After cold drawn seamless steel tubes are needed stress relief annealing, to eliminate the residual stress of the material, improve the organization of materials, improved plastic material, so as to achieve the purpose of preventing seamless steel pipe fracture failure occurs. Deformation is too small to reach the surface finish and dimensional accuracy requirements, they can not achieve strength index components; deformation is too large, toughness reduced too much, but the grain is pulled excessively elongated, fibrous tissue formed in the metal will have a significant anisotropy. Cold drawn seamless steel tube axially parallel to the elongated direction of the grain, increased strength; cold drawn seamless steel pipe radially, perpendicular to the elongated direction of the grain, but lower strength, maximum stress and the hydraulic cylinder being present in the radial direction of which on, so much to give full play to the deformation properties of cold drawn tubes unfavorable.
The annealing is seamless, the process is a slow heating of the metal to a temperature sufficient to maintain the temperature, and then cooled to a suitable speed (slow cooling typically is sometimes controlled cooling) heat treatment of a metal. For the material after casting, forging and rolling, machining or welding, improve the ductility and toughness of the chemical composition uniformity, residual stress is removed in order to obtain the desired physical properties. Annealing process with different purposes and there are many, such as isothermal annealing, annealing uniform, ball annealing, stress relief annealing, recrystallization annealing, as well as stabilizing annealing, magnetic annealing. To make the cold drawn seamless steel stress relief annealing, in particular steel pipe is heated to slightly above the Ac1 temperature, after a certain time as the heat is cooled to 550 â,,? ~ 600 â,,? heat treatment furnace with an air-cooled called stress relief annealing. To stress the heating temperature is low, the annealing process without organizational changes, mainly used in rough machining of parts and components, is designed to eliminate the residual stress and rough parts, stable workpiece size and shape, reducing parts machining and use the deformation and cracking tendency.
For the fibrous tissue that appears in the steel and dislocations, vacancies and other crystal defects are generally taken annealing or normalizing heat treatment methods to eliminate them. The purpose is to refine the grain annealing, eliminating tissue defects, reduced hardness, improved ductility, but also facilitate cold. Cold drawn seamless steel pipe production, annealing equipment is indispensable, therefore, to develop an appropriate annealing process, cold drawn seamless organization is to ensure that qualified, the product does not appear necessary condition for breaking defects. If the manufacturer to unilaterally reduce production costs, reduce the annealing process is bound to have an adverse effect on product quality.
