| The surface of austenitic stainless steel has a dense passivation film,so it has excellent corrosion resistance.Therefore,improving the surface hardness of stainless steel,improving the wear resistance of the material for extending the service life of stainless steel and reducing the cost of materials have significant economic significance.Nitrogen is one of the effective methods to improve the surface hardness and wear resistance of austenitic stainless steel.But in austenitic stainless steel there is strong nitride forming chromium element,if chromium nitride precipitates out in nitriding layer,although improve the surface hardness of stainless steel,but at the expense of corrosion resistance of stainless steel.It will be of great significance to study the nitrogen content and existence form of modified stainless steel coating.In this paper,two kinds of austenitic stainless steels,AISI 304 and AISI 316L,were selected.By controlling the nitriding temperature,a surface modification layer with certain thickness and nitrogen content was obtained on the surface of the sample by gas nitriding method.The microstructure,composition,morphology and phase of the samples were analyzed by OM,EPMA,SEM and XRD.The microhardness,friction and wear coefficient,wear amount and wear morphology of nitriding layer were characterized by microhardness tester,friction and wear testing machine and three-dimensional topography instrument,and the wear resistance of nitriding layer was evaluated.The electrochemical workstation and the salt spray corrosion test chamber were used to study the corrosion resistance of nitriding layer.The results showed that the surface hardness of two kinds of austenitic stainless steels,AISI304 and AISI316L,increased by 2?5 times compared with that of the unnitrided samples after 5 hours of gas nitriding.430? specimen nitrogen content is low,at around 4%,nitriding layer deep around 9 microns,the nitrogen fixation in austenitic lattice,as inflation austenitic phase,which surface hardness is 1000 HV0.05.Nitriding temperature is 530 ?,generate Fe4N and Cr2N facies,infiltration depth is about 80 microns.Nitriding temperature increased,the form of the N by Fe4N,Cr2N phase into Fe2N,CrN and nitrogen content increasing,the maximum is 1050? specimen thick of carburized layer of about 200 microns,but the lowest surface hardness is 520 HV0.05 around;The wear resistance of nitriding samples increases significantly with the increase of temperature.The original samples have the largest wear amount after wear under the load of 20N,and there is a large amount of non-uniform flaky deposits on the wear surface.The wear mechanism is severe adhesive wear,accompanied by plastic deformation.After nitriding,the surface furrow of the wear mark is shallow and narrow,and the wear mechanism changes into slight wear.Austenitic stainless steel substrate itself has good corrosion resistance,AISI304 austenitic stainless steel by 430? after nitriding,corrosion resistance is slightly lower than matrix,and 1050? nitriding samples from higher corrosion current density of 5.26 ?A·cm-2,corrosion potential of 0.09 V is more close to the positive,ac impedance spectra after fitting the resistance value of the maximum is 2.01×104?.After salt fog test,430? and 1050? the untreated sample surface nitriding sample no corrosion products,in the temperature infiltration n improve the corrosion resistance of materials.The matrix corrosion resistance of AISI316L austenitic stainless steel is better than that of AISI304 austenitic stainless steel.Compared with the original sample,after 530? 650?,800? and 1050? after nitriding N combined with Cr into CrN,cause poor chromium on the surface of the material,have been varying degrees of damage to the corrosion resistance,corrosion current density decreases,ac impedance spectrum fitting after resistance smaller. |
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