Transformaciones de fase en aceros de bajo contenido en C microaleados con Nb y V
The phase transformations occurring during continuous cooling in Nb-V microalloyed steels have been analyzed in depth on this thesis. In particular, three compositions of niobium microalloyed steels and three steels microalloyed with vanadium have been characterized. The work is divided into six c...
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| Format: | info:eu-repo/semantics/doctoralThesis |
| Language: | spa |
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Servicio de Publicaciones. Univesidad de Navarra
2015
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| Online Access: | https://hdl.handle.net/10171/38977 |
| _version_ | 1793400547694346240 |
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| author | García-Riesco, P.M. (Pedro Manuel) Uranga-Zuaznabar, P. (Peio) López-Soria, B. (Beatriz) |
| author_facet | García-Riesco, P.M. (Pedro Manuel) Uranga-Zuaznabar, P. (Peio) López-Soria, B. (Beatriz) |
| author_sort | García-Riesco, P.M. (Pedro Manuel) |
| collection | DSpace |
| description | The phase transformations occurring during continuous cooling in Nb-V microalloyed steels have been analyzed in depth on this thesis. In particular, three compositions of niobium microalloyed steels and three steels microalloyed with vanadium have been characterized.
The work is divided into six chapters and begins with a brief introduction which aims to value the importance of the steel in the modern world. Then, on the second chapter, the most important metallurgical concepts related especially to low carbon steels in the literature have been reviewed and summarized.
Chemical compositions and experimental techniques carried out are detailed on the third chapter. Experimental techniques have consisted mainly in two types of tests (dilatometry and multipass torsion tests). The data obtained from the continuous cooling tests have been used to develop two mathematical models. These models aim to summarize the behavior of the analyzed steels according to three leading variables: the austenite grain size, accumulated deformation and cooling rate.
At the fourth chapter, the results obtained and the principles governing the two developed models have been described. This chapter is divided into four blocks, the first one consists on a summary of the microstructural characterization performed and continuous cooling diagrams (CCT diagrams) obtained by dilatometry tests. These tests were carried out with the three Nb microalloyed steels and C-Mn-V1.
In the second block of results, a predictive model of the austenite transformation kinetics is developed. The microstructures obtained are composed of one or more phases (ferrite, pearlite and bainite) upon cooling from different austenite microstructures (recrystallized and deformed).
On the third block the study has been focused on the austenite-ferrite transformation (low cooling rates). Besides the improvement in predicting the mean ferrite size, a model that takes into account the heterogeneity of the austenite grain size distributions before the phase transformation has been developed. The effect of heterogeneity in the austenite-ferrite transformation has been studied in terms of different variables (Effective Austenite grain size and cooling rate). The objective of the model is to predict the grain size distribution of transformed ferrite from different austenite conditions.
Finally, a study of the hot rolling process on different industrial profiles is described with two steels similar to C-Mn-V1 composition. The effect of varying temperatures and strain distribution has been studied by hot torsion multi-pass testing. Then, after quantifying the microstructural changes associated to these changes in the rolling process, the austenite-ferrite transformation model has been validated again. These microstructures correspond to a similar range of cooling rates compared to the microstructures obtained by dilatometry trials, which have been adjusted the model parameters.
