Equilibrium studies in the Co-Cr-C system : Solubility of Cobalt in M23C6 and M3C2

• Main Authors: Ekström, Karin, Kordbache, Shanar
• Format: Others
• Language: English
• Published: KTH, Materialvetenskap 2011
• Subjects: Other materials science; Övrig teknisk materialvetenskap
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-37914

This project concerns cemented carbides and the carbides that are formed when adding chromium. Cemented carbides are composites, often consisting of tungsten-carbide particles embedded in a cobalt-rich matrix, and are because of their extreme hardness used in for example cutting tools and drills. Chromium is sometimes added when making cemented carbides in order to lower the melting point, reduce grain growth and/or increase corrosion resistance. When adding chromium there is a risk of forming unwanted carbides such as M 23C6, M7C3and M3C2. It is therefore of great interest to know the stability of these carbides. The purpose of this work was to investigate the solubility of Co in M23C6 and M3C2by equilibrium studies. The aim was to produce samples equilibrated in the three-phase regions between liquid‐M23C6‐M7C3 and M3C2‐M7C3‐graphite, to study the solubility of Co in M23C6 and M3C2 respectively. Initial studies were performed at Sandvik Mining and Construction (SMC) to determine the compositions of the samples to be produced and temperatures for the heat treatments. The alloys were heat‐treated at 1450⁰C for three days and were thereafter investigated with LOM and XRD. The work was carried out in collaboration with Sandvik Mining and Construction (SMC). It was difficult to analyze the results with XRD since the intensity peaks in the diffractograms are close or overlapping for the M23C6 and M7C3 carbides. The solubility of Co in M23C6 could not be investigated accurately. The M3C2-M7C3‐graphite sample did not reach equilibrium in the three days of heat treatment. The conclusions that can be drawn from this project are that further work, using longer annealing times, has to be done in order to get more knowledge about the Co solubility in M23C6 and M7C3 carbides.