After shot blasting, the surface hardness of stainless steel can be further improved through subsequent processes. Shot blasting itself, through plastic deformation and work hardening, achieves a microhardness of HV350-400 on the surface of 304 stainless steel, with a hardened layer depth of approximately 50-100 μm, and forms a residual compressive stress layer. However, if further hardness improvement is required, the following methods can be combined:

Cold work hardening: For austenitic stainless steel (such as 304), cold working is the primary hardening method. Additional cold working (such as cold forging or cold drawing) can be performed after shot blasting. When the deformation exceeds 75%, the dislocation density increases, leading to lattice distortion, and the hardness can reach HV480 (approximately HRC48). However, it should be noted that cold working introduces residual stress, which may increase the risk of cracking. Therefore, annealing is recommended after moderate deformation to balance performance.

Heat treatment and chemical treatment: 304 stainless steel cannot be hardened by conventional heat treatment, but it can be hardened by nitriding or high-frequency quenching. Nitriding is performed at 500-550°C, causing nitrogen and chromium to form dispersed nitrides, significantly improving surface hardness. High-frequency quenching, through rapid heating and cooling, forms a hard layer on the surface, suitable for localized strengthening.

Process Optimization and Precautions: Shot blasting parameters (such as shot hardness and blasting pressure) directly affect the initial hardening effect. It is recommended to select shot with matching hardness (such as alloy steel shot, HRC52-58) to avoid surface whitening or powdering. Subsequent strengthening processes need to be adjusted according to the substrate type: austenitic stainless steel should prioritize cold working or nitriding, while martensitic stainless steel can also be quenched. Furthermore, all surface strengthening processes may introduce residual stress; if necessary, low-temperature annealing (such as 200-300°C) can release stress to avoid brittle fracture.