Numerical Simulation for the Hard‐Tooth Surface Heat Treatment Process of 20CrMnTi Steel Spiral Bevel Gear Based on Multifield Coupling Model

To obtain ideal fatigue resistance, low‐carbon steel spiral bevel gears for axles generally undergo continuous carburizing‐quenching‐tempering heat treatment (hereinafter referred to as hard‐tooth surface heat treatment). Herein, on the basis of multifield coupling effects, a multifield coupling model of hard‐tooth surface heat treatment is established. The model considers the latent heat generated via phase transformation and the influence of surface carbon concentration on the temperature at which martensitic transformation commences ( M s ). A numerical simulation and experimental verification are conducted on the hard‐tooth surface heat treatment process for the 20CrMnTi steel spiral bevel gear. Results show that the maximum relative errors in carbon concentration, hardness, retained austenite content, and residual stress between the predicted and measured values are 4.8, 4.3, 4.6, and 7.6%, respectively. In addition, the article investigates the microstructure and stress evolution patterns of the spiral bevel gear during quenching. The results reveal that M s decreases with increasing carbon concentration on the gear surface, resulting in the martensite transformation on the surface lagging significantly behind that at the core. The proposed model provides a reference for developing a formulating strategy for a realistic hard‐tooth surface heat treatment process of spiral bevel gear.