Experimental Research On Stress Corrosion Cracking Of Shot Peening304Austenitic Stainless Steel

As one of material strengthening techniques, shot peening process can improve the mechanical and fatigue property of the metal surface efficiently. In recent years, more attention have been gradually paid on research of the effect of shot peening on stress corrosion resistance of metallic material all over the world, and some exploratory achievements have been obtained, however, little research was carried on the effect of shot peening technological parameters on stress corrosion resistance. Stress corrosion cracking is the most common failure mode of austenitic stainless steel, and stress corrosion can cause sudden breaks on stainless steel equipments, which will result in catastrophic accident. Therefore, it is extremely important to carry out intensive research on the effect of shot peening strengthening on the stress corrosion resistance of stainless steel, not only for improving the safety of equipment usage but also reducing casualties and loss of property.Type304stainless steel plates were treated by glass bead peening in this thesis. The micro-hardness and grain size of steel plates were measured by optical microscope, and the effects of glass bead diameters, shots coverage and shot peening pressure on surface hardness and grains were studied. The stress corrosion susceptibility of304stainless steel in chloridion solution has been studied on the basis of slow strain rate test and the influence law of different shot peening technological parameters on the index of stress corrosion susceptibility is summarized. Main conclusions are summarized as follows:(1) Shot peening process can improve the surface hardness of the type304stainless steel specimen, the hardness at the surface decreases sharply with the increase of depth from the surface and finally remain stable with the inflection point at the depth of150～200μm from the surface. The surface hardness of the specimen shows an increasing rate, following the increase in the diameter of shots, shots coverage and shot peening pressure. (2) Shot peening process on the specimen surface can refine surface grains. Shots impact causes plastic deformation on the specimen surface, and austenite grains are elongated and fragmentized, which generates small grains with high degrees of dislocation. The grain refinement occurs at the depth of150-200um from the surface.(3) The resistance of stress corrosion of304stainless steel is improved and the susceptibility of stress corrosion is reduced after the shot peening process, and the effects above are more obvious in the cross-weld specimens than that in base metal test specimen.(4) Among all the parameters of the shot peening strengthening, the diameters of the shots and the shots coverage have unobvious effects on the index of stress corrosion susceptibility. However, the effect of shot peening pressure is obvious. The effect is not remarkable on the index of stress corrosion susceptibility when shot peening pressure is about0.25MPa, while the index of stress corrosion susceptibility shows an obvious decrease after shot peening treatment when the pressure is above0.25MPa.