Quenching is one of the basic means of steel strengthening, quenching the steel into martensite, followed by tempering to improve toughness, is the traditional method of obtaining high mechanical properties of steel.
The metal workpiece is heated to a suitable temperature and maintained for a period of time, then immersed in the quenching medium in the rapid cooling of the metal heat treatment process. Commonly used quenching medium with salt water, water, mineral oil, air and so on. Quenching can improve the hardness and wear resistance of metal parts, which is widely used in various tools, molds, measuring tools and surface wear parts (such as gears, rollers, carburizing parts, etc.). Through quenching and tempering with different temperatures, can greatly improve the metal strength, toughness and fatigue strength, and can be obtained between these properties (integrated mechanical properties) to meet the different requirements. In addition, quenching can also make some special properties of steel to obtain a certain physical and chemical properties, such as quenching the permanent magnet to enhance its ferromagnetism, stainless steel to improve its corrosion resistance. The quenching process is mainly used for steel parts. Commonly used steel in the heating to the critical temperature above, the original organization at room temperature will be all or most into austenite. Then the steel immersed in water or oil in the rapid cooling, austenite that is converted to martensite. Compared with other organizations in steel, martensite hardness is the highest. Rapid cooling during quenching will produce internal stress inside the workpiece, when it is large to a certain extent, the workpiece will be distorted or even cracked. To this end, you must choose the appropriate cooling method. According to the cooling method, quenching process is divided into single-liquid quenching, dual-medium quenching, martensitic grading quenching and bainite isothermal quenching four categories.