Laser Cladding Of No Tungsten Low Carbon Moderate Cobalt Alloy Powder On Nuclear Valve Sealing Surface

Laser cladding on nuclear valve sealing surface to get alloy layer with compactstructure, no cracks and no pores, and the cladding layer has good metallurgicalcombination with the substrate. This is one of the most important methods tomanufacture high performance and long life nuclear valve in the nuclear powerequipment manufacturing enterprises. As the commonly used material for valvesealing surface, cobalt-base alloy has incomparable comprehensive performancescompared with other materials, such as wear resistance, corrosion resistance,oxidation resistance, erosion resistance, high temperature oxidation resistance andhigh temperature red hardness (at650℃temperature). However, its cost and Cocontent are too high. This has prompted the researchers to study suitable materialwhich has low Co content.For the same alloy powder, the laser cladding can get much denser and hardercoating than other overlaying methods. While cracking phenomenon easily happensduring the laser cladding. Aiming at decreasing the Co content in cobalt-base alloyand based on the above facts, FCo-5self-fluxing cobalt-base alloy powder with notungsten, low carbon content and medium cobalt content was developed. Adoptingsynchronous feeding powder and reasonable laser process parameters, monolayersingle-channel laser cladding was conducted with FCo-5alloy on the surface of0Cr18Ni12Mo3Ti stainless steel nuclear valve to get cladding layer with betterquality.Base on expanding the applied range of FCo-5for large area laser claddingwithout defects, monolayer double-channel laser cladding was conducted on nuclearvalve sealing surface by using the process parameters and method of monolayersingle-channel laser cladding. The microstructure characteristics, phase structure, hightemperature red hardness, and the relationship between microstructure and3 micro-hardness of the cladding layer were researched to discuss the applied range forlarge area laser cladding. And the feasibility of FCo-5self-fluxing alloy powder toreplace current CoCr-A cobalt-base alloy was judged. Finally, the graphic calibrationfor FCo-5monolayer single-channel laser cladding was proposed. The experimentresults shows:(1)、Under appropriate laser process parameters, the coatings got by monolayersingle-channel and monolayer double-channel laser cladding both have a goodmetallurgical bonding with the substrate. And the cladding layer is smooth, with nopores and no cracks.(2)、 FCo-5monolayer double-channel laser cladding layer mainly consists ofγ-Co austenite dendrite, interdendritic eutectic organization and Cr23C6particle phasegenerated in-situ. The micro-hardness curve of cladding layer cross-section was ‘M’type, the minimum hardness value are192HV0.2higher than that of substrate.(3) The structure characteristics, micro-hardness, high temperature hardness ofFCo-5monolayer double-channel laser cladding layer are conform to therequirements of the nuclear valve sealing surface, this material can replace high cobaltcontent of CoCr-A alloy, and the use of this material can reduce secondary pollutionand the cost of nuclear valve.(4)、Using graphic calibration could obtain Processing highly and breadth of seal-ing surface base on Cross-section micro hardness of Single-channel cladding layer；in the same way, Maximum height and surface hardness could obtain base on the se-aling surface width. in guidance nuclear valve sealing surface in the production andprocessing of laser cladding layer has a certain engineering application value.