A study of grain boundary embrittlement in an Fe–8%Mn alloy

A time–temperature ‘C’ curve for intergranular fracture in an Fe–8wt.%Mn alloy has been established by tensile ductility tests at −78°C. In the water quenched condition Auger electron spectroscopy measurements showed N on the intergranular facets with no enhancement of Mn. Two peaks were evident on age hardening curves. On ageing at 450°C a rapid grain boundary segregation of Mn, P, and N was noted with the Mn concentration approaching its equilibrium value. An Arrhenius plot of the embrittlement data suggested that diffusion of N in ferrite was the rate controlling step in the embrittlement of the alloy on ageing. However it is argued, but not proved, that Mn per se will cause embrittlement in the absence of N and P. A kinetic analysis of the segregation rate of Mn and P at 450°C was consistent with the bulk diffusion of these elements in ferrite. Methods of improving impact toughness for possible cryogenic applications are summarised.