Effect of Mn and C on Grain Growth in Mn Steels
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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.
The authors would like to thank NSERC (Canada) for financial support. MB thanks Mr. C. Butcher for his guidance with electropolishing and EBSD, Mr. J. Garrett for vacuum sealing the samples for all the grain growth experiments, Mr. K. Furumai for allowing us to use the Fe-1Mn microstructure, and Professor. G. Miyamoto for his help in grain boundary reconstruction from EBSD data. MB would also like to thank Dr. T. Garcin and Dr. M. Militzer (Department of Materials Science and Engineering, University of British Columbia) for their help with the LUMet measurements, and Dr. F. Fazeli and Mr. J .Saragosa (CanmetMATERIALS, Hamilton, Canada) for their help with thermal etching experiments.
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