONSTRUCTION MATERIALSMaterial Classification Mechanical

PropertiesComments

Natural PolymersWood Polymer/Natural

CompositeAs strong in tension asin compression

Limited lifetime, due tonatural decay

EngineeredCeramics/CompositesSun-Dried Bricks Clay Ceramic/

Ceramic PowderModicum of strengthin compression: zeroin tension

Limited lifetime, especiallyin a wet environment.Perhaps 75 years in an aridclimate.

Fired Bricks Ceramic. The first"Engineered Material"

Strong inCompression. Weak inTension

Lifetime is measured inmillennia.

Concrete Composite of anaggregate in cement. Aceramic material

Strong inCompression. Weak inTension

Lifetime is measured inmillennia.

NaturalCeramics/CompositesLimestone/Marble/Travertine/Tufa

Rock /NaturalComposite/Ceramic

Strong inCompression. Weak inTension

All are based on the mineral,calcite (CaCO3). Marble is ametamorphic rock, the othersare sedimentary.

Sandstone/Quartzite Rock /NaturalComposite/Ceramic

Strong inCompression. Weak inTension

Based on quartz (silica:SiO2). Sandstone issedimentary, quartzite ismetamorphic

Granite Rock /NaturalComposite/Ceramic

Strong inCompression. Weak inTension

Plutonic Rock. Contains e.g.,quartz, feldspar and mica

SELECTED EXAMPLESSELECTED EXAMPLES

Building Timeframe Locale Construction CommentsStonehenge Finished ca.

1700BCBritain Post and Beam. Masonry

construction.Copied from earlierwooden rings. Thetrilithons, consisted of twouprights and a beam. Thebeam had a small span,which minimized tension.

Ziggurats 3rd MillenniumBC

Mesopotamia Sun-dried, and fired-brick.

Stresses should becompressive only.

Pyramids 3rd MillenniumBC

Egypt Masonry(Limestone/Granite/Sandstone)

Stresses should becompressive only.(However, it is possiblefor shear stresses todevelop, if not builtproperly, which mayexplain the collapse of theMeidum Pyramid).

GrecianTemples, e.g.,the Parthenon

Middle 1st

Millennium BCAthens (forexample)

Masonry (often Marble) Patterned after theMycenaean Megaron.Significant tensile stressesdevelop. Roof designswere intellectuallysqualid.

RomanBridges andAqueducts

Late 1st

MillenniumBC/Early 1st

MillenniumAD

WesternEurope

Arches to accommodatestresses. Masonry, and/orconcrete construction

Very advanced materials'usage, and designconcepts.

RomanTemples (e.g.,the Pantheon

Late 1st

MillenniumBC/Early 1st

MillenniumAD

Rome Arches and Domes toovercome tensile stresses.Concrete Construction

Very advanced materials'usage, and designconcepts.

STONEHENGE: POST AND STONEHENGE: POST AND BEAM CONSTRUCTIONBEAM CONSTRUCTION

THE ZIGGURAT AT UR: SIR THE ZIGGURAT AT UR: SIR LEONARD WOOLEY DRAWINGLEONARD WOOLEY DRAWING

THE PYRAMIDS AT GIZATHE PYRAMIDS AT GIZA

THE PARTHENON: POST AND THE PARTHENON: POST AND BEAM CONSTRUCTIONBEAM CONSTRUCTION

THE PARTHENON AND THE PARTHENON AND WROUGHT IRON WROUGHT IRON

REINFORCEMENTREINFORCEMENT

aa

Iron/SteelDowelIron/SteelDoubleT- ClampRecess inthe Marble

LeadCasingMarbleBlocksa) b)

“Pure” Iron“Steeled” Iron

c) d)

THE ARCH, COMPRESSIVE THE ARCH, COMPRESSIVE AND “OUTWARD STRESSES”AND “OUTWARD STRESSES”

a

WeightCCO Oa)b)

c)

THE ROMAN AQUEDUCT: ITHE ROMAN AQUEDUCT: I

a

SubstructioArcuatioSpecus

THE ROMAN AQUEDUCT: IITHE ROMAN AQUEDUCT: II

a

Brick or MasonryConcrete or RubblePaving SlabMortar Lining

THE PANTHEON: TEMPLE FOR THE PANTHEON: TEMPLE FOR ALL THE GODSALL THE GODS

CONCRETE CONSTRUCTION CONCRETE CONSTRUCTION OF THE PANTHEONOF THE PANTHEON

The Pantheon is constructed The Pantheon is constructed predominantly of concrete!predominantly of concrete!

The walls have a “graded” The walls have a “graded” specific gravity”, being specific gravity”, being densest at the bottom, and densest at the bottom, and least dense at the top.least dense at the top.

The dome is lightweight, the The dome is lightweight, the aggregate being highly aggregate being highly porous tufa, and volcanic porous tufa, and volcanic pumice.pumice.

The roof panels were The roof panels were “coffered”, which minimized “coffered”, which minimized weight, without sacrificing weight, without sacrificing strength.strength.

a

TravertineTravertine + TufaTufa + Pummice

Tufa + BricksBrick FragmentsTufa + BrickFragments