Effect Of Roughness On Fatigue Life Of 18CrNiMo7-6

As a key part widely used in military and civil fields such as aircraft and high-speed railway,the service life of gears often determines the maintenance period and service life of equipment.As a kind of gear steel material with high strength and toughness,18crnimo7-6 is widely used in the manufacturing of high strength gear.Surface quality is an important content of surface integrity and a major factor affecting the fatigue life of parts.The study on the effect of roughness on fatigue life is of great significance for the anti-fatigue manufacturing of parts.Because the three-dimensional surface topography of parts contains more comprehensive surface information,it can describe the microscopic surface contour of parts more accurately.By using three-dimensional roughness parameters to explore the influence of roughness on the fatigue life of parts,the way and characteristics of the influence of surface topography on the fatigue life can be more comprehensively explored.The surface texture in different directions will produce different stress concentration under the same stress direction.When the stress is applied in the stress sensitive direction,the fatigue life of the parts will be reduced.Therefore,three-dimensional roughness Sa will affect the fatigue life of parts,and different surface texture directions will also affect the fatigue life of parts.Rotary bending fatigue is a widely used high cycle fatigue test at room temperature.It is a widely used test method in high cycle fatigue test.In this paper,the rotary bending fatigue samples with different texture directions and 3d roughness values were obtained through grinding process to explore the influence of different 3d roughness Sa on the fatigue life of 18crnimo7-6 steel.The specific research content of this paper is as follows:?1?The analysis of characteristics of different surface morphology parameters and its represents meaning,microstructure and surface roughness parameters of common measurement methods,combined with the function of the different surface roughness parameters,selected that is associated with the fatigue life of surface roughness parameters,combined with the existing test conditions,the three dimensional surface roughness parameters is determined.?2?The rotary bending fatigue samples with two texture directions and four roughness levels were ground by the axial grinder of the rotary bending fatigue samples.The 3d roughness S_a,root mean square deviation S_q,surface 10-point height S_z,surface skewness S_sk,surface kurtosis S_ku,and deep valley volume S_v of all samples were detected by the 3d topography detector,and a reasonable rotary bending fatigue test scheme was developed.?3?The national standard was adopted for the rotary bending fatigue test,and the results were compared to analyze the impact of different three-dimensional roughness Sa,other three-dimensional roughness parameters related to the fatigue life,and texture direction on the fatigue life of 18crnimo7-6 steel.?4?Through experiment found that the roughness of the Sa 0.09 mu m axial texture sample rotating bending fatigue life than roughness Sa 0.09 microns of circumferential texture sample rotating bending fatigue life increased by 2.32 times,which has in parallel to the direction of the fatigue stress machining texture than in vertical direction of the fatigue stress machining is harmful to the smaller grain;That is to say,reducing the surface roughness of 18crnimo7-6 can effectively improve the fatigue life of the specimen under rotational bending.The texture direction was parallel to the fatigue stress direction,and the surface skewness Ssk had no obvious effect on the fatigue life of the parts.