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What is the difference between high frequency quenching, normalizing, tempering, and heating annealing?

What is the difference between high-frequency quenching and normalizing, tempering, and heating annealing?
1. Process technology is different:
Normalizing is the heating of the product workpiece to Ac3 (Ac refers to the final temperature at which free ferrite is completely transformed into austenite during heating, usually from 727 ° C to 912 ° C) or Acm (Acm is the actual heating) The critical temperature line of the complete austenitization of the hypereutectoid steel is above 30~50 °C. After a certain period of heat preservation, the heat treatment process of the metal material in the air or sprinkling, spraying or blowing cooling is taken out from the furnace.
The tempering treatment refers to cooling the steel material subjected to induction hardening or normalization treatment at a certain speed after being immersed in a temperature lower than the critical temperature for a certain period of time.
Heating annealing is a metal material heat treatment process in which a metal material is heated to a certain temperature for a sufficient period of time and then cooled at a suitable rate (usually relatively slow cooling, sometimes controlled cooling).
The high-frequency quenching of steel is to heat the steel to a temperature above the critical temperature Ac3 (hypoeutectoid steel) or Ac1 (hyper-eutectoid steel), keep it aerated for a certain period of time, and then austenitize it in whole or in part, and then exceed the critical cooling rate. The cold speed is rapidly cooled to below Ms (or isothermal near Ms) to perform a heat treatment process in which martensite (or bainite) is converted.
Quenching, normalizing, tempering, annealing

2. The changes in raw material organization are different:
After normalizing, the sub-aluminum steel is ferrite + pearlite, the eutectoid steel is pearlite, and the hypereutectoid steel is pearlite + secondary cementite, and it is discontinuous.
The low temperature tempering is obtained by martensite structure; the structure obtained by medium temperature tempering is tempered torsite; and the high temperature tempering and quenching and tempering treatment is tempered sorbite structure.
After heating and annealing, the grains are refined, the structure is adjusted, and the tissue defects are eliminated.
High-frequency quenching transforms supercooled austenite into martensite or bainite to obtain martensite or bainite structure, and finally obtains martensite-based unbalanced structure (also has bainite as needed) Or maintain single-phase austenite).

3. The results of raw material performance changes are different:
In normalizing, the crystal grains of the steel can be refined in the rapid cooling, which not only can obtain satisfactory strength, but also can significantly improve the flexibility (AKV value) and reduce the cracking tendency of the member. - After low-alloy hot-rolled steel sheets, low-alloy steel forgings and castings are normalized, the overall mechanical properties of the raw materials can be greatly improved, and the cutting performance is also improved.
After tempering, it will be subjected to high-frequency quenching and normalization treatment and returned to the intermediate temperature for immersion (aging) for a certain period of time, which will promote the precipitation of a part of the carbides, and at the same time, it can eliminate some residual stress caused by rapid cooling, thereby improving the raw materials. Flexibility and flexibility.
Heating annealing can reduce Rockwell hardness, improve machinability, eliminate residual stress, stabilize the outer dimensions, reduce the tendency of deformation and cracking, refine grains, adjust microstructure, and eliminate tissue defects. Uniform raw material organization and composition, improve raw material properties or prepare for future heat treatment.
High-frequency quenching can greatly improve steel rigidity, Rockwell hardness, wear resistance, fatigue strength and flexibility, so it meets the different requirements for various mechanical parts and tools. It is also possible to meet the physical and chemical properties of certain special steels such as ferromagnetism and corrosion resistance by high-frequency quenching.

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