The Research Of Cavitation Erosion And Strengthening Of 304 Stainless Steel In The Water Cavitation Peening

In this paper.Water Cavitation Jet(WCJ)of varied stress and time was used on the surface of 304 stainless.By tracking the surface morphology change on scanning electron microscope after the WCJ treatment,the process and mechanism of cavitation erosion were analyzed on the surface of 304 stainless,the microstructure of surface and deformation mechanism was investigated at the same time.The results are as follows:As to the different of damage rate and mechanism,cavitation damage zone can be divided into Jet impact zone,Transition zone and Turbulent zone from center to periphery,among them,the damage degree of Jet impact zone was the worst,transition zone was the weakest.The damage of Jet impact zone accelerated when the jet pressure was 35MPa for 40min,and it presented clear characteristics of fatigue damage,the initiation and propagation of fatigue crack in the area of slip band and grain boundary is one of the important reasons lead to the spalling damage;In Turbulent zone there is no obvious spalling in the whole process of shot peening,it’s mainly plastic deformation.The pressure of shot peening is one of the important parameters affecting the degree of cavitation erosion damage,and the jet impact zone is more vulnerable to the influence of shot peening pressure than the turbulent area.Jet impact area does not produce obvious injury the jet pressure was 25MPa for 120min,but the turbulent zone presented clear characteristics of plastic deformation.Water cavitation peening can make the surface of 304 stainless steel a apparent reinforcement,Overall hardness of sample have improved by about 30HV than it before processing when the jet pressure was 35MPa for lOmin,But long time of WCP makes the damage of jet impact zone worse which leads a lower reinforcement.The hardening layer of Transition zone and Turbulent zone were thicker than the Jet impact zone.The surface roughness of sample will rise with the peening time,the biggest rise is the jet impact area,the second is turbulent zone,transition zone is minimal.The highest surface roughness of sample after WCP is less than it of nomal machining process,and the roughness meet the use of requirements.The twin layer of Transition zone and Turbulent zone were thicker than the Jet impact zone in the cross-sectional microstructure,and the thickness of the twin layer in Turbulent zone was 140μm,this is in conformity with the measurements of cross-section microhardness;Under the condition of this experiment,the main deformation mode of 304 stainless steel is slip deformation,the second is twin deformation.There are two kinds of cavitation erosion mechanism under the process of cavitating water jet,one is fatigue failure under cyclic loading,the other is arc pit caused by plastic deformation,necking and spalling.The treatment of WCP can make the surface of sample form a useful residual compressive stress.The residual stress of Jet impact zone is about 401 MPa,it improved by about 300 MPa coMPared with the residual stresses(about 71.93 MPa)of sample surface without WCP.