Microstructure vs. impact toughness relationship in Hadfield's austenitic manganese steel

Abstract

Austenitic manganese steels are solution annealed and quenched to remove the embrittling grain boundary carbides present in as-cast condition. Their poor machinability makes the direct assessment of their mechanical properties by specimen preparation and testing expensive. Microstructural characterization is a desirable way to observe if satisfactory mechanical properties have been achieved. However, uncertainties exist in this practice as the grain boundary features are heterogeneously distributed and also a differentiation must be made between thin and thick carbides. The former requires an averaging process over a sufficiently large number of views, and the latter, a minimum 200H magnification. A procedure to evaluate grain boundary coverage by the embrittling constituents, and a relationship between observed coverage and impact toughness are presented.