Effect of austempering temperatures on microstructure and mechanical properties of 52CrMoV4 spring steel

• The refined bainite-martensite composite structure prepared by austempering at 300 °C can increase the impact toughness of 52CrMoV4 spring steel to 53.1 J·cm −2 without loss of strength, which is 32.1 % higher than that of the traditional oil quenching and tempering specimen (40.2 J·cm −2 ). • The tempering after austempering·redistributes carbides and reduces dislocation density, thereby minimizing cleavage crack nucleation sites. The detailed TEM and EBSD evidence of this mechanism is novel and aligns with fracture surface observations (quasi-cleavage to microvoid coalescence transition). • The study identifies 360 °C as the optimal tempering temperature for maximizing impact toughness while maintaining strength. The discovery that excessive tempering (>400 °C) reintroduces brittleness via carbide coarsening further highlights the originality of the process optimization. • This study validates firstly that austempered 52CrMoV4 steel can replace costlier alloys in high-stress applications requiring simultaneous strength and impact resistance, such as automotive suspension systems, which expands the application range of the 52CrMoV4 steel. 52CrMoV4 alloy spring steel has excellent mechanical properties and is widely used in the production of automobile suspension systems, spring sheets, torsion bars, and other parts. This paper improves the traditional oil quenching process. Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Electron Backscattered Diffraction (EBSD), tensile testing, and other methods were used to experimentally study the effect of heat treatment process on the microstructure and mechanical properties of 52CrMoV4 alloy spring steel. The results showed that specimens treated with traditional oil quenching process have higher strength but poor impact toughness. The introduction of bainite into the microstructure was achieved via austempering at 300 °C followed by low-temperature tempering, leading to a 32.1 % enhancement in impact toughness while maintaining the strength level. Furthermore, we demonstrated that tempering can effectively improve the distribution of carbides in the microstructure and reduce its dislocation density. By reducing the formation of nucleation sites on cleavage planes of impact specimens, this process significantly enhances the impact toughness. By optimizing the bainite austempering process of 52CrMoV4 spring steel, it can achieve excellent comprehensive mechanical properties, especially impact toughness. Thus, it can reduce the risk of damage under the impact and ensure the safety of equipment and personnel.