6. Gas Tungsten Arc Welding Joints: Impact of Post Weld Heat Treatment (PWHT) and Nitrogen Addition in Shielding Gas

In this study, the UNS S32304 duplex stainless steel was welded by gas tungsten arc welding. The influences of the post weld heat treatment (PWHT) and the nitrogen addition to the shielding gas on the microstructure evolution, ferrite/austenite ratio, and mechanical characteristics of weld joints were investigated. Microstructural investigation showed the presence of coarse austenite laths with smoother boundaries with the matrix. From the results, the austenite and ferrite were observed with no evidence of undesired intermetallic phases. The phase percentage indicated that the best result for reaching an equivalent percentage of austenite and ferrite phases was obtained after using nitrogen gas and PWHT. It was concluded that specimens with the addition of nitrogen gas followed by PWHT show the highest mechanical characteristics among the conditions. The fracture surface of the specimen with the addition of nitrogen shows a small dimple size and a high percentage of separated voids while that after PWHT depicted relatively large dimples.