Why do annealed electric heating wires turn black
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Why do annealed electric heating wires turn black
In recent days, when the company sells electric heating wires and other related products, the keyword "annealing" is often used. Some customers are not very familiar with the term annealing or do not understand it at all. Therefore, Yancheng Yuheng Electric Heating Technology Co., Ltd. has specially compiled some questions about annealing from customers and shared them with everyone.
Question 1: What is annealing and its definition?
Q&A: The heat treatment process of heating the electric heating wire to an appropriate temperature, holding it for a certain period of time, and then slowly cooling (usually with furnace cooling) is called annealing.
The main purpose of annealing is:
1. Reduce the hardness of steel and improve plasticity to facilitate cutting and cold deformation processing.
2. Refine the grain size, homogenize the structure and composition of the steel, improve the performance of the steel, or prepare for future heat treatment.
3. Eliminate residual internal stress in steel to prevent deformation and cracking.
Question 2: Why does the annealed electric heating wire turn black?
Answer: Yuheng Technology believes that the surface of the heating wire has oxidized, so it looks black.
Question 3: Why can annealing reduce the hardness of electric heating wires?
Answer: The microstructure after annealing is mainly pearlite, with relatively lower hardness compared to lower bainite and martensite
Question 4: Why can annealing reduce hardness?
Answer: The electric heating wire forms austenite during heating, and depending on the purpose, it cools slowly or rapidly from high temperature to cause transformation.
The transformation products and properties of austenite vary greatly at different temperatures.
Slowly cooling results in a mixture of cementite and ferrite - pearlite; And rapid cooling results in martensite, while austenite has no hardness, while martensite has hardness. The quenching of heat treatment results in martensitic structure.
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