Sinterización y dilatometría de aceros pulvimetalúrgicos para piezas de amortiguador.
The main attraction of PM steels related to automotive industry is to produce large number of parts of complex geometry with a net shape manufacturing approach achieving very tight dimensional tolerances without the need for secondary operations and using most of the raw material. The associated red...
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| Format: | info:eu-repo/semantics/doctoralThesis |
| Language: | spa |
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Servicio de Publicaciones. Universidad de Navarra.
2017
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| Subjects: | |
| Online Access: | https://hdl.handle.net/10171/44179 |
| _version_ | 1793400438508224512 |
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| author | Bilbao-Varela, C.(Cristina) Castro-Fernández, F. (Francisco) Sainz-Rodríguez, S. (Shandra) |
| author_facet | Bilbao-Varela, C.(Cristina) Castro-Fernández, F. (Francisco) Sainz-Rodríguez, S. (Shandra) |
| author_sort | Bilbao-Varela, C.(Cristina) |
| collection | DSpace |
| description | The main attraction of PM steels related to automotive industry is to produce large number of parts of complex geometry with a net shape manufacturing approach achieving very tight dimensional tolerances without the need for secondary operations and using most of the raw material. The associated reduction of process costs makes PM steels very competitive in comparison with alternative processing and shaping methods. For the manufacturing of parts with this technology, it is necessary to know not only the microstructural events that induce the dimensional changes during sintering but also their relationship with the mechanical properties required for the material application. PM is consequently an economical way for obtaining a large number of components with high geometrical complexity in a single pressing operation. In order to avoid the costly set of precision tools needed, the powder blend is commonly pressed using relatively low pressures, which consequently results in attaining green densities between 6.1 - 6.8 g/cm3.
Linked to the dimensional changes this research work aims at gaining a deep understanding of the behavior and the redistribution kinetics of alloying elements during sintering. Special attention has been devoted to the study of the Fe-Cu-C system typically used by the PM industry for the manufacturing of shock absorber parts. For this matter, this study considers not only the influence of the chemical composition of the powder blend (Cu and C, wt%) but also different graphite grades (natural and synthetic) whose dissolution in Fe takes place at different temperatures. For comparison purposes, the Fe powder grade (sponge or atomized) has been another aspect taken into account in this study.
As Cu and Ni are commonly found in alloy systems for high demanding applications, the influence of Ni was also introduced preparing selected powder blends. The results show that the presence of Ni causes important alterations in the behavior of the material, particularly influencing events like Cu swelling and the redistribution of Cu and C during sintering. With these data, the mechanisms involving the interaction between Ni, Cu and C can therefore be determined. Hence, with this thesis it is expected to understand the micromechanisms involved in the microstructural development of steels within the Fe-Cu- Ni-C system to determine the role of these elements in the dimensional changes of the compact and their diffusion paths. To this aim, several factors must be considered both during sintering (temperature and time) and those related to compaction (density, particle size, Cu, Ni and C concentration, Fe base grade, etc.).
Firstly, dilatometry tests were carried out for different Fe-Cu-Ni-C combinations. Green compacts containing Cu, C and Ni within ranges 0.5-3.5%Cu, 0.3-0.9%C and 0, 1, 4, 10 and 28%Ni where die pressed for the sintering experiments. This technique is not used to quantify the exact dimensional change in the compact but to identify the most important features in the alloy system and relate them with the micromechanisms engaged. Moreover, as dilatometry is a helpful method to reveal the key temperatures where micromechanisms take place, then, interrupted sintering experiments for selected specimens have been done at those temperatures showing the microstructural development of the material. Mechanical properties and total dimensional change at the end of the cycle in a tridimensional measuring machine were also evaluated.
