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Quenching furnace cooling process knowledge Continuous cooling method is often used in heat treatment

Want to learn to operate the quenching furnace, it is inevitable to learn the relevant process expertise, the following small articles for everyone to explain the knowledge of quenching furnace cooling, may be able to bring inspiration for everyone's process technology, let's take a look at it.



What is the choice of the cooling medium for the quenching furnace?


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.


Brine and alkaline water

After adding a proper amount of salt and alkali to the water, the high temperature workpiece is immersed in the cooling medium, and the crystals of the salt and the alkali are precipitated at the vapor film stage and immediately burst, the vapor film is destroyed, and the scale on the surface of the workpiece is also broken, which can be improved. 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.


Oil cooling media generally use 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.


Haituo electromechanical high-speed quenching oil is a quenching oil with improved cooling rate in high temperature zone. There are two basic ways to obtain high-speed quenching oil. One is to select mineral oils of different types and different viscosities, and mix them with appropriate ratios to improve the cooling capacity of the high temperature zone by increasing the characteristic temperature. The other is to quench the ordinary heat. An additive is added to the oil to form a ash-like float in the oil. The additive is a sulfonium salt, a sodium salt, a calcium salt, and a phosphate, a stearate, and the like. Production practice shows that the cooling rate of high-speed quenching oil in the unstable region of supercooled austenite is significantly higher than that of ordinary quenching oil, while the cooling rate in the low temperature martensite transformation zone is close to that of ordinary quenching oil. In this way, high hardenability and hardenability can be obtained, and deformation is greatly reduced, which is suitable for quenching of alloy steel workpieces with complicated shapes.


Bright quenching oil keeps the workpiece on a shiny surface after quenching. Brightening quenching oils with different cooling rates can be obtained by adding polymer additives of different properties to the mineral oil. The main component of these additives is a brightener, which functions to suspend the aged product that is insoluble in the oil to prevent accumulation and precipitation on the workpiece. In addition, the bright quenching oil additive also contains an antioxidant, a surfactant, a refrigerant, and the like.


Haituo Electromechanical Vacuum Quenching Oil is a cooling medium used for vacuum heat treatment quenching. Vacuum quenching oil must have a low saturated vapor pressure, high and stable cooling capacity, and good brightness and thermal stability, otherwise it will affect the effect of vacuum heat treatment.

2. The heating temperature is based on the critical point of phase transformation of steel. When heating, fine and uniform austenite grains are formed, and fine martensite structure is obtained after quenching. The quenching heating temperature range of carbon steel is shown in Fig. 1. The quenching temperature selection principle shown by this figure also applies to most alloy steels, especially low alloy steels. The heating temperature of the hypoeutectoid steel is 30 to 50 ° C above the Ac3 temperature.


3. Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing methods, heat treatment generally does not change the shape of the workpiece and the overall chemical composition, but by changing the microstructure inside the workpiece, or changing the surface of the workpiece. Chemical composition that imparts or improves the performance of the workpiece. It is characterized by improved intrinsic quality of the workpiece, which is generally not visible to the naked eye.
 



How to understand the temperature rise in the heat treatment and the cooling with the furnace?


Increasing the temperature with the furnace means placing the cold parts in a cold furnace and heating them together to the specified temperature.

After the furnace is cooled, the heating in the furnace is stopped. The parts are slowly cooled to room temperature in the furnace together with the furnace.
 

What are the four types of continuous cooling that are commonly used in heat treatment?

Cooling method: cooling with the furnace, cooling in the air, cooling in the water, cooling in the oil.

The slowest cooling with the furnace, generally used for stress relief annealing;

The water is cooled the fastest and is generally used for quenching.


The above is the answer to some questions related to the cooling of the quenching furnace. The knowledge of the above theory has a great effect on the operation of the quenching furnace and the quenching process. Everyone can learn well!
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