Navegando por Autor "Haut, Christian"

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    Comparative study of high temperature oxidation behaviour in AISI 304 and AISI 439 stainless steels.
    (2003) Sabioni, Antônio Claret Soares; Huntz, Anne Marie; Luz, Elizete Conceição da; Mantel, Marc; Haut, Christian
    This work deals with a comparison of high temperature oxidation behaviour in AISI 304 austenitic and AISI 439 ferritic stainless steels. The oxidation experiments were performed between 850 and 950 °C, in oxygen and Ar (100 vpm H2). In most cases, it was formed a Cr2O3 protective scale, whose growth kinetics follows a parabolic law. The exception was for the the AISI 304 steel, at 950 °C, in oxygen atmosphere, which forms an iron oxide external layer. The oxidation resistance of the AISI 439 does not depend on the atmosphere. The AISI 304 has the same oxidation resistance in both atmospheres, at 850 °C, but at higher temperatures, its oxidation rate strongly increases in oxygen atmosphere. Concerning the performance of these steels under oxidation, our results show that the AISI 439 steel has higher oxidation resistance in oxidizing atmosphere, above 850 °C, while, in low pO2 atmosphere, the AISI 304 steel has higher oxidation resistance than the AISI 439, in all the temperature range investigated.
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    Oxidation of AISI 304 and AISI 439 stainless steels.
    (2007) Huntz, Anne Marie; Reckmann, A.; Haut, Christian; Sévérac, C.; Herbst, M.; Resende, Fernando César Teixeira; Sabioni, Antônio Claret Soares
    The oxidation behaviour of AISI 304 and AISI 439 stainless steels was studied at high temperatures, under various oxygen pressures and in the presence or not of water vapour. Thermogravimetric analyses were conducted in isothermal conditions from 850 to 950 ◦C for 50 h and microstructural and chemical analyses of the oxide films grown by oxidation were performed by SEM and EDX. The oxide films were also analysed by grazing X-ray diffraction and by X photoelectron spectroscopy (XPS). The AISI 439 steel has higher oxidation resistance than AISI 304, above 850 ◦C, under high oxygen pressures. On the other hand, the AISI 304 steel has higher oxidation resistance under low oxygen pressures in the whole temperature range. In order to check whether the growth kinetics of Cr2O3 formed by the oxidation of stainless steels was controlled by oxygen or/and chromium diffusion through the oxide film, the oxidation constants were theoretically calculated on the basis of diffusion data using Wagner’s Theory. The calculated values of the oxidation constants agree reasonably well with experimental values, therefore confirming the role of diffusion processes on the growth of chromia on stainless steels.