Study On Nuclear Valve Sealing Surface Co-free Fe-based Alloys And Properties Of Laser Coating

Nuclear valves are necessary and important control components for normal safe operation of nuclear power station. The quality of nuclear power valve sealing surface surfacing is an important factor of safety security of nuclear power. The current nuclear valve sealing surface surfacing material is generally cobalt alloy. However, Co-based alloy is not only expensive, but also particularly when working in a nuclear environment, wear and corrosion debris of cobalt-based alloy is stimulated from Co-59 to isotope Co-60 which have long half-life of nuclear radiation. So the nuclear valve sealing surfaces of the third-generation need Co-free materials.A new Co-free Fe-based alloy powder is designed to be applied in the valve sealing surface overlaying, in which the Iron as the main body, C, Ni, Cr, B, Si, W, V, Mo, Mn and other alloy elements are added. And the new alloy powder is named CL-1.Surfacing layer not only depends on performance and quality surfacing materials, but also to a large extent also depends on the welding methods and process. In this paper, the internal laser feeding technology is applied and the powder is cladded on stainless steel substrate. Circular hollow light compared with the commonly used solid Gaussian shows that the beam energy distribution of hollow light and weld pool convection patterns has many advantages, such as the higher quality melting layer, better organizational performance.Micro-hardness test shows that hardness of laser cladding layer is 1.6-1.8 times the matrix; through the structural organization of SEM analysis shows that: cladding layer followed by an organization presents a narrow cellular crystal, coarse dendrite area, small branches crystal and equiaxed grain zone. Such a trend; by XRD phase analysis of coating was found mainly Fe63Mo37, Fe2Si, Fe0.4Mn3.6C, Fe2SiV, Ni2Si and Fe7.79Mn2.20Si6 other phase. Meanwhile, the cladding layer contains many of the small variety of carbides, such as Fe3C, Fe5C2, Mn5C2 Such carbide itself has a higher hardness.Same time, because their existence, generation a large number of dislocations and stacking faults and other structures in the cladding layer, while they themselves will play a dispersion strengthening effect.XRD analysis also found that the diffusion through the matrix elements, alloying elements may cause infiltration of solid solution strengthening and the second phase strengthening; EDS spectrum analysis found that the process of laser cladding elements occurred in the proliferation of cladding layer and the substrate to achieve a good metallurgical bonding. Found through the hot corrosion test, CL-1 Fe-based Co-free alloy powder laser cladding of corrosion resistant than Noremo02 Fe-based alloy cladding layer, close to Stellite6 Co-based heat-resistant alloy cladding corrosion.High temperature friction and wear test results show that CL-1 Co-free Fe-based alloy powder at high temperature performance in between, better than Noremo02, close to Stellite6 Co-based alloy.Synthesis of the test results suggest that the performance of CL-1 Co-free Fe-based alloy powder is close to Stellite6 Co-based alloy powder. To a certain extent, it can replace Stellite6 Co-based alloy powder into nuclear power valve sealing surface weld overlay material.