Abstract
The subject of this work was the study of processes occurring during sintering of water atomized AISI 316L austenitic stainless steel powder modified by the addition of graphite nanoparticles. The main purpose of the work was to determine the effect of modification of the AISI 316L stainless steel austenitic powder by the addition of graphite nanopowder on the sintering kinetics and oxide reduction mechanism. The phenomena occurring during the sintering process and oxide reduction mechanisms were subjected to detailed characterizations. Mixtures with two types of nanopowder with a high BET (measurement technique of the specific surface area of materials based on Brunauer–Emmett–Teller theory) specific surface area of 350 and 400 m2/g and for comparison with graphite micropowder with a poorly developed BET specific surface area of 15 m2/g were tested. The conducted thermal analysis showed that the samples made of austenitic stainless steel doped with 0.2% and 0.3% by weight graphite nanopowder with a BET specific surface area of 400 m2/g, sintered best the oxide reduction reactions, with a more intensive participation of carbon, for these samples.
Highlights
Powder metallurgy is a technology involving the production of metallic powders and products from these powders and their mixtures with non-metals or with alloy or partially alloyed powders, using forming and sintering processes
Graphite powders differing in the degree of BET specific surface area of particles were used in the tests
Graphite during the sintering process acts as an activator of the reduction reaction of the oxide coating covering particles of the tested steel
Summary
Powder metallurgy is a technology involving the production of metallic powders and products from these powders and their mixtures with non-metals or with alloy or partially alloyed powders, using forming and sintering processes. In the case of stainless steel powders, the necessary condition for starting the sintering process is the reduction of the oxide coating formed on the surface of the powder particles. AISI 316L stainless steel owes its very good corrosion resistance to high chromium and molybdenum content. Chromium oxides—Cr2 O3 forming a coherent layer protecting the surface of powder particles against corrosion are classified as very stable and difficult to reduce oxides. Molybdenum oxides increase the corrosion resistance of steel under operating conditions at elevated temperatures [9,10,11,12,13,14,15,16]. Silicon oxide—SiO2 is another very stable oxide that must be removed during sintering These oxides in austenitic stainless steels are a residue from the Materials 2020, 13, 4569; doi:10.3390/ma13204569 www.mdpi.com/journal/materials
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