Study On Microstructure And Heat Resistance And Corrosion Resistance Of High Aluminum Lightweight Stainless Steel

The papper design a lightweight stainless steel Fe-6Al-9Cr-0.02C-0.2%N-0.5Si,on the basis of literatures and theories.The 9.06Cr-5.37Al-0.47Si-0.03C-0.018N-Fe lightweight steel was melted by vacuum induction furnace,and its density was measured by the method of drainage.The microstructure of the steel was analyzed by Zeiss optical microscope,electron microscope and X ray diffraction;With muffle furnace and thermal analyzer test the oxidation resistant performance of the lightweight stainless steel at 800?,1000?,1100?and 1200?in air.The corrosion resistance of lightweight stainless steel was inverstigated by acid leaching test and neutral salt spray test.The following conclusions are obtained:The microstructure of Fe-9Cr-5Al-0.5Si-0.02N-0.03C steel is compact,there are no macro cracks and holes in steel ingot,and the grain boundaries are clear and small.Its main phase is?-Fe,ordered phase Fe₃Al,FeCr and a small amount of AlN compound.Its average microhardness is 197 HV0.5,which is similar to that of the commonly used 304 stainless steel?215HV0.5?.The density of the lightweight steel is7.30g/cm³,which is reduced by 9.54%by 0.77g/cm³ than that of 3Cr13 stainless steel;The grain size of Fe-9Cr-5Al-0.5Si-0.02N-0.03C steel is very large,and its diameter is about 0.5mm.There are two main reasons for the grain coarsening:First,aluminum and chromium can significantly increase the lattice constants of the?-Fe,reduce the density of the steel,make the atoms in the steel easy to migrate,and accelerate the growth of grain.Second,because the matrix structure of the steel is a single-phase?-Fe,there is no crystal transformation,and there is no grain refinement in the solidification process;The average oxidation rate of Fe-9Cr-5Al-0.5Si-0.02N-0.03C steel in air at 800?is about 0.068 g/h m².The average oxidation rate was less than 0.1g/h m² specified by the GB/T13303-199l standard,reached the level of total antioxidant.The oxidation film formed by oxidation of Fe-9Cr-5Al-0.5Si-0.02N-0.03C steel at800?consists of Fe₂Al Cr?AlFeO₃?AlFe₆Si??FeCr?₂O₃?Fe₄O₃?Cr₂O₃.After 1000?of oxidation,the oxide film is Al₂O₃?SiO₂?Fe₂AlCr?Al₂SiO₅?CrO₂.The oxidation film of 1100?is Al₂O₃?Fe₂SiO₄?Al₂SiO₅?Cr₂O₃.At 1200?,the surface oxide film phase phase in addition to Cr₂O₃?SiO₂?Al₂O₃,and a large number of complex composite compounds of iron,aluminum,oxygen,silicon,chromium,such as:Fe₃+₂Al₂?SiO4?₃?Fe₂AlCr??AlCr?₂O₃?Al₂SiO₅?Fe?CrAl?₂O₅.Comparison of different temperature on film structure,it is found,with the increase of oxidation temperature,chromium oxide from low to high valence state,aluminum oxide increasing,complex oxide species increased,the degree of oxidation with temperature increasing;The oxide film of Fe-9Cr-5Al-0.5Si-0.02N-0.03C steel is mainly composed of purple and green oxide,the purple oxide may be Fe₂O₃,and the green oxide may be Cr₂O₃.There are many white-island structures distributed in the matrix of the oxide film,and there are many red concentric circles in the white-island structures,and the white-island structure may be Al₂O₃,the red concentric circles may be Fe₂O₃,which may be reducted by the selective oxidation of aluminum and iron in steel.In addition,there are many black-island structures distributed in the matrix of the oxide film,and the central part of the black-island is pale yellow,the black island structure may be Fe₃O₄,and the central part of the pale yellow phase may be Al₂O₃;After immersed in concentrated nitric acid for three days,the samples of Fe-9Cr-5Al-0.5Si-0.02N-0.03C steel and the contrast 3Cr13 steel showed no signs of corrosion.After immersed in concentrated nitric acid tenth days,There are many network reducted by corrosion was beginning showing on the entire surface of the Fe-9Cr-5Al-0.5Si-0.02N-0.03C steel sample.Meanwhile,there are many small black spots and stripes appear on the surface of 3Cr13 steel samples.After 23 days of immersion,Fe-9Cr-5Al-0.5Si-0.02N-0.03C steel corroded seriously.However,3Cr13steel was thoroughly corroded,there is a lot of honeycomb loose corrosion on the specimen surface.After 96 hours salt spray test,Fe-9Cr-5Al-0.5Si-0.02N-0.03C steel has been serious corrosed.There are a lot of corrosion products on the surface of the sample after 360 hours salt spray test.According to the experimental results of corrosion resistance test,the corrosion resistance of Fe-9Cr-5Al-0.5Si-0.02N-0.03C steel is equivalent to that of 3Cr13 stainless steel.Comparedwiththeheatresistanceandcorrosionresistanceof Fe-9Cr-5Al-0.5Si-0.02N-0.03C steel,Fe-9Cr-5Al-0.5Si-0.02N-0.03C steel has a better development and application prospect in heat-resistant steel.