Influence of QPQ Technology on the Microstructural, Mechanical and Corrosion Properties of Ck67 Steel Used in Automobile Components

Quench-Polish-Quench(QPQ) is a low temperature process in a liquid salt bath and is used for modifying the surfaces of metals to enhance corrosion and wear resistance. In this research, the effects of the compound and oxide layers on microstructure and corrosion properties of steel CK67 were investigated. The QPQ process was carried out by nitriding at 580°C for 120 minutes, followed by the oxidation treatment at 380°C for 20 minutes. The modified surface was then studied by using optical microscopy (OM ), scanning electron microscopy (SEM ), X -ray diffractometer (XRD), corrosion and microhardness tests. The results show that the surface layer consists of Gamma prime (γ'), iron, magnetite, and epsilon nitride(Ɛ ). Accordingly, the nitriding and the following oxidation treatment led to the enhanced corrosion properties and hardness in comparison to the steel before applying the QPQ process. The most achieved value of hardness was 587 HV which was nearly three times higher than that without the QPQ process. In addition, after 144-hour salt spray testing, corrosion products were observed on the coated surface.