The hot extrusion process of seamless steel pipe is a pressure forming method, which is to place the tube blank in a pressure-resistant container, and apply external force to cause the tube blank to plastically deform under the state of three-dimensional compressive stress. During extrusion, the tube blank is in a state of three-way compressive stress, so it can obtain a larger plastic deformation than rolling and forging. Depending on the material and extrusion method, the extrusion elongation coefficient can reach 5~500, or even higher. Because the extruded seamless steel pipe has the characteristics of high dimensional accuracy, dense metal structure and stable mechanical properties, hot-extruded seamless steel pipe is widely used in nuclear power, thermal power, petrochemical, aviation, aerospace, transportation and other fields .
Hot extrusion process
Billet preparation → annular furnace preheating → vertical induction furnace heating → glass powder lubrication → vertical press punching (expanding) → phosphorus removal → vertical induction furnace reheating → glass powder lubrication → extrusion → cutting and pressing → cooling
When using hot extrusion technology to produce seamless steel pipes, the broken pipes must be hollow billets. One is a hollow billet for perforating a forged or cast billet, and the other is a hollow billet for centrifugal casting. There are 3 different piercing methods for perforating forging or casting billets according to their steel grades and specifications:
①The solid tube blank is perforated on the vertical perforator;
② Drill a small hole (also called a pilot hole) in the center of the broken pipe in advance, and perform perforation on a pressure perforator;
③ Drill a large hole with a diameter slightly larger than the extrusion core rod in the center of the broken pipe, and send it directly to the extruder for extrusion.
During extrusion, the glass mat between the tube and the extrusion die melts and acts as a lubricant. The outer diameter of the extruded seamless steel pipe depends on the inner diameter of the die hole, and the gap between the mandrel and the die hole determines the thickness of the steel pipe. After the extrusion is completed, the steel pipe is cooled and collected, and subjected to heat treatment and hardcover treatment