The Regulating Research Of Cladding Layer Section Shape And Micro-hardness Of Cobalt-based Alloy’s Used In Nuclear Valve Sealing Surface

Nuclear valve with high parameters works in high temperature, high pressure and strong corrosive medium environment, as its poor working condition and the difficulty of repairing and replacement, the standards and requirements for the manufacturing materials and quality of processing are very strict. Nuclear valve sealing surface is the key part which affects the quality of sealing, reliability and service life. Using surface engineering technology to manufacture high-performance and long-life valve sealing surface is a pressing matter of the moment in the nuclear power equipment manufacturing enterprises.The nickel-based or cobalt-based alloy powder laser cladding for nuclear valve sealing surface is one of the main methods for the development of high-parameter nuclear valve. Through this method we can obtain a cladding layer with the comparative advantages that traditional welding does not have such as dense structure, small thermal distortion and good controllability of thickness, composition and dilution rate. The layer also has high abrasion resistance, corrosion resistance, anti-oxidation, hot gas corrosion and erosion performance.On the basis of basically solving the defects of cladding layer like deformation, cracking and porosity, and making sure the process parameters can stably get a relatively flat cladding road, based on the facts that the layer section often presents a half-moon shape, the annular cladding way is out of circularity and there exists a hardness gradient from the outside to the inside of the layer, comprehensively considering the factors such as the layer eventually has a sufficient wide sealing surface size after machining and matching with an ideal hardness value, this text takes the cobalt-based alloy laser cladding layer as the research object and carries out the regulation research of cladding layer section shape with micro-hardness.Firstly, this paper proposes the concept of formulating the process dimension of laser cladding width for nuclear valve sealing surface. Secondly, we obtained constant thickness of cladding layers through the cobalt-based alloy laser cladding experiments which using the method of pre-coating. Thirdly, based on the data tested by large-size tool microscope and vickers microhardness tester, we respectively established highly relevant mathematical models of cladding layer section shape’s curvature radius and the mathematical model of the microhardness gradient distribution of the cladding layer. Finally, setting the minimal powder dosage as the objective function, the laser power P and laser scanning speed v as the design variables, the relationship among the sealing width process dimensionl, laser powerP, laser scanning speed v, cladding layer thickness h0, radius curvature ra, cladding layer area s and vickers hardness H as the constraint conditions, we established the mathematical model of regulation of cladding layer section shape with micro-hardness and also developed an application program for the regulation based on MATLAB. The program has the following characteristics:By changing the final value of the width l0of the sealing surface, we can get the design parameters and process parameters which guide the production; The Final hardness value of the cladding layer surface can be adjusted according to the reasonable hardness difference between the valve body and the valve deck, the design parameters and process parameters of laser cladding.The significance of this study is as follows:the relationship among sealing surface’s geometric parameters, mechanical properties parameters and laser processing parameters is clarified; the optimization design model which sets the powder dosage as the objective function is established, and the regulation of cladding layer section shape with micro-hardness is realized; the theoretical significance and application value for those who manufacture high-performance and long-life nuclear valve sealing surface by laser cladding. The research methods and routes of this paper can also be extended to related research fields.