The phase-structural state and mechanical properties of 60Si2CrVA steel in the state of Q-n-P-T treatment

The article is dedicated to the effect of low-temperature tempering (at 200, 250, 300C for 90 min) on microstructure and mechanical properties of 60Si2CrVA steel, subjected to Q-n-P treatment. It has been found that the Q-n-P treatment greatly enhances the mechanical properties of 60Si2CrVA steel as compared to conventional treatment (quenching and tempering at 300С). This is due to the formation of a heterogeneous structure combining martensite, lower bainite and residual austenite. A low-temperature tempering at 200-300C after Q-n-P treatment results in a 2-fold increase in ductility while maintaining higher strength and hardness. After Q-n-P and Q-n-P-T treatments the steel can be destroyed through a more ductile mechanism combining a quasi-cleavage and the dimples formation. The tempering at 300C provides the highest level of the PSE («strength/ductility»), but causes a 30% decrease in impact toughness as compared to Q-n-P treatment. As the tempering temperature rises, the amount of residual austenite decreases to 14 vol. % with the increase in carbon concentration in residual austenite. The tempering at 300C leads to the formation of cementite carbides, which bring about a decrease in the impact toughness and the brittle component increase on the fracture surface