TIG welding of EN 1.3964 low-magnetic austenitic stainless steel: effects of welding parameters on microstructure, mechanical behavior, and ferrite stability

Abstract

EN 1.3964 nitrogen-alloyed austenitic stainless steel is widely employed in naval and offshore structures because of its high strength, corrosion resistance, and low magnetic response. This study investigates the influence of TIG welding current and argon shielding-gas flow rate on the microstructural evolution, ferrite content, hardness distribution, tensile properties, and overall weld quality of 2.5 mm EN 1.3964 plates. Optical microscopy, scanning electron microscopy/x-ray spectroscopy, ferrite measurements, Vickers microhardness testing, tensile testing, and analysis of variance were used to establish process–microstructure–property relationships. The results demonstrate that welding current is the dominant parameter controlling thermal history, grain refinement, heat-affected-zone width, and mechanical performance, whereas shielding-gas flow primarily affects arc stability and surface protection. Approximately 3% δ-ferrite area fraction was measured under all investigated conditions, indicating stable phase balance within the examined processing window. Lower heat input promoted finer microstructures, smoother hardness gradients, and superior tensile properties. Statistical analysis confirmed the significance of welding current for the measured mechanical responses. The optimum parameter combination was 65 A and 12 l min−1, providing the best balance between weld quality, tensile performance, and microstructural stability. The findings provide practical guidance for fabrication of low-magnetic stainless-steel structures for naval applications.