QPQ technology is a composite process combining carbonitriding and oxidation, evolved from salt bath nitriding. It involves a single oxidation treatment following the entire pollution-free salt bath composite treatment process. After QPQ treatment, workpieces retain the advantages of carbonitriding—high wear resistance, high corrosion resistance, minimal deformation, and environmental friendliness—while the added oxidation process significantly enhances corrosion resistance and improves surface aesthetics.