| Low carbon martensitic precipitation hardening stainless steel FV520B is widely utilized in load-bearing components,e.g.impellers in centrifugal compressors,for its comprehensive properties of high strength and toughness,as well as good corrosion resistance.Due to the harsh environment,impellers are prone to failure because of fatigue,abrasion or fracture.On the economical side,repairing the damaged parts it can not only reduce resource and energy consumption to repair the damaged parts,but also save costs.Furthermore,it is significant in ensuring the equipment operation and extend the service life of impellers.Laser hot wire cladding is one of efficient repair technologies comparing to traditional methods with the advantages of low heat input and high utilization rate of material and energy.The new interface formed between cladding and substrate after repairing.It is significant to assess the part quality and mechanical property quantitatively with consideration of interfacial behavior,which contributes to improvement of the quality and reliability of parts.This paper aimed to comprehensively evaluate the process and interface performance of FV520B material in laser hot wire cladding.Firstly,volumetric defect ratio was defined as one of criteria to evaluate the forming quality of cladding layers.The laser deposition experiments of FV520B stainless steel were designed and analyzed by using Taguchi method.The optimum combination of laser power(P),scanning speed(Vs),wire feed rate(Vf)and wire current(I)was obtained according to the analysis of signal-to-noise(S/N)ratio.Analysis of Variance(ANOVA)was performed to measure percentage contribution of each factor.The results showed that the good metallurgical bonding was achieved in the interface between cladding layer and substrate.The uniform microstructure was observed based on the optimized process parameters and no defects and cracks were found.The good forming quality results from the stable and continuous process control with selected optimum parameters.Secondly,response surface methodology(RSM)was used to analyze the influence of the single factor and multiple factors interaction.The regression model and the empirical formula were established in terms of the relationship between processing parameters and forming quality.Meanwhile,the multi-point temperature measurement experiment was designed under the premise of stable wire transfer,in order to obtain three-dimensional spatial distribution of the temperature field in laser hot wire cladding.The mapping relationship among the temperature,microstructure and performance was analyzed by establishing the cladding process temperature field distribution model.Finally,the mathematic model of cladding layer overlapping rate was set up to analyze the process of multi-pass layer cladding quantitatively with combination of the empirical formula between process parameters and forming quality.On the basis of optimization of process parameters,the measuring method and experimental equipment were designed in order to quantitative characterize interface bonding strength between cladding and substrate.The result shows that the optimum cladding parameters are the laser power of 1910 W,the scanning speed of 6.5 mm/s,the wire feed rate of 2.5 m/min,the wire current of 50 A and overlapping rate of 43.13%.Through parameter optimization,the homogenized microstructure with fine martensite was obtained in a large part by using laser multi-pass cladding.The interface bonding strength is 1026.6MPa that is close to the original substrate strength of FV520B stainless steel.It indicates that process optimization can achieve good cladding repairing effect. |
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