Heat treatment of steel can be carried out in various ways. Specialists distinguish the following options:
1. Firing.
2. Normalization.
3. Hardening.
4. Vacation.
Heat treatment of steel by firing is the heating of the product to a temperature of from 840 to 900 degrees. At the indicated temperature, exposure is carried out for at least two hours, cooling occurs together with the furnace.
Steel processing by this method is used in the manufacture of products from already hardened or in the case when a new hardening of the product is necessary due to a bad past. Subsequent thermal exposure to cracks can form cracks on unbaked parts, which will lead to heterogeneity in the metal structure. This, in turn, will significantly degrade the quality of the product.
To burn small parts, massive, heated steel headquarters are used, along with which they are cooled. In some cases, an acetylene burner is used for heating. To gradually cool the product, the burner is gradually removed from it.
Heat treatment of steel by normalization is the heating of parts to the required temperature and cooling them in air.
Quenching is heating and rapid cooling. This heat treatment of steel is used for carbon and some alloyed types of metal. As a result of such an effect, the crystal lattice of the material changes — it acquires enhanced anticorrosion properties and hardness. When the carbon content in steel is up to 0.3%, hardening is not carried out. The heating temperature is selected depending on the grade of metal. Exceeding the maximum allowable temperature (“burning”) will lead to the loss of steel of its properties. The result is an irreparable marriage.
To prevent overheating of small parts, a pre-heated stand (headquarters) is used. Rapid cooling of the product provides a hard hardening. As a result, significant internal stresses can form, in some cases even cracks. However, with slow cooling, the hardness required by hardness may not work.
As cooling media, water, oil, an aqueous solution or air is used. Salt (regular), saltpeter or caustic soda, added to the coolers, can accelerate cooling. In order to reduce the cooling rate, soap solution, water glass, oil emulsion, milk of lime and other components are added to the water.
When sequentially hardening several products, a large vessel is used or water is often changed. In this case, uniform quenching is ensured.
Quite fast and uniform cooling of steel occurs in an 8-12 percent solution of salt and water or caustic soda at 20 degrees.
Vacation is the heating of parts to a certain temperature, exposure and rapid cooling. This processing method is applied after cooling the products during hardening to reduce brittleness and partially hardness. There are three types of vacation: high, low and medium. The most common is the low form of processing. So, when heated to 170 degrees, the internal stress of the product is removed without changing the hardness of the material.
A separate type is the chemical-thermal treatment of steel. This process combines exposure to temperature and surface saturation of a metal with one or another element. This treatment allows you to change the chemical composition, properties of the surface layers and the microstructure of the material.
Chemical-thermal effects include nitriding, cementation, alitization, cyanidation, silicification and other methods.