Publication: Nuevos aceros inoxidables dúplex fabricados por vía pulvimetalúrgica mediante sinterización asistida por campo eléctrico
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2016-10
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2016-10-27
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Abstract
El principal objetivo de este trabajo de investigación es determinar la viabilidad de los aceros inoxidables dúplex procesados por vía pulvimetalúrgica utilizando una técnica de sinterización asistida por campo eléctrico (Field-Assisted Sintering Technique, FAST). Mediante esta técnica de menor activación térmica y mayor velocidad de calentamiento y enfriamiento, se podría evitar la formación de fases frágiles. Se estimará la competitividad de estos nuevos aceros inoxidables dúplex en el mercado actual de los aceros. Por otro lado, se ha conseguido limitar con éxito el espesor de una zona de interdifusión entre las fases ferríticas y austeníticas, de la cual hay información en la literatura para el caso de aceros inoxidables dúplex sinterizados de manera tradicional y con contenidos en austenita superiores al 50 % en peso. Esta tercera fase es el resultado de la difusión durante un tiempo limitado de elementos de aleación, entre los que se encuentran principalmente el Ni y el Cr.
Por lo tanto, en este proyecto se diseñan tres aceros inoxidables dúplex usando como materia prima dos polvos atomizados en gas, uno inoxidable austenítico (316L) y otro ferrítico (430L). Con el fin de incrementar la tenacidad y la resistencia a corrosión de estos aceros, la cantidad de austenita es siempre superior a 70 % en peso. Por consiguiente, se mezclan los polvos en una túrbula con el siguiente diseño de composición (% en peso):
- Dúplex 1: 70 % AISI 316L – 30 % AISI 430L.
- Dúplex 2: 80 % AISI 316L – 20 % AISI 430L.
- Dúplex 3: 90 % AISI 316L – 10 % AISI 430L.
Para evaluar viabilidad de los tres aceros inoxidables dúplex sinterizados por una técnica FAST, se consolidan los mismos por compactación asistida por campo eléctrico, que es una técnica basada en la aplicación simultánea de corriente alterna y presión para calentar las muestras por efecto Joule.
Los aceros consolidados se analizan microestructuralmente y composicionalmente mediante Microscopía Electrónica de Barrido (MEB) unido al Análisis de Energía Dispersiva por rayos X. Además, se determinan sus propiedades mecánicas por nanoindentación y ensayos de tracción. Los resultados evidencian que se obtiene una densidad casi total, con una estructura homogénea y una baja porosidad. Estas características microestructurales conducen a unas magníficas propiedades mecánicas, en particular en el Dúplex 1, con un 70 % de porcentaje en peso de austenita.
The main objective of this research is to determine the viability of processing duplex stainless steels (DSS) by a powder metallurgy (PM) route, including the use of a Field-Assisted Sintering Technique (FAST). The use of this technique , in which lower thermal activation values and higher cooling rates than in traditional PM techniques are involved, may lead to the suppression of the brittle phases. The competitiveness of these novel DSS, with respect to those being currently commercialised in the market, will be estimated. Furthermore, the thickness of an interface located between the ferrite and the austenite phases, which was reported in the literature in the case of DSS sintered by traditional ways and with an austenitic content superior to 50 wt. %, is successfully limited in the present work. This phase is the result of a limitation in the time available for the diffusion of the alloying elements, mainly Ni and Cr, which are the principal contributors to the existence of this third phase. Thus, in this investigation three new DSS are designed using commercial gas atomised austenitic (AISI 316L) and ferritic (430L) stainless steel powders as raw materials. In order to increase the toughness and the corrosion resistance of DSS, the quantity of austenite introduced is always higher than 70 wt. %. Therefore, the powders were mixed in a turbula mixer following the next designed compositions (in wt. %): - Duplex 1: 70 % AISI 316L – 30 % AISI 430L. - Duplex 2: 80 % AISI 316L – 20 % AISI 430L. - Duplex 3: 90 % AISI 316L – 10 % AISI 430L. To assess the viability of sintering these duplex stainless steels by a FAST technique, the consolidation is performed by Field-Assisted Hot Pressing, which is a technique based on the simultaneous application of an alternating current and a pressure to heat the sample by a Joule effect. The FAHP-DSS are microstructurally and compositionally analysed by Scanning Electron Microscopy (SEM) coupled to Energy Dispersive X-ray analysis (EDX). Moreover, their mechanical properties are determined by nanoindentation and tensile tests. The results highlight that almost full-density consolidated samples are obtained, with homogenous microstructure and low porosity. These microstructural characteristics lead to outstanding mechanical properties, in particular in the case of the Duplex 1, with 70 wt. % of austenitic phase.
The main objective of this research is to determine the viability of processing duplex stainless steels (DSS) by a powder metallurgy (PM) route, including the use of a Field-Assisted Sintering Technique (FAST). The use of this technique , in which lower thermal activation values and higher cooling rates than in traditional PM techniques are involved, may lead to the suppression of the brittle phases. The competitiveness of these novel DSS, with respect to those being currently commercialised in the market, will be estimated. Furthermore, the thickness of an interface located between the ferrite and the austenite phases, which was reported in the literature in the case of DSS sintered by traditional ways and with an austenitic content superior to 50 wt. %, is successfully limited in the present work. This phase is the result of a limitation in the time available for the diffusion of the alloying elements, mainly Ni and Cr, which are the principal contributors to the existence of this third phase. Thus, in this investigation three new DSS are designed using commercial gas atomised austenitic (AISI 316L) and ferritic (430L) stainless steel powders as raw materials. In order to increase the toughness and the corrosion resistance of DSS, the quantity of austenite introduced is always higher than 70 wt. %. Therefore, the powders were mixed in a turbula mixer following the next designed compositions (in wt. %): - Duplex 1: 70 % AISI 316L – 30 % AISI 430L. - Duplex 2: 80 % AISI 316L – 20 % AISI 430L. - Duplex 3: 90 % AISI 316L – 10 % AISI 430L. To assess the viability of sintering these duplex stainless steels by a FAST technique, the consolidation is performed by Field-Assisted Hot Pressing, which is a technique based on the simultaneous application of an alternating current and a pressure to heat the sample by a Joule effect. The FAHP-DSS are microstructurally and compositionally analysed by Scanning Electron Microscopy (SEM) coupled to Energy Dispersive X-ray analysis (EDX). Moreover, their mechanical properties are determined by nanoindentation and tensile tests. The results highlight that almost full-density consolidated samples are obtained, with homogenous microstructure and low porosity. These microstructural characteristics lead to outstanding mechanical properties, in particular in the case of the Duplex 1, with 70 wt. % of austenitic phase.
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Keywords
Aceros inoxidables, Pulvimetalurgia, Field-Assisted Sintering Technique (FAST), Sinterización