Heat Treatment Quenching Medium

3″ New quenching medium and its application 3.1 “Organic polymer quenching agent” In recent years, the most noticeable development of new quenching medium is the research and application of organic polymer quenching agent. This kind of quenching medium is to dissolve the organic polymer in water, and adjust the concentration and temperature of the solution as needed to prepare an aqueous solution with cooling performance that meets the requirements. It has a cooling rate close to water in the high temperature stage and close to oil in the low temperature stage. .

Its advantages are non-toxic, smokeless, odorless, non-corrosive, non-combustible, anti-aging, safe and reliable in use, good cooling performance, adjustable cooling speed, wide application range, uniform hardening of the workpiece, and can significantly reduce deformation and cracking The tendency, therefore, can improve the quality of the workpiece, improve the working environment and labor conditions, and bring energy-saving, environmental protection, technical and economic benefits to the factory.

At present, organic polymer quenching agents are used more in large-scale, single-variety heat treatment, especially for workpieces with water quenching cracks, large deformation, and oil quenching that are not hardened. Organic polymer quenching agents are a more successful choice. The use of organic polymer quenching agent is more economical, efficient and energy-saving than quenching oil. From the perspectives of improving the quality of workpieces, improving working conditions, avoiding fires and energy saving, organic polymer quenching agents have a tendency to gradually replace quenching oil (the original circulating cooling system used for quenching oil can be replaced by organic polymer quenching agents.

No need to modify and replace) is the main development direction of quenching medium. The cooling rate of  organic polymer quenching agent is affected by three basic parameters: concentration, use temperature and stirring degree. Generally speaking, the higher the concentration, the slower the cooling rate; the higher the use temperature, the slower the cooling rate; the more intense the stirring, the faster the cooling rate. The role of stirring is very important: ①make the solution concentration uniform; ②enhance the heat conductivity of the solution, so as to ensure that the workpiece has high hardness and uniform distribution after quenching, and reduce the tendency of quenching soft spots, deformation and cracking.

By controlling these factors, the cooling rate of the organic polymer quenching agent can be adjusted to achieve the desired quenching effect. Generally speaking, the concentration used in summer can be lower, and the concentration used in winter can be higher, and sufficient mixing is required. Most of the organic polymer quenching agents are sold as concentrated liquids containing water. In use, they can be diluted with water to different concentrations according to the characteristics and technical requirements of the workpiece, and then quenching liquids with various quenching intensities can be obtained to adapt to different quenching need.

In addition, pay attention to careful maintenance, prevent pollution, try to keep the good cleanliness of the quenching liquid, which is very important for the long-term stable use of the organic polymer quenching agent.  Different types of organic polymer quenching agents have significantly different cooling characteristics and stability, which can be adapted to the needs of different quenching processes [2]. At present, the most stable and widely used organic polymer quenching agent in the world is polyalkylene glycol (PAG) quenching agent.

This kind of quenching agent has inverse solubility and can be formulated into quenching fluids of different quenching intensities that are slower than salt water and closer to mineral oil. Its concentration is easy to measure and control, which can reduce deformation and cracking of the workpiece and avoid the generation of quenching soft spots. Long life, suitable for all kinds of induction heating quenching and overall quenching.

In addition, polyacrylate (ACR) quenching agents and polyoxypyrrolidone (PVP) quenching agents are non-reversible varieties, and their cooling rate at 300°C is slow, and they are also used. The polyethyloxazoline (PEO) quenching agent, which has been vigorously promoted and promoted, also has inverse solubility, and its cooling rate at 300°C can be reduced to a level equivalent to that of oil, but there are some problems in production and application [3]. There are not many practical applications abroad, and this is generally the case in my country.

Organic polymer quenching agents have been developed abroad for more than 40 years. The United States, Japan, the former Soviet Union and other countries have conducted a lot of in-depth research and have been widely used. In recent years, experimental research work has also been carried out in China. A variety of organic polymer quenching agents have been successfully developed, such as polyether-ethylene glycol developed by Beijing Institute of Mechanical and Electrical Technology, hydroxyethyl cellulose developed by Jiangxi Institute of Technology, Shenyang Industrial The XL water-soluble quenching medium developed by the university [4],

and many factories provide a series of products for production, for example, Jinyu 8-20 and 8-50 water-soluble quenching agents developed and produced by Beijing Huali Fine Chemical Company , It is refined by using high-quality foreign raw materials and additives. It is a PAG quenching agent. It has adjustable cooling characteristics, easy to measure and control concentration, good thermal stability, strong anti-pollution performance, long service life, and has a good effect on quenching tanks and workpieces.

Very good anti-corrosion and anti-rust performance, no smoke, no combustion during quenching, clean production environment, low output, and a series of advantages such as direct tempering of the workpiece after quenching. It is an excellent water-soluble quenching medium brand It is suitable for quenching and cooling of carbon steel and alloy steel. So far, it has been successfully applied in more than 200 factories in more than 20 provinces, municipalities and autonomous regions across the country. In addition, AQ251 and AQ364 produced by Shenzhen Houghton Company are PAG quenching agents, AQ3610 is a PEO quenching agent, and UCON A and UCON E produced by United Carbide Company are PAG quenching agents, etc., which have also obtained certain application.

