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.
The research is jointly supported by the National Natural Science Foundation of China (Grant Nos. 51461006 and 51571066), the Natural Science Foundation of the Guizhou Province, China (Grant Nos. 2003 and  6012) and the Guizhou Science and Technology Project (Grant No. (2015) 7646).
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