Occurrence and elimination of cold drawn seamless steel pipe

Occurrence and elimination of cold drawn seamless steel pipe breakage

 

The seamless steel cold drawn, due to the hot rolled billets the presence of defects such as cracks, or high-precision cold-drawn tube is made after the tank, the fracture occurs in the use of the process, almost no plastic deformation occurs, generally are brittle fracture. Brittle fracture is caused by a variety of reasons. : 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.

Global precision cold drawn seamless approach is through the increase in the metal alloy to improve the material properties, the seamless steel pipe in the cold drawn after the need for stress relief annealing, to eliminate the residual stress of the material, and to improve the organization of the material, increase the plasticity of the material, thus preventing a failure occurs, the purpose of seamless steel pipe rupture.

Currently, cold drawn seamless steel pipe material are ordinary 45 # or 20 of # steel 27SiMn steel by cold drawing deformation of the metal strength improved; However, it is at the expense of metal plasticity, toughness of the cost. Precision cold drawn seamless based on its high dimensional accuracy and high strength properties 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, reduction of the material adversely affected.

Cold drawn seamless 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, seamless steel pipe ductility, toughness reduce excessive grain pulled over elongated, the formation of fibrous tissue, the metal will have a significant anisotropy. Cold drawn seamless steel tube in the axial direction, parallel to the elongated direction of the grains, the strength is increased; radial, cold drawn seamless grains perpendicular to the elongated direction, the strength but decreased, and the maximum stress of the hydraulic cylinder n exists in the radial direction of a seamless steel pipe, and therefore, the deformation is too large giving full play to the performance of the cold drawn pipe adversely.

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 seamless steel pipe production, annealing equipment indispensable, therefore, to develop an appropriate annealing process, is to ensure that the cold drawn seamless steel tubes 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, is bound to adversely affect the quality of products.www.netgms.com