Effects of laser shock peening in different processes on fatigue life of 32CrNi steel

Abstract

To further understand the effects of LSP on large components of high strength steel and provide improved solutions, this paper conducts research on effects of surface integrity on fatigue life in the LSP process with absorbent coating (LSPC), without absorbent coating (LSPN), without absorbent coating but with axial polishing (LSPP) respectively. The research also put a baseline specimens (BSL) before LSP for a comparison. Results show that average fatigue life in the LSPN process is 47.8% shorter than that of baseline specimens, and crack site area presents an obvious splitting-like tearing step. In the LSPC process, fatigue life is 31.7% longer than that of baseline specimens, and crack initiation site develops from surface to subsurface. In the LSPP process, the specimens show the longest fatigue life of 2.53 × 105cycles, with multiple fine microcracks developing simultaneously. Axial polishing removes ablative layer and tensile residual stress in the LSPN process and reduces dislocation pile-ups and refines grains in the LSPC process, resulting in a surface roughness of Ra 0.61 μm, surface residual stress of −531MPa and microhardness of 405HV0.025.Thus, the fatigue performances were found to be significantly affected by multiple surface integrity indicators induced by different LSP processes. In this paper, the effect of LSP on surface integrity on the subface and its influence on crack initiation and propagation have also been discussed, the crack initiation mechanisms in different processes were explained by using Murakami's Kmax equation.