Microstructural and Performance Analysis of 304 Stainless Steel Narrow Gap Oscillating TIG Welded Joints

GAO Hui; QU Jiajun; ZHANG Dongsheng; CHENG Jincai

doi:10.3969/j.issn.1674-6457.2026.04.012

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Journal of Netshape Forming Engineering ›› 2026, Vol. 18 ›› Issue (4) : 117-125. DOI: 10.3969/j.issn.1674-6457.2026.04.012

Advanced Joining Technology

Microstructural and Performance Analysis of 304 Stainless Steel Narrow Gap Oscillating TIG Welded Joints

GAO Hui^*, QU Jiajun, ZHANG Dongsheng, CHENG Jincai

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Abstract

The work aims to investigate the applicability of narrow-gap oscillating TIG welding technology for stainless steel pipes and the microstructural and mechanical property distribution patterns of narrow-gap single-pass multi-layer welded joints in 304 stainless steel U-groove pipes using 316L welding wires. Narrow-gap oscillating TIG welding technology was employed to weld 304 stainless steel. The microstructural distribution of the welded joints was observed with an optical microscope. Additionally, tensile experiment, impact experiment, microhardness experiment, and electrochemical corrosion experiment were conducted on the welded joints using equipment such as a tensile testing machine, Vickers hardness tester, and impact testing machine, followed by analysis. The results showed that a high-quality welded joint with a thickness of 20 mm was obtained, featuring an aesthetically pleasing weld bead formation, no weld porosity, and no incomplete fusion on the side walls. The weld microstructure consists of directional austenite with a small amount of discontinuous skeletal ferrite dispersed in the matrix. Its morphological characteristics are mainly determined by the inhibitory effect of Ni and Mo in the welding wire on ferrite formation, as well as the phase transformation and microstructure evolution during multilayer welding. The weld heat-affected zone (HAZ) exhibited a microstructural gradient: near the fusion line, the austenite grains were significantly coarsened, while in the distant regions, the grains were refined to the base metal state. The weld microstructure was significantly directional, while the HAZ was weakly directional, primarily consisting of equiaxed grains. The hardness of the joint decreased in the following order: weld center, heat-affected zone, and base metal. The average tensile strength of the weld was 563 MPa, the average elongation after fracture was 31.2%, and the average impact toughness of the HAZ was 407 J/cm², which was higher than that of the weld zone and the fusion line region. The corrosion resistance and stability of the weld zone were superior to those of the HAZ and the base metal. Narrow-gap oscillating TIG welding technology is suitable for stainless steel welding, and the welded joint performance of 304 stainless steel paired with 316L welding wire is excellent.

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304 stainless steel / narrow-gap / single-pass multi-layer welding / microstructure / mechanical properties

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GAO Hui, QU Jiajun, ZHANG Dongsheng, CHENG Jincai. Microstructural and Performance Analysis of 304 Stainless Steel Narrow Gap Oscillating TIG Welded Joints[J]. Journal of Netshape Forming Engineering. 2026, 18(4): 117-125 https://doi.org/10.3969/j.issn.1674-6457.2026.04.012

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