Production and Elimination of Fracture in Cold Drawn Seamless Steel Tube

    Cold drawn seamless steel pipe, the hot-rolled tube blank cracks or other defects or high-precision cold drawn tubes are made after the cylinder, the fracture occurred in the course of use, almost no plastic deformation occurred, are generally brittle fracture. Brittle fracture is caused by a variety of reasons. Such as: precipitates on the grain boundary, regardless of its strength than the matrix strength is strong or weak, are all the causes of cracks; segregation of inclusions in the grain boundary is also the cause of fracture; In addition, even in far less than the yield limit of the intersection Variable load, also can cause fatigue fracture phenomenon.

    In general, hydraulic (pneumatic) components used in the design of mechanical properties are based on the assumption that the material is uniform, continuous, isotropic, according to this method is considered a safe design of the design, and sometimes accidents Fracture accident. The study found that during the low stress brittle fracture that occurs in high-strength metal materials, the material organization is far from homogeneous and isotropic. There will be cracks in the organization, there will be inclusions, pores and other defects, these defects can be seen as micro-cracks in the material. In addition, the brittle fracture is also related to the service temperature of the component. People through the study found that when the temperature is lower than a certain value of temperature, the material will be transformed into a brittle state, the impact absorption decreased significantly, this phenomenon is called cold and brittle, so the design time but also based on component operating temperature Select the material with suitable cold and brittle transition temperature.

    High-precision cold-drawn seamless steel pipe is generally increased by adding alloys in the metal to improve the performance of materials, seamless steel pipe after cold drawing, are required to stress relief annealing to eliminate the residual stress of the material to improve the material organization, Improve the plasticity of the material, so as to achieve the purpose of preventing the failure of the seamless steel pipe from breaking.

    At present, China's cold-drawn seamless steel pipe are made of ordinary 45 # or 20 # steel 27SiMn steel, cold-drawn deformation to improve the strength of the metal; However, it is at the expense of metal plasticity, toughness for the price. High-precision cold drawn seamless steel pipe is based on its high dimensional accuracy and high strength performance and based on the market, it must ensure that the deformation in a certain range, in order to maximize the performance of materials to reduce the material Negative Effects.

    Cold drawn seamless steel pipe deformation is too small, can not meet the requirements of surface finish and dimensional accuracy, also can not reach the component strength indicators; deformation is too large, seamless plastic pipe ductility, too much reduction, and the grain is too much Slender, forming a fibrous tissue, the metal will have significant anisotropy. Cold-drawn seamless steel tubes in the axial direction, parallel to the direction of elongation of the grains, the strength increased; radial drawing seamless steel tubes, perpendicular to the direction of elongation of the grains, the strength but lower, and the maximum hydraulic cylinder stress Exist in the radial direction of seamless steel pipe, so too much deformation on the full performance of cold-drawn tube adverse.

    For steel fibers appear as well as dislocations, vacancies and other crystal defects, usually take annealing or normalizing and other heat treatment to be eliminated. The purpose of annealing is to refine grains, eliminate tissue defects, reduce hardness, improve ductility, and facilitate cold working. Cold drawn seamless steel pipe production, an indispensable annealing equipment, therefore, to develop a suitable annealing process is to ensure that the organization of cold drawn seamless steel pipe, the product does not appear the necessary conditions for fracture defects. If the manufacturer in order to reduce production costs, reduce the annealing process, will certainly adversely affect product quality.

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