Application Of Surface Strength And Remanufacture On Nuclear Pump Materials By Cold-welding

The nuclear pump is one of the most important facilities in the nuclear power plants, thenuclear pumps play a vital role in which guarantee the ensuring the nuclear power plantwork reliably, safely, efficiently. But the working environment of nuclear pump is poor, suchas the long time working in the high temperature and pressure, the surface of the material isextremely easy to be damaged by the wear and corrosion, which reduce the using life of thenuclear pump and affect the nuclear power plant’s normal operation. Laser welding likehigh-energy pulse precision cold welding technology has many advantages, such as highboding strength, high machining precision, small heat affected zone, little weldingdeformation, convenient and flexible operation, etc. So the welding technology is suitablefor welding the equipment parts which are not easy to be taken apart and no deformationafter welding.The Fe-based alloy and Ni-based alloy coatings were synthesized on austenitic stainlesssteel substrate which was used for pump by Laser welding like high-energy pulse precisioncold welding technology. The microstructure, chemical composition, and phase structure ofthe coatings were investigated by light optical microscopy (LOM), X-Ray diffraction (XRD),scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) andmicrohardness. The mechanical poperty tribological property, cavitation erosion resistanceand electrochemical equipment were employed to analyze the performance of alloy coatingswith the micro hardness tester, the fiction and wear testing machine, ultrasonic cavitationerosion meter, electrochemical measurement.The experimental results showed that the welding can obtained a dense modified layerwith good metallurgical bonding to the substrate. The phases of Fe-based alloys in this studyincluded α-Fe、Cr23C6, Cr7C3. The microstructure was mainly directed dendritic growth. Butat the surface of alloy layer, it was not grown with directed dendritic. The averagemicrohardness of the3Cr13alloy layer and4Cr13alloy layer is510HV and600HVrespectively. The Ni-based cladding layer was mainly composed of γ-Ni, FeNi3, NiMo,Ni3Mo, FeCrMo and CrB. The microstructure of Ni-based alloy layer with the direction ofsolidification appears plane crystal and dendrite in order, and there was rich-Mo phase at thesurface of the cladding. The average microhardness of the Ni-based alloy layer is540HV.Compared with the304stainless steel substrate, the relative wear resistance of Fe-based andNi-based alloy layers are both significantly improved. The relative wear resistance of4Cr13alloy layer is5.32, the3Cr13alloy layer is3.88, the Ni-based alloy layer is4.39. Through the electrochemical corrosion in3.5%NaCl solution and the cavitation corrosion test resultsshowed that the corrosion resistance of Ni-based alloys is the best. After cavitation5h, theNi-based alloy layer’s weight loss ΔG, line roughness Raand surface roughness Saare1/7,1/17,1/8to the304stainless steel substrate respectively.