Microstructure and corrosion resistance of underwater laser clad duplex

During the long-term service of nuclear power plants, the duplex stainless steel (DSS) plate in the spent fuel pool ages. Its failure mechanism is mainly uniform corrosion, stress corrosion cracking (SCC) and pitting corrosion, which poses a serious threat to the safe operation of nuclear power plants. Repairs are usually done by underwater welding technology to reduce the equipment maintenance costs and exposure to radiation.

Combined with the technologies of underwater local dry laser cladding (ULDLC) and underwater local dry laser remelting (ULDLR), a DSS coating has been made in an underwater environment. The phase composition, microstructure, chemical components and electrochemical corrosion resistance were studied. The results show that after underwater laser remelting, the phase composition of DSS coating remains unchanged and the phase transformation from Widmanstätten austenite + intragranular austenite + (211) ferrite to (110) ferrite occurred. The ULDLR process can improve the corrosion resistance of the underwater local dry laser clad coating. The corrosion resistance of remelted coating at 3 kW is the best, the corrosion resistance of remelted coating at 1kW and 5kW is similar and the corrosion resistance of (110) ferrite phase is better than grain boundary austenite phase. The ULDLC + ULDLR process can meet the requirements of efficient underwater maintenance, forming quality control and corrosion resistance. It can also be used to repair the surface of S32101 duplex stainless steel in underwater environments.

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