QPQ is an abbreviation for “Quench—Polish-Quench”. A more accurate description is called “salt bath composite treatment technology”.

After salt bath treatment, to reduce the roughness of the workpiece surface, the workpiece surface is polished once and then oxidized in the salt bath again. This is very necessary for precision parts and workpieces with high surface smoothness requirement. QPQ process can greatly improve the wear resistance and corrosion resistance of the metal surface, while the workpiece hardly deforms. This technology is the combination of nitriding and oxidation processes, results in the combination of nitride and oxide, achieves wear resistance and corrosion resistance at the same time, and is a mixture of heat treatment and anti-corrosion technology.