{"id":59556,"date":"2018-03-09T22:47:25","date_gmt":"2018-03-09T22:47:25","guid":{"rendered":"https:\/\/www.deberes.net\/tesis\/sin-categoria\/interacion-entre-los-procesos-de-ablandamiento-y-de-precipitacion-inducida-por-deformacion-en-aceros-microaleados-con-niobio\/"},"modified":"2018-03-09T22:47:25","modified_gmt":"2018-03-09T22:47:25","slug":"interacion-entre-los-procesos-de-ablandamiento-y-de-precipitacion-inducida-por-deformacion-en-aceros-microaleados-con-niobio","status":"publish","type":"post","link":"https:\/\/www.deberes.net\/tesis\/metalurgia\/interacion-entre-los-procesos-de-ablandamiento-y-de-precipitacion-inducida-por-deformacion-en-aceros-microaleados-con-niobio\/","title":{"rendered":"Interacion entre los procesos de ablandamiento y de precipitacion inducida por deformacion en aceros microaleados con niobio"},"content":{"rendered":"<h2>Tesis doctoral de <strong> Cristina Iparraguirre Medrano <\/strong><\/h2>\n<p>Titulo: interacci\u00f3n entre los procesos de ablandamiento y de precipitaci\u00f3n inducida por deformaci\u00f3n en aceros microaleados con niobio resumen: en los aceros microaleados la precipitaci\u00f3n de carbonitruros inducida por deformaci\u00f3n es un fen\u00f3meno que puede tener lugar durante el conformado en caliente de estos materiales interfiriendo con los procesos de ablandamiento est\u00e1ticos que ocurren entre pasadas de deformaci\u00f3n.%&#038;\/La fuerza impulsora para los procesos de ablandamiento disminuye con la anulaci\u00f3n y reagrupamiento de las dislocaciones (restauraci\u00f3n) y con la nucleaci\u00f3n y crecimiento de nuevos granos, libres de dislocaciones, en la austenita deformada (recristalizaci\u00f3n). Al mismo tiempo, las dislocaciones proporcionan los lugares necesarios para la precipitaci\u00f3n de carbonitruros de los elementos de microaleaci\u00f3n. Estos precipitados inducidos por deformaci\u00f3n afectan al movimiento de las dislocaciones debido a un fen\u00f3meno de anclaje. Si los procesos de ablandamiento se desarrollan antes de que la precipitaci\u00f3n comience, el n\u00famero de lugares para la nucleaci\u00f3n de los precipitados se ver\u00e1 reducido y el comienzo de la precipitaci\u00f3n se ver\u00e1 retrasado a tiempos m\u00e1s largos. Si por el contrario, la precipitaci\u00f3n comienza antes o durante los procesos de ablandamiento, estos se retrasar\u00e1n y\/o se parar\u00e1n. Dentro de los elementos de microaleaci\u00f3n, el niobio es el elemento que mayor retraso produce sobre los mecanismos de ablandamiento, no s\u00f3lo en forma de precipitado, sino tambi\u00e9n en soluci\u00f3n. Debido a esto, los aceros microaleados con niobio se utilizan principalmente en la laminaci\u00f3n controlada convencional. En este tipo de laminaci\u00f3n se intenta lograr un material muy deformadoantes de la transformaci\u00f3n, de forma que el tama\u00f1o de grano presente en el material, al final de su conformado, sea rino. Las nuevas rutas de producci\u00f3n de acero encaminadas a la reducci\u00f3n de costes, y basadas en la uni\u00f3n del proceso de colada del acero en formas semiacabadas con el proceso de laminaci\u00f3n presentan importantes diferencias con respecto a las t\u00e9cnicas de procesado convencionales. Dentro de estas diferencias, las m\u00e1s importantes son: un mayor tama\u00f1o de grano de austenita previo a la laminaci\u00f3n, una distribuci\u00f3n de las segregaciones diferente y una mayor concentraci\u00f3n de elementos en soluci\u00f3n antes de empezar la laminaci\u00f3n. Este \u00faltimo punto se traduce en una mayor fuerza impulsora para la precipitaci\u00f3n en los nuevos procesos de conformado que en los convencionales. Dada la importancia del proceso de precipitaci\u00f3n inducida por deformaci\u00f3n a la hora de determinar las propiedades del material tras el proceso de conformado, el presente trabajo pretende ahondar en el conocimiento sobre los mecanismos que gobiernan este proceso, y principalmente, sobre su interacci\u00f3n con la restauraci\u00f3n y recristalizaci\u00f3n est\u00e1ticas. En este sentido se han empleado aceros microaleados con niobio y se ha empleado la deformaci\u00f3n en caliente bajo torsi\u00f3n y la t\u00e9cnica de relajaci\u00f3n de tensiones tras la deformaci\u00f3n en caliente del material mediante compresi\u00f3n plana. A partir de estos ensayos se ha obtenido informaci\u00f3n acerca de las cin\u00e9ticas de ablandamiento y del estado de la microestructura. La caracterizaci\u00f3n de la precipitaci\u00f3n se ha realizado mediante microscop\u00eda electr\u00f3nica de transmisi\u00f3n y mediante extracci\u00f3n qu\u00edmica. Finalmente, se han comparado los resultados obtenidos con modelos emp\u00edricos propuestos en bibliograf\u00eda y se ha desarrollado un modelo f\u00edsico capaz de predecir la evoluci\u00f3n microestructural que tiene lugar tras la deformaci\u00f3n en caliente de aceros microaleados con nb en t\u00e9rminos de una contribuci\u00f3n simult\u00e1nea de los procesos de ablandamiento y precipitaci\u00f3n se ha observado que, dentro de la sencillez del modelo, \u00e9ste es capaz de describir de forma razonable las cin\u00e9ticas de precipitaci\u00f3n as\u00ed como las de ablandamiento capturando la interacci\u00f3n esencial que se da entre ambos procesos. A temperaturas elevadas esta interacci\u00f3n se da principalmente entre recristalizaci\u00f3n y precipitaci\u00f3n, siendo la interacci\u00f3n entre la restauraci\u00f3n y la precipitaci\u00f3n la que domina a bajas temperaturas.  