Research on the evolution of material surface characteristics and anti-fatigue based on thermal field assisted rolling strengthening

Aiming at the challenge of enhancing the fatigue life of vehicle torsion bars under higher strength requirements, a rolling strengthening method based on thermal softening was proposed. This technique employs heat-assisted rolling (HTDR) to improve the surface characteristics of the material. Following quenching and low-temperature tempering, a high-strength martensitic structure was achieved. With increasing temperature, the flow stress of the material decreased, indicating notable thermal softening behavior. Experimental results show that, compared to room-temperature rolling, the HTDR process reduces the average surface roughness and enhances the magnitude of residual compressive stresses. The modified surface layer features a refined grain structure, increased dislocation density, a higher fraction of recrystallized grains, and greater plastic deformation. Additionally, the HTDR process produced a nano-gradient surface layer with fine grains and abundant precipitates distributed along grain boundaries. The optimal treatment at 160°C-DR resulted in the highest fatigue life, while the HTDR process overall effectively reduced crack propagation rates. These findings offer valuable technical insights for surface modification and fatigue-resistant manufacturing of difficult-to-machine ultra-high-strength steels.