| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 89 === In this work, the phase transformations under three different heat treatments (continuous cooling, isothermal and up-quench processes) have been carried out in a modified 2.25Cr-1Mo steel.
In continuous cooling process, the effect of the different austenitizing temperature on continuous cooling transformation has been investigated. The result shows that the lower austenitization temperature promote the bainitic reaction and that the higher austenitization temperature favors the martensitic reaction.
In isothermal process, The effect of the different amount of plastic deformation on the bainitic transformation has been studied. The result shows that the total amount of bainitic ferrite transformation decreases with increasing defromation and that Bainitic transformation start temperature (Bs) in this steel is about 580℃.
In up-quench process, the bainite which formed during isothermal heat treatment was immediately tempered. On optical metallographs, decomposed-bainite shows dark region. The result gives evidence to suggest that severe deformation leads to mechanical stabilization of austenite against bainitic reaction.
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