Study On Equipment And Process Of Plasma Carburizing Surface Hardening Of Austenitic Stainless Steel At Low Temperature

Low temperature plasma carburizing can be used to improve the surface hardness and wear resistance of austenitic stainless steel without degradation of its corrosion resistance.Because of austenitic stainless steel LTPC technology request higher temperature uniformity,but the heat treatment equipment in the existing market cannot satisfy its technological requirement.This subject designed and developed a set suitably to use for austenite stainless steel LTPC device.The body structure,cooling system,the furnace parts and the hydraulic system parts were drawn by the AutoCAD.The design supplied the foundation of mass industrial application of the LTPC treatment technique.In this dissertation,three stainless-steel types(AISI 316L,AIS1321,AIS1304) were plasma-carburized at low temperature.Carburized layers were observed and analyzed by field emission scanning electron microscope(SEM),X-ray diffraction (XRD),optical microscope(OM),microhardness tester and the electrochemical testing technique.It was discussed about the effect of carburizing temperature, carburizing time,and substrate material on phase structure,microstructure, microhardness and corrosion resistance of the carburized layer.The experimental results show that the microstructures and properties of carburized layers are significantly affected by the carburizing temperature, carburizing time and substrate material.At low temperature and in short time,a precipitation-free carburized layer ofγ_c phase structure can be produced.At higher temperatures and with prolonged carburizing time,the depth of carburized layer increases,but the chromium carbide began to precipitate in the carburized layer, which reduced corrosion resistance of the carburized layer.The harder and thicker layers can be produced in Mo and/or Ti containing austenitic stainless steels.In this dissertation,the mechanism of LTPC was studied.It was found that the LTPC should be a process of initiative adsorption and desorption.The activated carbon atoms and the Fe atoms which sputtering from the cathode surface compound generated FexC,and the FexC particles were adsorbed on the sample surface which was activated.After the FexC particles were hit by other particles,and formγ_c phase carburized layer.It also studied on the application of LTPC.Plasma carburizing of austenitic stainless steel valve parts were carded out at low temperature to improve the surface hardness,and obtained a nice carburization hardening effect.It's testified the superiority of LTPC technology in this field.