| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 105 === In steel, it will be added some alloy elements to improve its strength, toughness. mechanical properties. Silicon and Aluminum are the common alloy elements in it. They both are ferrite stabilizer elements. In this study, there are titanium and molybdenum which precipitate nanometer carbides to interphase-precipitated strengthen in materials. Consequently, the goal of this study is to discuss the interaction of interphase precipitation strengthened steels with the addition of silicon and aluminum.
Through the different heat treatment, we also can observe different characteristics of steel. By dual-phase holding temperature lowing, the grain size becomes small and harder; by increasing austenitization temperature, grain size generally increases but the values of hardness also increases. Through transmission electron microscope, there are intense interphase-precipitated carbides in steel at the higher austenitization temperature, and it contributes more strength to steel, becomes stronger.
Replacing some silicon by aluminum can give rise to different effect. The aluminum can accelerate the growth of the ferrite. It is not only can be observed by optical microscope but also in TTT curve. The TTT curve will move to the left when adding aluminum to steel. The aluminum can make the whole phase transformation earlier. On the other hand, the silicon has an outstanding influence of solid solution strengthening and makes the phase region of ferrite bigger. However, it tends to precipitate big size carbides at high temperature and to weaken the mechanism of interphase precipitation strengthening.
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