Analysis of Weld Microstructure and Corrosion Resistance in Local Dry Underwater Laser Wire Filling Welding at L-shaped Corners of 304L Stainless Steel

QI Shikong; ZHU Jialei; ZENG Caiyou; WANG Chengyuan; LI Zhehui; ZHANG Ziyue; ZHAO Zhibo

doi:10.3969/j.issn.1674-6457.2026.05.011

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Journal of Netshape Forming Engineering ›› 2026, Vol. 18 ›› Issue (5) : 123-132. DOI: 10.3969/j.issn.1674-6457.2026.05.011

Advanced Joining Technology

Analysis of Weld Microstructure and Corrosion Resistance in Local Dry Underwater Laser Wire Filling Welding at L-shaped Corners of 304L Stainless Steel

QI Shikong, ZHU Jialei^*, ZENG Caiyou, WANG Chengyuan, LI Zhehui, ZHANG Ziyue, ZHAO Zhibo

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Abstract

To address the need for online repair of damages at the L-shaped corner of 304L stainless steel cladding in spent fuel pools of nuclear power plants, the work aims to investigate the repair of corner joints with local dry underwater laser wire filling multi-layer multi-pass cladding technology under simulated high-pressure underwater conditions (20 m depth, 0.2 MPa). The microstructure and corrosion resistance of the laser wire repaired L-shaped corner joints in a high-pressure environment were systematically examined through metallographic analysis, X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), microhardness testing, and electrochemical corrosion measurements. The weld surface exhibited a uniform fish-scale pattern without macroscopic defects such as cracks or pores. However, the intensified activity of gas molecules under high-pressure conditions accelerated heat loss and increased the cooling rate of the molten pool, reducing its fluidity and resulting in diminished surface flatness. The microstructure of the L-shaped corner joint consisted primarily of austenite and residual ferrite. Compared to the base metal, the weld zone showed increased Cr and Ni contents. Polarization curves and Nyquist plots confirmed that the corrosion resistance of the weld zone was superior to that of the base metal. Additionally, the average hardness of the weld was higher than that of the base metal, attributable to grain refinement from rapid cooling and the strengthening effect of Mo, Cr element. The findings demonstrate that this process effectively ensures the repair quality of 304L stainless steel in high-pressure underwater environments, offering excellent corrosion resistance and mechanical properties and providing a viable technical solution for in-situ underwater repair of corner areas in nuclear power plant pools.

Key words

spent fuel pool / laser welding / corner repair / local dry method / microstructure

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QI Shikong, ZHU Jialei, ZENG Caiyou, WANG Chengyuan, LI Zhehui, ZHANG Ziyue, ZHAO Zhibo. Analysis of Weld Microstructure and Corrosion Resistance in Local Dry Underwater Laser Wire Filling Welding at L-shaped Corners of 304L Stainless Steel[J]. Journal of Netshape Forming Engineering. 2026, 18(5): 123-132 https://doi.org/10.3969/j.issn.1674-6457.2026.05.011

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Funding

Beijing Natural Science Foundation Project (3262002); National Natural Science Foundation Joint Fund Key Support Project (U22B20127); The Classified Development Projects of Beijing Municipal Institutions (11000023T000002199202)