Study On Gear Carburizing Induction Heat Treatment And Friction And Wear Behavior

In this thesis,the surface carburizing quenching process and performance study is carried out for 18Cr2Ni4 W low-carbon medium-alloy steel.By controlling the induction heating time and temperature in stages and optimizing induction heating temperature matches with the carbon concentration gradient,a carburizing quenched and strengthened layer with excellent performance is obtained.By characterizing and analyzing the microstructure and mechanical properties of the carburized layer with different quenching processes,the strengthening mechanism based on the matching of induction quenching temperature-time and carbon concentration of the carburized layer is explored.Furthermore,frictional wear experiments with resistance applied to the grinding subsets were designed to study the fatigue wear behavior under critical sliding conditions,characterizing and analyzing the wear characteristics of surfaces and circumferential sections,and discussing the microscopic wear mechanisms of different carburized hardened layers.This thesis carried out the finite element calculation of fatigue contact stress field based on experimental data to optimize and modify the model parameters with the help of COMSOL finite element analysis to obtain the stress field distribution of different induction quenching processes during fatigue contact with the existence of resistive moment,and then elucidated the effect mechanism of induction quenching temperature-time and carburizing layer carbon concentration matching on fatigue wear behavior.The main conclusions are as follows:(1)The carburizing-induction quenching-cryogenic treatment-tempering process of 18Cr2Ni4 W low carbon medium alloy steel is studied to obtain a carburizing hardened layer that best matches the carbon concentration gradient,analyzed the toughening mechanism of the carburizing hardened layer,and explored the influence of the mechanical properties of the hardened layer on the microscopic mechanism of wear behavior.Different induction quenching temperature-time and carburizing layer carbon concentration matches exhibit different hardened layer strengthening mechanisms,including martensitic intrinsic strengthening,solid solution strengthening and precipitation strengthening.At lower quenching temperatures(770°C),more massive and strip-like carbide precipitates occurred at microscopic defects positions such as grain boundaries and twinning boundaries,with the solid solution carbon atoms in the matrix reduced,dominated the precipitation phase strengthening;the stress-affected zone generated during the fatigue wear process is large,prone to significant stress concentration at the carbide/matrix interface,triggering fatigue cracks.At 830°C induction quenching,the surface of the sample reached the complete austenitization temperature,and the transition zone is properly homogenized with uniform microstructure distribution,obtaining the induction heating layer thickness that best matches the carbon concentration gradient and the better mechanical properties;as well as the excellent anti-wear properties.The higher quenching temperatures(900°C)caused a large amount of carbon atoms to dissolve into the matrix,with the strengthening mechanism primarily involving martensitic intrinsic strengthening and solid solution strengthening.After induction quenching,the surface contained a significant amount of residual austenite,after 24 hours of cryogenic treatment and lowtemperature tempering,resulting in 10.04% residual austenite in the hardened surface layer.In addition,the abundant residual austenite induced TRIP effects during the fatigue wear process,delaying the initiation of fatigue wear cracks.(2)The fatigue wear behavior of different quenched carburized layers under critical sliding conditions of heavy-duty gears is investigated by applying additional resistance on the counter-abrasive pair during the fatigue wear test.The additional resistance increased the friction coefficient to around 0.45,approaching the sliding state,and intensified the rolling contact fatigue wear process.Compared with the noresistance torque test,the weight loss due to wear increased by about 100 times.At the same time,an phenomenology model is constructed for the evolution of wear loss and the microstructure of the hardened layer,exploring the correspondence between the toughness of the hardened layer and the wear resistance performance.(3)Based on the measured parameters of the gradient mechanical properties of the carburizing-induced quenching layer and combined with the actual service wear conditions of heavy-duty gears,a gradient-carburized-induced quenching torque fatigue wear model is established.In the results of the induction quenching model with different temperatures under the effect of resistive moment,the stress maximum and depth changes are not obvious.The maximum stress in the upper ring occurred on the surface layer,and the maximum stress in the lower ring appears at 0.78 mm depth with a maximum value of about 980 MPa.Moreover,the average stress of the lower ring increases twice compared to the stress in the no-torque resistance model.As the value of the material hardness property parameter increases,the area of the stress-affected zone gradually decreases.Combined the 830 °C induction quenching model with its microstructure analysis,the best anti-fatigue performance is obtained due to the smallest stress-affected zone and fewer carbon precipitates in the structure delayed the initiation of cracks.This thesis explores the induction quenching process of low-carbon alloy carburized steel after carburizing,fully exploits the advantages of the alloy system of the material,expands the process space for induction quenching of high-carbon gradient steel materials,achieves the guarantee of excellent mechanical properties after induction quenching of high-carbon concentration carburized layers,which provides useful support for the process optimization of heavy-duty gears with large carburized layers.