Influence of multiphase on the strain hardening behavior of 60Si2CrVAT spring steel treated by a Q-P-T process.

A strong strain hardening ability in ultra-high strength spring steel 60Si2CrVAT was achieved by the design of multiphase microstructures using a quenching-partitioning-tempering process. The microstructure consisted of ~ 70% martensite/bainite and ~ 30% retained austenite, which was obtained at an optimized partitioning temperature of 380 °C. The corresponding yield strength ratio and the product of strength and elongation were 0.81 and 34,828 MPa%, respectively. Interestingly, this sample exhibited a double-stage strain hardening characteristic with a concave-down shape, which was distinct from that of the other samples. The excellent performance of the ultra-high strength spring steel was mainly due to the interactions between the multiple phases and the stability of the retained austenite during cold deformation. This paper provides a new way of obtaining a strong strain hardening ability in ultra-high strength steels, which is expected to be applicable to the cold coiling process. [ABSTRACT FROM AUTHOR]