Fatigue Properties Of 30Cr15Mo1N High Nitrogen Stainless Bearing Steel

As essential parts of rail transportation and the aerospace industries,bearings seriously affect the lifespan and reliability of equipment.With the development of the equipment manufacturing industry,there is an increasing demand for bearings with long-serving lives,high-temperature resistance,and corrosion resistance,which also raises the bar for the comprehensive performance of the bearing steel.The high nitrogen stainless bearing steel(HNSBS)with the merits of high strength,high hardness,long life,and superior corrosion resistance has become a popular topic in the development of novel bearing materials.The research on fatigue properties is behind due to the late commencement of HNSBS manufacturing in our country.Consequently,HNSBS has been used as the research object.Systematic and in-depth investigations on the microstructure,mechanical properties,rotatory bending fatigue(RBF),rolling contact fatigue(RCF)and fatigue mechanism of HNSBS have been conducted to reveal the effect of microstructure tunning on the fatigue properties.By studying the microstructure and properties of HNSBS,it was found that Vmicroalloying can refine the austenite grain size of HNSBS quenched at 1050℃from 16.0 μm without V-microalloying to 10.3 μm.After tempering at 180℃,the tensile strength is increased from 1899.7 MPa to 1985.3 MPa.The results indicated that the temperature to attain the peak effect of the secondary hardening of the HNSBS was 500℃.For V-microalloying steel,the tensile strength could be raised to 2257.6 MPa and the hardness could reach 60.6 HRC.After tempering at 500℃for 20 hours,the matrix still maintains an ultra-high hardness and strength of 60 HRC and 2200 MPa,with excellent tempering stability.According to the investigation on the RBF property of HNSBS,it was found that after tempering at 180 ℃,the fatigue strength of non microalloyed steel was 715MPa,and that of V-microalloying steel was 866.7MPa,an increase of 1 52MPa.The grain size refining and enhancement of matrix toughness arising from Vmicroalloying were the main reasons for the increase in fatigue strength.The fatigue strength of V-microalloying steel tempered at 500℃ was further promoted to 1020 MPa.Based on the analysis of RBF fracture characterization,it was found that the matrix structure was the main crack source causing RBF failure except for inclusions.The fatigue failure mechanisms of "intergranular fracture" and "twinmartensite fracture" were proposed.Based on the investigation of the RCF property of HNSBS,it was found that after tempering at 180℃,the RCF life L10 of non microalloyed steel was 1.67×107,and L10 of V-microalloying steel was 3.99 × 107,increased by about 2.4 times compared to non microalloyed steel.The refinement of the grain size in the matrix were the main reasons for the improvement of RCF life.The L10 of the non microalloyed steel tempered at 500℃ was 2.85 × 107,which was 1.7 times higher than that of the steel tempered at 180℃.Through a systematic study of the microstructure and fatigue properties of HNSBS,it was found that V-microalloying not only significantly refined the grain size,but also significantly improved the RBF strength and RCF life of HNSBS.The fatigue crack sources of HNSBS with "intergranular fracture" and "twin-martensite fracture" were found except for inclusions.Through the theory of dislocation accumulation,a fatigue model for bearing steel based on microstress concentration was proposed,revealing the grain size control mechanism of RBF and RCF properties of HNSBS,providing a theoretical basis for the development of higher performance bearing steel.