Effect of Cr on Lamellar Spacing and High-Temperature Stability in Eutectoid Steels

In order to clarify refinement of lamellar spacing and high temperature stability of lamellae in pearlite by the addition of Cr, we investigated in terms of supercooling, diffusion coefficient of C and Cr, and spheroidizing of cementite using Fe-0.8%C binary and Fe-0.8%C-Cr ternary steels. Equilibrium transformation temperature of pearlite was increased by the addition of Cr. At a fixed pearlite transformation temperature, pearlite lamellar spacing of Cr addition steel was refined by increasing of supercooling compared with Fe-0.8%C steel. On the other hand, in spite of the same supercooling, lamellar spacing was refined by increasing of Cr content. This is caused by decreasing of the diffusion coefficient of C in the austenite by addition of Cr. Spheroidizing of cementite in pearlite at high temperature was inhibited by inceasing of Cr content. Spheroidizing rate reduced by the addition of Cr. Spheroidizing of cementite in pearlite by increasing of Cr content was inhibited by increasing of the contribution of diffusion of Cr for the coarsening reaction of cementite.