What Is Quenching?

The quenching of steel is to heat the steel to a temperature above the critical temperature Ac3 (hypoeutectoid steel) or Ac1 (hypereutectoid steel), keep it warm for a period of time to make it fully or partially austenitized, and then cool it with a cooling rate greater than the critical cooling rate. A heat treatment process for rapid and rapid cooling below Ms (or isothermal near Ms) for martensite (or bainite) transformation. Usually, the solid solution treatment of aluminum alloy, copper alloy, titanium alloy, tempered glass and other materials or the heat treatment process with rapid cooling process is called quenching.
The purpose of quenching:
1. Improve the mechanical properties of metal products or parts.
For example: improving the hardness and wear resistance of tools, bearings, etc., increasing the elastic limit of springs, improving 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, correct quenching methods are also required. The commonly used quenching methods mainly include single-liquid quenching, double-liquid quenching, graded quenching, isothermal quenching, and partial quenching.
3. Steel workpieces have the following characteristics after quenching:
① Unbalanced (that is, unstable) structures such as martensite, bainite, and retained austenite are obtained.
② There is a large internal stress.
③ The mechanical properties cannot meet the requirements. Therefore, steel workpieces generally have to be tempered after quenching.