Numerical Simulation And Process Optimization Research On Hot Extrusion Of Custom 450 Steel

Custom 450 high-strength stainless steel possesses a combination of high strength,corrosion resistance,good plasticity,toughness,and machining properties.Thereby,it is widely used in aviation,aerospace,steam turbines,food processing and other military or civilian fields.In recent years,with the rapid development of high-end equipment in China,there has been a greater demand for profiles with special-shaped sections of this steel.Taking factors such as the yield rate and the cost of production of the profiles into account,the hot extrusion process is generally used at the current stage.However,Custom 450 steel has the characteristics of high alloy content,poor thermal conductivity,high resistance to high temperature deformation and narrow forming temperature range,which brings some difficulties to hot extrusion forming.In this article,Custom 450 steel special-shaped cross-section extrusion materials is used as the research object.The hot deformation behavior of Custom 450 steel was studied with the help of Gleeble hot compression experiment.Based on the optimized design of the extrusion die,the method of combining numerical simulation calculation and industrial implementation is taken to study the evolution of the macroscopic field quantity in the hot extrusion forming process,and the extrusion plan and process parameters are further optimized.The main research results can be drawn as follows:Firstly,based on the thermal simulation compression experiment,the thermal deformation behavior of Custom 450 steel under the conditions of deformation temperature of 900～1200℃and strain rate of 0.01～10 s^-1 was studied.The hyperbolic sine function was used to construct the the constitutive equation of experimental steel.The dynamic recrystallization kinetic equation,critical strain（ε_c）,peak strain（ε_p）,dynamic recrystallization grain size(d _DRX)and the quantification of Zener-Holloman parameter（Z）were also established.The relationship between Prasad and Murty instability criteria in Custom 450 steel was discussed,and the thermal processing map of Custom 450 steel under the Murty instability criterion was constructed.The best thermal deformation interval of the steel was determined as follows:the deformation temperature range is 1050～1200℃,the strain rate range is 0.1～1 s^-1,the deformation temperature range is 1100～1200℃and the strain rate range is 1～10 s^-1.Secondly,a hot extrusion forming scheme of the Special-shaped material with a"J"-shapedcross-section is designed.The hot extrusion forming process is simulated and calculated with the help of DEFORM-3D finite element software.The blank preheating temperature determined by the orthogonal test method is 1200℃.Under the optimal process including a pressing speed of 230 mm·s^-1 and an extrusion ratio of 11.15,The"J"-shaped section of the extruded material prepared under this process has a complete shape without cracks and other defects.The sampling and analysis results of different positions show that the grain size is5～6 grade,which realizes the uniformity control of the J-shaped material.But there are still some slight curvatures in the length direction of the profile,and the dimensional accuracy is not enough.Thirdly,in order to solve the problem of shape control of the"J"-shaped section,an extrusion molding plan for a special-square tube with a"concave"section was designed.The hot extrusion process was further calculated and studied by DEFORM-3D finite element software.The best process parameters includes a blank preheating temperature of 1200℃and an extrusion rate of 180 mm·s^-1.The results show that,under the optimized process parameters,the extrusion molding scheme with a"concave"section can lead to extrusion material with good flatness,high dimensional accuracy.At the same time,the best matching of 6～7 grade uniform grain and Cv value of tensile strength fluctuation is 0.17%.