Secondary Hardening Characteristics and Those Effects on the Wear and Thermal Shock Resistance of 5%Cr-Mo-V Steel Roll for Cold Strip Mill

Secondary hardening characteristics and those effects on a wear and a thermal shock resistance of the 5%Cr-2%Mo-1%V steel roll for cold strip mill were studied.The secondary hardening by a tempering was induced both by the precipitation of carbide during holding stage and by the transformation of retained austenite to a fresh martensite (FM) during the cooling stage.The increase in FM volume % raised the hardness in secondary hardening. The hardness of FM was calculated as Hv935. The wear and thermal shock resistance decreased as the volume % of FM increased. This is due to the preferential carbide precipitation on grain boundaries.On the practical viewpoint, the suitable micro-structure for the work roll is the tempered martensite containing a 20% of FM. The work roll showed an excellent wear and thermal shock resistance compared to the conventional roll tempered at low temperature.