quenching oil on roller furnace of heat treatment mesh belt furnace of selection principle and method
1. Cooling curve of heat treatment
The transformation of austenite and pearlite into pearlite by heating and cooling is mainly controlled by different heating and cooling processes. Generally, martensite is expected to be obtained during quenching, and tempered martensite (low temperature), troostite (troostite, medium temperature) and sorbite (high temperature) are obtained according to the different tempering temperatures. It basically reflects the gestational time, transformation completion time and transformation of eutectoid steel at different temperatures
In the actual heat treatment production, there are many cases of continuous cooling except the step isothermal quenching process. The speed of martensite structure must be greater than the critical cooling rate, and the cooling rate of the surface is generally greater than that of the core. One of the selection principles of quenching oil: in order to obtain martensite, the cooling rate must be greater than the critical cooling rate, and the deformation should be reduced to prevent cracks. The cooling rate must be moderate and not too large.
2. Ideal quenching method
According to the law of steel cooling transformation, it is hoped that the cooling rate will be high at the critical temperature, and pass through the nose area of C curve as soon as possible, so as to avoid transformation into pearlite or bainite. In the dangerous area where martensite transformation begins, the cooling rate must be slowed down to reduce the deformation and even cracks caused by structural stress caused by structural transformation. This is the reason why double liquid quenching is first quenched in water and then transferred to oil for cooling. Single liquid quenching requires the cooling medium to have such cooling characteristics: the cooling speed is fast at the critical temperature, and slow down at the temperature of dangerous area. The second selection principle of quenching oil: fast cooling at high temperature and slow cooling at low temperature, taking into account the requirements of hardness and deformation.
3. Cooling curve of quenching oil
Heat treatment quenching oil needs to have the above cooling performance. The cooling speed of parts at critical temperature is fast, and the cooling speed of parts in dangerous area is slow down. The cooling characteristic curve of quenching oil at different oil temperatures shows the relationship between cooling time, cooling rate and temperature, and indicates the cooling capacity of quenching oil at different temperatures.
4. Hardness requirement and deformation effect
The critical cooling rate of different materials is different, the hardness requirements of parts are different, the precision and deformation control requirements of parts are also different, so it is necessary to select the appropriate quenching oil according to the actual situation of hardness requirements and deformation control technology requirements. After the quenching oil is selected, the quenching temperature, oil temperature, stirring cooling speed and time, oil feeding time and other control measures are adjusted by controlling the quality and selection of raw materials (part materials and oil materials). Combined with the tempering process, tempering temperature and tempering time parameter test after quenching, the hardness requirements and metallographic structure requirements of the parts can be met through the heat treatment process In the range of reasonable control of machining and heat treatment.
5. Selection of quenching oil for heat treatment
Starting from the heat treatment quenching process, the selection principle of quenching oil is mentioned: the cooling performance of quenching oil must meet the requirements of hardness (fast cooling speed) and no cracks are allowed, and the deformation of heat treatment should be controlled within a reasonable minimum range (slow cooling speed is required), and the contradictory cooling speed requirements are different temperature ranges This provides a direction for the development of heat treatment quenching oil. In view of the limitation of testing conditions, in the production practice of heat treatment in the factory before, we could only make a rough range selection of quenching medium according to general knowledge and experience, and then verify it by test. The wide application of cooling characteristic instrument provides a kind of testing tool analysis means, which helps us to optimize the scientific selection of quenching oil and analyze and compare. We can conditionally test or outsource the test or require the oil company to provide the test data report of quenching oil cooling characteristics, so as to provide scientific basis for the selection of quenching oil.
According to the above method, there are many kinds of quenching oil that meet the requirements of use. According to the actual production situation and the company's quality policy, the quenching oil meeting the cooling performance requirements should be compared with other technical indicators and comprehensive comparison to select the most suitable. The stability and oxidation resistance of quenching oil, repeatability and reproducibility of cooling performance, brightness, safety and cost are all factors to be considered. QB / t0001-2007, JB / t7951, SH / t0220 put forward the technical requirements for the kinematic viscosity, flash point, ignition point, moisture, pour point, corrosion, brightness, saturated vapor pressure (vacuum quenching oil), thermal oxidation stability, cooling performance, maximum cooling rate and cooling time of cooling oil for heat treatment.
6. Conclusion
Selection principle and method of quenching oil. Quenching oil, base oil, additives, have many factors affecting cooling performance, involving a wide range. Quenching is an extremely important part in the process of heat treatment, which must be carefully selected. Through analysis and comparison, the recommended quenching oil is preliminarily determined, and then the selection of quenching oil is finally determined by means of test verification, industry application effect, market survey, and comprehensive consideration of technical requirements, safety, quality, cost and other factors.
On 2018-08-08 11:45:46
