Air cooling quenching heat treatment process

The gas quenching process is usually carried out under high pressure and is therefore often referred to as high pressure gas quenching (HPGQ). In HPGQ, the workpiece, which has been austenitized or chemically heat treated, is quenched in an inert gas flow at a pressure of 1 to 20 bar and a flow rate of 0.5 to 20 m/s. When a nozzle is used, the speed is higher and can reach 80 to 160 m/s. In a few cases, pressures up to 25 bar are used. In most cases, HPGQ is combined with vacuum heat treatment, such as low pressure carburizing (LPC); in a few applications, HPGQ is used after conventional gas carburizing. HPGQ is usually followed by tempering.
In most cases, the purpose of the gas quenching process is to increase the hardness of the workpiece. After austenitization, the workpiece is subjected to HPGQ to transform the microstructure from austenite to martensite, thereby obtaining the desired increase in hardness. Compared with liquid quenching, such as oil, polymer solution or water quenching, high pressure gas quenching is an environmentally friendly and low-distortion quenching process. Compared with liquid quenching, dry gas quenching has the following advantages: the workpiece surface is clean after heat treatment and does not need to be cleaned. The control of quenching intensity is very flexible. It can significantly reduce heat treatment deformation.