interaction between softening processes and strain induced precipitation in niobium microalloyed steels strain induced precipitation is a key phenomenon that can take place during hot rolling of microalloyed steels interacting with softening processes that happen between deformation passes. The driving force for softening processes is reduced through the rearrangement of dislocations (recovery process) and the nucleation of new grains, free of dislocations, growing in the deformed austenite (recrystallization process). At the same time, the dislocations provide preferential sites for the nucleation of carbonitrides of microalloying elements. These strain induced precipitates affect the movement of dislocations due to a pinning effect. That is, the deformation of microalloyed austenite sets the stage for the simultaneous processes of recovery, recrystallization and precipitation. If softening processes develop before precipitation occurs, the number of precipitate-nucleation sites (dislocations) will be reduced and the onset of precipitation retarded. In contrast, if precipitation occurs before or during softening processes, these will be retarded and eventually, halted. Amongst microalloying elements, niobium is known to be the most effective in retarding softening processes, not only asprecipitate, but al so, in sol id solution. Thus, niobium microalloyed steels are mainly used in conventional controlled rolling. The aim of this type of rolling is to produce a completely deformed material (not recrystallized) before the austenite to ferrite transformation, so that the grain size present in the material is fine at the end of the rolling process which is the only way to obtain a good combination of strength and toughness in low carbon microalloyed steels. The new steelmaking routes orientated to reduce manufacturing costs and based in the union of the process of near net shape casting and rolling (direct rolling), present important differences, from a metallurgical point of view, with respect to the conventional ones. Amongst these differences, the most important are: a larger austenite grain size before rolling, a different segregation distribution and a greater amount of alloying elements in solution. The latter means a greater driving force for precipitation in the new steelmaking routes than in conventional ones.  Due to the importance of strain induced precipitation process establishing the mechanical properties of the final products, the aim of the present work is to deepen in the knowledge of the mechanisms that govern this process, and mainly, in the interaction between precipitation and static recovery and recrystallization. For this purpose niobium microalloyed steels have been tested using hot torsion and stress relaxation technique after hot plane compression. Deformation conditions have been selected in order to simulate conventional processes and the new trends in steelmaking. From these tests information about softening kinetics and microstructural evolution have been obtained. Transmission electron microscopy and chemical extraction measurements have been use for precipitation characterization. Finally, the data obtained have been compared with different empirical models proposed in the bibliography and a physical based model of the evolution of niobium microalloyed austenite following deformation has been developed. The main feature of the model is that takes into account the simultaneous contributions of recovery, recrystallization and precipitation processes. It has been observed that the model within its simplicity describes reasonably well precipitation kinetics as well as recrystallization and softening kinetics capturing the essential interaction between them. The interaction between recrystallization and precipitation dominates the microstructural evolution at high rolling-temperatures, being the interaction of precipitation and recovery important at low rolling-temperatures<\/p>\n<p>&nbsp;<\/p>\n<h3>Datos acad\u00e9micos de la tesis doctoral \u00ab<strong>Interacion entre los procesos de ablandamiento y de precipitacion inducida por deformacion en aceros microaleados con niobio<\/strong>\u00ab<\/h3>\n<ul>\n<li><strong>T\u00edtulo de la tesis:<\/strong>\u00a0 Interacion entre los procesos de ablandamiento y de precipitacion inducida por deformacion en aceros microaleados con niobio <\/li>\n<li><strong>Autor:<\/strong>\u00a0 Cristina Iparraguirre Medrano <\/li>\n<li><strong>Universidad:<\/strong>\u00a0 Navarra<\/li>\n<li><strong>Fecha de lectura de la tesis:<\/strong>\u00a0 29\/06\/2007<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<h3>Direcci\u00f3n y tribunal<\/h3>\n<ul>\n<li><strong>Director de la tesis<\/strong>\n<ul>\n<li>Beatriz L\u00f3pez Soria<\/li>\n<\/ul>\n<\/li>\n<li><strong>Tribunal<\/strong>\n<ul>\n<li>Presidente del tribunal: Jos\u00e9 manuel Martinez esnaola <\/li>\n<li>eva Novillo d\u00edaz (vocal)<\/li>\n<li>Jos\u00e9 Mar\u00eda Cabrera marrero (vocal)<\/li>\n<li>  (vocal)<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Tesis doctoral de Cristina Iparraguirre Medrano Titulo: interacci\u00f3n entre los procesos de ablandamiento y de precipitaci\u00f3n inducida por deformaci\u00f3n en [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center 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