Annealing knowledge
1.Introduction: During the cold drawing process, the microstructure and mechanical properties of the steel wire change, resulting in work hardening. As the degree of cold drawing deformation increases, the tensile strength, hardness, and elastic limit of the steel wire generally increase, and the elongation and the area shrinkage rate decrease. Due to the phenomenon of work hardening, when the deformation of the drawing reaches a certain level, the cold working property of the steel wire will be significantly reduced, and it is not suitable to continue drawing. At this time, the steel wire is subjected to an intermediate heat treatment to restore various processing properties, and the process of the intermediate heat treatment is called annealing.
2.There are many types of annealing, which vary with equipment, process and wire materials. Common wire rod drawing (large dialing) annealing, stainless steel wire bright (hydrogen) annealing and so on.
Stainless steel wire bright annealing principle: stainless steel wire bright annealing, also known as stainless steel wire hydrogen annealing, that is, using NH3, high temperature cracking into H2 and N2, H2 is a reducing agent, has strong reducibility under high temperature conditions, can The black oxide on the surface of the steel wire is restored, thereby restoring its original appearance and regaining the bright color of the surface of the steel wire. In addition, H2 can also prevent the surface of the steel wire from being further oxidized under high temperature conditions, thereby protecting the steel wire.
The wire rod drawing annealing equipment includes a crane, a coal feeder, an annealing tank, an annealing kiln (furnace) and the like.
The black annealed wire is a product obtained after the low carbon steel wire rod is drawn to a certain wire diameter and subjected to high temperature annealing. It has good elasticity and softness and is treated with oil and anti-corrosion. The color is black, so it is also called black soft silk, fire silk, oiled silk. The black annealed wire is mainly processed into a roll, a bobbin, a large roll, or further straightened and cut into a cut wire, a U-shaped wire, or the like.
3.Purpose: Annealing is the slow heating of the metal to a certain temperature for a sufficient period of time and then cooling at a suitable rate. The purpose is to reduce hardness, improve machinability, eliminate residual stress, stabilize size, reduce deformation and crack tendency, refine grains, adjust microstructure, and eliminate tissue defects. The bright annealing of the stainless steel wire (hydrogen annealing) also has the effect of making the wire bright.
4.Process: The drawn low carbon steel wire or stainless steel wire is placed in an annealing bath or an annealing furnace, heated to a suitable temperature at a high temperature, and then slowly cooled, and the annealing is achieved after the removal. The annealing time is generally about 2 to 12 hours. The annealed wire is called an annealed wire.
5.Substance: Annealing is the process of reducing the internal molecular structure of the wire and restoring its cold workability (flexibility, ductility, plasticity, etc.) to meet the need for re-drawing. The annealed wire is commonly referred to as "cooked wire". Conversely, the wire that has not been annealed is "raw wire". The drawing of raw silk is called cold drawing, the product after cold drawing is cold drawing, the surface oxide of cold drawing is removed during the drawing process (commonly called “peeling”), the surface becomes bright, and the silk is cold drawn. wire.
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