Effect of Mn and C on Grain Growth in Mn Steels

Grain growth in Fe-Mn austenites was examined at 1373 K and 1473 K as a function of Mn (0 to 30 wt pct) and carbon (0 to 0.5 wt pct) content. The addition of Mn had the effect of reducing the rate of grain growth. The observed inhibiting effect of Mn is believed to be mainly due to an increase in the occurrence of annealing twins with increasing Mn content. It is hypothesized that, upon intersecting with High-Angle Grain Boundaries (HAGBs), the twins result in low-energy, low-mobility boundary segments which ultimately slow the overall growth kinetics. Solute drag does not appear to significantly contribute to the slowing of the grain growth kinetics for Mn contents greater than 6 wt pct. Atom probe tomography studies confirmed weak or negligible segregation of Mn to HAGBs. The carbon content had a small but measurable effect on the grain growth kinetics. Reduction of the carbon content in an Fe-30 wt pct Mn alloy resulted in a decrease in effective grain boundary mobility.