Study On The Control Of The Decarburization Of GCr15 Seamless Pipe In Isothermal Spheroidizing Annealing Process

GCr15 bearing steel is a kind of low alloy content and excellent performance high carbon bearing steel,widely used at home and abroad.In China,product bearing ringuse GCr15 seamless tube as raw material,whichproduced pass the heating and cooling roll,ball and multi pass drawing.Because of the higher carbon content of GCr15 bearing steel,due to the heating of long time,decarburization can cause during the spheroidizing annealing process of steel pipe,the surface decarburization depth is one of the key indicator due to heating for a long time of the products.This paper simulation analysised the TTT curve andthe CCT curve of GCr15 bearing steel by the JMatpro software,analysis shows that before austenitizing temperature cooling to isothermal temperature,GCr15 steel begins to change pearlite,during isothermal spheroidizing,but the change is not complete,and begin to pearlite isothermal transformationat a rapid speed,in less than 1300 secends,completebecome the pearlite organization.In the simulation of decarburization,we should use diffusion coefficients of carbon atoms in austenite above 725°C,during 725~650°C should be using diffusion coefficient of carbon atoms in pearlite,ang we think than decarbonization behavior does not occur below 650°C.The simulation analysis of thermodynamic equilibrium composition shows that the equilibrium austenite carbon content of GCr15 steel is 0.74%,When austenitizing is heated at 790°C.Research and analysis of the influence of diffusion coefficient,transfer coefficient,heat transfer coefficient of the diffusion problem during the heat treatment process,conside the diffusion coefficient as a function of temperature and carbon content,at the same time,the Arrhenius equation is applied to transfer coefficient established transfer function coefficient and temperature,improved the accuracy of the simulation.Applying the diffusion principle,establish the finite element model of decarburization simulation in DEFORM,and confirmed the accuracy of the numerical calculation model of heat treatment of decarburizationthrough comparing experiments result with simulation result,and revised the carbon content of the decarburization layer to 0.88%.Study the control of decarburization during the spheroidizing annealing process combined with a company produced GCr15 seamless steel tubes.Research shows that the substrate material containing more carbon,the higher carbon content in the material after heat treatment.When the carbon potential is more than 0.65,the decarburization layer depth conforms to the national standard GB/1854-2002,when the carbon potential is between 0.7~0.75,neither decarburization nor carbon,when the carbon potential reached 0.8,the workpiece will be slightly carburizing.Based on the above conclusions,through the analysis of the whole process of the company,this paper puts forward the measures to eliminate decarburization in the process of GCr15 seamless steel tube productionin the end.