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Two different ferritic stainless steels (AISI 409Nb and 434L) with different Cr level were manufactured through powder metallurgical techniques. These sintered steels are typically used for exhaust pipes and turbochargers. Both materials were uniaxially compacted and then vacuum sintered at 1225 and 1275 ºC respectively. Microstructural features and physical properties (density, porosity) of as sintered materials were examined. Oxidation performance was evaluated through isothermal experiments in air and thermogravimetry techniques. Global weight gains are very similar for both steels in isothermal tests carried out at 700, 800 and 900 ºC for 240 h. However, oxidation at 1000 ºC is different for both steels. X-ray diffraction and scanning electron microscopy allow to explain the differences of kinetics in base of composition of scale layers. Finally, thermogravimetry gives information regarding the kinetics of oxidation processes.

Non-commercial, 434L ferritic stainless steel powders prealloyed with 2% of Si were uniaxially compacted at 700 MPa and sintered in 100% H2 atmosphere for 30 min at three different temperatures (1225, 1250 and 1275 °C). For comparison, standard, commercial 434L powders were sintered in the same conditions, and 434L+2%Si powders were also sintered in vacuum. The porosity and grain size of the 9 sintered stainless steels were measured by image analysis methods. Tensile strength and Vickers hardness tests show that the steels with 2% of Si exhibit higher mechanical properties. Oxidation tests were carried out in air at 800 and 900 °C. H2-sintered 434L steels prealloyed with Si exhibit higher weight gains per unit of apparent surface than 434L steels sintered in the same conditions, due to the higher porosity of the former. The sintering atmosphere affects the nature and morphology of the scales observed by XRD and SEM. Vacuum sintering of 434L+2%Si stainless steels promotes the formation of more protective scales and lower mass gains (for identical porosity volume) than H2 sintering.