Influence of hydrogen on surface integrity and phase transformation of laser peened 316L stainless steel

To investigate the influence of hydrogen atoms on the surface integrity and the phase transformation of type 316L stainless steel after laser peening, specimens of laser peened 316L austenitic stainless steel were cathodic hydrogen charged. The surface residual stress of samples subjected to laser peening, the metallurgical structures and the microhardness were studied. The result shows that compressive residual stress is induced by laser peening. The compressive residual stress is 35.55 MPa, 46 MPa and 72 MPa, respectively, when the laser energy is 2 J, 5 J and 8 J. Meanwhile, laser peening refines the grain size, and the surface microhardness reveals that laser peening suppress the increase of microhardness caused by hydrogen atoms. Compared with unimpacted specimens, the amount of hydrogen attacked holes on impacted samples is decreased. The X-ray diffraction reveals that hydrogen charging is responsible for the martensite formed on the surface and the laser peening suppress the formation of martensite.