Study On Composite Strengthening Mechanism Of Cryogenic Treatment-laser Peening And Wear Resistance Of GCr15 Bearing Steel

Automotive generator bearings serve under harsh operating conditions such as dry friction,mud and rain,with problems such as wear,fatigue and corrosion failure,and new material processes,residual stress distribution,precise performance regulation and strengthening effects need to be addressed.This topic is targeted to put forward GCr15 bearing steel cryogenic treatment-laser peening composite strengthening technology program,combined with theoretical analysis and experimental research,GCr15 bearing steel residual stress distribution,composite strengthening mechanism and friction and wear performance of key technology research.The main works are as follows:(1)Automotive generator bearing process analysis was carried out and cryogenic treatment-laser peening composite strengthening process was proposed based on the theoretical technology foundation of cryogenic treatment and laser peening.The cryogenic treatment-laser peening composite strengthening mechanism was described according to the theory of volume shrinkage effect,second phase strengthening theory,laser induced plasma shock wave,dislocation density and residual stress.(2)The optimization of cryogenic treatment-laser peening composite strengthening process for GCr15 bearing steel was studied.The distribution law of residual stress induced by laser peening with different shock times was investigated,and the distribution law of residual compressive stress,half height width FWHM value and micro-hardness induced by cryogenic treatment-laser peening composite strengthening with different cryogenic time was studied.The results show that cryogenic treatment-laser peening composite strengthening improves the plastic deformation resistance,the amplitude of residual compressive stress and half width,and the dislocation density.(3)The microscopic mechanism of modification by cryogenic treatment-laser peening composite strengthening was revealed.XRD,SEM,EDS and TEM were used to investigate the residual austenite content,precipitation phase,dislocation density and dislocation entanglement and other microstructural characteristics of cryogenic treatment-laser peening composite strengthened GCr15 bearing steel.The results show that cryogenic treatment promotes phase precipitation,and after laser peening,the precipitated phase can pin dislocations,hinder the movement of dislocations,improve the density and stability,and the strengthening effect is better.(4)A study on the nano-indentation and wear resistance of cryogenic treatment-laser peening composite strengthening of GCr15 bearing steel was carried out.The results show that the nano-hardness and elastic modulus of GCr15 bearing steel increased by 12.94% and 32.61%respectively relative to the untreated specimens after composite strengthening,which improved the wear resistance and deformation resistance of GCr15 bearing steel.At the same time,the wear quantity and friction coefficient of GCr15 bearing steel are reduced by composite strengthening,the surface of the specimen is smoother and flatter,the plough furrow is shallow and narrow,the size and quantity of bonded debris is small,showing slight abrasive wear,adhesive wear and oxidative wear,which effectively improves the wear resistance of GCr15 bearing steel.