Ruth Russo discusses "steel" in Homer's works; discusses how "steel' was formed by quenching iron and other methods.

Academic / Technical Report
Ruth Russo

Ruth Russo, "The Heart of Steel: A Metallurgical Interpretation of Iron in Homer," Bulletin for the History of Chemistry 30 (2005): 23-29

Bulletin for the History of Chemistry
Ruth Russo
Reading Public

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These iron treasures are so valuable that it is possiblethey depict not wrought iron, but carburized iron. Inthe case of the grizzled, gray objects, it seems unlikely,for another type of iron appears in the Homeric texts:aithôn sidêros—the gleaming or shining iron more resemblingflashing steel. Athena adopts the guise of asailor trading copper for “gleaming iron” (Od. 1:182).In the Iliad, Telemonian Ajax cuts down Simoisius withshining iron (4:485). “Gleaming iron” is brought to afeast, along with bronze, cattle, and slaves (7:472). Finally,Hector vows to fight Achilles, even if Achilles’rage be “burnished iron” (20:371). Aithôn sidêros hast he appearance of steel and could be what is referred to by the formula “polukmêtos te sidêros” (hard wrought iron), since steel, while toilsome to produce, makes afar superior weapon than simple wrought iron.

Archaeological evidence indicates that the advent of consistent, deliberate steeling of iron occurred by 1000 B.C.E., and that production of carburized iron objects increased rapidly after 900 B.C.E. (22). Thus it is likely that audiences hearing the Homeric poems at any time after the 9th C B.C.E. would be able to distinguish the three principal types of iron as well as, or better than, modern readers (23).

Steel, an alloy of carbon and iron, and harder than bronze, is made in three stages: carburization, quenching, and tempering. To make carburized iron, the smith places wrought iron in an oxygen-poor, white-hot fire (above 800o C). The higher the temperature and the longer the iron sits in the fire, the more carbon diffuses into the iron. While cooling in air, the steel adopts a pearlite microstructure, referring to the tiny, alternating layers of ferrite (pure iron) and iron carbide. The smith then cold-hammers this steel in order to harden it: hammered steel with 1.2% carbon is about twice as strong as bronze (14).

Steel is made even harder by quenching, i.e. plunging the white-hot iron into water. Iron carbide cannot form when iron is cooled so quickly; rather, the carbonis simply frozen in solution in the ferrite, producing the needle-like microstructure called martensite. Martensiteis the hardest but most brittle steel (24). Brittleness is not a problem for small objects like arrowheads, which do not need to withstand much force. Nor is brittleness a problem for thick objects like axe heads, for though the exterior turns to martensite—brittle but strong—the interior cools more slowly, producing a pearlite microstructure that reduces the tendency for the thick object to fracture.

The problem of brittleness is the most acute for the sword, a long and thin weapon. The brittleness of a sword is reduced by tempering, or reheating the iron at a relatively low temperature (under 725° C)after quenching. This causes some carbon to fall out of solution s diffuse iron carbide, a modified pearlite. The higher concentration of pearlite reduces both brittleness and hardness at the same time. Tempering is an inexact technology, since the temperatures required for tempering are lower than red or white heat.Without a visible color change of the metal, the ancient smith would have gauged the temperature of the forge and the optimal tempering time by trial and error,and such understanding would then be passed down from master to apprentice in the family trade.

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