Abstract: Microstructures of the cutting superficial layer has an important influence on the service performance of mechanical components. To obtain machined surfaces with excellent performance, theoretical calculation and test analysis were carried out to investigate the internal correlation between microstructure evolution and mechanical property enhancement of superficial layers of high-strength alloy steel (HSAS) under different cutting velocities. Results showed that the medium-high cutting velocity can achieve the formation of gradient microstructures of machined surfaces of HSAS maximally. From the outside to the inside, they are respectively the recovery layer where dense nano equiaxed crystals are located, and the rheological layer with high-density substructure and the distorted layer where grains are in the residual distortion. The average grain size is relatively smallest (392.1 nm) at medium-high speeds, and the dislocation density is relatively highest (1.072 5×10¹² cm^-2). Substructures such as deformation strain, dislocations and small-angle grain boundaries are highly concentrated in the rheological layer. Based on performance test experiments, it was also found that The medium-high cutting speed achieves the simultaneous improvement of the hardness, surface quality and toughness of the superficial layer of HSAS, which is the result of the combined effect of the fine grain strengthening and the dislocation strengthening formed by the microstructure changes above brought about by medium-high cutting velocity.

Key words: high-strength alloy steel, microstructure, superficial layer, gradient-distribution, surface performances