Effects Of Material And Morphology Coupling Elements On Rolling Fatigue Wear Of 20CrMnTi Steel

As a typical low hardenability steel,20 CrMnTi steel has good toughness,weldability and cutting ability after quenching.It is widely used in transmission parts of automobile.The failure mode of the parts is that under the cyclic action of alternating stress,cracks are initiated and propagated at the place where the stress is concentrated,and then spalling occurs when the cracks extend to a certain extent.Although 20 CrMnTi steel meets the requirements of toughness,its material has low strength and poor wear resistance.In order to improve its wear resistance,the factory often through carburizing heat treatment,improve its carbon content to meet its strength needs.However,through carburizing heat treatment,on the one hand,it needs more energy consumption and long carburizing cycle,on the other hand,it is easy to form the original materials with hard outside and no infiltration inside,and it is easy to produce fatigue cracks at the soft hard interface.Therefore,it is necessary to find a new processing method to replace the traditional carburizing heat treatment process.In this paper,on 20 CrMnTi steel material,combined with Biomimetic Coupling Theory,the biomimetic unit with high hardness is prepared on the surface of the base material by laser processing technology.The high hardness unit and the low hardness base material form a kind of coupling biomimetic structure similar to the soft and hard phases of the biological surface,which can effectively improve the anti rolling fatigue wear performance of the surface of the base material.However,the carbon content of20 CrMnTi steel is low,and the supersaturated martensite structure can not be obtained by laser quenching,so the hardness of 20 CrMnTi steel can be improved.Therefore,the laser melting and self quenching process limits the improvement of the fatiguewear performance of low carbon steel.In order to improve the anti rolling fatigue performance of materials,five kinds of bionic coupling elements with different hardness were prepared by laser melting,laser carburizing and laser cladding.The best bionic element is selected through the experiment of rolling fatigue wear,and its stress field is simulated and analyzed by the finite element software.The shape bionic design of the selected unit is carried out,and the wear conditions under different shapes are analyzed,and the best bionic shape is selected.Experiments show that Laser Biomimetic has the advantage of replacing the traditional carburizing heat treatment.The experimental results show that the rolling wear resistance of low hardenability steel is improved to some extent by laser surface strengthening technology.Generally speaking,the harder the unit is processed,and the stress simulation analysis shows that the unit distributes most of the stress to the sub layer to protect the matrix,the better the wear resistance.However,it is necessary to consider the combination and decomposition of the cladding particles of the unit,select the best MSIC unit for different coupling element design,and analyze the impact of different unit spacing on the wear resistance.It is found that the bionic coupling specimen with MSIC element has the best anti-wear performance,and the bionic coupling specimen with 5 mm transverse spacing and 4 mm longitudinal spacing has the strongest anti rolling fatigue performance.In the same case,the weight loss of the bionic sample with MSIC unit is 10.2% of the original matrix sample and 57.3% of the sample after carburizing heat treatment.For the samples prepared by traditional carburizing heat treatment,the linear soft hard alternating layer,which is hard on the outside and soft on the inside,is easy to produce fatigue cracks because it can not be deformed under stress.The existence of the laser element body can obtain a certain bending and stretching stress deformation fatigue layer,which can reduce and disperse the stress,protect the matrix structure,so as to greatly improve its wear resistance,and fundamentally reduce the crack initiation,so as to improve the service life of the steering shaft ball joint.