The influence of pre-cooling deformation on the microstructure and properties of Cr-Mn-Ni series low-alloy ultra-high-strength steels with varying Mo contents

In order to investigate the impact of the pre-cooling deformation on the microstructure and properties, three experimental steels were subjected to the pre-cooling deformation prior to heat treatment. The results indicated that an increase in the Mo resulted in a decrease in pearlite within the microstructure subsequent to pre-cooling deformation, as well as a decline in the work-hardening response. The texture of the 0 Mo steel approximated the Copper-type texture, that of the 0.15 Mo steel was closer to the combination of the Copper-type and the Cube-type texture, and the 0.25 Mo steel basically conformed to the Goss-type texture. After heat treatment (HT), all the precipitated phases were cementite. As the Mo increased, the morphology of the cementite changed from short rod-like to long strip-like. After pre-cold deformation+heat treatment (CD-HT), the microstructure became finer, and apart from cementite, the Cr 7 C 3 and (Mo/Fe) 3 C alloy cementites also emerged. The improvement of the work-hardening phenomenon by the Mo is the cause of the decrease in yield strength, the maximum tensile strength is 1840 MPa, and the maximum impact energy is 75 J. The reduction in lath width and the increase in dislocation density are the primary reasons for the increase in tensile strength. The residual austenite is uniformly distributed in a film-like form between the martensite laths, which is the crucial reason for the good plasticity and toughness. After HT process, as the Mo increases, the proportion of Σ1 and Σ3 grain boundaries rises, leading to an increase in impact energy and elongation.