Complementarily, another study collaborating with PMG Polmetasa was carried out. PMG Polmetasa assumes the competence relative to marketing, development and manufacturing of the components for shock absorber applications being de biggest European producer of these components. Dimensional variation and quality of the final parts during process is mainly, if not entirely, a consequence of the events that occur at the sintering temperature. In this regard, a study comparing laboratory sintering conditions (extremely controlled conditions, same number of specimens in each cycle and controlled atmospheres with vacuum purges before de beginning of the sintering process, etc.) with industrial conditions (high productivity, changes in furnace mass depending on industrial objectives, etc.) is also performed. Based on the results obtaining in the laboratory, the study has been directly applied in an industrial part, particularly in a shock absorber component, to check them in the industrial scope. The outcome of this analysis is essential to guarantee the robustness of the sintering cycle. Along those lines, sintering window between 1100-1120 °C and within ranges 0 - 15 minutes of isothermal holding has been developed to optimize the process preserving a good relationship between microstructural development, control over dimensional changes and mechanical properties required in the material application. |
| format | info:eu-repo/semantics/doctoralThesis |
| id | oai:dadun.unav.edu:10171-44179 |
| institution | Universidad de Navarra |
| language | spa |
| publishDate | 2017 |
| publisher | Servicio de Publicaciones. Universidad de Navarra. |
| record_format | dspace |
| spelling | oai:dadun.unav.edu:10171-441792022-02-08T09:00:52Z Sinterización y dilatometría de aceros pulvimetalúrgicos para piezas de amortiguador. Bilbao-Varela, C.(Cristina) Castro-Fernández, F. (Francisco) Sainz-Rodríguez, S. (Shandra) Dilatometry. Liquid phase sintering. Cooper swelling. Desarrollo microestructural. Cambios dimensionales. Amortiguador. The main attraction of PM steels related to automotive industry is to produce large number of parts of complex geometry with a net shape manufacturing approach achieving very tight dimensional tolerances without the need for secondary operations and using most of the raw material. The associated reduction of process costs makes PM steels very competitive in comparison with alternative processing and shaping methods. For the manufacturing of parts with this technology, it is necessary to know not only the microstructural events that induce the dimensional changes during sintering but also their relationship with the mechanical properties required for the material application. PM is consequently an economical way for obtaining a large number of components with high geometrical complexity in a single pressing operation. In order to avoid the costly set of precision tools needed, the powder blend is commonly pressed using relatively low pressures, which consequently results in attaining green densities between 6.1 - 6.8 g/cm3. Linked to the dimensional changes this research work aims at gaining a deep understanding of the behavior and the redistribution kinetics of alloying elements during sintering. Special attention has been devoted to the study of the Fe-Cu-C system typically used by the PM industry for the manufacturing of shock absorber parts. For this matter, this study considers not only the influence of the chemical composition of the powder blend (Cu and C, wt%) but also different graphite grades (natural and synthetic) whose dissolution in Fe takes place at different temperatures. For comparison purposes, the Fe powder grade (sponge or atomized) has been another aspect taken into account in this study. As Cu and Ni are commonly found in alloy systems for high demanding applications, the influence of Ni was also introduced preparing selected powder blends. The results show that the presence of Ni causes important alterations in the behavior of the material, particularly influencing events like Cu swelling and the redistribution of Cu and C during sintering. With these data, the mechanisms involving the interaction between Ni, Cu and C can therefore be determined. Hence, with this thesis it is expected to understand the micromechanisms involved in the microstructural development of steels within the Fe-Cu- Ni-C system to determine the role of these elements in the dimensional changes of the compact and their diffusion