Study Of Subcritical Quenching And Low Temperature Gas Multi-elements Permeation Composite Processes On Microstructure And Properties Of 50CrVA Steel

The leaf spring is the key component of CRH3 high speed train steering rack.At present our country developed composite heat treatment process to meet or exceed the performance of foreign products.But because our country vast geographic,low temperature toughness of plate spring put forward higher requirements.The domestic 50CrVA materials,explore the material structure and property of composite process and quenching + tempering+ multicomponent infiltration after,especially the toughness and fatigue properties of low temperature impact,and provide theoretical and experimental support for the localization of the plate spring.The optimal parameters of 50CrVA material composite was studied,the microstructure observation,the surface layer hardness test,low temperature impact strength,tensile properties,fatigue properties,the neutral salt spray corrosion resistance,electrochemical polarization curve measurement,and other technologies are described in.This paper furst studied the effects of different composite treatment on Microstructure and properties of the composite,the optimum process parameters.The test results show that:the process of quenching can make the material grain refinement,and keep part of undissolved ferrite.Composite 50CrVA materials after intercritical quenching + tempering +Multicomponent Infiltration of surface tissue,white layer and diffusion layer,microstructure of Troostite and patches of ferrite is tempered,material surface has higher microhardness.After the composite process,low temperature impact toughness of materials increases,increased by 140%than the foreign plate spring material;fatigue performance between 1100 MPa and 1200 MPa,about 38%higher than that of foreign plate spring.At the same time,the material has better corrosion resistance to salt spray,increased by 50 times than the foreign plate spring material.The electrochemical corrosion resistance is due to the improvement of the corrosion potential and passivation region has greatly enhanced.Through the fracture of tensile and fatigue,the composite process,tensile fracture mechanism is ductile and brittle mixed fracture of the samples,and analyzed the reason of.Based on the fatigue fracture surface of sample research,established the calculation model of fatigue limit enhanced after surface treatment,obtained according to the formula of depth of hardening layer,micro hardness and residual stress data calculation of fatigue strength.