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Heat Treatment Of Steel Wire
Sep 07, 2018

Heat treatment of wire rod or semi-finished steel wire heat treatment method see.

Heat treatment includes 3 types of raw material heat treatment, intermediate heat treatment and finished product heat treatment.

(1) The heat treatment of raw material i.e. wire rod is used in the production of high carbon steel wire and alloy steel wire in part, the aim is to improve the microstructure and inhomogeneity of wire rod and eliminate the internal stress to improve the plastic and cold drawing performance of wire rod. 

(2) The intermediate heat treatment is the steel wire semi-finished product is the middle line of heat treatment, the main purpose is to eliminate the process of cold-drawn processing hardening, to restore the plastic billet, in order to facilitate further drawing.

such as the production of non-finished product heat treatment process, the finished product drawing before the Q heat treatment also requires to ensure that the finished steel wire should have the organization and performance.

(3) The finished product heat treatment in the finished product after drawing, the role is to make the product meet the requirements of the Organization and performance, whether the decision on the delivery requirements. Drawing on the Wire drawing machine reel is the winch (see Wire drawing machine) traction, wire rod or intermediate billet through the drawing die hole deformation, to reduce the cross-sectional shape to obtain the size, shape, performance and surface quality are in line with the requirements. The drawing of the wire is usually carried out in several lanes, and the surface reduction rate (see area shrinkage rate) is about 10%~40% between the two. Drawing steel wire used in the mold mainly has a fixed die, roller die (see roller die Drawing), rotating mold, and fixed mode-based. The fixed die is made of the whole material form a round cake shape and the center of the hole-type drawing die, the mold is fixed in the drawing process. The early use of steel plate and chilled cast iron mold, later due to wear-resistant and low service life is eliminated. At present, tungsten carbide mold is widely used, in addition to cemented carbide, the natural diamond is also a molding material, but because of its scarce resources and expensive, confined to drawing alloy steel filament and very fine wire used. Since the 1970s, there has been the production of poly-polycrystalline, synthetic diamond and corundum ceramics, such as wire drawing die. The roll mold is a mold made up of four or three rotatable rollers. Roller die drawing is usually used to pull out some special-shaped steel wire and difficult deformed steel wire, but with the increase of rigidity of the roller mold device, the accuracy of the improvement and adjustment has become easier, its scope of use is constantly widening. The body structure of the mold is the same as that of the die when the rotary die is drawn, but in the process of drawing, it rotates around the wire axis under the driving mechanism. The advantage is to change the direction of friction between steel wire and die wall in drawing, increase the shearing stress on the steel wire, make the steel wire easy to deform, which can reduce the drawing force and pulling power, and reduce the axial friction to reduce the uneven deformation of the inner and outer layer of the steel wire during drawing. As the mold rotates at high speed, The roundness and surface roughness of the steel wire are improved. However, the use of rotary die when the wire easily rotated with the mold and even twist, so at present only limited to coarse wire drawing.

In the case of the use of fixed-mode drawing, if the steel wire at the inlet end of the tension is applied to form an anti-tensile pull, if the mold applied ultrasonic vibration to form an ultrasonic wire drawing, if the use of static pressure or hydrodynamic lubrication is called forced lubrication drawing. The microstructure and mechanical properties of steel wire are changed during cold drawing process, resulting in processing hardening. With the increase of cold deformation, the tensile strength, hardness and elastic limit of steel wire are increased, and the elongation and cross section shrinkage rate are decreased. Due to the existence of processing hardening, so when the degree of deformation of the drawing reached a certain value, because the steel wire cold processing performance is not suitable to continue drawing, the need for intermediate heat treatment to restore its processing performance, generally a pull-off of the surface rate of about 70%~90%.

Therefore, the production process of steel wire has the characteristics of reciprocating circulation. The ability of a wire drawing machine is generally expressed by the size of its reel diameter and the number of rolls. Drawing speed is related to steel Wire's steel grade, diameter, heat treatment quality, lubrication and cooling conditions, deformation degree, structure of wire drawing machine and disk weight of rod.

With the modernization of steel wire production, drawing speed is constantly improving. In order to reduce friction, reduce drawing force and die consumption, and obtain a product that meets the requirements of smooth, size and shape, the lubricant must be lubricated when drawing.

The use of solid lubricant is called dry wire drawing, the use of a lubricant aqueous solution and in which the drawing process of the wet drawing, the equipment used is a water tank wire drawing machine. In the process of drawing, due to the transformation of friction and deformation of the heat, steel wire and mold temperature rise, especially in high-speed drawing when the temperature rise more significant (see Wire drawing heat). The increase in mold temperature affects its service life, while the rise in wire temperature causes its toughness (torsional and flexural properties) to decrease. In order to reduce the temperature rise, the mold and reel must be cooled, the direct water cooling of the wire has also been developed (see drawing cooling).