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What are the quenching heat treatment cooling media

Commonly used quenching media are water, aqueous solution, mineral oil, molten salt, molten alkali and the like.
 
Water and water are quenching media with strong cooling capacity. Wide source, low price, stable composition and not easy to deteriorate. The disadvantage is that in the "nose" area of ​​the C curve (about 500 ~ 600 ° C), the water is in the vapor film stage, the cooling is not fast enough, it will form a "soft point"; and in the martensite transformation temperature zone (300 ~ 100 ° C), When the water is in the boiling stage, the cooling is too fast, and the martensite transformation speed is too fast to generate a large internal stress, which causes the workpiece to be deformed or even cracked. When the water temperature rises, the water contains more gas or mixed with insoluble impurities (such as oil, soap, mud, etc.), which will significantly reduce its cooling capacity. Therefore, water is suitable for quenching and cooling of carbon steel workpieces having a small cross-sectional size and a simple shape.
 
The salt water and the alkaline water are added with an appropriate amount of salt and alkali in the water, so that the high temperature workpiece is immersed in the cooling medium, the salt and alkali crystals are precipitated in the vapor film stage and immediately burst, the vapor film is destroyed, and the scale on the surface of the workpiece is also broken. This can improve the cooling capacity of the medium in the high temperature zone. The disadvantage is that the medium is highly corrosive. In general, the concentration of the brine is 10%, and the concentration of the aqueous caustic soda is 10% to 15%. It can be used as quenching medium for carbon steel and low alloy structural steel workpieces. The temperature should not exceed 60 °C. It should be cleaned and rust-proofed after quenching.

 

The oil cooling medium is generally made of mineral oil (mineral oil). Such as oil, transformer oil and diesel. The engine oil is generally made of No. 10, No. 20, No. 30 engine oil. The larger the oil number, the greater the viscosity, the higher the flash point, the lower the cooling capacity, and the higher the use temperature. The new quenching oils currently used are mainly high-speed quenching oil, bright quenching oil and vacuum quenching oil.
 
The new quenching agent is an aqueous solution of polyvinyl alcohol and an aqueous solution of trinitrogen. Polyvinyl alcohol is usually used in an aqueous solution having a mass fraction of between 0.1% and 0.3%, and the co-cooling capacity is between water and oil. When the workpiece is quenched into the solution, a vapor film and a gel film are formed on the surface of the workpiece, and the two films cool the heated workpiece. After entering the boiling stage, the film ruptures and the workpiece cools faster. When the low temperature is reached, the polyvinyl alcohol gel film is formed again, and the cooling rate of the workpiece decreases. Therefore, the solution has low cooling capacity in the high and low temperature regions and is cooled in the middle temperature region. High capacity and good cooling characteristics.
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