Effect Of Non-Metallic Inclusions On The Rolling Contact Fatigue Life Of Bearing Steels

In order to understand the effect of non-metallic inclusions on the rolling contact fatigue（RCF）life of bearing steels,effect of aluminum content of the steel,metallurgical process and cerium content on the RCF life of high carbon chromium bearing steels were experimentally studied,and the effect of non-metallic inclusions on the RCF life of bearing steels was studied using finite element simulation.Inclusions in the bearing steels with varied aluminum contents were analyzed and the RCF life was detected.The initial spherical Ca O-Mg O-Al₂O₃ complex inclusions were modified into dendritic ones in the steel when the content of aluminum element increased from 160 ppm to 480 ppm,characteristic size of the maximum inclusions increased from22.3μm to 32.21μm,and the L₁₀ fatigue life and the L₅₀fatigue lives of the bearing steel were decreased by 6.7%and 42.4%,respectively.Compared to the Generalized Pareto Distribution（GPD）method,the prediction of the Statistics of Extreme Values（SEV）method for the experimental data were more consistent with the fatigue life distribution of the steel.The investigation of the RCF life of bearing steels with different RH refining processes indicated that the number density of>3μm inclusions was one of the main factors having influence on the RCF life of high carbon chromium bearing steels.The RCF life of the steel was increased by 12%,when the number density of inclusions was reduced from 0.63/mm² to 0.44/mm².The effect of deoxidation method on inclusions and the fatigue life of the steel was investigated.The number density and maximum characteristic size of inclusions in the non-aluminum deoxidized bearing steel were 2.18times and 1.53 times of the aluminum deoxidized bearing steel,and the L₁₀ fatigue life and L₅₀ fatigue life of the non-aluminum deoxidized bearing steel were lowered by 41.66%and 59.05%,respectively.Effects of cerium treatment on the non-metallic inclusions,microstructure and RCF life of the high carbon chromium bearing steel were revealed using experiments.With the increase of the cerium content,the modification sequence of inclusions in bearing steels was Al₂O₃→Ce Al₁₁O₁₈→Ce Al O₃→Ce₂O₂S→Ce S.The Ce Al₁₁O₁₈ inclusion transformed into Al₂O₃ and Ce Al O₃ inclusions during cooling.With the increase of the cerium content in the steel,the RCF life of the high carbon chromium bearing steel increased first and then decreased.The fatigue life of the high carbon chromium bearing steel containing 33ppm cerium was the highest,the L₁₀ fatigue life and L₅₀ fatigue life were 2.7 and 2.5 times of the ordinary bearing steel,respectively.Based on the calculation of Vickers hardness of different kinds of inclusions and the steel matrix,when the cerium content in the bearing steel ranged from 0 to 33 ppm,the size,physical property parameters and number density of oxide inclusions showed the greatest harm to the RCF life of the bearing steel,and when the cerium content ranged from 33 to 91 ppm,the sulfide inclusions led to the greatest harm to the RCF life of the bearing steel.A micro-structure sensitive model of polycrystalline materials containing inclusions was established according to the crystal orientation of bearing steels microstructure combined with the stress-strain response of slip system and Fatemi-Socie multi-axial fatigue criterion.A method to evaluate the RCF life of the bearing steel by the RCF damage was proposed.Based on the characterization of subsurface equivalent plastic strain and fatigue damage of the bearing steel,the prediction method of the subsurface fatigue crack initiation location of bearing steels was proposed,and effects of the size and Young’s modulus of inclusions on the RCF life of the bearing steel were quantitatively analyzed using the volume average method.