paths. To this aim, several factors must be considered both during sintering (temperature and time) and those related to compaction (density, particle size, Cu, Ni and C concentration, Fe base grade, etc.). Firstly, dilatometry tests were carried out for different Fe-Cu-Ni-C combinations. Green compacts containing Cu, C and Ni within ranges 0.5-3.5%Cu, 0.3-0.9%C and 0, 1, 4, 10 and 28%Ni where die pressed for the sintering experiments. This technique is not used to quantify the exact dimensional change in the compact but to identify the most important features in the alloy system and relate them with the micromechanisms engaged. Moreover, as dilatometry is a helpful method to reveal the key temperatures where micromechanisms take place, then, interrupted sintering experiments for selected specimens have been done at those temperatures showing the microstructural development of the material. Mechanical properties and total dimensional change at the end of the cycle in a tridimensional measuring machine were also evaluated. Complementarily, another study collaborating with PMG Polmetasa was carried out. PMG Polmetasa assumes the competence relative to marketing, development and manufacturing of the components for shock absorber applications being de biggest European producer of these components. Dimensional variation and quality of the final parts during process is mainly, if not entirely, a consequence of the events that occur at the sintering temperature. In this regard, a study comparing laboratory sintering conditions (extremely controlled conditions, same number of specimens in each cycle and controlled atmospheres with vacuum purges before de beginning of the sintering process, etc.) with industrial conditions (high productivity, changes in furnace mass depending on industrial objectives, etc.) is also performed. Based on the results obtaining in the laboratory, the study has been directly applied in an industrial part, particularly in a shock absorber component, to check them in the industrial scope. The outcome of this analysis is essential to guarantee the robustness of the sintering cycle. Along those lines, sintering window between 1100-1120 °C and within ranges 0 - 15 minutes of isothermal holding has been developed to optimize the process preserving a good relationship between microstructural development, control over dimensional changes and mechanical properties required in the material application. El principal atractivo de los aceros PM dirigidos al sector de la automoción es la fabricación de piezas de geometría compleja de forma casi final con tolerancias dimensionales acotadas, evitando operaciones secundarias que encarezcan el proceso y aprovechando la mayor parte de la materia prima. La fabricación de piezas por esta tecnología requiere, por lo tanto, conocer las causas que producen los cambios dimensionales durante la sinterización, así como el desarrollo microestructural que finalmente confiere al material sinterizado las propiedades necesarias para su fabricación. Dentro de este marco, los utillajes tienen un papel muy importante a la hora de su diseño para la obtención de piezas compactadas en una sola operación de prensado, ya que pudiendo constar de múltiples elementos, son susceptibles de dañarse en funcionamiento. Con objeto de minimizar daños y evitar fracturas, generalmente se utilizan a bajas presiones, produciendo consecuentemente compactos en verde, que para el caso de elementos de amortiguador tienen densidades entre 6.1 y 6.8 g/cm3. Este trabajo recoge un estudio detallado del comportamiento de aceros pulvimetalúrgicos dentro del sistema de aleación Fe-Cu-C elaborados a partir de mezclas elementales. Para ello y debido a que típicamente los aceros PM, particularmente aquellos elaborados a partir de mezclas de polvos elementales, desarrollan su microestructura, y por consecuencia sus propiedades, durante la sinterización, el estudio considera no sólo la influencia de la composición química de la mezcla (concentraciones de Cu y C) sino también diferentes grados de grafito (natural y sintético) cuya temperatura de disolución en el Fe es diferente y dos tipos de Fe base (esponja y atomizado) que también influirán en el desarrollo microestructural. Adicionalmente, una vez comprendidos los mecanismos y el papel que desempeñan tanto el Cu como el C en el desarrollo de la microsestructura, se amplía el sistema de aleación al Fe- Cu-Ni-C con la intención de estudiar el papel del Ni dentro del sistema. Para