Tempering of martensite: A field ion microscope study

Abstract

As-quenched martensite in an Fe-0.88% C-0.45% Mn steel was tempered in the field ion microscope. During the first stage of the tempering process, precipitation of two types of ε-carbide is observed—in an ordered fashion along twin planes, and as dispersed random particles in untwinned regions of high dislocation density. Further tempering causes cementite precipitation to occur most rapidly in those regions which contain random ε-carbide dispersions. Continued tempering causes the cementite thus nucleated to grow, and causes the transformation of low-carbon martensite to cementite and ferrite to proceed to completion. This is seen by the steady decrease and ultimate absence of the twin boundaries in the image.