Abstact Due to the intense concentration of heat in the heat source of welding, the regions near the weld line undergo severe thermal cycles, thereby generating in homogeneous plastic deformation and residual stresses in weldment. Residual stresses are generally detrimental, increasing the susceptibility of a weld to fatigue damage, stress corrosion cracking and fracture. Monel 400 is a High-Nickel Alloy that is subjected to SCC when it is exposed to hydrofluric or hydrochloric acid in the presence of oxygen and residual stress. In this research in order to study the effect of welding parameter on the residual stress of this alloy, four specimens welded by Gas Tungsten Arc Welding (GTAW) Under the different heat input. Also in order to reduce the residual stress in this alloy, specimens welded by LPW, HSW and LPHSW technique. In addition eight specimens were welded by GTAW under same heat input. After welding, stress relieving heat treatment was performed in different times and temperatures. Then for whole of specimens, the residual stresses were determined by using the Hole-Drilling Method according to ASTM standard E837. The results of measured showed that increase of heat input has minor it ' s influence on the transverse residual stresses and was more at standing on the longitudinal residual stresses. It was discovered that it ' s not possible to create wide range of change to reduce residual stress by altering GTAW welding parameters. Different technique showed that via the LPW technique it ' s possible to reduce longitudinal residual stresses greatly. In HSW and LPHSW techniques tensile longitudinal residual stresses changed to compressive stresses. Measured residual stress for heat treated specimens showed that heat treatmaent couldn ' t relieved the residual stresses completely. Also distinguished that increasing the temperature of stress relieving heat treatment more than 650°C and increasing time of stress relieving more than one hour don ' t have significant influence on percentage of reduction residual stress.
