Research On The Mechanism And Control Technology Of Residual Stress Of Pin Shaft During Induction Hardening

The pin used for connecting boom and arm is of great importance for an excavator.Thereby,it requires high impact toughness,fatigue and wear resistance and etc.Generally,induction quenching could improve the mechanical properties,production quality and service life by changing the microstructures of materials.This research aims to obtain proper depth of hardening and residual compress stress after induction hardening and tempering(IQT)on the pin.The compositions and microstructure of SNCM447(JIS)and 45CrNiMoVA(GB)grades were analyzed.In addition,the TTT curve,phase transition dynamics and electromagnetic properties of the two grades were built and imported in the induction quenching model coupled with temperature field,microstructure filed,stress field and electromagnetic field.The influence of processing parameters on the microstructure evolution,temperature,depth of hardening and residual compress stress was investigated.The mechanism of the creation of compressive residual stress was illustrated as well.By processing parameters optimization,the compressive residual stress was enlarged.Furthermore,the grinding process was simulated to explain the decrease of residual stress.In this paper,the results can be obtained as follows:① The hardenability of 45CrNiMoVA(bigger than 100mm)is better than that of SNCM447(about 33mm)by Jominy test combined with material analysis.The good hardenability is benefit for enlarging the residual compressive stress.In addition,the material models of the two grades were created and updated.② The influence of processing parameters on the depth of hardened layer and residual compressive stress was investigated.The creation of residual compressive stress was illustrated.The correlation analysis showed the negative correlation of the hardened layer and residual compressive stress.In addition,the processing parameters(power of 100kw,frequency of 1250Hz,quenching speed of 1.8mm/s and tempered at 160℃)were optimized to otain a proper hardened layer with bigger residual compressive stress.③ Grinding simulation was carried out to analyze and explain the effect of grinding on residual stress.Great heat was generated and applied to heat the material during grinding,resulting in residual tensile stress which therefore leads to the significant decreases of residual compressive stress on the pin surface.