Research On Heating Process And Oxidative Decarburization Behavior Of 42CrMo4 Ring Forging Billet

The 42CrMo4 yaw bearing is the core component of the wind turbine,used for the yaw rotation of the wind turbine nacelle,with high performance requirements.The ring production process can be roughly divided into three stages:heating before billet forging,free forging billet plus ring rolling and heat treatment after forging.The heating quality of the forging blank before forging directly affects its internal quality and performance;the oxidation and decarburization of the surface layer during heating directly affects the utilization rate of the material and the comprehensive mechanical properties of the product surface.The existing pre-forging heating process is based on generally applicable empirical heating specifications,and there is no reasonable analysis and design for a specific product.In this paper,the blank heating process of42CrMo4 yaw bearing of a certain company is taken as the research object.First,the high temperature oxidation and decarburization behavior of 42CrMo4 is analyzed,and the corresponding dynamic model is established.With the help of the finite element simulation software Deform-3D,the change process of temperature,stress and structure transformation in the heating process of the blank is explored.The kinetic model is used to predict the theoretical thickness of the oxide layer and decarburized layer,and then optimize the heating process parameters to reduce the total heating time,the theoretical calculation depth of the oxide layer and the decarburized layer,and finally analyze the comprehensive mechanical properties and metallographic structure of the trial product.The main research contents and conclusions are as follows:The 42CrMo4 oxidation weight gain curve was measured,and the oxidation activation energy Q value was calculated by fitting to 217k J/mol,which can be converted into the oxidation rate constant K_P·T at different temperatures.SEM was used to analyze the surface morphology and cross-section morphology of the oxide layer at different temperatures.Observe and analyze the morphology and structure of the decarburized layer of the sample at different temperatures through OM,and measure and calculate the average thickness of the decarburized layer.According to Fick’s second law,the theoretical calculation formula for the thickness of the decarburization layer is designed,and the correction coefficient n=1.05 is set in combination with the thickness of the burned oxide layer and the suppression of the oxide layer on the decarburization.The depth of the decarburized layer obtained by theoretical calculation is close to the experimental measurement value.Summarize and design the oxidation and decarburization kinetic model of 42CrMo4 at high temperature under variable temperature conditions.The approximate comprehensive heat transfer coefficient of the billet in the flame furnace is calculated.The thermophysical parameters of 42CrMo4 are calculated based on Jmatpro.The empirical heating process is formulated according to the general technical conditions for heating of free forgings.Using the finite element simulation software Deform-3D,combined with the corresponding parameters,simulate the change process of temperature,phase transition,stress,oxidation and decarburization during the heating process of the blank under the empirical heating specification.Among them,due to the excessively large radial dimension of the blank,three peak temperature differences of 293.41°C,321.81°C and 521.49°C appeared during the heating process.The axial stresses corresponding to the first two peak temperature differences in the low temperature range are 364 MPa and 272 MPa,respectively,which are lower than the yield strength of the material at the same temperature.Based on the oxidation and decarburization kinetic model of 42CrMo4,the temperature change and time during the heating process are used as variables to calculate and predict the oxidative decarburization behavior of the billet during the heating process.The law of the oxidative decarburization process conforms to the second chapter.The phase change holding temperature,phase change heating holding time and initial forging temperature are used as the experimental design factors,and the total heating time and theoretical calculation of the oxide layer decarburization layer thickness are the response targets.Single factor analysis shows that increasing the phase change holding temperature,phase change holding time,and lowering the initial forging temperature are beneficial to reduce the degree of oxidative decarburization.But increasing the phase change holding time will greatly increase the total heating time.Based on the BBD design test plan,select appropriate test design factors,use Deform-3D simulation to obtain sample data,establish the response surface model of optimization targets and test design factors,and then use Design-expert to select the optimal heating process:initial forging temperature 1200℃,phase change holding temperature 900℃,phase change heating holding time 25min.The mechanical properties and metallographic structure of the trial-produced product meet the requirements after analysis.This topic combines experimental analysis,dynamic model calculation,finite element analysis,and response surface model.Designed to effectively reduce the heating time and reduce the heating process parameters of oxidative decarburization.Provide theoretical basis and technical support for the billet heating process of the same type of large forgings.