Study on microstructure characterization and mechanical properties of AISI 444 Ferritic Stainless Steel Joint by high frequency pulse K-TIG welding

Abstract

Abstract In this study, high frequency pulse K-TIG was used to weld AISI 444 ferritic stainless steel (FSS) with a thickness of 6 mm, and the welding process window was determined, and complete penetration was achieved in the state of single pass autogenous welding. The influence law of technological parameters and weld appearance was analyzed. The microstructure characteristics of weld zone (WZ) and heat-affected zone (HAZ) was analyzed. Finally, the mechanical properties of welded joints are evaluated. It is found that the thermal conductivity of FSS is large, so the welding process window is relatively narrow, and the welding heat input determines whether the weld can achieve complete penetration. The second phase, such as σ phase, χ phase and Laves phase, is precipitated in WZ and HAZ phases. At the crystal boundary, the σ phase and χ phase appears, while the Laves phase is dispersed in the intragranular and crystal boundary. In addition, NbC isfound in the HAZ. The brittle-hard phase and coarse grain have great influence on tensile properties and impact toughness at room temperature. The tensile strength of the weld is equivalent to 70.57% of the parent material, which is 596 MPa. Its average impact toughness value is 29.7J, which is equivalent to 43.04% of the BM. Although the strength and toughness of FSS joints welded with high-frequency pulse K-TIG are lower than that of BM, the welding efficiency is significantly improved, and it is suitable for components with slightly lower load requirements.