High strength and high ductility of 60Si2CrVAT spring steel through a novel quenching and partitioning (Q-P) process

Abstract

The balance between strength and ductility in spring steel is a perennial issue. However, production using traditional quenching and tempering (Q-T) process is challenging because tempered martensite provides high tensile strength but significantly reduces ductility. To solve this problem, we propose a novel quenching and partitioning (Q-P) process to enhance the comprehensive properties of 60Si2CrVAT spring steel. The novel Q-P process introduced 31.56% excellent mechanical stability retained austenite, which existed mostly as a film-like between the martensite and bainite laths, and ensured a continuous and long-lasting transformation-induced plasticity (TRIP) effect. Moreover, Q-P process reduced the effective grain size due to the diffusion of carbon, and changed the fracture behavior due to the coordinated deformation of multiphase microstructure. Consequently, the total elongation of the spring steel increased by approximately 180%, from 7.8% to 21.7%, while the tensile strength of the spring steel was not affected and remained at a high of 1809 MPa. In conclusion, the novel Q-P process adjusted the volume fraction of the martensite, bainite, and retained austenite multiphase microstructure, and fully leveraged the synergistic effect of the multiphase microstructure to optimize the properties of spring steel.