Study on the surface integrity distribution of 300M ultrahigh strength steel subjected to different surface modification treatments

Abstract

The surface integrity of 300M steel subjected to shot peening (SP), laser shock peening (LSP), ultrasonic surface rolling process (USRP), and hybrid laser shock peening with ultrasonic surface rolling process (LSP + USRP) processes were compared. The results indicate that USRP and LSP + USRP generate a smooth surface with Ra in the range of 0.05 μm ~ 0.10 μm while SP and LSP increase the Ra magnitude regarding grinding by 56.5 % and 18.8 %, respectively. Severe plastic deformation is introduced on the treated specimens, owing to which a gradient microstructure with nanostructured grains at the topmost surface (320 nm ~ 1130 nm in thickness) is observed. The depth of the compressive residual stress layer after SMTs achieves in the range of 200 μm ~ 2000 μm, of which the LSP + USRP generates the maximum value. The magnitude of surface compressive residual stress significantly increases compared with the control sample, which locates in the range of −709 MPa ~ −1167 MPa. An obvious work hardening is characterized after SMTs, of which the SP process presents a 31.2 % increase in the magnitude of surface microhardness and LSP + USRP holds the deepest hardening layer of 600 μm ~ 700 μm. Comparing the single SMT, the hybrid LSP + USRP treatment was found to be the most effective surface modification technique.