CHARACTERISTICS OF AISI 420 STAINLESS STEEL MODIFIED BY COMBINING GAS NITRIDING AND CrN COATING

AISI 420 stainless steel is widely used in applications where good mechanical properties and corrosion resistance are required. However, the heat treatment and nitriding process can reduce the corrosion resistance of this stainless steel. This article focuses on investigating the influence of tempered substrate and efficiency of the gas nitriding at temperatures of 520 degrees C and 550 degrees C on some properties of CrN coating. The experiments were carried out to evaluate the surface hardness, microstructure and phase composition of nitrided layers. The coating adhesion and load capacity of the coating were performed according to VDI 3198 standard. Electrochemical testing was performed in a solution of 3.5% NaCl and then using the Tafel method to determine the corrosion current and corrosion potential. The thickness of CrN and CrN/CrN coating was 1.6 mu m and 3 mu m, respectively. The study showed that the corrosion resistance of coatings fabricated through duplex technology was affected not only by the normal defects but also by the porosity on the nitrided surface. The multilayer duplex coating improved a better corrosion resistance than mono-layer duplex coating due to its ability to cover and reduce pores and pitting defects.