Hot extrusion technology is a metal above the recrystallization temperature for extrusion, the billets extruded from a die orifice, to obtain the shape of the die hole metal forming method of the cross-sectional pipe. In the hot extrusion process (from the tube blank to the blank pipe), the tube is in the third state to the compressive stress deformation. This is not only solve the difficult deformed steels, steel pipe forming, and can be avoided by the tensile stress caused by shortage tube defects of the inner and outer surfaces. Hot extrusion molding method is particularly suitable for a variety of alloy steel, stainless steel, high-strength steels, nickel-based superalloy, profiles, pipes forming.

Hot extrusion production process
Hot extrusion technology to produce seamless steel pipe, tube hollow billet. A perforated hollow billet forging billet or slab, another hollow billet is centrifugal casting. Perforated of forging billet or slab, in accordance with the different steel grades and specifications, can take three different perforation method: ① solid tube perforated vertical punch; ② pre-drill a small hole in the tube center ( also called guide hole) in the pressure on the piercing mill piercing; ③ in the tube center drilling large holes of a diameter slightly larger than the extruded core rod extruded directly sent to the extruder. When the solid billet perforated vertical punch, tube by heating and descaling the sticks on the surface of a layer of glass powder, into a perforated tube.

When the start of the perforation, the perforation rod and perforated mandrel downward pressure to the blank tube upper end. Pressure is applied to the blank tube, the first billets upsetting, be filled with perforated cylindrical hollow shell after the piercing rod with the perforated mandrel disengagement, perforated rod its self weight in the tube, while the piercing mandrel (mounted at its front end a piercing plug) continue perforated down. In this case, the metal flows upwardly to form a hollow billet. Perforated tube below a support mandrel. Its role like a shutter, in the piercing plug reaches the end of a predetermined position before the perforation stroke, prevent perforation residual material was cut and shedding. The perforation after, the piercing plug falling more than expected, and the perforated cylinder and a hollow shell out. After piercing the temperature of the hollow shell has been reduced, must be re-heated in order to reach the required extrusion temperature. Hollow shell after heating, the temperature was raised to 1 180 to 1 250 ° C, to reach the plastic deformation state. Heated tube first descaling, then scroll on the glass powder and glue a layer of glass powder. Glass frit from the role of lubricating and insulation. The cylindrical tube loaded horizontal extruder extrusion cylinder. Extruded rod built in the bottom of the extrusion cylinder equipped with extrusion die and glass mat;
A circular core rod (also known as piercing needle) extends die hole. Extruded rod into the extrusion cylinder, squeeze the tube to the die hole end by squeezing the pad, with the increasing pressure applied before the tube upsetting coarse eliminate the gap between the tube and squeeze tube wall , and then be extruded from the die hole.

With the rapid development of science and technology, the growing demand for high-alloy seamless steel pipe, hot extrusion technology has been widely used as an efficient and mature processing methods, high alloy steels difficult deformation a seamless steel pipe than ideal production methods.