Solute-element partitioning and austenite stabilization in steels

Abstract

Considerable amounts of thin film retained austenite have been found in low to medium carbon lath martensitic structural steels. The existence of this metastable phase at room temperature has been attributed to several mechanisms which involve diffusion and redistribution of carbon during the austenite to martensite transformation. In this investigation electron microscopy (TEM), convergent beam electron diffraction (CBED) and field ion-atom probe (FIAP) analysis methods have been utilized to measure the C and other solute element distributions in retained austenite, ..gamma.., and martensite laths, ..cap alpha..'. Considerable carbon partioning to ..gamma.. and to ..cap alpha..'/..gamma.. interfaces occurs during cooling, but there was no detectable change in substitutional alloying elements (Cr, Mn, Ni, Si) between ..cap alpha..' and ..gamma... Thus while C plays a vital role in stabilization, it cannot account completely for this phenomenon. It is concluded that mechanical stabilization and the size effect are also major factors.