Abstract
The success of semi-solid metal processing mostly depends on the formation of suitable starting microstructure, which must consist of solid metal spheroids in a liquid matrix. Various methods of obtaining this structure have been established; they include recrystallisation and partial melting (RAP), strain-induced melt-activated (SIMA), or simple mechanical stirring, to name a few. These methods, as widely discussed, have mostly been applied with light alloys, mainly aluminium based. This article discusses solid–liquid structural break-up in M2 tool steel subjected to a direct re-melting procedure from the as-annealed condition. The role of carbide dissolution in the grain boundary liquation of the steel is described. This leads to the production of near spheroidal solid grains in a liquid matrix, a microstructure suitable for the thixoforming process. Microstructural examination revealed that carbide particles contained in bands at 1220 °C slowly disappeared with temperature. At 1300 °C, the solid grains seemed to be free from carbides. Most of the carbides had now re-precipitated at the grain boundaries. Thixoforming carried out at 1340 and 1360 °C revealed the thixotropic properties of the semi-solid metal slurries. The results indicate a widening of the range of potential routes to thixoformable microstructures.
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Acknowledgements
The authors wish to thank Universiti Kebangsaan Malaysia (a.k.a National University of Malaysia), Malaysia, for financial assistance, and the University of Sheffield, UK, for the provision of laboratory facilities.
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Omar, M.Z., Atkinson, H.V., Howe, A.A. et al. Solid–liquid structural break-up in M2 tool steel for semi-solid metal processing. J Mater Sci 44, 869–874 (2009). https://doi.org/10.1007/s10853-008-3181-1
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DOI: https://doi.org/10.1007/s10853-008-3181-1