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Advances in Materials Science and Engineering
Volume 2013 (2013), Article ID 789373, 16 pages
http://dx.doi.org/10.1155/2013/789373
Research Article

Parameters Controlling the Oxide Reduction during Sintering of Chromium Prealloyed Steel

1Institute of Materials Research of SAS, Watsonova 47, 040 01 Košice, Slovakia
2Department of Materials and Manufacturing Technology, Chalmers University of Technology, Rännvägen 2A, 412 96 Göteborg, Sweden
3University of Veterinary Medicine and Pharmacy, Komenskeho 73, 041 81 Košice, Slovakia

Received 21 May 2013; Accepted 28 August 2013

Academic Editor: Jörg M. K. Wiezorek

Copyright © 2013 Monika Hrubovčáková et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Temperature intervals of oxide reduction processes during sintering of the Fe-3%Cr-0.5%Mo prealloyed powder using continuous monitoring of processing-exhaust gas composition (CO, CO2, and H2O) were identified and interpreted in relation to density (6.5–7.4 g/cm3), sintering temperature (1120 and 1200°C), heating and cooling rates (10 and 50°C/min), carbon addition (0.5/0.6/0.8%), type (10%H2-N2, N2), and purity (5.0 and 6.0) of the sintering atmosphere. The progress in reduction processes was evaluated by oxygen and carbon contents in sintered material and fracture strength values as well. Higher sintering temperature (1200°C) and density <7.0 g/cm3 resulted in a relative decrease of oxygen content by more than 80%. The deterioration of microclimate purity of inner microvolumes of compacts shifted the thermodynamic equilibrium towards oxidation. It resulted in a closing of residual oxides inside interparticle necks. The reducing ability of the N2 atmosphere can be improved by sintering in a graphite container. High density of 7.4 g/cm3 achieved by double pressing indicated a negative effect on reduction processes due to restricted replenishment of the microclimate atmosphere with the processing gas. In terms of strength properties, carbon content should not be higher than ~0.45%.