Simulation And Experimental Research On Vertical Extrusion Process For P91 Thick Wall Steel Tube

P91 seamless tube with large diameter and thick wall is the key component of nuclear power equipment and steam power plant. At present, vertical extrusion is a perfect process to produce such special tube. The technology is blockaded by foreign countries. There is no systematic research for it in domestic.The vertical extrusion process for P91 thick wall steel tube is simulated in this paper. Gleeble-3500 thermal simulation machine is used to conduct one-dimension hot compression of P91. The high temperature flow stress-strain curve of P91 steel is determined. Combining with metallographic analysis, the influence of deformation temperature and strain rate on P91 flow stress and austenitic dynamic recrystallization is obtained. As the deformation temperature increases and strain rate decreases, the flow stress decreases due to the remarkable effect of dynamic recrystallization softening. High temperature and low strain rate can increase grain size which is benefit for dynamic recrystallization. The influence of deformation temperature on grain size of recrystallization is increased as the strain rate decreased. The influence of strain rate on grain size of recrystallization is increased as the deformation temperature increased.Based on Avrami equation, P91 mathematical model of dynamic recrystallization is regressed.This model is integrated into Deform software to simulate dynamic recrystallization. Simulated values are in good agreement with metallographic ones. It is indicated that the said model is correct, and can be used in the grain size prediction of hot forming of P91.In this paper, numerical simulation and experimental billet temperature drop method are combined to obtain heat transfer coefficient q1=0.01J/(m2·s·℃) during billet lubrication. Error analysis between simulation result and scale-down extrusion experimental shows, by blanks-die composite lubrication solution with 100 mesh glass powder,80 mesh glass mat and water-based graphite, the friction coefficient ofμis 0.03-0.05. This provide accurate boundary conditions for vertical extrusion technology.Composite lubrication plan and glass mat preparation method is summarized after trail experiment in this paper. Extrusion process test is conducted onφ559 mm (outside diameter)×φ339 mm (inner diameter)×12000 mm large diameter thick wall seamless steel tube with the scale-down ratio of 1:8. extrusion ratio of 5,7 and 9.Through the metallography experiment for scale-down extruded P91 tube, the influence rule of deformation on microstructure and properties is obtained. The result is compared with P91 tube ofφ813 mm (outside diameter)×φ679mm (inner diameter)×6500 mm (extrusion ratio is 5.8). It is shown that extrusion ratio within the scope of 5-7 is reasonable, and scale-down extrusion process test can provide the basis for practical production.