Effect of machining processes on the quenching and tempering surface layer of ultra-high strength steel

The initial characteristics of the surface layer following the quenching and tempering treatment of ultra-high-strength steel play a significant role in determining the subsequent precision machining. This study focus on investigating the influence of machining processes on the quenching and tempering surface layer. The machining processes affect both the oxidation of the quenching and tempering treatment and the development of a distinct preferred grain orientation. Gradual diminishment of surface abrasions leads to the transformation of the needle-like oxidation pattern into a layered oxidation structure. The preferred orientation of the grains prevents the grains from shear sliding, thereby enhancing the Taylor effect. Formation mechanisms of the microhardness and residual stress of the quenching and tempering surface layer induced by machining processes were also discussed and completely revealed. The microhardness is mainly attributed to the dynamic Hall-Petch effect, while plastic strain, dislocation energy storage, and phase transformation contribute to the residual stress changes.