Role of vanadium additions on tensile and cryogenic-temperature charpy impact properties in hot-rolled high-Mn austenitic steels

Abstract

It is well known that the vanadium addition can effectively enhance yield strength of high manganese austenitic steel, and numerous fine VC particles can precipitate in matrix in a relatively low annealing temperature range of 600–800 °C. Unfortunately, a relatively low annealing temperature strongly deteriorates cryogenic impact toughness at -196 °C due to grain boundary segregation and precipitation. Hence, it is of significance to understand the role of vanadium additions in high manganese austenitic steel, which is a hopeful cryogenic material. It has been determined that an effective strength increment can be attained as the vanadium addition reaches 0.6 wt.%, and the double strengthened modes of precipitation strengthening and hardened structure strengthening are found due to vanadium additions in the studied Fe-24Mn-0.6C-1.9Al high manganese austenitic steel. The results show that there is a minor increase in yield strength by the vanadium addition of 0.31 wt.%, but the high vanadium addition of 0.60 wt.% can greatly enhance the yield strength by ~113 MPa, and the cryogenic toughness can still achieve a high level of 121 J. The grain refinement and solid solution strengthening effects of vanadium are rather weak, whereas the high vanadium addition strongly suppresses recrystallization and recovery. Moreover, high-density dislocations in hardened structures suppress the twinning activities, leading to sparse twins of the V-0.6 steel. Due to the sparse twins and small carbide size, the retardation effect of carbides on twinning is considered to be small. The negative effects of carbides and grain size on cryogenic toughness are relatively small compared to that of high-density dislocations in the V-0.6 steel. To summarize, the V-0.6 steel exhibits a better combination of yield strength and cryogenic toughness compared to the reported high manganese austenitic steels.