Normalizing Process Simulation And Parameter Optimization Of SA508-3 Nuclear Power Head

It is easy to form the phenomenon of coarse grain and uneven microstructure in the process of forging and heating treatment due to the nuclear power head's large size(maximum diameter is 2990mm).In order to eliminate the above microstructure defects,the heat treatment process of normalizing after forging is often adopted.Therefore,this paper took SA508-3 nuclear power head as the research object,organized a research and analyzed the nuclear power head's distribution of the temperature field and stress field and the microstructure when it's being normalized by adopting the method of combining the numerical simulation and physical test.And the normalized heating process parameters are optimized.The research of this paper laid the theoretical basis to achieve the microstructure of the nuclear power head elaboration and homogenization.The specific research contents and results are as follows:The effects of heating temperature,holding time and heating speed on the formation and growth of crystal nuclei in SA508-3 steel were studied by physical experiments.Found that the average austenite grain size growth as the heating temperature rise when the temperature is under 900?,but there is a sharp rise in the grain growth rate when the temperature is higher than 900 ?;Average austenite grain size with the increase of the holding time are on the increase,so the proposal is that the normalization heat treatment temperature is 890 ?;In the high temperature zone(above Ac3),the grain size increased significantly when holding time was within 1h,but the grain size tended to remain unchanged when the holding time continued to extend.When it's heated at low velocity(? 500?/h)in the high temperature,austenite nucleation delay,nucleation quantity is little,and the austenitic grain internal has no longer produced new austenite crystal nucleus,and organization genetic was produced,so the influence of heating rate should be fully considered when making head normalizing process parameters.Numerical simulation of heat treatment is very important for predicting microstructure and deformation.Based on heat transfer,phase change dynamics and elastoplastic mechanics,a mathematical model describing the heat treatment process of SA508-3 steel was established in this paper,the temperature field,stress field and microstructure transformation of the normalizing process of nuclear head were analyzed with the finite element simulation software DEFORM-3D.The results show that the internal and external temperature difference is large in the heating process,and the stress generated is also large,and the distribution is uneven.Therefore,the parameters are optimized by adjusting the heating temperature,heating speed and holding time.The optimized process is: first heating the temperature to 450 ? at a speed of 50 ?/h and holding 4h;then heating the temperature to 650 ? at a speed of 40 ?/h and holding 6h;Finally heating the temperature to 890 ? at a speed of 20 ?/h and holding 9h;air cooling to the room temperature.By means of numerical simulation and physical test,the process after parameter optimization is analyzed,and it is found that the internal and external temperature difference is obviously reduced,and the stress was reduced and distributed evenly.The austenization time interval was shortened and the austenization was completed at the end of heating.After normalizing,the grain size of all positions of the sealing head is around grade 8,and the overall austenite grain size is fine and even.The microstructure matrix of each position of the head after air cooling is granular bainite structure,and the distribution is uniform.The optimized process parameters are reasonable.