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Surface and bulk oxygen in Super Duplex Stainless steel powder

  • : Björn-Olof Bengtsson1
  • : 1Carpenter Powder Products AB
  • : PDF Download
  • : 2014

Abstract

On each powder particle the oxygen is located in two areas. On the surface is a thin oxide layer formed by oxidation of the surface. This oxygen is coming from the oxidation by the atmosphere. The oxygen that was dissolved in the liquid metal prior to atomization is due to the rapid solidification forming an evenly distributed mass of small oxides inside the particle and this is the bulk oxygen. An investigation has been done to measure and calculate the amount of oxygen on the surface and in the bulk. The thickness of the surface oxidized layer was measured and the amount of surface oxygen estimated with regards to composition, density and thickness. The surface oxide thickness was found to be constant with no influence of particle size. The contribution of surface oxygen to total oxygen is then depending on the total powder surface area, less surface area per volume is achieved by increasing powder particle size. The normal variation in surface oxygen is within XX ppm and no proven influence on impact strength was found. This level of surface oxygen corresponds to the naturally formed surface oxidation due to the chemistry of the Super Duplex Stainless steel. Conclusion is that on Super Duplex Stainless steel the total oxygen influence impact strength. The surface oxide layer thickness is constant and determined by the chemistry. During any handling of the powder in air a constant surface oxygen level will be achieved corresponding to the same amount as normally comes out of CPP AB´s powder production. To decrease the contribution of surface oxygen to the total oxygen a coarser powder needs to be used.
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