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Title: Surface phenomena during the early stages of sintering in steels modified with Fe–Mn–Si–C master alloys

The characteristics of the metallic powder surface play a critical role in the development of strong bonds between particles during sintering, especially when introducing elements with a high affinity for oxygen. In this study, Mn and Si have been combined in a Fe–Mn–Si–C master alloy powder in order to reduce their chemical activity and prevent oxidation during the heating stage of the sintering process. However, when this master alloy powder is mixed with an iron base powder, differences in chemical activity between both components can lead to an oxygen transfer from the iron base powder to the surface of the master alloy particles. The present research is focused on studying the evolution of the master alloy particle surface during the early stages of sintering. Surface characterization by X-ray Photoelectron Spectroscopy (XPS) shows that the master alloy powder surface is mostly covered by a thin easily reducible iron oxide layer (∼ 1 nm). Mn–Si particulate oxides are found as inclusions in specific areas of the surface. Evolution of oxides during sintering was studied on green compacts containing iron powder, graphite and Fe–Mn–Si–C master alloy powder that were heat treated in vacuum (10{sup −6} mbar) at different temperatures (from 400, 600, 800more » to 1000 °C) and analyzed by means of XPS. Vacuum sintering provides the necessary conditions to remove manganese and silicon oxides from the powder surface in the range of temperatures between 600 °C and 1000 °C. When sintering in vacuum, since the gaseous products from reduction processes are continuously eliminated, oxidation of master alloy particles due to oxygen transfer through the atmosphere is minimized. - Highlights: • Mn and Si were introduced in sintered steels using a master alloy powder. • Surface of the master alloy is mainly covered by an easily reducible iron oxide. • Temperature ranges for oxidation/reduction are identified. • Vacuum conditions avoid oxygen transfer to oxidation sensitive elements. • Chemical activity of Mn and Si is lowered when combined in a form of master alloy.« less
Authors:
 [1] ;  [2] ;  [1] ;  [2] ;  [3] ;  [1]
  1. Department of Materials and Manufacturing Technology, Chalmers University of Technology, Rännvägen 2A, SE-41296 Gothenburg (Sweden)
  2. Department of Materials Science and Engineering, IAAB, Universidad Carlos III de Madrid, Av. Universidad 30, 28911 Leganés, Madrid (Spain)
  3. (Spain)
Publication Date:
OSTI Identifier:
22288691
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Characterization; Journal Volume: 86; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; GRAPHITE; HEAT TREATMENTS; IRON OXIDES; LAYERS; MANGANESE; POWDERS; SILICON OXIDES; SINTERING; STEELS; SURFACES; X-RAY PHOTOELECTRON SPECTROSCOPY