矽與鋁對界面析出強化鋼之碳化物析出行為與肥粒鐵相變動力學影響

Abstract

眾多的鋼鐵材料中都會添加一些合金元素來達到所要求的強度、韌性等機械性質。其中矽與鋁為常見的合金元素，皆為肥粒鐵相穩定元素。本實驗中仍有鈦與鉬在肥粒鐵相基地析出奈米碳化物以進行界面析出強化。因此，本研究目的在於探討添加矽與鋁在界面析出強化鋼材中所產生的交互作用。 除了改變合金元素外，藉由不同的熱處理，鋼材也可以有不同的特性。隨著兩相持溫溫度的降低，晶粒尺寸下降且硬度上升；隨著沃斯田鐵化溫度的提高，普遍晶粒尺寸皆上升但硬度仍然提高。藉由穿透式電子顯微鏡的觀察，在較高的沃斯田鐵化溫度，具有密集的界面析出碳化物。此界面析出碳化物的變化透過換算而得之貢獻強度也因變密集而上升，使鋼材更為堅固。 取代部分矽為鋁添加於鋼鐵材料中，也造成不同的效果。鋁對於肥粒鐵的生長具有明顯的加速作用，不僅透過金相可以觀察此特性之外，也反映在相變曲線上。有添加鋁的鋼鐵材料會使相變曲線往左移動，使整體相變態反應提早。而矽的添加對於肥粒鐵相的固溶強化有顯著的影響，且可以使肥粒鐵相區擴大，但在高溫時傾向析出大尺寸的碳化物，影響界面析出強化機制之削弱。

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.