Research On Shot Peening Strengthening And Tribological Performance Of CF53 Steel For Camshaft Of High-speed And Heavy-duty Diesel Engine

The camshaft is one of the five key components of a diesel engine,and its function is to control the opening and closing of the valve.In addition to the certain bending and torsional load of the camshaft during the working process,the cam part also bears varying extrusion stress and friction of the tappet.Therefore,the surface is very prone to wear,which affects the working efficiency and service life of the diesel engine.CF53 steel has the advantages of high strength,good processing technology and low cost,but it still has shortcomings in terms of wear resistance.In this thesis,shot peening technology is applied to improve the surface properties of CF53 steel,thereby improving its anti-friction and wear resistance ability and prolonging the service life of parts.Exploring the combination of heat treatment process parameters of CF53 steel through orthogonal experiments.The heat treatment plan is preferably to keep the temperature at 800℃for 25 min,then use 15%Na Cl solution for quenching,then place the sample at 360℃for 2 h,and finally air-cool to room temperature.After the heat treatment of this program,the microhardness of the material reached 481.2 HV_0.2,the static toughness reached 14694 MPa·%,of which the tensile strength was 1580 MPa and the elongation was 9.3%.The effects of shot peening process parameters such as shot peening air pressure,shot diameter and coverage rate on the surface properties of CF53 steel samples were studied.The results show that shot peening will cause plastic deformation of the surface of the sample,significantly refine the surface structure of the sample and increase the surface residual compressive stress,increase the surface microhardness,but also increase the surface roughness.With the increase of shot peening air pressure and shot diameter,the structure refinement layer,microhardness,surface residual compressive stress and surface roughness of the sample increase significantly,while the increase in coverage has little effect on the various surface properties of the sample.After shot peening,the surface microhardness of the sample increased from 481.2 HV_0.2 to 575.5 HV_0.2;the surface residual stress increased from-340 MPa to-619MPa;the surface roughness Ra increased from 0.627μm to 2.604μm.The friction and wear properties of CF53 steel samples treated with different shot peening parameters were studied.The results show that shot peening can effectively reduce the average friction coefficient and wear rate of the samples,and the decrease rates of the two are 43.0%and 69.1%,respectively,and the wear resistance of the samples is significantly improved.The wear mechanism of untreated specimens is mainly severe fatigue wear with furrows and cracks as the main features.After shot peening,the wear mechanism of the specimens changes to fatigue wear with delamination as the main feature.Taking the lowest wear rate as the optimization target,0.5 MPa shot peening air pressure,0.8 mm shot diameter and 200%coverage are selected as the shot peening process parameters of CF53 steel camshaft parts.A bench test device for the diesel engine valve train was designed and built,and the shot-peened CF53 steel camshaft and flat-bottomed tappets with different strengthening methods were studied for 500 hours of fatigue test assessment and life prediction.The results show that the wear depth of the contact pair between the shot peening cam and the unstrengthened tappet is the lowest,which is 35.7%～84.8%lower than that of the unstrengthened contact pair.It can be seen that shot peening applied to the CF53 steel camshaft can significantly improve its wear resistance.Extended service life.For the CF53 steel camshaft-flat-bottomed tappet contact pair,a wear depth calculation model based on Archard theory was established to predict the life of the camshaft and flat-bottomed tappet.Compared with the bench test results,the calculation error of the model solution was within 10%It is helpful to evaluate the reliability of the service life of camshaft and flat tappet parts.