Controlling carbide precipitation during tempering in Fe-C martensitic alloys through Mn distribution and martensitic lath width

The supersaturated carbon atoms in Fe-C martensitic matrix diffuse out to form clusters, transition carbides and cementite when tempering temperature increases. It has been recently found that heterogeneous Mn distribution in retained austenite (RA) and martensite can fully inhibit the carbide precipitation in lath martensite. However, it is still unclear how to control the carbide precipitation in lath martensite during tempering. Both experimental results and DICTRA simulations in the present study indicate that when the width of martensitic lath decreases and the Mn content increases in the RA adjacent to the martensite, the carbide precipitation can be reduced and even fully inhibited. The former factor is due to the shorter diffusion distance for carbon from martensite to adjacent RA with refinement of martensite laths, whereas a higher Mn content in the RA enhances the diffusion of carbon. This outcome provides an avenue for design of the advanced high-strength steels through controlling carbide formation during tempering.