Quenching medium

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Common quenching media 1. Water Water is the earliest, most widely used, and most economical quenching medium; it is inexpensive and readily available, non-toxic, non-flammable, has stable physicochemical properties, and possesses strong cooling capabilities. By controlling the water temperature, increasing pressure, raising flow velocity, using circulating water, and leveraging magnetic fields, the cooling properties of water can be improved, deformation and cracking can be reduced, thereby achieving a relatively ideal quenching effect. However, since these methods require additional specialized equipment and the properties of the workpieces after quenching are not very stable, they have not been widely adopted. That’s why. Pure water is only suitable for quenching a few types of steel components with low carbon content, low hardenability, and simple shapes. 　　2. Quenching oil: Mineral oils used for quenching are typically based on highly refined neutral paraffin-based oils. They possess advantages such as a high flash point, low viscosity, minimal smoke production, good oxidation and thermal stability, as well as a long service life, which makes them suitable for use as quenching oil. Quenching oil is used only for workpieces with good hardenability, not too thick walls, complex shapes, and low requirements for quenching deformation. Quenching oil causes significant pollution to the surrounding environment, and it can easily lead to fires during quenching. 　　The main factor affecting the cooling capacity of quenching oil is its viscosity; at room temperature, oils with lower viscosity have a greater cooling capacity than those with higher viscosity. As the temperature rises, the fluidity of the oil increases, thereby enhancing its cooling capacity. Appropriately increasing the operating temperature of the quenching oil can also enhance its cooling capacity. 　　3. Molten salts, molten alkalis These quenching media are characterized by the fact that no phase changes occur during the cooling process. The quenching of workpieces relies mainly on convection cooling; the cooling rate is fast in high-temperature areas and slow in low-temperature areas. They offer excellent quenching properties, strong penetration capacity, and produce narrow quenched zones, with almost no cracks forming. However, they cause significant environmental pollution, result in poor working conditions, require high energy consumption, and are costly. They are commonly used for quenching workpieces and molds with complex shapes and large variations in cross-sectional dimensions. Melting salts include sodium chloride, nitrates, nitrites, etc. Quenching the workpiece in a salt bath allows for achieving a high hardness with minimal deformation and reduced risk of cracking; it is commonly used for isothermal quenching or step quenching. Its disadvantage is that the molten salt ages easily and has an oxidizing and corrosive effect on the workpiece. Caustic alkalis include sodium hydroxide, potassium hydroxide, etc. They possess strong cooling capabilities; if the workpiece does not oxidize during heating, a clean silver-gray surface can be obtained after quenching, which gives them certain applications. However, caustic soda vapor is corrosive and can irritate the skin; therefore, it is necessary to ensure good ventilation and take protective measures when using it. 　　4. New quenching media and their applications Organic polymer quenchants In recent years, the most notable advancement in new quenching media has been the research and application of organic polymer quenchants. Such quenching media involve dissolving organic polymers in water, and adjusting the concentration and temperature of the solution as needed to create an aqueous solution whose cooling properties meet the required standards; its cooling rate is close to that of water at high temperatures, and close to that of oil at low temperatures. Its advantages include being non-toxic, producing no smoke or odor, being non-corrosive and non-flammable, having anti-aging properties, offering safe and reliable use, as well as good cooling performance with adjustable cooling speeds. It has a wide range of applications; it enables uniform hardening of workpieces, significantly reducing the tendency for deformation and cracking. Thus, it improves the quality of workpieces, enhances the working environment and conditions, and brings energy savings, environmental benefits, as well as technical and economic advantages to factories. Currently, organic polymer quenchants are more commonly used in heat treatment on a large scale for single types of components. Especially for workpieces that suffer from cracking upon water quenching, experience significant deformation, or do not achieve sufficient hardness through oil quenching, using organic polymer quenchants is more economical, efficient, and energy-saving than using quenching oils. From the perspectives of improving workpiece quality, enhancing working conditions, preventing fires, and saving energy, organic polymer quenchants are showing a trend of gradually replacing quenching oils, and represent the main direction of development for quenching media. 　　The cooling rate of organic polymer quenchants is influenced by three basic parameters: concentration, operating temperature, and degree of stirring. Generally speaking, the higher the concentration, the slower the cooling rate ； The higher the operating temperature, the slower the cooling rate ； The more intense the stirring, the faster the cooling rate. The role of stirring is very important ； 1. Make the solution concentration uniform ； 2. Improve the thermal conductivity of the solution, thereby ensuring high hardness in the workpiece after quenching with a uniform distribution of this hardness, and reducing the tendency to form soft spots, deformation, and cracks. By controlling these factors, the cooling rate of organic polymer quenching agents can be adjusted to achieve an ideal quenching effect. Generally, a lower concentration can be used in summer and a higher concentration in winter, with thorough mixing required. Most organic polymer quenching agents are available in the form of aqueous solutions; during use, they can be diluted with water to various concentrations depending on the characteristics of the workpiece and the technical requirements. This allows for the creation of quenching fluids with different levels of hardening power, thereby meeting various quenching needs. 　　Different types of organic polymer quenchants possess significantly different cooling properties and stability, enabling them to meet the requirements of various quenching processes. At present, the most stable and widely used organic polymer quenchants in the world are polyalkylene glycol (PAG)-based quenchants. These types of quenching agents possess reverse solubility, allowing the preparation of quenching solutions with varying degrees of intensity that are slower than saline solutions but still relatively similar to mineral oil. Their concentration is easy to measure and control, which helps to reduce deformation and cracking of the workpieces, prevents the formation of soft spots during quenching, and ensures a long service life; they are suitable for various types of induction heating quenching and overall quenching processes.