Reasons for fracture of cold-drawn seamless steel tube

  • When the carbon seamless steel tube is cold drawn, the hot rolled tube blank has defects such as cracks. For example, after the high-precision cold-drawn tube is made into an oil cylinder, the fracture that occurs during use has almost no plastic deformation and is generally a brittle fracture. Brittle fracture is caused by a variety of reasons. For example, when there are precipitates at the grain boundary, no matter whether their strength is stronger or weaker than that of the matrix, it is the cause of cracks; the segregation of inclusions at the grain boundary is also the cause of fracture; in addition, even at the intersection point much smaller than the yield limit, Fatigue fracture also occurs under variable loads.

    In general, the mechanical performance metrics used in the design of hydraulic (pneumatic) parts assume that the material is homogeneous, continuous, and isotropic. According to this approach, the design is considered safe, and sometimes accidents can occur. breakage accident. It has been found that the material structure is far from homogeneous and isotropic during low-stress brittle fractures of high-strength metallic materials. Defects such as cracks, inclusions, pores, etc. will appear in the structure, and these defects can be regarded as micro-cracks in the material.

    seamless steel tube

    In addition, brittle fracture is also related to the service temperature of the part. Through research, it is found that when the temperature is lower than a certain temperature value, the material will transform into a brittle state, and its impact absorption work will decrease significantly. This phenomenon is called cold brittleness. Therefore, the design should also be based on the operating temperature of the components. Choose a material with a suitable cold-brittle transition temperature.

    At present, the material of cold-drawn seamless steel tube (a53 seamless) is ordinary 45# or 20# steel 27SiMn steel in my country, which improves the mental strength through cold-drawing deformation; however, this is at the expense of the plasticity and toughness of the metal. High precision cold drawn seamless steel tube is based on its high dimensional accuracy and high strength properties. It is necessary to ensure that the deformation amount is within a certain range in order to maximize the performance of the material and reduce the adverse effect on the material.

    If the deformation of a cold-drawn seamless steel tube is too small, it cannot meet the requirements of surface finish and dimensional accuracy, and the strength index of components cannot be achieved; if the deformation is too large, the plasticity and toughness of the seamless steel tube will be reduced too much, and the grains will be pulled too large. Elongated, forming a fibrous structure, the metal will have obvious anisotropy. The axial direction of the cold-drawn seamless steel tube is parallel to the elongation direction of the grain, and the strength increases; the radial direction of the cold-drawn seamless steel tube is perpendicular to the elongation direction of the grain, and the strength decreases instead. The maximum stress of the hydraulic cylinder exists in the seamless steel tube. the radial direction of the tube,

    For dislocations, vacancies, and other fibrous structures and crystal defects in steel, heat treatment methods such as annealing or normalizing are generally used to eliminate them. The purpose of annealing is to refine grains, eliminate structural defects, reduce hardness, improve plasticity, and facilitate cold working. In the production of cold-drawn seamless steel tubes, annealing equipment is essential. Therefore, formulating an appropriate annealing process is a necessary condition to ensure that the cold-drawn seamless steel tube is qualified and the product does not have fracture defects. If the manufacturer reduces the annealing process in order to unilaterally reduce the production cost, it will definitely have an adverse effect on the product quality.

    Tianyang Steel Tube, a seamless steel tube enterprise in China, provides seamless steel tubes with high quality, welcome to consult and purchase.