The heat treatment method of the heat treatment wire rod or the steel wire semi-finished product is described in the steel wire heat treatment. The heat treatment includes three types of heat treatment of the raw materials, intermediate heat treatment, and heat treatment of the finished product.
(1) The heat treatment of the raw material, that is, the wire rod, is used in the production of part of the high carbon steel wire and the alloy steel wire, and the purpose is mainly to improve the structure and unevenness of the wire rod and eliminate the internal stress to improve the plasticity and cold drawing performance of the wire rod.
(2) The intermediate heat treatment is the heat treatment of the semi-finished steel wire, that is, the intermediate wire blank. The main purpose is to eliminate the work hardening generated during the cold drawing process and restore the plasticity of the wire blank to facilitate further drawing. If there is no heat treatment process in the production, the medium heat treatment before the drawing of the finished product is also required to ensure the structure and performance of the finished steel wire.
(3) The heat treatment of the finished product is carried out after the finished product is drawn, and the function is to make the product meet the specified organization and performance, and whether it is determined by the delivery requirements.
The wire rod or the intermediate wire blank is deformed by the drawing die hole under the drawing of the wire drawing reel or the winch (see the wire drawing machine), so as to reduce the shape of the cross section and change the shape to obtain the size, shape, performance and surface quality. Steel wire. Wire drawing usually requires multiple passes, and the pass reduction rate (see area reduction ratio) is between 10% and 40%. The molds used for drawing steel wire mainly include fixed molds, roll molds (see roll mold drawing), rotary molds, etc., and are mainly fixed molds. The fixed mold is a wire drawing die made of a monolithic material and having a hole shape in the center, and the mold is fixed during the drawing process. In the early days, steel plate molds and chilled iron molds were used, which were later eliminated due to lack of wear resistance and low service life. At present, cemented carbide molds are widely used. In addition to hard alloys, natural diamonds are also used as molding materials. However, due to their scarce resources and high price, they are limited to the use of drawn alloy steel filaments and ultrafine filaments. Since the 1970s, wire drawing dies made of polymeric polycrystalline, synthetic diamond and corundum ceramics have appeared. The roll mold is a mold composed of 2 to 4 rotatable rolls. Roller drawing is usually used to draw some irregular steel wires and difficult-to-deform steel wires. However, as the rigidity of the roller die device is improved, the precision is improved and the adjustment becomes easier, the range of use is continuously widened. The mold has the same body structure as the fixed mold when the rotary die is drawn, but it rotates around the wire axis under the drive of the transmission mechanism during drawing. The utility model has the advantages that the direction of the friction between the steel wire and the mold wall during drawing is changed, the shear stress acting on the steel wire is increased, the steel wire is easily deformed, thereby reducing the pulling force and the drawing power; and reducing the axial friction force The uneven deformation of the inner and outer layers of the steel wire is reduced when drawing; the mold hole wear becomes uniform due to the high-speed rotation of the mold, and the roundness and surface roughness of the steel wire are improved. However, when the rotary die is used, the wire is easily rotated or even twisted with the mold, so it is currently limited to the drawing of the thick wire. In the case of using the fixed die drawing, if the post tension is applied to the inlet end of the steel wire, a reverse pulling force is drawn; if ultrasonic vibration is applied to the mold, ultrasonic drawing is formed; if static pressure or hydrodynamic lubrication is used, it is called forced lubrication. Pull.
During the cold drawing process, the microstructure and mechanical properties of the steel wire change, resulting in work hardening. As the degree of cold deformation increases, the tensile strength, hardness, and elastic limit of the steel wire generally increase, and the elongation, the reduction ratio of the section, and the like decrease. Due to the existence of work hardening, when the degree of deformation of the drawing reaches a certain value, it is not suitable for further drawing due to the significant decrease in the cold working property of the steel wire, and intermediate heat treatment is required to restore the processing property, generally the reduction rate of one drawing It is about 70% to 90%. Therefore, the process of steel wire production has the characteristics of reciprocating cycle.
The capacity of the wire drawing machine is generally expressed by the size of its roll diameter and the number of rolls. The drawing speed of the wire drawing machine is related to the steel type, the diameter of the steel wire, the quality of the heat treatment, the lubrication and cooling conditions, the degree of deformation, the structure of the wire drawing machine, and the weight of the wire rod. With the modernization of steel wire production, the drawing speed is constantly increasing.
In order to reduce friction, reduce drawing force and mold consumption, and obtain a product with a smooth surface, size and shape, it must be lubricated with a lubricant when drawing. The use of a solid lubricant is referred to as dry drawing; the wetting type drawing is carried out using an aqueous lubricant solution in which the drawing process is completed, and the apparatus used is a water tank drawing machine.
During the drawing process, the temperature of the steel wire and the mold rises due to the heat generation of the friction and deformation work, and the temperature rise is more remarkable especially at the time of high-speed drawing (see drawing heat). The rise in mold temperature affects its service life, while the rise in wire temperature causes its toughness (torsion and bending properties) to decrease. In order to reduce the temperature rise, the mold and the reel must be cooled, and the direct water cooling of the steel wire is also developed (see drawing cooling).