ello, se obtienen resultados sobre la influencia del Ni tanto en el hinchamiento causado por el Cu como en la redistribución del Cu y C. Se analizan también los fenómenos que ocurren durante la interacción entre el Ni, Cu y C. El objetivo de esta tesis es contribuir al estudio de los micromecanismos involucrados en el desarrollo microestructural de los aceros dentro del sistema Fe-Cu-C. Se persigue determinar la influencia que ejercen tanto las variables del ciclo de sinterización (temperatura y tiempo) como aquellas relativas a la elaboración de los compactos (densidad, gradiente de densidad en verde, tamaño de partícula, concentración de Cu, tipo y cantidad de C y tipo de Fe base) sobre el control dimensional de estos. Los resultados se organizan recogiendo en primer lugar ciclos de dilatometría para diferentes combinaciones Fe-Cu-Ni-C con contenidos de Cu/C/Ni comprendidos en los rangos 0.5- 3.5%Cu, 0.3-0.9%C y 0,1,4,10 y 28%Ni, no con el fin de cuantificar la variación dimensional exacta sino para identificar los principales cambios que se dan en el sistema de aleación y relacionarlos con los micromecanismos que los producen. Además, las trazas de dilatometría sirven de gran ayuda para seleccionar las temperaturas clave donde se producen los micromecanismos más relevantes y, en segundo lugar, realizar ciclos de sinterización interrumpidos a esas temperaturas para observar su desarrollo microestructural. Se complementa el trabajo con ensayos de tracción y mediciones de dureza de todas las composiciones con el fin de determinar las propiedades mecánicas del material, así como los cambios dimensionales que se cuantifican utilizando un equipo de metrología tridimensional. Paralelamente, se realizó otro estudio en colaboración con la empresa PMG Polmetasa, cuya actividad se centra en la fabricación de componentes sinterizados para los amortiguadores de automóvil. En esta línea, el trabajo considera datos obtenidos de piezas fabricadas en las instalaciones industriales. Desde este punto de vista, en una primera etapa, se realizó un estudio comparativo entre sinterización en condiciones de laboratorio (condiciones más controladas al trabajar con un número reducido de probetas, hornos muy estables y atmósferas controladas) e industriales (elevada productividad, cambios de masa térmica en los hornos constantemente…etc.). A partir de aquí, se pasa a una segunda etapa con los conceptos obtenidos en el laboratorio para implementarlos el proceso industrial. Para ello, se seleccionó el pistón como componente representativo, que a modo de prototipo se empleó para verificar la aplicabilidad de los resultados en la práctica industrial. Tendente a la optimización del proceso, se hizo un análisis detallado de la sinterización en condiciones industriales manteniendo un adecuado desarrollo microestructural, un buen control sobre los cambios dimensionales y apropiadas propiedades mecánicas en el material. Los ciclos se realizaron a temperaturas entre 1100 °C y 1120 °C con incrementos de 5 °C y tiempos entre 0 y 15 minutos en intervalos menores a 5 minutos. 2017-10-19T07:22:27Z 2017-10-19T07:22:27Z 2017-10 2017-09-28 info:eu-repo/semantics/doctoralThesis https://hdl.handle.net/10171/44179 spa info:eu-repo/semantics/openAccess application/pdf Servicio de Publicaciones. Universidad de Navarra. |
| spellingShingle | Dilatometry. Liquid phase sintering. Cooper swelling. Desarrollo microestructural. Cambios dimensionales. Amortiguador. Bilbao-Varela, C.(Cristina) Castro-Fernández, F. (Francisco) Sainz-Rodríguez, S. (Shandra) Sinterización y dilatometría de aceros pulvimetalúrgicos para piezas de amortiguador. |
| title | Sinterización y dilatometría de aceros pulvimetalúrgicos para piezas de amortiguador. |
| title_full | Sinterización y dilatometría de aceros pulvimetalúrgicos para piezas de amortiguador. |
| title_fullStr | Sinterización y dilatometría de aceros pulvimetalúrgicos para piezas de amortiguador. |
| title_full_unstemmed | Sinterización y dilatometría de aceros pulvimetalúrgicos para piezas de amortiguador. |
| title_short | Sinterización y dilatometría de aceros pulvimetalúrgicos para piezas de amortiguador. |
| title_sort | sinterización y dilatometría de aceros pulvimetalúrgicos para piezas de amortiguador. |
| topic | Dilatometry. Liquid phase sintering. Cooper swelling. Desarrollo microestructural. Cambios dimensionales. Amortiguador. |
| url | https://hdl.handle.net/10171/44179 |
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