A Study On Effects Of Shot-peening On Stress Corrosion Cracking In Stainless Steel Welded Joints

Residual stresses induced by welding are sufficient to cause stress corrosioncracking (SCC). However, shot peening can impose compressive stresses on the surfaceof welded joints that negate the tensile stresses to prevent welded joints from SCC. Basedon X-ray stress measurement, SCC test in 42% magnesium chloride and finite elementanalysis, the mechanism of shot-peening against SCC is studied and the susceptibility ofweldments peend by glass beads and steel shots to SCC is evaluated. Main research work and conclusions are summarized as follows: (1) The distribution of residual stress caused by welding is measured using X-raymethod. The maximum stress in the weld is close to the yield strength of AISI 304stainless steel, and the stresses are negative at the both ends of the weld and far from theweld. (2) Also using X-ray method to measure stress caused by shot-peening. The resultsshow that the higher peening coverage, the higher residual compressive stresses in thesurface of weldments; while under the same Almen intensity, the residual compressivestresses induced by glass beads shot-peening are larger than those by cast steel shots. Andwhen the peening coverage of glass-bead shot peening is increased to 200%, austeniteschange into martensites in target material. (3) Temperature and stress fields of welding are simulated by FEM using ABAQUScodes. The 3-D solid elements are used in FEM model, and temperature dependedmaterial properties are considered as well as the convection and radiation as boundaryconditions. Gaussian function heat flow method is applied to simulate the heat source,and model-change ability to simulate multi-pass weld. The temperature field and residualstress field of 3-D multi-pass weld are obtained. The results of simulation and testing areidentical. (4) The shot peening process is simulated by FEM using ABAQUS codes. The 3-D IIIABSTRACTlinear reduced-integration elements are used. Hourglass, kinematic hardening of targetmaterial, coverage and initial residual stress induced by welding are considered. Stressfields in the weldments peend by glass-bead and steel shots are obtained, and comparedunder the same Almen intensity. The higher peening coverage in glass-beads shotpeening results in higher residual compressive stress in the surface of weldments thansteel shots, which agrees with the experimental results. (5) All weldments, unpeened and peened, are immersed in boiling 42% magnesiumchloride stress corrosion test. Unpeened specimens crack within 6 hours. Thesteel-peened specimens with 50% coverage crack in the MgCl2after immersion for 310hours, while the steel-peened specimens with 100% coverage crack after immersion for3500 hours. However, steel-peened specimens with 200% coverage and glass-peenedspecimens with 50%, 100% and 200% coverage are tested for a total of 3500 hourswithout visible stress corrosion cracks in the peened surfaces. In a word, shot peening isan effective method for protecting weldments against SCC, and weldments peened byglass beads resist SCC better than those peened by steel shots.