Effects of Deep Rolling on Surface Residual Stress and Microhardness of JIS SS400 MIG Welding

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Metal Inert Gas (MIG) welding process is a common welding process for carbon steels. During the cooling after welding, non-uniform cooling cause tensile residual stress on the surface of welded joint and, in most cases, in Heat Affected Zone (HAZ) also. The tensile residual stress is undesirable because it affects the strength and shorten the workpiece fatigue life. In order to convert the tensile residual stresses to desirable compressive residual stresses, the mechanical surface treatment like deep rolling process was used in this research. The surface residual stresses were measured by XRD machine with the sin2ψ method. For statistical analysis of significant factors used in deep rolling process, there are three factors each factor has two levels: rolling pressure, rolling speed and number of passes. Taguchi experimental design was used in conjunction with a deep rolling process to determine factors affected the surface residual stresses and surface microhardness. The results of the research showed that the most significant factors that affect the surface residual stress and surface microhardness were the number of passes, followed by the rolling pressure and the rolling speed, respectively. The maximum compressive residual stress measured at the welded joint was -521.5 MPa. The highest measured surface microhardness was 266.2 HV at the welded joint. The appropriated factors of deep rolling process for JIS SS400 MIG welding were rolling pressure 270 MPa, rolling speed 1,500 mm/min and number of passes 3 times.