Hydrogen Embrittlement And Fatigue Resistance Of High Peformance Carburizing Steel

It is necessary for high peformance carburizing steel to have high hardness,high strength,good rotating bending fatigue performance,high contact fatigue strength,excellent toughness,high hydrogen embrittlement resistance because of their special working conditions and structural characteristics.Taking the Ni-Cr-Mo bearing steel,which is refined by double vacuum,obtaininggood strength and toughness by controlling heat treatment processas as tested materials,then the anti-hydrogen embrittlement of the test steel was investigated by thermal desorption spectrometry and slow strain rate tensile test,mechanisms of the anti-hydrogen embrittlement wereexplored;Moreover,The rotating bending fatigue and contact fatigue performance of the carburizing steel were investigated,and the mechanisms of fatigue fracture wereexplored.The study results of resistance to hydrogen embrittlement shows that the tested steel has good resistance to hydrogen embrittlement.When the hydrogen content of the tested steel reaches 1 ppm,the plasticdecline of tested steel is not obvious.On the one hand,the reson why the tested steel has excellent resistance to hydrogen embrittlement is the number of hydrogen traps in the tested steel is small,the hydrogen of the texted steel is easy to spread out,after 12 h,the hydrogen content of tested reduced from1 ppm to 0.36 PPM.On the other hand,the small grain size will dispersed the hydrogen of the tested steel into evenly.So that aggregate amount of hydrogen in stress concentration less than the critical hydrogen content which make the material brittle fracture.The nitrided layer of the test steel consists of cryptocrystalline martensite,residual austenite and a small amount of carbide,the depth of carburizing layer is 1.71 mm,the surface hardness is 727 HV,the core of the steel obtained ultra-fine lath martensite,a large number of small and dispersed carbide,a small amount of residual austenite,excellent organizational characteristics is the key to ensure the fatigue properties.Rotating rotary bending fatigue tests showed that when surface roughnessofthe sample is 800 nm,the limit value of rotating bending fatigue was 921 MPa,when the surface roughness of the sample is reduced to below 300 nm,the rotating bending fatigue limit went up to 1000 MPa,the initiation of fatigue is mainly caused by the high surface roughness and the oxide inclusions in sub-surface.By reducing the surface roughness and metallurgical process control,controlling the size and number of inclusions in steel strictlycan improved the rotating bending fatigue properties of the steel.Contact fatigue tests showed that the test steel has high contact fatigue resistance,and the initiation of fatigue crack due to subsurface maximum shear stress around the inclusion ofconcentrate stress and the crack initiated from here and expand to the surface and peel off,and the contact fatigue life of the steelcan be improved by strictly control the size and distribution of inclusions in steel with double vacuum smelting process.