Microstructure and Low-Temperature Mechanical Properties of 304 Stainless Steel Joints by PAW + GTAW Combined Welding

The combined double-pass process of plasma arc welding (PAW) + gas tungsten arc welding (GTAW) was performed on 304 austenitic stainless steel with the thickness of 12 mm. Results indicated that two different morphologies of ferrite (e.g., lathy δ-ferrite and skeletal δ-ferrite) were formed within the austenite matrix in PAW weld metal (PAW-WM). GTAW weld metal (GTAW-WM) was mainly composed of fine austenite and skeletal δ-ferrite. In transition zone between PAW-WM and GTAW-WM, epitaxial growth contributed to cellular dendritic crystals transforming into columnar crystals. The tensile strength of joint is about 700 MPa. The impact toughness of WM varied from 281 J (20 °C) to 122 (−196 °C), while the impact toughness of heat-affected zone (HAZ) varied from 205 J (20 °C) to 112 J (−196 °C).