Vacuum furnace quenching liquid for heat treatment
Heat treatment vacuum furnace quenching is to heat the metal parts to the phase transition temperature above, after heat preservation in the quenching medium rapidly cooling martensite structure; So as to improve or adjust the hardness and wear resistance of parts. In this process requires quenching medium (quenching liquid) has a good low deformation, low burning crack, heat resistance, washing, degreasing, rust resistance, cooling, brightness, and so on a series of performance requirements, usually quenching liquid according to the composition is divided into oil-based and water-based two categories.
Oil base quenching fluid
The oil first used is animal and plant oil, which has a weak cooling ability, but still has enough cooling ability. Moreover, when the oil temperature rises, it has little influence on the quenching ability, and is an ideal quenching medium. Due to the limitation of price and source of raw materials, mineral oil is often used in industry, such as 0# diesel oil, 15~32# viscosity grade mechanical oil, etc. Mineral oil has different cooling capacity and operating temperature with different viscosity and flash point. Due to its slow cooling speed, it is not easy to quench carbon steel and low alloy steel with large section, and the surface of the material is easy to stain. Can be used to improve the oil cooling ability, raise the oil temperature (usually in the range of 80 ℃ below adjustment), strong stirring circulation and adding additives, etc. Add additives such as sodium sulfonate, barium sulfonate, calcium sulfonate and calcium naphthenate to the oil. When quenching and cooling, the additive is adhered to the workpiece surface and becomes the particle of the second domestic product's steam bubble, which makes the stable steam film not easy to form and improves the cooling ability in the high temperature area. This oil is called "fast quenching oil". In addition, in the light oil and solvent refining method was used to extract the quenching oil adding heat stabilizer, the ash of surfactant state commonly used 1% m Lin sodium oleate and 0.3% T501, can make the workpiece surface was quickly after quenching oil film coated infiltrates without carbon black, the sedimentation of the surface so that the workpiece surface bright and clean after quenching, this oil is called "bright quenching oil". In addition, the addition of surfactant to mineral oil can make the metal quenching uniform and facilitate the cleaning of mineral oil after quenching. For example, if 2%~5% non-ionic emulsifiers such as nonylphenol polyoxyethylene (6) ether are added to the mineral oil for quenching, the mineral oil can be removed by rinsing the metal products with water after quenching.
Water-base quenching fluid
Water is the most economical quenching medium. It has high chemical stability and high heat capacity. But pure water in high temperature cooling capacity is not strong, and near 300 ℃ cooling capacity is very big, therefore, the pure water cooling characteristics precisely and we require that the ideal characteristics of quenching medium, on the other hand, this is the cause of the pure water rarely used. The commonly used water-base quenching solutions include saline water, alkaline water, saturated calcium chloride, three-nitrate aqueous solutions (NaNO3, NaNO2, KNO3), organic polymer aqueous solutions, etc. In the late 1950s, the United States put forward the non-toxic, odorless, non-flammable and cooling performance between water and oil.
The quenching medium of adjustable polyvinyl alcohol (PVA) and aqueous solution was later developed into water-base quenching liquid of polyalkyl ethylene glycol (PAG), polyoxyethylene glycol (GLY) and polyvinyl pyrrolidone (PVP). In the late 1970s, a non-martensitic quenching liquid - alkaline polyacrylate (ACR) was developed for the quenching of bainite, which has high viscosity and is suitable for the quenching of isothermal quenching, hot forging of forgings, high-speed steel and martensitic stainless steel. In addition, there are new kinds of quenching liquid, such as polyacrylamide (PAM), methyl cellulose (CMC) and high molecular weight polysoap aqueous solution.