Study On Mechanical And High Temperature Oxidation Resistance Of FeCrAl Stainless Steel

Ferritic stainless steels have become one of the most popular materials in automotive exhaust systems due to their excellent heat,thermal conductivity,and oxidation resistance.However,since the implementation of the National VI emission standard in 2020,the exhaust emission requirements have been strict,which makes the working temperature of the exhaust system higher and higher.Therefore,the study of ferritic stainless steel mechanics and high-temperature oxidation resistance has become an inevitable trend.In this paper,five groups of stainless steel were obtained by smelting FeCrAl ferritic stainless steel composite chemical components.The thermodynamics of inclusion formation were calculated,the size of inclusions was counted,and the microstructure and mechanical properties of experimental steel were observed by metallographic microscopy(OM).Analyze the oxidation kinetics of practical steel and calculate the oxidative activation energy;X-ray diffraction(XRD)was used to detect the oxidized surface phase of the sample surface,and the morphology and energy spectrum of iron oxide scale were characterized by scanning electron microscopy(SEM)to characterize the element distribution,and the following results were obtained:(1)Through the thermodynamic calculation of inclusions,the inclusions in Y,Ti,and Zr steel are mainly aluminum oxides;The main inclusions in Y-containing steel are aluminum oxide,yttrium oxide,and a small number of composite inclusions;The main inclusions in Y and Ti steel are aluminum oxide,titanium oxide,yttrium oxide and a small number of composite inclusions.The main inclusions containing Y,Ti,and Zr are aluminum oxide,zirconium oxide,titanium oxide,yttrium oxide,and a small number of composite inclusions.By adding chemical components in the smelting process,the oxygen content in the experimental steel is significantly reduced,and the cleanliness of the molten steel is significantly improved.(2)The microstructure of experimental steel containing Y,Ti,and Zr was refined;The experimental steel is cold-rolled with aging,and the ferrite grains obtained are more uniform and fine;At room temperature,Y,Ti,and Zr increase the elongation of the material without reducing the strength of the material,and have no significant effect on the section shrinkage.(3)After the constant temperature oxidation of the experimental steel,the oxidation thermodynamics were calculated,the constant temperature oxidation kinetic curve was determined,and the oxidation activation energy was calculated;The activation energy gradually increased during the oxidation process of experimental steel,indicating that Y,Ti,and Zr could reduce the oxidation weight per unit area,improve the oxidation resistance at high temperature,and reduce the reaction rate at the initial stage of oxidation.(4)In the atmospheric environment,the oxidative weight gain curve of ferritic stainless steel shows a parabolic law;The iron oxide layer of steel can be divided into an outer oxide layer composed of aluminum oxide and an inner oxide layer composed of FeCr oxide;When stainless steel is unstably oxidized in a water vapor environment,the oxide film peels off,forming a larger oxide,and the thickness of the oxide layer increases.(5)The addition of chemical components improves the oxidation resistance of stainless steel;The spinel structural oxide formed on the surface of the composite steel after oxidation is small in size and closely distributed,and it is rarely found to fall off,and the oxide film is relatively dense and well combined with the matrix.The oxide film without Y,Ti,and Zr steel is peeled off in small quantities;The oxide film generated by the experimental steel has a similar phase composition,mainly aluminum oxide with good protection,and the oxidation process is very easy to expose the iron matrix,and the adhesion between the oxide layer and the matrix is low.Y,Ti,and Zr modified FeCrAl ferritic stainless steel inclusions control the grain size of the ferrite and reduce the rate of high-temperature oxidation reaction,so as to meet the mechanical properties of room temperature and improve the oxidation resistance of the material.