The Research On Heat Treatment Process And Corrosion Behavior Of Corrosion Resistant 60Si2Mn Spring Steel

Spring steel 60Si2Mn is widely used in the railway industry.In recent years,with the rapid development of the railway industry,it has high requirements for the corrosion resistance of spring steel.In this paper,the alloy composition design is based on the chemical composition of spring steel 60Si2Mn.The austenite continuous cooling phase transformation behavior,oxidative decarburization behavior,heat treatment process and corrosion behavior in simulated industrial atmospheric environment of new corrosion resistant spring steel were studied.The main work contents and conclusions are as follows:(1)The chemical composition design of the corrosion resistant 60Si2Mn was carried out,and the corrosion resistance elements Cu and Ni were added to the 60Si2Mn component and increase the Cr content.The critical phase transition points Ac1,Ac3,An and Ar3 of the corrosion resistant 60Si2Mn were measured.Its austenite continuous cooling phase transition behavior be studied and draw its static CCT curve,these works provide references for the corrosion resistant 60Si2Mn heat treatment process.(2)The oxidative and decarburization behavior of corrosion resistant 60Si2Mn was studied.The results show that when the heating temperature is between 850℃ and 1100℃,the holding time is between 30 minutes and 120 minutes.With the increase of heating temperature and the extension of the holding time,the oxidation weight loss rate of the corrosion resistant 60Si2Mn increases,and the thickness of the total decarburized layer increases.(3)The heat treatment process of corrosion resistant 60Si2Mn was studied.The influence of the change of quenching temperature and tempering temperature on the microstructure and mechanical properties of the experimental steel was analyzed.The results show that the microstructure of the experimental steel after the heat treatment process is tempered troostite,and the change of tempering temperature has much greater influence on the microstructure and mechanical properties than the quenching temperature.The best heat treatment process for corrosion resistance 60Si2Mn is 870℃/45min quenching and 440℃/60min tempering,the yield strength of the experimental steel is 1606MPa,the tensile strength is 1716MPa,the elongation is 5.3%,the HRC hardness is 50.22.(4)The corrosion behavior of corrosion resistant 60Si2Mn and 60Si2Mn was analyzed by 360h simulated periodic infiltration corrosion test of industrial atmospheric environment from corrosion weight loss rate,rust layer morphology,rust layer corrosion products and cro-ss section element distribution.It is found that the phase change of corrosion products of spring steel rust layer is divided into two stages,Fe3O4 and γ-FeOOH in the early stage,andα-FeOOH and γ-FeOOH in the later stage.The corrosion product size of corrosion resistant 60Si2Mn is smaller than 60Si2Mn;The Cr element accumulates in the rust layer of 60Si2Mn and corrosion-resistant 60Si2Mn in the early stage of corrosion.In the later stage of corrosion,Cu,Ni and Cr in the corrosion resistance 60Si2Mn are concentrated in the rust layer near the substrate.The addition of the corrosion-resistant elements do not change the phase of the rust layer,but it can refine the size of the corrosion product and play a vital role in forming a dense rust layer in the later stage of corrosion.(5)The corrosion mechanism of rusted experimental steel under simulated industrial atmosphere was studied by electrochemical experiments.The polarization curve results show that as the corrosion cycle is prolonged,the self-corrosion potential of the experimental steel increases and the self-corrosion current decreases.The EIS results show that the corrosion electrochemical reaction of the rust experimental steel is controlled by the charge transfer between electric double layers and diffusion of reactants.The equivalent circuit is made according to the Nyquist curve.The fitting results show that the corrosion resistance of the experimental steel rust layer increases with the extension of the corrosion cycle,and the addition of corrosion resistant alloying elements can increase the impedance of the rust layer.