Distortion in 100Cr6 and nanostructured bainite

A series of experiments on 100Cr6 and a nanostructured carbide-free bainitically transformed steel are performed. The effect of heat treatment conditions on the degree of distortion due to phase transformation is established. By transforming bainitically other than martensitically, cooling rate plays a major role in decreasing distortion by one order of magnitude in 100Cr6. Additional distortion reductions are possible by further decreasing the cooling rate when forming nanostructured carbide-free bainite. By invoking thermodynamic calculations and employing a neural network, it is shown that distortion can be engineered. When large amounts of retained austenite are present (such as the case of nanostructured bainite), this can be used to accommodate distortion. Additionally, it is possible to balance the expansion due to bainite formation with the contraction due to stress relaxation by controlling the amount of retained austenite. Exploitation of those mechanisms may aid in reducing distortion as a result of phase transformation (dimensional change) during the manufacturing of heat treated components.

► Distortion is proportional to the cooling rate from the high temperature phase.
► Bainitic steels distortion is one order of magnitude smaller than martensitic.
► Nanostructured carbide-free bainite experiences nearly no distortion.
► Distortion can be engineered via thermodynamic calculations in bainite.
► The amount of retained austenite in bainite has to be larger than zero.