The Research On Hot Extrusion Process Of P91Larger Diameter Thick-walled Seamless Steel Pipe Based On FEM Modeling

The thick-walled seamless pipe of P91is proverbially used in boiler tube that resistantto elevated temperatures due to its favorable heat resistance, better corrosion resistance andlow thermal expansibility. However, there are only a few enterprises are able to produce P91thick-walled seamless pipes, because of their high content of alloys, difficult metal-processing, low rates of end products, slow improvement of technology and high costs. Inthis situation, the domestic products are in inferiority compared with the same products thatproduced abroad, so, the consumption mainly relies on import in our country.High quality thick-walled seamless pipe of P91has been produced by hot extrusionwith series of success in developing heavy extrusion equipments since2009. In this paper,based on FEM simulation technology, we analyzed the process of piercing and hot extrusionof P91thick-walled seamless pipe by DEFORM, and also analyzed the laws of metalflowing, velocity field, temperature field and equivalent stress field by thermal-mechanicalcoupled in the piercing process.During the analyzing of hot extrusion, the reliability of the model was tested bycomparing with measured data of related documents, and then mainly analyzed the all kindof field quantities including temperature field of mould and the situation of surface wearingof P91thick-walled seamless pipe during the hot extrusion. At last, the deformation lawswere revealed in the hot extrusion.The results show that the highest extrusion stress is199MN on the temperature of1250℃, velocity of extrusion of100mm/s. When the temperature descends50℃, theamplification of extrusion stress reaches about20%. Comparing with different extrusionratios, the highest extrusion stress is102MN when the extrusion ratio reaches5, and thehighest extrusion stress is262MN when the extrusion ratio reaches9at the same case, atwhich the amplification reaches156.9%. The effects of different mold cavity cures onextrusion stress are little (relative differences of two examples is less than1%in this paper),but on the stress state are bigger. When the deviation of inner and outside of the circle centreis20mm, in order to make the extrusion axis coincide with the blank line, extrusion stress of28.2MN are needed in the horizontal direction of extrusion press standers.