In this paper, the effects of two parameters named width of the roller and exerted force on it in direct and indirect rolling, on residual stresses in Friction Stir Welding (FSW) process of SU304 steel have been studied. FSW numerical modeling has been performed by ABAQUS. In both direct and indirect rolling, five levels have been considered for each variable. Based on the results, it has been shown that both variables have significant effects on the pattern and maximum of residual stresses. In general, in both direct and indirect rolling, by increasing the rolling force, residual stresses decrease intensely. In direct rolling, tensile residual stresses decrement happens locally by using relatively narrow rollers and increasing the rolling force. While in wide rollers, the decrement in tensile residual stresses occurs constantly. Based on the results, using direct rolling causes more decrement in welding tensile residual stresses in comparison with indirect rolling. In direct and indirect rolling, the minimum tensile residual stresses take place when the width of roller is equal to diameter and half of the diameter of welding tool, respectively. In this situation, the maximum of tensile residual stresses decreases 97.4% for direct rolling and 57.3% for indirect rolling.
