Studies Of Stainless Steels Nitrided By Hollow Cathode Discharge-assisted Plasma Nitriding Technology

The stainless steels are widely used in the industry of oil,chemistry,medicine and food for their good intensity,toughness and corrosion resistance.But their low hardness and poor friction resistance limit their use whenever the hardness is required. Plasma-nitriding can improves the friction resistance of stainless steels.In this paper,the hollow cathode discharge-assisted plasma nitriding was used for AISI 304 austenitic stainless steels in order to study the effect of hollow cathode discharge-assisted plasma nitriding on the AISI 304 austenitic stainless steels and discuss the effect of temperature of this treatment on the modified layers finding the temperature of CrN precipitation in the floating potential.The micro-hardness of modified layers is measured by micro-hardness apparatus,morphology by optical microscope and scan electrical microscope,composition by X-ray diffraction,corrosion resistance with potentiodynamic scan.The study presents that the temperature have the important effect on the properties of modified layers.The modified layers with good friction resistance,corrosion resistance, lubricous face,symmetrical composition and no CrN precipitation can be formed using the hollow cathode discharge-assisted plasma nitriding in low temperature.The hardness of modified layers increased and the corrosion resistance decreased with temperature increasing.When the samples was in the condition of anodic potential,CrN began to precipitate at 480℃.It is CrN that decrease the corrosion resistance of modified layers.Besides,the paper studied the process of hollow cathode discharge-assisted plasma nitriding and the effect of the potential conditions on the nitriding treatment of austenitic stainless steel.The study indicated that the modified layers with good friction resistance and corrosion resistance can be formed in low temperature whenever in the anodic,floating and cathodic potentials.The hardness of the samples nitride in the cathodic potential is higher than that in the anodic and floating potentials,but they are in the same quantitative indicator,when the samples was nitrided in the cathodic and floating potentials CrN precipitate more easily.Hollow cathode discharge-assisted plasma nitriding used two cylinders as cathode,it improves the probability of collision between electron and nitriding gas and saves energy.The process of hollow cathode discharge-assisted plasma nitriding is composed of active state producing,cathode spattering and diffusing out of samples,adsorption and diffusing in the samples.