| 316L stainless steel has excellent corrosion resistance,oxidation resistance and heat transfer performance,which is an important material for the production of nuclear power steam generator,hydropower turbine and other key parts of the generator set.However,due to the complex service environment and the disadvantage of low hardness and poor wear resistance of 316 L stainless steel,the stress corrosion cavitation failure phenomenon becomes more frequent,which greatly reduces the service life of the generator set.As a new surface treatment technology based on deformation strengthening mechanism,abrasive water jet surface strengthening has many distinct characteristics,such as less stress concentration,full coverage of strengthening area and low cost,which is expected to improve the hardness and wear resistance of 316 L stainless steel,and thus improve the operation reliability and use economy of generator unit components.Therefore,the surface strengthening mechanism,process optimization and quality improvement strategy of AWJ for 316 L stainless steel are studied in this paper.The coupling strengthening mechanism of liquid-solid phase is studied by comparing the impact characteristics of abrasive and continuous water relative to the workpiece and combining the wetting effect of water medium film.Taking surface hardness and surface roughness as strengthening quality indexes,the influence of process parameters on strengthening quality indexes is analyzed.The regression prediction model of abrasive water jet strengthening quality index is established to optimize the combination of process parameters.On this basis,the experiments and feasibility analysis of multi-level energy decline strengthening and indirect strengthening are carried out.The main research contents are as follows:(1)Analysis of jet flow field and mechanism of abrasive-water coupling.Based on the theoretical model of fluid mechanics,the basic flow field characteristics of abrasive water jet are analyzed.Based on the simulation model of nozzle internal and external flow field,the velocity distribution law of abrasive and water in internal and external flow field under different parameters is analyzed.The impact action model of abrasive and continuous water on 316 L workpiece surface is established to analyze the coupling action mechanism of abrasive and water on 316 L surface.It is clear that the abrasive particles play a leading role in the deformation strengthening of the workpiece,and the positive and negative effects of the wetting and cooling effect on the impact of the abrasive particles are analyzed.(2)Study on the effect of process parameters on strengthening quality index.The changes of microstructure and macroscopic characteristics of workpiece before and after jet strengthening are analyzed.Based on the distribution characteristics of workpiece surface strengthening area,a regression prediction model of optimal feed is established to provide guidance for the feed of multi-channel jet strengthening.The effect law of system pressure,target distance,traverse speed and cycle times on strengthening quality index is analyzed,which can be shown as: the strengthening quality index increased with the increase of system pressure and cycle times,and decreased with the increase of target distance and traverse speed.(3)Study on the optimization of surface strengthening process based on genetic algorithm.The process parameters of orthogonal test are optimized based on single factor test results.A multi-objective optimization model for strengthening quality index is constructed based on strengthening quality regression prediction model.Based on multi-objective genetic algorithm,the optimal pareto solution set corresponding to each strengthening quality index is solved.(4)Study on the quality improvement strategy of abrasive water jet strengthening.Taking the main influence factor of surface roughness index,the thickness of dielectric layer and the material as parameter variables,the comprehensive improvement benefits of multilevel energy decline strengthening and indirect strengthening on workpiece strengthening quality index are investigated respectively.The mechanism of dielectric layer in indirect strengthening is analyzed,and the direct strengthening,indirect strengthening and multi-level energy decline strengthening are compared comprehensively to verify the feasibility and advantages of the latter two quality improvement strategies. |
PDF Full Text Request