METHODS OF THERMAL PROCESSING OF METALS
Any material used in forging possesses its characteristics properties. They correspond to its internal structure and chemical composition. If the characteristics need to be changed, then this can be achieved by heat treatment. In modern metallurgy for each type of material, tables have been developed indicating the necessary treatment. In the practice of art forging, there is no equipment for such processing, and in many cases even the chemical composition of the material being processed is not known.
With artistic forging, metal materials divide, as if the position, onto the malleable steel also tool steel . To produce decorative locks, shields, hinges, leaves and flowers, the material is very plastic and soft. In this case, annealing will help. The material to be processed is heated at 650-720 ° C for 2-3 hours. Under conditions when there is no electric furnace, heat is produced in the furnace using charcoal, under which the atmosphere is gradually blown. Cooling the material should be as slow as possible. When using an electric furnace, the material is cooled together with the furnace after it is turned off. If the annealing is done on charcoal, the best medium is sifted ash. The ash is heated in the furnace, it is buryed by the annealed billet and left to cool. After such finishing the material becomes very viscous, also from it it is possible to receive the most complex forms. If you want to soften the copper, then they do the opposite. Copper is heated to 500-600 ° C and is hastily cooled in water. The material is very ductile at the same time.
The master of art forging is usually put in such conditions that he has to make an impressive part of the instruments himself. In this lesson you can not do without quenching - the most common method of steel processing. The main purpose of this treatment is to obtain steel with the highest hardness. Hardening is also a slow, uniform heating of the steel to the quenching temperature also in a hurry. Rigorous cooling is necessary in order to prevent changes in the metal that occur during a non-rapid cooling, i.e., the precipitation of ferrite, plus the transformation of austenite into perlite. All of the austenite is quenched by transformation into martensite, which later cementite is the hardest also brittle component. The means of cooling depends primarily on the grade of steel.
The cooling media used have different cooling capacities. The highest cooling rate is provided by cold water, the more moderate - oil and the most moderate - the atmosphere. Cooling ability of water can be increased by the addition of table salt or blood salt or hydrochloric acid (approximately 1:10), however, reduce - by heating or mixing limestone substances. When the cooling medium moves, its cooling effect increases. Carbon steel is cooled, as if the position, in water, alloyed - in oil, and high-alloyed - in the flow of the atmosphere. In a tool used in artistic forging or plumbing, the position is quenched, as only the working share, which directly serves the product.
As already noted, quenching is characterized by the transformation of austenite into a brutal also very fragile martensite. When the heat is low, martensite passes over to other structural components - bainite, troostite or sorbitol - which, although the plus is not as hard as martensite, but also not fragile. The hardened gun in this state is called released. The tool, heated for quenching, does not cool everything, but only its working part. After cooling, the tool is removed from the coolant and also clipped on the flint. At the cleaned room, the color of the metal is observed, changing due to the heat coming from the still heated elements of the instrument (see table). When the necessary paint appears, the hardened part of the gun is again lowered into the coolant and allowed to cool the entire implement.
Table. The temperature scale is also the color of steel when hardened