3.2   Inorganic aqueous solution quenching agent Add appropriate amount of certain inorganic salts, alkalis or their mixtures to the water to form various inorganic aqueous solutions, which can increase the cooling rate of the workpiece in the high temperature zone, improve the cooling uniformity, and make the workpiece obtain after quenching The higher hardness reduces quenching cracking and deformation, and is non-toxic and non-polluting. The workpiece is easy to clean and easy to use and manage. Commonly used inorganic quenching agents are:

(1) sodium chloride solution: the commonly used concentration is 10%-15%, the brine temperature is 20-40℃, and its cooling uniformity is good, the quenching ability is strong, and the quenching hardness is high. It can reduce the occurrence of quenching cracks, deformation and soft spots, is pollution-free, and has low cost. It is widely used for quenching of carbon tool steel and some structural steel workpieces. However, salt water has a rust effect on the workpiece, so it must be cleaned after quenching.

(2) Sodium hydroxide aqueous solution: There are two types of commonly used concentrations: 10% and 50%. When the concentration is 10%, the cooling rate in the high temperature zone is higher than that of pure water and brine, and the cooling rate in the low temperature zone is slightly lower than that of pure water and brine, so the hardness of the workpiece after quenching is high and uniform, and it is not easy to produce cracks and deformation , And the surface of the workpiece is bright and beautiful, suitable for the quenching of steel with low hardenability; when the concentration is 50%, the cooling rate in the high temperature zone and the low temperature zone is significantly reduced, suitable for the quenching of steel that is prone to deformation and cracks . However, the aqueous sodium hydroxide solution is more corrosive, so pay attention to protection when using it.

(3) Calcium chloride aqueous solution: It can replace water-oil dual-medium quenching, and is suitable for quenching carbon steel and low-alloy structural steel.

(4)  Magnesium chloride aqueous solution: when the concentration is high, the boiling point and viscosity are higher, the cooling rate in the low temperature stage (100~300℃) is obviously reduced, and the higher cooling rate is maintained in the high temperature zone (~600℃), which can quench the workpiece After obtaining higher hardness, it can reduce deformation and cracking. (5)  Supersaturated nitrate aqueous solution: mainly trinitrate aqueous solution, which has ideal cooling capacity and can reduce deformation and cracking. It can replace water-oil double medium quenching, and is suitable for quenching carbon steel and low hardenability alloy steel. .

(6) Sodium carbonate aqueous solution: the usual concentration is 3%-15%, and its cooling capacity is slightly lower than sodium chloride aqueous solution at the same concentration.  (7) Water glass aqueous solution: Dilute the water glass with water and add some salt and alkali to increase its cooling rate. It can be used to replace water-oil dual-medium quenching, and it can also replace quenching oil. At present, my country has successfully developed some new varieties of inorganic aqueous quenching agents, and they have been used in heat treatment production to a certain extent. For example, zinc chloride and calcium chloride aqueous quenching agents have good quenching and cooling capacity. , The workpiece has small cracking, small deformation, and non-toxic and harmless.

It can be used for the quenching of 45 steel, T10, 40Cr, GCr15 and other steel materials. It is a new type of inorganic aqueous quenching agent worth promoting. 3.3 “Fluid bed cooling” The cooling capacity of the fluid bed quenching tank is generally between air and oil, but closer to oil. Its advantages are stable and adjustable cooling capacity within a certain range, uniform cooling, small deformation and cracking tendency of the workpiece, smooth surface, no cleaning after quenching, non-aging fluid bed, low pollution, safe use, and program control can be achieved.

Using fluidized bed cooling can replace salt bath quenching, providing alternative methods for two-liquid quenching, bainite austempering, and martensite graded quenching, suitable for complex shapes and cross-sections made of high hardenability alloy steel Quenching of small workpieces. In recent years, people have done a lot of experimental research work on the cooling characteristics and mechanism of fluidized bed, and it has been applied in the quenching and cooling of the heat treatment of steel and aluminum alloy, and its development prospect is eye-catching.

4 “Development direction of quenching medium 4.1” Strengthen basic theoretical research of quenching cooling Quenching cooling is a very complicated process, the austenite continuous cooling transformation mechanism of steel, the principle of new quenching medium, the concentration of water-soluble quenching agent, liquid temperature and degree of stirring The influence of quenching intensity, the effect of quenching medium cooling characteristics on the quality of quenched workpieces, the relationship between quenching intensity and the hardness distribution of quenched workpieces, the best internal stress and control methods of quenched workpieces, the measurement and evaluation of quenching medium cooling capacity, quenching Research on the pollution process and maintenance of the medium, the computer simulation of the quenching process and the establishment of mathematical models should be strengthened. These have important guiding significance for the development of new quenching media, improving and improving the performance of the original quenching media, perfecting the quenching process, reducing the deformation and cracking of the workpiece, and improving the performance and quality of the workpiece.

