The Microstructure Analysis And Numerical Simulation For Hot Extrusion Forming Based On Thick-wall Pipe Of As-cast P91 Steel

P91 large-diameter thick-wall seamless steel pipe are the significant large components in the industry of petrochemical, aerospace and military et al. In recent years, with the speedy development in national economy and industry construction, the demand for P91 large-diameter thick-walled seamless steel pipe were rapidly increased in China. A new forming process was proposed by professor Li, which is a compact route production technique with casting and extrusion forming. This technique solved the disadvantages of traditional methods like lengthy period of process, material and energy consumption as well as low productive efficiency. The new technique, which can be of great benefit to economy and society, is conductive to implementation of industrial reduction.As-cast P91 heat-resistant alloy steel was employed as the research object,the experiments research, numerical simulation in castex forming of as-cast P91large-diameter thick-wall seamless steel pipe were investigated in this paper.The unidirectional compression experiments were investigated on Gleeble-3500thermal-simulation machine. The true stress-strain curves of as-cast P91 material were collected. The high temperature rheological behaviors of as-cast P91 material was examined by the curves and laying the foundation of building material model for numerical simulation. The micro-structure evolution law of as-cast P91 heat-resistant alloy steel in different thermal condition is analyzed by mentallographic experiment. The deformation condition of dynamic recrystallization can determined. The complete dynamic recrystallization model is established and providing experimental foundation for castex forming numerical simulation. The as-cast P91 heat-resistant alloy steel material model is established by using Deform finite element numerical simulation software. The extrusion process of castex forming simulation is conducted on ?720mm×?520mm×12000mm large-diameter thick-wall seamless steel pipe with the scale-down ratio of 1:8. Macro and micro change of casting blank in the entireprocess is analyzed and providing reasonable basis for pipes' quality forecast in actual production. In addition,the extrusion process of as-cast P91 heat-resistant alloy steel under different technology parameters was simulated. The effect of different extrusion ratio,initial extrusion temperature and extrusion speed on pre-form tubes' field variables and micro-structure were analyzed.Ultimately,the appropriate technology parameters are confirmed,extrusion ratio is about9,initial extrusion temperature is 1120-1180? and extrusion speed is26-36mm/s.