Carbon in Solution and the Charpy Impact Performance of Medium Mn Steels

Abstract

Carbon is a well known austenite stabiliser and can be used to alter the stacking fault energy and stability against martensitic transformation in medium Mn steels, producing a range of deformation mechanisms such as the Transformation Induced Plasticity (TRIP) or combined Twinning and Transformation Induced Plasticity (TWIP + TRIP) effects. However, the effect of C beyond quasi-static tensile behaviour is less well known. Therefore, two medium Mn steels with 0.2 and 0.5 wt pct C were designed to produce similar austenite fractions and stability and therefore tensile behaviour. These were processed to form lamellar and mixed equiaxed + lamellar microstructures. The low C steel had a corrected Charpy impact energy (KV10 ) of 320 J cm−2 compared to 66 J cm−2 in the high C steel despite both having a ductility of over 35 pct. Interface segregation, e.g., of tramp elements, was investigated as a potential cause and none was found.