O’zbekistоn respublikasi оliy va o’rta maxsus ta`lim vazirligi

Improvement . Hardening with high tempering is called improvement. The main purpose of improvement is the creation of a dispersed structure.
In the case of low-carbon steels, the puzzle itself acts as an improvement, since even without high tempering, the steel receives high toughness with increased strength. Usually, the tempering temperature during improvement is determined by the required level and combination of hardness, strength and toughness properties and depends on the carbon content of the steel. In the case of medium carbon steels (for example, used in nitriding), the improvement is assigned to obtain the appropriate properties (toughness) of the core. Often, the improvement is used both to obtain sufficient strength (viscosity) properties, and to increase the machinability of steel.
Chemical-thermal treatment is used to improve the anti-friction properties of metals and increase their wear resistance by diffusion saturation or modifying them with compounds of chemically active elements.
Chemical-thermal treatment performed in solid, liquid and gaseous media is divided into two main groups:
1) chemical-thermal treatments used to increase wear resistance by increasing the surface hardness of parts (cementation, nitriding, cyanidation, boriding);
2) chemical-thermal treatments designed mainly to improve the anti-seize properties of metals by creating thin surface layers of metals enriched with chemical compounds with active elements that prevent seizing and scuffing during friction (sulfiding, sulfocyanation, selenization, tellurization , treatment in iodide-cadmium salt bath). The effect of these types of treatment is to reduce the coefficient of friction and localize the incipient tear (at the same time, the surface hardness remains almost unchanged).
Carburizing is used for low-carbon unalloyed and alloyed steel with a content of (0.08 ... 0.30)% carbon. The concentration of carbon in the surface layer with a thickness of (0.15…2.0) mm after cementation is usually (0.8…1.0)% Surface hardness after cementation followed by low tempering is HRC 58-64.
After carburizing and quenching, alloy steel parts are recommended to be subjected to surface work hardening, as a result of which the residual austenite turns into martensite.
After heat treatment, the cemented layer has the structure of acicular martensite with small globules of carbides and a small amount of residual martensite, which is characterized by high wear resistance.
Nitriding enriches the surface layer with nitrides to a depth of (0.25 ... 0.7) mm, which increases wear resistance, resistance to erosion and cavitation , pins, rollers, gears, valves, connecting rods, bolts, plungers, bushings, etc.).