Making tube billet is the main deformation procedure of hot extrusion production for thick wall P91 steel tube. For thick wall P91 steel tube billet, with an outer diameter of Φ535 mm, an inner diameter of Φ250 mm and a length of 1900 mm, the numerical simulation of backward extrusion process was carried out by Forge software. The temperature field distribution and extrusion force with the changes of punch stroke were obtained. The two local high temperature zones in the temperature field were confirmed, namely the area vertically below the punch head and the outflow location of tube billet. Moreover, the extrusion force had the stage characteristic of slow, linear, gradual and rapid increasing with the increase of punch stroke. Through studying on effects of both the initial temperature and the extrusion speed on making tube billet process, it is showed that the increases of billet initial temperature and extrusion speed can decrease the max extrusion force obviously. Thereforce, the billet initial temperature of 1100-1200 ℃, extrusion speed of 200 mm·s-1 and equipment tonnage of 36 MN have been recommended in the practical production.
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