Small-diameter No. 20 precision steel pipe

Small-caliber precision steel pipes are small-caliber seamless pipes with high dimensional accuracy and good surface finish for mechanical structures and hydraulic equipment. Choosing precision seamless pipes to manufacture mechanical structures or hydraulic equipment can greatly save machining man-hours, increase material utilization, and at the same time help improve product quality. The tube billet is continuously rolled on the automatic rolling mill, and finally the wall thickness is evened by the equalizer, and the diameter is sizing by the sizing machine to meet the specification requirements. The use of continuous rolling mills to produce hot-rolled small-diameter precision steel pipes is a more advanced method. It is carried out on a two-high rolling mill. The small-diameter precision steel pipe is rolled in an annular pass formed by a variable cross-section circular hole groove and a fixed tapered tip. Cold drawing is usually carried out on a single-chain or double-chain cold-drawing machine. In the extrusion method, the heated tube is placed in a closed extrusion cylinder. The perforated rod and the extrusion rod move together, so that the extruded part is extruded from a smaller die hole. This method can produce small diameters. Caliber precision steel pipe. An annealing process in which precision seamless steel pipes are heated to a certain temperature (usually below the phase transition temperature or recrystallization temperature), kept for a period of time, and then slowly cooled to eliminate the internal stress of various precision seamless steel pipes. In the process of pressure processing, casting, welding, heat treatment, cutting processing and other processes, the product may generate internal stress. In most cases, after the end of the process, a part of the residual stress will remain in the metal. Residual stress can cause the workpiece to crack, deform or change in size. Residual stress also improves the chemical activity of the metal, and it is particularly easy to cause intergranular corrosion and cracking under the action of residual tensile stress. Therefore, the residual stress will affect the performance of the precision seamless steel pipe or cause premature failure of the workpiece. During stress relief annealing, the precision seamless steel pipe undergoes internal local plastic deformation (when the stress exceeds the yield strength of the material at this temperature) or a local relaxation process (when the stress is less than the yield strength of the material at this temperature) under a certain temperature. Time) to relax the residual stress to achieve the purpose of elimination. During stress relief annealing, the workpiece is generally slowly heated to a lower temperature (500~550℃ for gray cast iron, 500~650℃ for precision seamless steel pipe, and below the recrystallization starting temperature for non-ferrous metal alloy stamping parts), and keep it for a period of time After that, cool slowly to prevent the generation of new residual stress. Stress-relief annealing can not completely eliminate the residual stress in the precision seamless steel pipe, but only mostly eliminates it. To completely eliminate the residual stress, the precision seamless steel pipe needs to be heated to a higher temperature. Under such conditions, other organizational changes may be brought about, endangering the performance of precision seamless steel pipes. Bright annealing can keep the appearance and dimensional accuracy of precision steel pipes, which is becoming more and more popular with customers. Annealing of cold-rolled strips with no oxidation and no decarburization on the surface realized in a protective atmosphere. The protective atmosphere has a single inert gas argon or helium, and a mixed gas CO-H2-N2-CO2 (DX), N2-H2 (HNX), N2-CO2-H2, etc. The composition of these mixed gases can be adjusted to make the oxidation and reduction, decarburization and carburization speeds equal in the annealing process of the strip, so as to realize the annealing without oxidation and decarburization of the strip. After annealing, there is an invisible oxide film on the surface of the strip to protect the metallic luster. According to the chemical reaction between furnace gas and steel and its changing law, prepare and apply protective atmosphere to determine the conditions to prevent oxidation and decarburization. CO2 and H2O can oxidize and decarburize the surface of the strip; CO and CH2 can reduce the oxide layer on the surface of the strip and carburize the surface of the steel; although H2 can reduce the oxide layer, it can also decarburize the surface of the steel. Bright annealing factors depend on the redox reaction of H2O, CO2, H2 atmosphere and Fe. N2 and other inert gases are the neutral protective atmosphere for steel, of which N2 is the most used, but the oxidizing atmosphere must be removed in order to play a good protective role. Generally, a mixed protective atmosphere of N2 and H2 is commonly used.