Tailoring the strength and ductility of T91 steel by partial tempering treatment

T91 ferritic/martensitic steel (modified 9Cr-1 Mo steel) with high strength and high ductility is considered one of the promising structural materials for various industrial applications. Recent studies show that equal channel angular pressing can improve the yield strength of 191 steel to 1.6 GPa but degrade the uniform elongation to similar to 1%. Here, we report that by using a modified quenching and tempering treatment, 191 steel can achieve a high yield strength of 1.4 GPa and a uniform elongation of similar to 5.5%. Extensive microstructure analyses show the formation of transition carbides and ultra-fine martensite within bainite grains. This study provides an alternative approach to obtain a combined enhancement of strength and ductility for 191 steel. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.