Research On Microstructure Evolution And Friction And Wear Properties Of 45 Steel By Induction Hardening

45 steel is a favorable carbon structural steel,which is widely used in industry.In the power-assisted steering system of an automobile,the raw material of the rack is 45 steel,and wear failure is the main factor that leads to the performance failure of the steering system.Induction hardening was performed on 45 steel after quenching and tempering treatment in this thesis.Using a combining theoretical analysis and experimental research to explore the microstructure evolution and hardness change of 45 steel under induction quenching treatment.On this basis,the mechanism of enhancing the wear resistance of 45 steel was discussed.The main researches and conclusions of this thesis are as follows.(1)Based on the principle of electromagnetic induction,45 steel was subjected to induction hardening treatment,and XRD,metallographic observation,and hardness test were used to explore the influence of induction hardening on the surface hardness and phase structure of 45 steel.The results show that after induction hardening treatment of 45 steel,there will be no decarburized layer on the surface,and the metallographic structure will transform from the original tempered sorbite and ferrite to cryptocrystalline martensite.The structure was composed of three parts:hardening layer,transition zone,and matrix.When the cooling rate increases from 50 L/min to 70 L/min,the surface hardness increases by19.86%,and the depth of the hardening layer increases from 650?m to1000?m.(2)A transmission electron microscope was used to analyze the microstructure of 45 steel after induction hardening.The micro morphology,dislocation density and grain size of martensite in 45 steel under different cooling rates were explored.On this basis,the evolution mechanism of the grain refinement of martensite in 45 steel is revealed.The results show that martensite nucleates inside austenite and produces a large number of density increased from 1.21×10¹⁵/m2 to 4.54×10¹⁵/m²,A large number of dislocations provide conditions for martensite nucleation and promote the refinement of martensite,to improve the surface mechanical properties of 45 steel.(3)The CFT-I multifunctional friction and wear tester,scanning electron microscope(SEM)and energy spectrometer were used to test and analyze the tribological properties of 45 steel with induction hardening.The results show that the friction coefficient of 45 steel is reduced from 0.467 to about0.122 after induction hardening,and the wear mechanism is changed from fatigue wear and adhesive wear to abrasive wear.As the cooling rate rises,the better the wear morphology of the material will be and the better wear resistance will be shown.(4)The strengthening mechanism of martensite to wear resistance is proposed.The SEM test method was used to analyze the characteristics of the wear morphology of 45 steel after induction hardening.Based on the analysis of the microstructure,the strengthening mechanism of induction hardening on the wear resistance of 45 steel is obtained.Studies have shown that due to the high yield strength of lath martensite,the contact stress is less than the yield strength of the material surface at the initial stage of wear,so the wear resistance of the material is significantly improved.At the same time,the substructure of lath martensite is dislocation,high Density dislocation hinders plastic deformation during wear,which is the strengthening effect of martensite on wear resistance.At the same time,as the cooling rate increases,the finer the martensite grains,the smaller the concentrated stress during the friction and wear process,the smaller the plastic deformation,the stronger the wear resistance it exhibits.