LOW-TEMPERATURE TOUGHNESS OF 6%Mn STEELS.

Fe-Mn alloys have microstructures similar to those of Fe-Ni alloys in iron-rich regions; therefore they have potentials as structural materials at cryogenic temperatures. Fe-Mn alloys, however, lose their toughness by catastrophic intergranular failure when tested at low temperatures. This is attributed to the segregation of impurities to grain boundaries. The segregation can take place at higher temperatures than 600 degree C, in both austenite( gamma ) and two-phase( alpha plus gamma ) regions. An addition of molybdenum has been found to be effective in reducing the segregation of phosphorus in the two-phase region and enhancing toughness. However, no perceivable difference was observed in segregation in the gamma field. Double temper has been also identified as a beneficial treatment for improving toughness, which promoted the reversion of austenite along grain boundaries and reduced the susceptibility to intergranular failure.