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One-Minute Mentor: Heat Treating and Properties of Ductile Iron
December 05, 2018
Source: ASM International
The basic structural differences between the ferritic and austenitic classes are shown in the graph. It shows a continuous cooling transformation (CCT) diagram and cooling curves for furnace cooling, air cooling, and quenching.
It can be seen that slow furnace cooling results in a ferritic matrix (the desired product of annealing), whereas the cooling curve for air cooling, or normalizing, results in a pearlitic matrix, and quenching produces a matrix microstructure consisting mostly of martensite with some retained austenite.
Tempering softens the normalized and quenched conditions, resulting in microstructures consisting of the matrix ferrite with small particles of iron carbide (or secondary graphite). Actual annealing cycles usually involve more than just furnace cooling, depending on alloy content and prior structure.
Materials Processing and Treatment | Heat Treating
Metals and Alloys | Cast Irons