Research On Surface Strengthening Of 42CrMo Steel Crankshaft Connecting Rod Journal By Induction Hardening

As one of the important parts of automobile engines,crankshafts have a harsh working environment and complex stress conditions.Therefore,the performance and life requirements of crankshafts are increasing day by day.The crankshaft connecting rod journal,as the power transmission part,bears the main force and is prone to cracks leading to failure.Therefore,it needs to be induction hardened and strengthened.This article takes 42 Cr Mo steel crankshaft connecting rod journal as the research object,First,the theoretical analysis of electromagnetic field and temperature field of electromagnetic induction hardening is completed,and then the finite element simulation software is used to simulate and analyze the temperature field distribution law of the crankshaft connecting rod journal induction hardening process,and according to the temperature field distribution at the end of heating,the prediction of the depth of the hardened layer is completed;Then,the influence of induction quenching under different quenching power and heating time on the morphology,microstructure,residual stress and mechanical properties of the hardened layer on the surface of the connecting rod journal is explored;Finally,the effects of different hardened layer depths on the surface structure and properties are studied.The research results show that after induction hardening,the surface temperature of the connecting rod journal increases rapidly.Due to the effect of heat conduction,the connecting rod journal section presents a certain temperature gradient.The area where the temperature is higher than the austenitizing temperature will undergo structural transformation,and a hardened layer will be formed after cooling.According to the simulated temperature field distribution,the depth of the hardened layer is predicted,which is close to the measured result,which proves the feasibility of the simulation result.After induction hardening,the connecting rod journal section is composed of three parts: hardened layer,transition layer and base body.The structure of the hardened layer is fine and uniform martensite,the transition layer is a mixed structure of martensite and tempered sorbite,and the matrix structure is tempered sorbite.The residual stress on the surface of the connecting rod journal changes from tensile stress to compressive stress,and the residual stress is the largest in the middle of the connecting rod journal surface.As the quenching power increases,the surface hardness of the connecting rod journal first increases and then decreases.When the power is2500 W,the surface hardness increases from 290 HV to 751.3HV,which is an increase of 2.55 times,and the wear resistance is significantly improved.As the heating time increases,the surface hardness first increases and then decreases.When the heating time is 6.5s,the surface hardness increases to 753.6HV,and the wear resistance is enhanced.Finally,the study found that a reasonable depth of hardened layer can ensure higher mechanical properties of the connecting rod journal surface,as the depth of the hardened layer increases,the martensite structure gradually grows,the surface residual stress first increases and then decreases,and the surface properties first increase and then decrease.When the depth of the hardened layer is too small,the hardened layer is incomplete and the surface properties are low;but when the depth of the hardened layer is too large,the surface residual stress is reduced,and the mechanical properties are greatly reduced.When the depth of the hardened layer is increased from 2.83 mm to 4.15 mm,the surface residual compressive stress is reduced from-777.5MPa to-598.1MPa,the surface hardness is reduced from 747.9HV to 581.6HV,and the wear resistance is greatly reduced.