Efecto de los parámetros de laminación y post-tratamiento térmico por inducción en la mejora de propiedades mecánicas de aceros microaleados.
High Strength Low Alloy (HSLA) steels are widely used in many industrial sectors such as, infrastructure edification, automotive and naval industry. These sectors demand materials that meet different requirements, which change depending on the application. In response to the demands imposed by the m...
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| Tipo de recurso: | tesis doctoral |
| Fecha de publicación: | 2017 |
| País: | España |
| Institución: | Universidad de Navarra |
| Repositorio: | Dadun. Depósito Académico Digital de la Universidad de Navarra |
| Idioma: | inglés |
| OAI Identifier: | oai:dadun.unav.edu:10171/45292 |
| Acceso en línea: | https://hdl.handle.net/10171/45292 |
| Access Level: | acceso abierto |
| Palabra clave: | Laminación en caliente. Tratamiento térmico por inducción. Aceros microaleados. Mecanismos de endurecimiento. Hot rolling. Microstructure. |
| Sumario: | High Strength Low Alloy (HSLA) steels are widely used in many industrial sectors such as, infrastructure edification, automotive and naval industry. These sectors demand materials that meet different requirements, which change depending on the application. In response to the demands imposed by the market, nowadays there is a severe control over the composition of the material the process parameters, which are the main factors controlling the microstructure and therefore, the mechanical properties of the material. That is the main reason why the relationship between process parameters, microstructure and mechanical properties must be studied. This thesis is framed in three research projects. “Desarrollo de las bases metalúrgicas para la simulación numérica de los procesos de laminación y el desarrollo de aceros AHSS de tercera generación”(PI-2014-1-129) financed by the Basque Government, “Nanometer-sized particle hardening of structural steels” (MAT2012-31056) financed by the Ministry of Economy and Competitiveness of Spain and “Virtual Rolling Mill” (RFSR-CT 2013-00007) of the European RFCS program. The latter has been carried out in a consortium of several universities, research centers and European companies. In all the projects, three steels with the same content of carbon but with different amount of niobium, molybdenum and titanium have been used. Firstly, the effect of the composition and the different process parameters on the mechanical properties of the hot rolled sheet coils have been studied. With that purpose, plane strain compression tests have been carried out with all the microalloyed steels of the study, modifying the coiling temperature. From the obtained samples, the generated microstructures have been analyzed via different characterization techniques: optical microscopy, field emission gun scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) technique. Tensile and Charpy specimens have been machined from the plane strain compression samples to analyze the effect of the coiling temperature on the tensile and toughness properties. Afterwards, with the obtained results from the microstructural analysis and the tensile tests, the contributions of every strengthening mechanisms (solid solution, grain size, dislocation density, presence of secondary phases and fine precipitation) have been estimated for each condition of composition and coiling temperature. Likewise, an equation to predict the impact transition temperature has been developed which takes into account the effect of microstructural heterogeneity and the presence of hard secondary phases such as MA islands. Moreover, with the aim of exploring the possibility of achieving an additional microstructural refinement, the influence of the time between the last deformation pass and the accelerated cooling has been studied. Therefore, plane compression tests have been carried out modifying the final coiling temperature and the time between last deformation pass and accelerated cooling. Furthermore, in order to have a better understanding of the link between the variation of holding time and restoration processes, stress relaxation tests have been performed. In a second part, the chance of improving the tensile properties of hot rolled plates by fast induction heat treatment has been explored. Firstly, a dilatometry study has been carried out to analyze the influence of the microstructure prior to the treatment and the temperature and the holding time of the induction heat treatment. Then, plane strain compression tests have been carried out to analyze the influence of the heat treatment temperature and the microstructure prior to the treatment on the mechanical properties. Finally, as in the previous section, the contribution of each strengthening mechanisms to the yield strength has been determined for all the conditions and the ITT estimation equation developed for the hot rolled sheet coils has been applied. |
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