Quenching steel is heated to above the critical temperature Ac3 or Ac1 temperature, holding time, so that all or part of austenite, then greater than the critical cooling rate of the cooling rate following rapid cooling to be martensitic transformation Ms heat treatment process. Usually solid solution alloy, copper alloy, titanium, glass and other materials processing or heat treatment process with a rapid cooling process called quenching. 

The purpose of of quenching is to make the supercooled austenite martensite or bainite were obtained martensite or bainite, and then with a different temperature tempering to a substantial increase in steel steel, hardness, resistance to wear resistance, fatigue strength and toughness, so as to meet the various mechanical parts and tools for different requirements. You can also meet some special physical and chemical properties of ferromagnetic special steels and corrosion resistance by quenching. 

Quenching Process 
The metal workpiece is heated to a suitable temperature and for a time, then immersion quenching medium rapid cooling of metal heat treatment process. Quench media is used saline, water, mineral oil, air or the like. Quenching can improve the hardness and wear resistance of the metal workpiece, which is widely used in various engineering, mold, measuring and require surface wear parts (such as gears, rollers, carburizing parts, etc.). By quenching and tempering with different temperatures, can greatly improve the strength of the metal, fell toughness and fatigue strength, and get fit (mechanical properties) between the performance of these to meet different requirements. Further hardening can also make some special properties of steel to obtain certain physical and chemical properties, such as hardened steel to enhance its permanent magnet magnetic iron, stainless steel to improve its corrosion resistance. Quenching process is mainly used for steel. Commonly used steels when heated above a critical temperature, at room 
temperature, the existing organization of the whole or most of the changes to austenite. The steel is then immersed in water or oil rapid cooling, i.e., the austenite into martensite. Compared with other organizations in steel, martensite highest hardness. Quenching rapid cooling causes internal stress generated when, when it reaches a certain degree of distortion of the workpiece occurs even cracking. To do this you must select the appropriate cooling method. The cooling method, liquid quenching quenching process is divided into single, dual media hardening martensitic quenching and Austempering.