Control of the metallographic and mechanical properties of Cr8 cold-work die steel by laser continuous/dispersed quenching

Abstract

Laser continuous/dispersed quenching techniques were used for surface hardening Cr8 cold work die steel, and its metallographic microstructures and mechanical properties are investigated in this work. Typical mixed structure which composed of carbides in different morphologies and acicular martensite can be obtained by laser quenching. The excellent wear resistance and surface hardness of Cr8 die steel are attributed to the synergistic effect of solid solution strengthening, grain refinement and high dislocation density. Meanwhile, the phase change hardening layer structure and residual tensile stress induced by full area coverage scanning (LCQ) are the main factors to deteriorate the impact toughness and bending performance after laser quenching. The soft substrate-hardened unit structure with laterally spaced distribution (LDQ) obtained by graphical scanning reduces the heat accumulation effect on the surface, which reduces concentration of deformation near the hardened layer. The bending property and fracture mechanism are studied. Compared with the forging die material treated by LCQ, the impact energy and bending resistances of forging die materials treated by LDQ are enhanced significantly. Consequently, Cr8 die steel takes into account the same wear resistance, and scanning strategy should be controlled to retain more interval distribution hardening units in layer structure for superior impact toughness and bending properties.