Generation of cold drawn tube fracture
When steel tube cold-drawn, due to the hot rolled billets be made after the tank, the presence of defects such as cracks, or high-precision cold drawn tube fracture occurred during use, almost no plastic deformation occurs, generally are brittle fracture. Brittle fracture is caused by a variety of reasons. For example: grain boundary precipitates, regardless of their strength than the matrix strength is strong or weak, are the cause of the cracks; inclusions in the grain boundary segregation is fracture causes; Further, even in far less than the yield limit alternating loads will cause fatigue fracture phenomena. Generally, the hydraulic pressure (pneumatic) parts at design time using the mechanical properties are assumed material is uniform, continuous, isotropic, and analyzed according to this method is considered to be safe design, sometimes accidents breakage. The study found that the process of the low stress brittle fracture occurs in the high strength metal material, the material structure is far from homogeneous, isotropic. Organization have cracks, inclusions, porosity and other defects, these defects can be seen as the micro-cracks in the material. Further, the brittle fracture is also related to the use temperature of the member. Through research found that when the temperature is below a specific temperature value, the material will be converted to a brittle state, the impact absorption energy was significantly decreased, a phenomenon known as cold brittle and, therefore, even when designed according to the working temperature of the member to Select the appropriate cold-brittle transition temperature of the material.
Eliminate of cold drawn tube fracture
Global precision cold drawn steel pipe is generally through the increase in the metal alloy approach to improve the material properties, the pipe in the cold drawn after the need for stress relief annealing, to eliminate the residual stress of the material, to improve the organization of the material, to improve the plasticity of the material , so as to achieve the to prevent steel pipe fracture failure occurs purpose. Cold drawn steel pipe material are ordinary 45 # or 20 of # steel 27SiMn steel, cold drawn deformed metal strength improved; However, it is at the expense of metal plasticity, toughness of the cost. Precision cold drawn steel pipe is based on its high dimensional accuracy and high strength properties and based on the market, it must ensure that the amount of deformation in a certain range, in order to maximize the performance of the material and reduce the adverse impact on the material. Cold drawn steel pipe deformation is too small and can not reach the surface finish and dimensional accuracy requirements, they can not achieve the strength index of the component; deformation is too large, the ductility, toughness of the steel pipe to reduce excessive and the grain pulled over slender, forming a fibrous tissue, the metal will have a significant anisotropy. Cold drawn steel pipe in the axial direction, parallel to the elongated direction of the grains, the strength is increased; cold drawn steel pipe radially, crystal grains perpendicular to the elongated direction, the strength but decreased, and the maximum stress of the hydraulic cylinder is present in the steel in the radial direction, therefore, the deformation is too large adverse full play to the performance of the cold drawn pipe. Fibrous tissue in the steel and dislocations, vacancies crystal defects, general annealing or normalizing heat treatment means were taken to eliminate them. The purpose of grain refinement annealing, eliminating the tissue defects, reduce the hardness to the plastic, but also to facilitate cold working. Cold drawn steel pipe production, indispensable annealing equipment, develop an appropriate annealing process is to ensure cold drawn steel pipe Organization qualified, the product the fracture defect does not appear necessary conditions. If the manufacturers to reduce production costs to one-sided, to reduce the annealing process, which is bound to adversely affect the quality of products.
Post time: Sep-24-2019