40CrNiMo Steel Composite Surface Modification On Surface Integrity And Fatigue Properties

40CrNiMo steel with high strength,high toughness and good hardenability is widely used in shafts,gears,fasteners and other products.Domestic axle,gear,such as short fatigue life and poor reliability problems,so by surface treatment to improve the fatigue life of the workpiece,the localization of equipment upgrading,make our country from a big manufacturing is of great significance towards a manufacturing power,but a single processing method has already can’t satisfy the service requirements of highend equipment,thus the workpiece processing using a variety of modified means to achieve better performance is of great significance,This paper proposes two surface modification techniques,namely AWJP+USRE and AWJP+USRE,for Abrasive water jet shot peening AWJP,Ultrasonic surface rolling extrusion USRE,and Plasma nitriding treating N.Explore 40 CrNiMo steel surface integrity,and the influence law of fatigue performance,and also study AWJP + USRE tempering treatment after 40 CrNiMo fatigue performance,using transmission electron microscopy,scanning electron microscopy(SEM),laser confocal microscope instrument analysis,such as microstructure,through the comprehensive analysis of microstructure,residual stress,hardness of 40 CrNiMo high cycle fatigue properties affect the following main conclusions:(1)Abrasive water jet shot peening experiment was carried out,and to explore the abrasive water jet shot peening for mass processing of 40 CrNiMo the influence of surface integrity,for 40 CrNiMo conditioning treatment,water pressure,the greater the sample surface by the erosion of the kinetic energy,the greater the roughness increases and brittle materials,for ultrasonic surface rolling,with the increase of rolling times,the surface of the sample will be peeling,and roughness increased with the increase of rolling times bigger.(2)Through the composite surface modification process,the gradient structure with good performance can be obtained.In the 40μm off-surface,the grain size is 70 nm,the deformation layer reaches 320μm,the roughness of the most surface reaches 0.06μm,and the residual stress of the most surface reaches-846mpa.The fatigue limit of the unmodified matrix increased from 510MPa to 595.7MPa(by 85.7 MPa),and the improvement of fatigue performance was mainly due to the reduction of surface roughness,the improvement of surface hardness,the formation of gradient structure and residual stress gradient.(3)After the composite surface modification,the surface residual stress of the sample changed from-846 MPa to-430 MPa after annealing treatment,but the depth of residual stress did not change,and the fatigue limit of the sample decreased from 595.7MPa to 544MPa(decreased 51.7MPa),indicating that the residual stress was still an important factor affecting the fatigue performance of the sample.(4)Plasma nitriding after composite surface modification was performed at a temperature of 500℃ for 20 h.The thickness of the nitriding layer was up to 420μm,which was 80μm higher than that of the sample without composite surface modification.The residual stress of the most surface reaches-954 MPa.After plasma nitriding of the composite surface modified sample,the fatigue limit reaches 626 MPa,30.3MPa higher than that of the composite surface modified sample 595.7MPa,and 116 MPa higher than that of the unmodified polished sample 510 MPa.The increase of fatigue limit of plasma nitriding samples after surface modification was attributed to the increase of residual stress and hardness gradient.