Publication: Partición de soluto a través de la intercara en estructuras laminares y nanopartículas en aceros ligeros
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2017-05-12
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Universidad Complutense de Madrid
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Abstract
Son cerca ya de 150 años los que el mundo de la metalurgia lleva estudiando la formación del microconstituyente laminar de ferrita y cementita conocido como perlita, y aún existen preguntas sin respuestas respecto a los mecanismos de transformación de la austenita en perlita. El objetivo de esta tesis es estudiar en detalle la transformación isotérmica de austenita en perlita para tratar de dar solución a algunas cuestiones sobre las que aún existe cierta controversia. Para abordar este trabajo se han diseñado distintas aleaciones para estudiar el efecto que tiene la composición, temperatura, el tamaño de grano austenítico de partida (TGA) o la partición de soluto a través de la intercara en este tipo de estructuras laminares. Primeramente se evaluó en un acero hipoeutectoide Fe-C-Mn el efecto de la temperatura de austenización y por tanto, del TGA, en los parámetros morfológicos de la perlita y se revisaron algunos conceptos clásicos de la literatura sobre la transformación perlítica. Los resultados obtenidos indican que a pesar de que la temperatura de austenización es independiente del espaciado interlaminar o del tamaño de colonia perlítica, sí que tiene un efecto directo en el ancho de las láminas de ferrita y de cementita (aun manteniéndose constante el espaciado) así como en la fracción de volumen de ferrita y de perlita obtenidas en la microestructura final. Para composiciones situadas fuera de la extrapolación de Hultgren se observaron microestructuras con una fracción en volumen de perlita mayor que para el caso de aleaciones situadas dentro de la extrapolación de Hultgren. Por este motivo se revisaron los modelos y ecuaciones que describen el flujo y concentración de carbono en la intercara austenita/perlita para poder justificar las diferencias observadas experimentalmente...
Despite metallurgists scientists started to study the formation of the lamellar microconstituent called pearlite, there are still some issues that need to be thoroughly studied. The goal of this thesis work is to study in-depth the isothermal austenite-to-pearlite decomposition in order to get answers of some questions about this transformation. Besides all the work reported, the pearlite reaction is still attracting the interest of many researchers, and nowadays, topics such as the non-steady growth (divergent pearlite) are discussed in literature. Moreover, there is a wide variety of research on the effects of microstructural parameters on the mechanical properties of pearlitic steels. A well-known fact is that the active nucleus for pearlite formation can be either ferrite or cementite, depending on the temperature and composition. The nucleation sites can be grain boundaries or inclusions, and once either one of the constituent phases is nucleated, the conditions surrounding the new nucleus are ripe for the nucleation of the other, and pearlite grows in a co-operative manner. Although the close relationship between grain-boundary area and potency of nucleation sites is well-known, the effect of austenite grain size (AGS) on pearlite transformation has not been described in detail yet. Therefore, one of the goals of this work is to study the effect of AGS on pearlite volume fraction and morphology parameters such as interlamellar spacing and pearlite colony size...
Despite metallurgists scientists started to study the formation of the lamellar microconstituent called pearlite, there are still some issues that need to be thoroughly studied. The goal of this thesis work is to study in-depth the isothermal austenite-to-pearlite decomposition in order to get answers of some questions about this transformation. Besides all the work reported, the pearlite reaction is still attracting the interest of many researchers, and nowadays, topics such as the non-steady growth (divergent pearlite) are discussed in literature. Moreover, there is a wide variety of research on the effects of microstructural parameters on the mechanical properties of pearlitic steels. A well-known fact is that the active nucleus for pearlite formation can be either ferrite or cementite, depending on the temperature and composition. The nucleation sites can be grain boundaries or inclusions, and once either one of the constituent phases is nucleated, the conditions surrounding the new nucleus are ripe for the nucleation of the other, and pearlite grows in a co-operative manner. Although the close relationship between grain-boundary area and potency of nucleation sites is well-known, the effect of austenite grain size (AGS) on pearlite transformation has not been described in detail yet. Therefore, one of the goals of this work is to study the effect of AGS on pearlite volume fraction and morphology parameters such as interlamellar spacing and pearlite colony size...
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica, leída el 17/11/2015