Design and analysis of machined shallow surface of high-strength alloy steel: From microstructure, performance to strengthening mechanism

• Finding the machining under appropriate cutting conditions can not only complete the machining tasks meeting the geometric size requirements, but also improve machined surface quality and performance. • Finding the machining can form superior gradient microstructure on the machined surface of high-strength alloy steel under suitable cutting parameters. • Exploring effect mechanism of machining on quality and performance of superficial layer of high-strength alloy steel in machining process. • Revealing gradient microstructure distribution regular of the superficial layer in the machined state. As a critical determinant of service performance, the gradient microstructure of processed surfaces governs both mechanical strength and fatigue resistance in high-strength alloys. To design and achieve superior processed surfaces, a combined method of theoretical calculations and experimental analysis was utilized to investigate the influence mechanism of machining on the performance and quality of the machined shallow layer in high-strength alloy steel (HSAS) in this study, aiming to reveal the intrinsic correlation between microstructure evolution, surface quality, and mechanical performance. The results demonstrate that machining can generate a gradient microstructure in the processed surface, which significantly enhances the surface’s performance. Quantitative analysis revealed a 33.35 % reduction in grain size, a 114.98 % surge in crystallographic defects and a 57.26 % decrease in lath dimensions, indicating severe grain refinement. The machining process induces considerable disturbances and randomization in crystal orientation, leading to uniform crystal orientation across the surface layer of the workpiece. Performance testing demonstrates that machining substantially improves the nano-hardness of the surface layer in HSAS, while also resulting in a modest enhancement of toughness. These improvements are attributed to the combined effects of fine-grain strengthening, grain-boundary strengthening, and dislocation strengthening, all of which are induced by the processing process described above.