Fergana polytechnic insitute mechanical engineering faculty department of mechanical engineering and automation

Chemical-thermal processing 
is a process of chemical and thermal impact 
on the surface layer of steel in order to change its composition, structure and 
properties. As a result of chemical-thermal processing, properties such as hardness 
of the steel surface, resistance to bending, corrosion resistance, and acid resistance 
increase. Because it is one of the most effective methods of strengthening steel parts 
to increase their long-term performance, chemical-thermal treatment is widely used 
in mechanical engineering. the scheme of the classification of the main types of heat 
treatment of metals and alloys is described. 

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Thermal treatment is divided into types of thermal treatment, 
thermomechanical work, and chemical-thermal treatment . 
Heat treatment is thermal treatment of metals or alloys. 
Thermomechanical processing is the implementation of plastic deformation 
in combination with thermal effects on metals and alloys. 
Chemical-thermal treatment is a thermal and chemical effect on metals and 
alloys. 
types of heat treatment : 1st type of softening, 2nd type of softening , 
tempering with polymorphic change, tempering without polymorphic change, metal 
or alloy surface wear and tear caused by melting. 
These types of thermal treatment apply to steel, non-ferrous metals and alloys. 
Each type of heat treatment is divided into different types, taking into account the 
characteristics of alloys based on different bases. 
Certain types of heat treatment are also found in initial and primary processes of 
forging and detailing, such as hot pressing, casting, welding, and various other 
operations. For example, in the field of foundry, after solidification of alloys when they 
are poured into a mold, rapid cooling of the casting is observed. As a result of the 
heating of the surface of the details, the tooth process can be observed. In welding, we 
can find recrystallizing softening and similar types of heat treatment in the zone of 
thermal exposure to welds. These types of additional heat treatments can be beneficial 
in some cases, but they can also cause unexpected structural and property changes in 
products. 
As a result, the homogeneous structure becomes unstable , the properties of 
the zagotovka are different in different places , and internal stresses appear. In 
addition, due to liquation (chemical unevenness), the chemical composition of the 
mixture will not be uniform. These nuq numbers are heat treated to remove them, 
which includes annealing and normalizing.