Decarburisation of bainitic ferrite laths and its influence on the microstructure in Fe-Cr-Si-C steel

The paper presents an investigation of the time required for the diffusion of carbon out of supersaturated laths of ferrite into the retained austenite. The purpose of the present paper is to demonstrate how a thermodynamic method can be used for solving a problem of the decarburisation of bainite laths. This should in principle enable to examine the partitioning of carbon from supersaturated ferrite laths into adjacent austenite and the carbon content in retained austenite using analytical method. The obtained results illustrates that the estimated times with the reference to the executed thermal processing are not capable of decarburising the sheaf of ferrite included thick laths of bainitic ferrite during the period of austempering. A consequence of the precipitation of cementite from austenite during austempering is that the growth of bainitic ferrite can continue to larger extent and that the resulting microstructure is not an ausferrite but it is a mixture of bainitic ferrite, retained austenite and carbides.