Influence of cold rolling on the microstructure and properties of lath martensite in alloy steels

Abstract

The influence of cold rolling on the microstructure and mechanical properties of lath martensite in 18% Ni maraging steel and two low-alloy steels, Mn-Cr-B and En24, has been investigated by measuring hardness and tensile properties, and using optical and transmission electron microscopy. It was found that the increase in hardness and strength obtained on cold rolling was much less for the maraging steel than for the Mn-Cr-B and En24 steels. The martensite in all the steels deformed by slip and not by twinning. The packet structure of the martensite itself was affected only at high magnitudes of strain (≥50% reduction). The dislocation configurations in the cold-worked state were distinctly different in the three steels. Straight dislocations were observed in the maraging steel and the dislocation density was not markedly high even at 50% plastic strain. The Mn-Cr-B and En24 steels deformed by the formation of cell structures, which persisted up to severe strains, and with significant increases in the dislocation densities thereafter.