Inter-particle connections development during sintering of Cr-Mo-alloyed steel powder in N2/H2 atmosphere

Examensarbete för masterexamen

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Type: Examensarbete för masterexamen
Master Thesis
Title: Inter-particle connections development during sintering of Cr-Mo-alloyed steel powder in N2/H2 atmosphere
Authors: Calderon, Maria Irene de Diego
Abstract: Powder metallurgy is one of the oldest metal processing techniques; it is a manufacturing process that is based on the production of metal, ceramic or composite components from powders. Manufacturing of ferrous powder metallurgy precision parts has increased in the last decades, in particular for automotive applications. The properties of a component manufacture by PM techniques may be tailored or improved by the addition of alloying elements; chromium and molybdenum are widely used in conventional metallurgy as alloying elements, but the tendency of chromium to form stable oxides and the decrease in compressibility it produces, have restricted its use in powder metallurgy. However, low chromium alloyed steels meet all the requirements for most structural components and for the market needs, so research and development of these steels is being carried out nowadays. In this study, specimens of the same composition (pre-alloyed water atomized powder of low Cr-Mo content) were sintered in a 90N2/10H2 atmosphere during 3 minutes and at different temperatures from 700°C to 1120°C. Two additional samples were sintered at 1120°C during 15 and 30 minutes each. Impact test was performed in all the specimens in order to produce fracture surfaces, which were studied using High Resolution Scanning Electron Microscopy (HRSEM) and EDX analysis. Microstructural investigation was carried out as well. The objective of this investigation was to evaluate the effect of the sintering temperature and time on both the inter-particle necks development and the inclusions evolution. It was found that Inter-particle necks development is enhanced with sintering temperature and time and that the reduction of the Fe-oxide layer on the powder particles is a pre-condition for the formation of solid metallic contacts. Furthermore, different failure mechanisms were found with increasing sintering temperature. It was also found that the morphology and size of the inclusions change with increasing sintering temperature and time.
Keywords: Materialteknik;Ytbehandlingsteknik;Materials Engineering;Surface engineering
Issue Date: 2009
Publisher: Chalmers tekniska högskola / Institutionen för material- och tillverkningsteknik
Chalmers University of Technology / Department of Materials and Manufacturing Technology
Collection:Examensarbeten för masterexamen // Master Theses

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