Theoretical Analysis And Numerical Simulation Of Hot Extrusion Of P91 Steel Based On Hollow Slab

Large diameter thick-walled seamless steel pipe is the crucial, important and basic part of thermal power, nuclear power, petroleum and chemical industries.In recent years, large diameter thick-walled seamless steel pipe is in increasing demand in our country and the related process of the corresponding hot extrusion technology and equipment research is also in rapid development. At present, the mainly process of the large diameter thick-walled seamless steel pipe is: smelting steel ingot- upsetting- perforation- squeeze- heat treatment-machining. Although the process shorten the production cycle, saving raw materials, saving energy consumption compared to free forging production.There are still issues including the lengthy process, needing more equipment,heating more times and wasting materials which restricted the rapid development of the large diameter thick-walled seamless steel pipe production.This paper is based on the research of the team led by Professor Li Yongtang and proposed a new technology which uses the hollow steel block extrude steel pipe directly for the theoretical studies, experimental studies and numerical simulation studies, and presented optimal parameters. The new process,compared with the traditional process, greatly shorten the process, reducing equipment, reducing energy consumption, saving materials, improving efficiency and increasing economic benefits, so it has good prospects.In This paper mechanical analysis was carried out on the extrusion process in theory. A computational model of pipe extrusion was established in the polar coordinate system. Using the principal stress method to analyze the extrusion process and the formula of thick-walled pipe and obtaining the variation pattern which the extrusion force increases with the extrusion ratio and decreases with the extrusion angle’s increase, and also to analyze the metal flow pattern during extrusion. Then applying the Gleebe-3500 thermal simulation machine to carry out a Isothermal compression experiments with the casting heat-resistant alloy P91 and the temperature flow stress- strain curve for casting P91 was obtained.From the curve we can conclude: when the strain rate is low and deformation temperature is high, dynamic recrystallization is more fully and flow stress emerge a peak and thus the constitutive equations is established. Using Jmatpro software to simulate the thermal conductivity, specific heat capacity, Poisson’s ratio and Young’s modulus of the curve for the casting P91 steel. Using DEFORM-3D simulation software to simulate the hot extrusion when scaled(ratio of 1:10) for casting P91 thick-walled pipe F1320mm′F920mm′12000mm. And analyzing metal flow during extrusion,extrusion pressure, velocity field, equivalent strain or stress, temperature field for billet and die. Finally analyzing the effect on extrusion pressure from these parameters by changing extrusion ratio, extrusion temperature, extrusion speed,squeezing angle.Ultimately the best technology was certain for the as-cast P91thick-walled pipe: extrusion ratio of 10, squeezing angle of 60°, extrusion temperature 1200 ℃, extrusion speed of 80mm/s and to provide a theoretical basis for the firm production.