Publication: Aceros inoxidables ferríticos pulvimetalúrgicos para aplicaciones a alta temperatura
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2005
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2005-12-16
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Abstract
El objetivo fundamental de esta Tesis Doctoral es el estudio y mejora de las propiedades mecánicas, la resistencia a la corrosión y la resistencia a la oxidación a alta temperatura de los aceros inoxidables ferríticos pulvimetalúrgicos. Los aceros inoxidables ferríticos sinterizados, debido a la buena combinación de propiedades mecánicas y a oxidación y al ahorro de material que suponen los procesos de metalurgia de polvos, se emplean en diversas aplicaciones industriales, principalmente en el sector automovilístico. Las ventajas que presentan frente a los aceros inoxidables austeníticos sinterizados son propiedades superiores a alta temperatura y un menor coste por estar menos aleados. Sin embargo, estas propiedades son inferiores a las de los aceros inoxidables de forja y de colada. Por ello, se ha estudiado la posibilidad de mejorar las propiedades mecánicas y la resistencia a la oxidación de los aceros inoxidables AISI 409LNb, 434L y 430L mediante distintas condiciones de sinterización. Por otro lado, se ha estudiado la mejora de las propiedades mecánicas y resistencia a la oxidación mediante la fabricación de materiales con distintos tipos de adiciones al material base 434L; este objetivo se ha conseguido con polvo prealeado con un mayor contenido en Si y con un material compuesto base 434L reforzado con itria. Una vez conformados, se caracterizan las propiedades físicas, mecánicas y frente a la corrosión de los aceros inoxidables a temperatura ambiente. Posteriormente se ensayan a alta temperatura y se caracterizan mediante difracción de rayos X (DRX), microscopía electrónica de barrido (MEB), espectroscopía de impedancia electroquímica (EIS), curvas de polarización y termogravimetría.
The main objective of this Ph.D. Thesis is the study and improvement of mechanical properties, corrosion resistance and oxidation resistance at high temperature of powder metallurgy ferritic stainless steels. Sintered ferritic stainless steels, due to their good combination of mechanical properties and oxidation behaviour and the material savings of P/M processes, are widely used in industrial applications, mainly in the automobile industry. Ferritic stainless steels present better performance at high temperature than austenitic stainless steels, and their cost is reduced as they have lower level of alloying. However, these properties are worst than in wrought stainless steels. Therefore, it has been studied the possibility of improving the mechanical properties and the oxidation resistance of AISI 409LNb, 434L and 430L stainless steel using different sintering conditions. Moreover, the improvement of mechanical properties and the oxidation resistance has been done through the manufacturing of materials with different additions to the 434L base material; this objective has been reached with prealloyed powders with a higher Si content and with a 434L based composite material reinforced with yttria. After manufacturing, the physical, mechanical and corrosion properties at room temperature of the ferritic stainless steels have been characterized. Then, they have been tested at high temperature and they have been characterized by means of X-Ray Diffraction (XRD), Scaning Electron Microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), polarization curves and thermogravimetry.
The main objective of this Ph.D. Thesis is the study and improvement of mechanical properties, corrosion resistance and oxidation resistance at high temperature of powder metallurgy ferritic stainless steels. Sintered ferritic stainless steels, due to their good combination of mechanical properties and oxidation behaviour and the material savings of P/M processes, are widely used in industrial applications, mainly in the automobile industry. Ferritic stainless steels present better performance at high temperature than austenitic stainless steels, and their cost is reduced as they have lower level of alloying. However, these properties are worst than in wrought stainless steels. Therefore, it has been studied the possibility of improving the mechanical properties and the oxidation resistance of AISI 409LNb, 434L and 430L stainless steel using different sintering conditions. Moreover, the improvement of mechanical properties and the oxidation resistance has been done through the manufacturing of materials with different additions to the 434L base material; this objective has been reached with prealloyed powders with a higher Si content and with a 434L based composite material reinforced with yttria. After manufacturing, the physical, mechanical and corrosion properties at room temperature of the ferritic stainless steels have been characterized. Then, they have been tested at high temperature and they have been characterized by means of X-Ray Diffraction (XRD), Scaning Electron Microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), polarization curves and thermogravimetry.
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Keywords
Acero, Acero inoxidable, Industria metalúrgica