What is quenching?
The quenching of steel is to heat the steel to a temperature above the critical temperature Ac3 (hypo-eutectoid steel) or Ac1 (hypereutectoid steel), keep it for a while, make it fully or partially austenitized, and then cool it at a temperature greater than the critical cooling rate. The heat treatment process of rapid cooling to below Ms (or isothermal near Ms) for martensite (or bainite) transformation. The solution treatment of aluminum alloy, copper alloy, titanium alloy, tempered glass, and other materials or the heat treatment process with a rapid cooling process is also called quenching.
The purpose of quenching:
1) Improve the mechanical properties of metal products or parts. For example: improve the hardness and wear resistance of tools, bearings, etc., improve the elastic limit of springs, improve the comprehensive mechanical properties of shaft parts, etc.
2) Improve the material properties or chemical properties of some special steels. Such as improving the corrosion resistance of stainless steel, increasing the permanent magnetism of magnetic steel, etc.
When quenching and cooling, in addition to the reasonable selection of quenching medium, there must be a correct quenching method. The commonly used quenching methods mainly include single-liquid quenching, double-liquid quenching, graded quenching, isothermal quenching, local quenching, etc.
The steel workpiece has the following characteristics after quenching:
① Obtained unbalanced (ie unstable) structures such as martensite, bainite, and retained austenite.
② There is a large internal stress.
③ The mechanical properties cannot meet the requirements. Therefore, steel workpieces are generally tempered after quenching.
