What is Heat Treatment?

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1. Quenching

The main purpose of the quenching treatment is to rapidly cool the steel material in order to obtain a very hard Asada bulk structure. There are three essential elements for the quenching treatment of steel, one of which is indispensable. They are: heating in the austenitic area for a period of time (that is, austrianization),avoiding Ar’ (waves) during cooling outer body), metamorphosis and hardening of the steel material by producing matian powder or toughening.

Quenching treatment can be divided into two procedures to implement, one is heating,the other is cooling. Usually the heating temperature is also called the quenching temperature or austenitic temperature, which varies with the heat-treated steel. The quenching temperature of hypoeutectoid steel is in the range of 30°C to 60°C above Ac3 temperature, and the quenching temperature of eutectoid steel and hypereutectoid steel is heated to the temperature range of 30°C to 60°C above Ac1 temperature. Cooling needs to be done in two stages during cooling. The steel pieces taken out of the heating furnace are cooled to the critical area before Ar” metamorphosis, and they must be cooled as quickly as possible; in the temperature area below Ar”, slow cooling is required. Otherwise, it is easy to cause quenching cracking or quenching deformation of the steel. This temperature area is also called a dangerous area.

2. Tempering

The general tempering treatment is often implemented after the quenching treatment in order to eliminate the adverse effects of the quenching treatment and retain and exert the quenching effect. Its main purpose is to make the structure formed by the quenching metamorphose or precipitate more stable (to form a tempered mata powder) , Reduce residual stress and improve related mechanical properties (improve material ductility). Different tempering temperatures will produce different combinations of mechanical strength and ductility. Generally, the tempering temperature is mostly below 600°C. Because of the higher tempering temperature, any steel will show a rapid softening trend, and the carbides will gradually condense at this time. Spheroidization and fat granules will recrystallize and grow into a continuous base, which is the main reason for softening.

3. Tempering Brittleness

Tempering treatment should avoid several temperature ranges that will produce temper brittleness. These brittleness temperature ranges vary depending on the type of steel, including: 270℃ to 350℃ embrittlement (also called low temperature temper brittleness or A. Brittleness). Most carbon steels and low-alloy steels are embrittled in this temperature range; 400℃ to 550℃ embrittlement, usually structural alloy steels will become embrittlement within this temperature range Phenomenon; 475℃ embrittlement (especially the fertilizer grain system stainless steel with a Cr content of more than 13%); 500℃ to 570℃ embrittlement, for tool steel or high-speed steel heated in this temperature range, precipitation and distribution Uniform carbide produces secondary hardening effect, but it is also easy to cause brittleness.

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Vacuum Heat Treatment Furnace

Editing by Baccata

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