In the fifth chapter of this work the conclusions and future lines of work have been presented. Finally, the three publications developed during the course of this thesis have been attached. Specifically, an international journal publication (ISIJ International, Vol 55, n.9, 2015), an international conference proceeding contribution (British Columbia, Canada, June 2015) and a contribution to the XIII National Materials Congress (Barcelona, June 2014). |
| format | info:eu-repo/semantics/doctoralThesis |
| id | oai:dadun.unav.edu:10171-38977 |
| institution | Universidad de Navarra |
| language | spa |
| publishDate | 2015 |
| publisher | Servicio de Publicaciones. Univesidad de Navarra |
| record_format | dspace |
| spelling | oai:dadun.unav.edu:10171-389772022-02-07T11:19:23Z Transformaciones de fase en aceros de bajo contenido en C microaleados con Nb y V García-Riesco, P.M. (Pedro Manuel) Uranga-Zuaznabar, P. (Peio) López-Soria, B. (Beatriz) Phase transformation. Mean grain size. Ferrita. Austenita. Modelización. The phase transformations occurring during continuous cooling in Nb-V microalloyed steels have been analyzed in depth on this thesis. In particular, three compositions of niobium microalloyed steels and three steels microalloyed with vanadium have been characterized. The work is divided into six chapters and begins with a brief introduction which aims to value the importance of the steel in the modern world. Then, on the second chapter, the most important metallurgical concepts related especially to low carbon steels in the literature have been reviewed and summarized. Chemical compositions and experimental techniques carried out are detailed on the third chapter. Experimental techniques have consisted mainly in two types of tests (dilatometry and multipass torsion tests). The data obtained from the continuous cooling tests have been used to develop two mathematical models. These models aim to summarize the behavior of the analyzed steels according to three leading variables: the austenite grain size, accumulated deformation and cooling rate. At the fourth chapter, the results obtained and the principles governing the two developed models have been described. This chapter is divided into four blocks, the first one consists on a summary of the microstructural characterization performed and continuous cooling diagrams (CCT diagrams) obtained by dilatometry tests. These tests were carried out with the three Nb microalloyed steels and C-Mn-V1. In the second block of results, a predictive model of the austenite transformation kinetics is developed. The microstructures obtained are composed of one or more phases (ferrite, pearlite and bainite) upon cooling from different austenite microstructures (recrystallized and deformed). On the third block the study has been focused on the austenite-ferrite transformation (low cooling rates). Besides the improvement in predicting the mean ferrite size, a model that takes into account the heterogeneity of the austenite grain size distributions before the phase transformation has been developed. The effect of heterogeneity in the austenite-ferrite transformation has been studied in terms of different variables (Effective Austenite grain size and cooling rate). The objective of the model is to predict the grain size distribution of transformed ferrite from different austenite conditions. Finally, a study of the hot rolling process on different industrial profiles is described with two steels similar to C-Mn-V1 composition. The effect of varying temperatures and strain distribution has been studied by hot torsion multi-pass testing. Then, after quantifying the microstructural changes associated to these changes in the rolling process, the austenite-ferrite transformation model has been validated again. These microstructures correspond to a similar range of cooling rates compared to the microstructures obtained by dilatometry trials, which have been adjusted the model parameters. In the fifth chapter of this work the conclusions and future lines of work have been presented. Finally, the three publications developed during the course of this thesis have been attached. Specifically, an international journal publication (ISIJ International, Vol 55, n.9, 2015), an international conference proceeding contribution (British Columbia, Canada, June 2015) and a contribution to the XIII National Materials Congress (Barcelona, June 2014). En esta tesis se han analizado en profundidad las transformaciones de fase producidas durante enfriamientos continuos en aceros microaleados con Nb y V. En concreto, se han caracterizado tres composiciones de aceros microaleados con niobio y otras tres de aceros microaleados con vanadio. El trabajo realizado se divide en seis capítulos, y comienza con una breve introducción donde se