Influence of Thermomechanical Treatment in Austenitic and Ferritic Fields on Tensile Properties of Reduced Activation Ferritic–Martensitic Steel

Abstract

In the present study, reduced activation ferritic–martensitic steel subjected to thermomechanical treatment (TMT), in austenitic phase field and ferritic phase field, was evaluated for tensile properties (at temperatures 300–923 K) and compared with those under normalized and tempered (N+T) condition. The steel subjected to TMT in austenitic phase field consists of fully tempered martensitic structure and that subjected to TMT in ferritic phase field consists of the fully ferritic structure within prior austenite grain boundaries (PAGBs) after tempering treatment. In the case of TMT in austenitic phase field, allotriomorphic ferrite was also observed along the PAGBs of steel. The tempered martensite of TMT steels is decorated with the increased population of finer precipitates of M₂₃C₆ and MX-type compared to the N+T condition. The TMT process improved the strength properties of the steel over the N+T condition without compromising the ductility of the material. Interestingly, the steel subjected to TMT in austenitic phase field resulted in higher yield and ultimate tensile strengths compared to that in ferritic phase field. The improved tensile properties of the steel in TMT condition, over N+T condition, is thus attributed to the microstructural features such as the increase in dislocation density and the increased population of fine M₂₃C₆ and MX-type precipitates in TMT steel.