The sealing surface of nuclear grade valves in third-generation nuclear power plants is prone to cracking due to differences in physical properties between iron-based alloys and stainless steel valve seats, which seriously affects the safe operation of nuclear power units. Starting from alloy design, a gradient composition transition layer was designed to release residual stress at the interface and suppress the precipitation of hard and brittle phases. A novel idea of accurately regulating the composition gradient by controlling the dilution rate of melt pool was proposed, relying on the hollow ring laser independently developed by our team. The quantitative relationship between the dilution rate of melt pool and laser process parameters such as laser power and scanning speed and the melt pool dilution rate was constructed. The effects of different dilution rates on the composition gradient, microstructure morphology, and heterogeneous interface compatibility were elucidated. The influence of gradient composition of transition layer on residual stress distribution and mechanical properties was clarified. The high-strength and high-quality heterogeneous interfaces between Norem02 alloy and F304/F316 stainless steel were achieved. This study can effectively suppress the formation of coarse hard brittle phases and low melting point phases, reduce the residual stress state at interfaces, and suppress the cracking. It provides important theoretical basis and technical support for solving the problem of sealing surface cracking of nuclear grade valves in third-generation nuclear power plants.

Composition design;Transition layer;Laser melting deposition;Melt pool behavior