pretende poner en valor la importancia que tiene el acero en el mundo moderno. A continuación, en el capítulo de revisión bibliográfica, se han resumido los conceptos metalúrgicos más importantes relacionados especialmente con los aceros de bajo contenido en carbono. En tercer lugar se han detallado las composiciones químicas y las técnicas experimentales llevadas a cabo. Principalmente las técnicas han consistido en dos tipos de ensayos (ensayos de dilatometría y torsión multipasada). Los datos obtenidos de los enfriamientos continuos realizados han sido empleados para desarrollar dos modelos matemáticos, cuyo objetivo es resumir el comportamiento de los aceros analizados en función de tres variables destacadas: el tamaño de grano de austenita, la deformación acumulada y la velocidad de enfriamiento. En el cuarto capítulo se han mostrado los resultados obtenidos y los principios que rigen los dos modelos desarrollados. Este capítulo se ha dividido en cuatro bloques, consistiendo el primero en un resumen de la caracterización microestructural llevada a cabo y los diagramas de enfriamiento continuo (Diagramas CCT) obtenidos mediante ensayos de dilatometría. Estos ensayos han sido realizados con los tres aceros microaleados con niobio y el C-Mn-V1. En el segundo bloque de resultados se ha trabajado en el desarrollo de un modelo de predicción de las cinéticas de transformación de la austenita. Las microestructuras obtenidas pueden estar compuestas por una o varias fases (ferrita, perlita y bainita) tras el enfriamiento a partir de diferentes microestructuras de austenita (recristalizada y deformada). En el tercer bloque el estudio se ha centrado en la transformación austenita-ferrita (velocidades de enfriamiento lentas). Además de la mejora en la predicción del tamaño medio de ferrita, se ha trabajado en la obtención de un modelo que tiene en cuenta la heterogeneidad en las distribuciones de tamaños de grano de austenita previas a la transformación. Se ha estudiado en qué medida afecta la heterogeneidad en la austenita a la transformación ferrítica en función de diferentes variables (tamaño de grano efectivo de austenita y velocidad de enfriamiento). El objetivo del modelo es poder predecir las distribuciones de ferrita que se forman a partir de diferentes condiciones de austenita. Por último, se ha realizado un estudio del proceso de laminación de diferentes perfiles industriales con dos aceros microaleados con vanadio de composiciones similares a la del C-Mn-V1. Se ha estudiado el efecto de variar las temperaturas y el reparto de deformaciones mediante ensayos de torsión en caliente de múltiples pasadas. A continuación, tras cuantificar los cambios microestructurales asociados a estas variaciones del proceso de laminación, se ha validado de nuevo el modelo de transformación austenita-ferrita con las microestructuras obtenidas. Éstas corresponden a un rango similar de velocidades de enfriamiento en comparación con las microestructuras obtenidas mediante ensayos de dilatometría, con las que se han ajustado los parámetros del modelo. En el quinto capítulo de este trabajo se han expuesto las conclusiones y líneas de trabajo futuras más destacadas. Finalmente, se han adjuntado las tres publicaciones desarrolladas durante el transcurso de esta tesis. En concreto, se trata de una publicación en revista internacional (ISIJ International, 2015), un congreso internacional (British Columbia, Canada, Junio 2015) y una exposición en el XIII Congreso Nacional de Materiales (Barcelona, Junio 2014). 2015-09-02T10:08:19Z 2015-09-02T10:08:19Z 2015 2015-06-19 info:eu-repo/semantics/doctoralThesis https://hdl.handle.net/10171/38977 spa info:eu-repo/semantics/openAccess application/pdf Servicio de Publicaciones. Univesidad de Navarra |
| spellingShingle | Phase transformation. Mean grain size. Ferrita. Austenita. Modelización. García-Riesco, P.M. (Pedro Manuel) Uranga-Zuaznabar, P. (Peio) López-Soria, B. (Beatriz) Transformaciones de fase en aceros de bajo contenido en C microaleados con Nb y V |
| title | Transformaciones de fase en aceros de bajo contenido en C microaleados con Nb y V |
| title_full | Transformaciones de fase en aceros de bajo contenido en C microaleados con Nb y V |
| title_fullStr | Transformaciones de fase en aceros de bajo contenido en C microaleados con Nb y V |
| title_full_unstemmed | Transformaciones de fase en aceros de bajo contenido en C microaleados con Nb y V |
| title_short | Transformaciones de fase en aceros de bajo contenido en C microaleados con Nb y V |
| title_sort | transformaciones de fase en aceros de bajo contenido en c microaleados con nb y v |
| topic | Phase transformation. Mean grain size. Ferrita. Austenita. Modelización. |
| url | https://hdl.handle.net/10171/38977 |
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