Effect of the Si Additions on the Mechanical Behaviour and High-Temperature Performance of Hydrogen Sintered 434L Stainless Steels

Abstract

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.