4.2   Continuously improve and improve the performance of the original quenching medium. The use effect of commonly used quenching mediums such as water and oil is not ideal. There is usually a saying that “water quenching cracks, oil quenching is not hard”, which has become increasingly unable to meet the requirements of heat treatment production. Therefore, the original quenching medium should be improved. For example, adding inorganic salts and organic polymers to the water can reduce the low-temperature cooling rate of the workpiece during quenching to varying degrees, thereby preventing the workpiece from quenching cracking and deformation, or obtaining higher quenching hardness and deeper quenching depth, thereby increasing The quality of the quenched workpiece.

On the basis of retaining its original advantages, quenching oil is still a promising quenching medium after increasing its cooling rate and improving some of its characteristics. For example, the development of high-efficiency and multi-purpose quenching oil added with refrigerant, antioxidant, brightener, etc., can obtain stronger cooling capacity, more reasonable cooling rate distribution and longer service life, or better maintain the brightness of the workpiece surface , It can reduce the deformation and cracking of the workpiece, so as to realize one oil and multiple uses.

In addition, improving the quenching equipment and using physical methods (stirring, spraying, ultrasound, etc.) to enhance cooling can increase the cooling rate of the quenching oil and meet the requirements of the quenching process. 4.3 “Vigorous research, development and application of new quenching media “Inorganic aqueous solution quenching agent and organic polymer quenching agent are the development focus of quenching media in my country, especially to strengthen the research on organic polymer quenching agent, and expand its application. With the deepening of research work, the applicability, stability and economy of organic polymer quenching agents have been further improved, and their applications have become more and more extensive.

We must closely monitor and analyze the development trends of foreign countries, track the research and application results of new organic polymer quenchers abroad, and develop and produce based on domestic and national conditions. The cooling rate is between water and oil, and can be based on A new type of organic polymer quenching agent that needs to adjust the cooling rate. For organic polymer quenching agents that have been successfully developed and put into production, it is necessary to increase varieties, improve quality, reduce costs, stabilize supply, ensure supply, do a good job in pre-sales consulting and after-sales technical services, and strive to create brand-name products to meet the needs of large quantities and low prices. Cost quenching process requirements. Vigorously promote the application of new quenching media and strengthen the use, management and maintenance of the production site are the prerequisites for good use of new quenching media. The above should become the research direction and work focus of new quenching media in my country in the future.

4.4   The new quenching medium closely cooperates with the new quenching cooling method. In order to achieve the ideal cooling of the workpiece and obtain the best quenching effect, in addition to selecting the new quenching medium according to the actual situation, it is necessary to continuously improve the existing quenching method and adopt new The quenching method. These new quenching methods are [5]:  (1)  high-pressure air-cooling quenching method: the workpiece is rapidly and uniformly cooled in a strong inert gas flow, which can prevent surface oxidation, avoid cracking, reduce deformation, and ensure that the required hardness is achieved. Quenching of tool steel. This technology has made rapid progress recently, and its application range has also been greatly expanded.

(2)  Strong quenching method: high-pressure jet quenching medium is used to spray it strongly on the surface of the workpiece. By controlling the pressure, flow and ratio of the sprayed quenching medium, the cooling capacity can be adjusted to promote uniform cooling and obtain uniform surface hardness. And high-quality workpiece with small deformation. “(3)” Water-air mixture cooling method: By adjusting the pressure of water and air and the distance between the atomizing nozzle and the surface of the workpiece, the cooling capacity of the water-air mixture can be changed and the cooling can be made uniform. This method has been successfully applied to surface induction heating hardening.

(4)   boiling water quenching method: using 100 ℃ boiling water cooling, a better hardening effect can be obtained, and it is used for quenching or normalizing of steel. (5) Hot oil quenching method: Using hot quenching oil, the temperature of the workpiece before further cooling is equal to or close to the temperature of the Ms point, so as to minimize the temperature difference and effectively prevent the deformation and cracking of the quenched workpiece.

(6)  Cryogenic treatment method: continue to cool the quenched workpiece from normal temperature to a lower temperature, so that the retained austenite continues to transform into martensite, the purpose of which is to increase the hardness and wear resistance of the steel and improve the structural stability of the workpiece And dimensional stability, effectively improve the service life of tools and molds.

5 “Conclusion” In summary, the quenching medium is an important guarantee for the implementation of the quenching process and has a great impact on the quality of the workpiece after heat treatment. However, there is a big gap between my country and foreign countries in the application of quenching medium, which is a weak link in the heat treatment industry and should be emphasized and strengthened. The development of new quenching media and improving the performance of the original quenching media are important development directions for quenching media.

The excellent new quenching medium is a high-tech product that integrates the achievements of contemporary advanced science and technology. It should not only have high-quality physical products (hardware products), but also use and maintenance technology (software products) matching it to meet The needs of heat treatment production development. Actively researching, developing, and popularizing the application of new quenching media has become a top priority to change the backwardness of my country’s heat treatment production and improve the quality of mechanical products. In heat treatment production, you can get twice the result with half the effort.