Semisolid Microstructure Evaluation of M2 High Speed Steel by Cooling Slope and Rolled - Annealed

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Amin Ahmadi, Behnam | 2009

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Type of Document: M.Sc. Thesis
Language: Farsi
Document No: 39697 (07)
University: Sharif University of Technology
Department: Materials Science and Engineering
Advisor(s): Aashuri, Hossein
Abstract:
In this research the effects of cooling slope angle and the temperature of molten steel on globular structure after holding the samples at semisolid state have been investigated. The globular structure of high speed steel in the form of rolled - annealed and as cast condition, has been investigated in the semisolid state. The results showed that the grain sizes of cooling slope samples were lower than the rolled- annealed samples after holding at semisolid temperature. On the other hand, rolled-annealed solid grains had better roundness compared with cooling slope samples. Dissolution of carbides in the austenite phase at grain boundary leads to formation of globular particles in the semisolid state. MC- type and M6C- type eutectic carbides reprecipitate during cooling cycle at grain boundaries. Variation of shape factor versus holding time and holding temperature were also investigated. The values of Ostwald ripening and coalescence constant calculated by use of Kexp.. The activation energy of austenite grains was also calculated.
Keywords:
Growth Rate ; Semi-Solid Processing ; M2 Tool Steel ; Shape Factor ; Globular Microstructure ; Eutectic Carbides

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