Abstract:

To address the compatibility issue between microstructure stability and mechanical property matching during the welding of high-nitrogen austenitic stainless steel, autogenous TIG butt welding was employed. With welding speed and shielding gas conditions kept constant, the welding current was used as the primary variable to systematically investigate its effects on the microstructural zoning characteristics, Cr₂N nitride precipitation behavior, and the evolution of mechanical properties of the welded joints. The results reveal that the welded joints exhibit typical microstructural zones, including the weld zone, coarse-grained heat-affected zone, and fine-grained heat-affected zone. Welding current significantly affects the grain characteristics and microstructural uniformity in each zone. XRD analysis indicates that Cr₂N is detectable in the weld metal at currents from 160 to 200 A, whereas when the welding current is increased to 220 A and above, the diffraction peaks of Cr₂N are significantly weakened and eventually disappear. Based on the analysis of welding thermal cycles, this suggests that higher welding currents kinetically suppress the precipitation process of Cr₂N by reducing the effective residence time of the weld zone within the critical temperature range sensitive to Cr₂N precipitation. Mechanical property tests show that the tensile strength and impact toughness of the welded joints exhibit a nonmonotonic trend with increasing welding current—initially decreasing, then increasing, and finally decreasing again. Optimal strength-toughness matching was achieved at 220 A. Overall, welding current plays a critical role in regulating Cr₂N precipitation behavior and microstructural gradient characteristics, thereby substantially affecting the microstructure stability and mechanical properties of high-nitrogen austenitic stainless steel welded joints.

Key words: high-nitrogen steel, TIG welding, microstructure, mechanical properties, bone nail, medical materials