What are the heat treatment processes for steel?
1. Normalizing heats the workpiece to an appropriate temperature, and after holding it for a period of time, the metal heat treatment process cooled in air is taken out of the furnace. The difference between normalizing and annealing is that the cooling rate of normalizing is slightly faster than that of annealing, so the normalizing structure is finer than that of the annealed structure, and its mechanical properties are also improved. In addition, the external cooling of the normalizing furnace does not occupy equipment, and the productivity is high, so normalizing is used as much as possible instead of annealing in production. The main application range of normalizing is: (1) used for low carbon steel, the hardness after normalizing is slightly higher than that of annealing, and the toughness is also good, which can be used as a pretreatment for cutting processing. (2) It is used for medium carbon steel, which can be used as a substitute for quenching and tempering treatment as the final heat treatment, and can also be used as a preparatory treatment before surface quenching by induction heating method. (3) It is used for tool steel, bearing steel, carburizing steel, etc., which can reduce or inhibit the formation of reticulated carbide, so as to obtain the good structure required for spheroidization annealing. (4) It is used for steel castings, which can refine the casting structure and improve the cutting performance. (5) It is used for large forgings, which can be used as the final heat treatment, so as to avoid a large cracking tendency during quenching. (6) It is used in ductile iron to improve the hardness, strength and wear resistance, such as the crankshaft, connecting rod and other important parts used in the manufacture of automobiles, tractors and diesel engines.
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2. Annealing is a metal heat treatment process that slowly heats the metal to a certain temperature, holds it for a sufficient time, and then cools it at an appropriate rate (usually slow cooling, sometimes controlled cooling). The purpose is to soften a material or workpiece that has been cast, forged, welded, or cut, improve plasticity and toughness, homogenize the chemical composition, remove residual stresses, or obtain the desired physical properties. There are many kinds of annealing processes depending on the purpose, such as recrystallization annealing, isothermal annealing, homogenization annealing, spheroidization annealing, stress removal annealing, recrystallization annealing, as well as stabilization annealing, magnetic field annealing, etc. It mainly refers to the heat treatment process in which the material is exposed to high temperatures for a long time and then slowly cooled. The main objectives are: (1) to relieve stress, (2) to increase the ductility and toughness of the material, and (3) to produce a special microstructure.
3. Tempering is a heat treatment process that heats the quenched steel into martensitic to a certain temperature below the critical point A1, holds it for an appropriate time, and then cools it to room temperature. The purpose of tempering is to eliminate the quenching stress and transform the microstructure of the steel into a relatively stable state. Improve the plasticity and toughness of the steel without reducing or appropriately reducing the hardness and strength of the steel to obtain the desired properties.
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Fourth, the heat treatment method of high temperature tempering after quenching and tempering is called quenching and tempering treatment. High temperature tempering refers to tempering between 500-650°C. Quenching and tempering can make the properties and materials of steel be adjusted to a great extent, and its strength, plasticity and toughness are good, and it has good comprehensive mechanical properties.
5. Surface heat treatment: Some parts require the surface to have high hardness, high wear resistance and fatigue resistance when used, while the core retains the original structure and properties, which requires the use of surface strengthening surface heat treatment methods. A wide range of applications are surface hardening and chemical heat treatment.
What are the types of cold stamping die steels with good toughness and high hardness?
(1) DC53 die steel is a die steel with relatively good crack resistance among cold work die steels, and the price is relatively affordable and easy to purchase.
The fracture resistance of DC53 die steel is about twice that of SKD11, and the hardness of 60-62HRC is used, and the wear resistance is sufficient, which can be used in occasions that require wear resistance and fracture resistance.
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(2) The wear resistance of Ld is similar to DC53, and the anti-cracking performance is better than DC53 die steel, which is also a more common die steel, among which Ld die steel is a cold heading die steel developed by the mainland, with a hardness of 61HRC, good wear resistance, and stronger fracture resistance than DC53, and the price is affordable, but the heat treatment process is not easy to control, so the quality is unstable, and the market response is not very good, which is also the key reason for the unsuccessful promotion of Ld die steel.
(3) SKH-51 is a wear-resistant toughness high-speed steel, with a hardness of 62-64HRC, and SKH-51 is a tungsten-containing high-speed steel, with wear resistance than DC53 and worse fracture resistance than DC53.