Study On The Surface Modification Of Duplex Stainless Steels By High Temperature Rapid Plasma Nitriding And Nitrocarburizing

The stainless steel is widely used in chemical, ship, medical and other fields for its excellent corrosion resistance performance, but its characteristics of low surface hardness, low wear resistance and make its application has also been a certain limit.The plasma nitriding is one of the widely used metal materials surface engineering technologies to improve the surface hardness, wear and corrosion resistance because of it can form nitrides. In traditional plasma nitriding process, the workpiece as the cathode, furnace as the anode, ionization low pressure nitrogen gas with high voltage,produce reactive nitrogen atoms diffused in sample to obtain a certain depth of the modified layer. As a result of the ion bombardment and sputtering, there will be edge effect and arcing effect defects on the sample. What’s more, to avoid precipitation of CrN, the nitriding temperature usually below 450℃.At the low temperature, nitrogen atom diffusion rate is slower, thus nitriding treatment need long time.In order to overcome above shortcomings, a double active screen was designed in our research. Using hollow cathode discharge effect and highly reactive ion bombardment the large screen is easily to be heated to the required temperature for treatment. The average temperature rise rate is about 30℃/min.The sample materials used in this study are SS2205 duplex stainless steels.By changing the influence factors of nitriding temperature, time and the carbon ventilation to explore the dynamics and thermodynamics of the nitriding process. By using the optical microscope,X-ray diffraction analysis,Scanning electron microscope, Laser confocal microscope testing instruments, measuring permeability layer thickness, phase composition and microhardness, evaluate the corrosion resistance, wear resistance and other performance.Experiments show the high temperature rapid plasma nitriding can heat the duplex stainless steel specimen in a short period of time and obtain a certain thickness layer.It can improve the surface hardness and wear resistance properties without deteriorating corrosion resistance.This way can improve the efficiency of the plasma nitriding.