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Heat treatment is a crucial process in metallurgy, where metals undergo controlled heating to alter their properties without remelting. Iron, a common metal, is almost always subjected to heat treatment. The presence of carbon in iron and steel creates compounds such as cementite (C3Fe), influencing hardness and brittleness. Metals exhibit various crystal structures, including ferrite, austenite, and pearlite, resulting in diverse properties based on their treatment. Phase diagrams help visualize these complex mixtures and states, assisting in understanding the behavior of steel with varying carbon content during heating and cooling processes.
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Industrial Products Selected Theory
Metals: 4.5 Heat treatment • after manufacture, many metals go through further heating steps to modify their properties • this does not involve remelting • iron is one metal that is almost always heat treated • metals are not homogeneous, even “pure” ones • C is present in iron & steel due to the process or by addition • it forms deposits and “compounds”, eg cementite C3Fe, which is very hard and brittle • there are 3 crystal structure forms of Fe atoms which also form: ferrite, austenite & pearlite • a piece of iron/steel may be a mixture of all four depending on how it is been made/treated
Phase diagrams • used to display the composition of complex mixtures in different “states” (not just metals) What happens to a steel containing 4.3%C as it cools very slowly from liquid? eutectic point If the steel is suddenly cooled when at a high T, it will be “trapped” in that state
Exercise 4.2 What would happen to a 0.5% steel if it was heated slowly from 25C back to 1000C, and then allowed to cool back to 750C before being suddenly chilled back to 25C?
