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?