Grain boundary embrittlement by Mn and eutectoid reaction in binary Fe–12Mn steel

Abstract

The grain boundary embrittlement in a binary Fe-12Mn is due to the grain boundary segregation of Mn. During tempering at 400 degrees C (higher than the equilibrium eutectoid reaction temperature 247 degrees C), reverted austenite particles were formed at lath and grain boundaries through the equilibrium reaction of lath martensite to ferrite austenite. Surprisingly, hydrostatic pressure, which is induced by the transformation of epsilon martensite to austenite during heating at the tempering temperature, resulted in the nonequilibrium eutectoid reaction producing alpha-Mn precipitates at the interface between lath martensite and the transformed austenite during the tempering. The segregation concentration kinetics of Mn formed a convex profile due to the active grain boundary precipitation of the reverted austenite particles and the alpha-Mn particles, which act as a sink for the segregated Mn. Finally, the convex segregation profile of Mn corresponded to the concave profile of intergranular fracture strength. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.