隨著現代經濟的發展，對於鋼鐵品質的要求愈來愈高。細化晶粒是能夠同時提升鋼鐵韌性及強度的唯一方法。而細小分散的高熔點介在物可用來誘導IGF的成核及抑制晶粒成長，因此透過介在物改質來獲得所需介在物變得更加重要。
本研究以 SM570 鋼種實際鋼液成分進行熱力學平衡計算，獲得 1873 K 條件下該鋼種的Mg、Al、Ti、O之間的熱力學平衡關係圖；計算結果顯示，Mg、Al、Ti之脫氧能力依次減弱； MgO、MgAl2O4、Al2O3在鋼液中的存在形態與鋼液中平衡的 Mg、Al、O 含量密切相關。並同時針對此鋼種進行加鎂實驗，之後對原始鋼種及不同鎂添加量之試樣進行分析。
實驗結果顯示在當前鋼液成分下向鋼液中添加微量 Mg 就可以使介在物實現改質，且對於介在物平均粒徑的減小有良好的效果，並得知隨著鎂添加量增加的介在物變性路徑為 Al2O3→ Spinel (Al2O3•MgO) →MgO。本研究最後所得到之結果為：在當前鋼液成分下添加 5.45 ppm Mg 時可以達到介在物改質的最佳效果，其介在物之平均粒徑最小、單位面積所含之介在物數量最多且可生成尺寸較小之 Spinel。

With the modern economic development, the demand of the steel quality is getting higher and higher. Grain refinement is the only way to enhance the toughness and strength of the steel at the same time. Because high melting point and small dispersed inclusions can be used to induce nucleation of IGF and inhibit the grain growth, using the modification of inclusions to obtain the desired inclusions become more and more important.
In this study, the chemical compositions of SM570 are used for thermodynamic equilibrium calculations to obtain the thermodynamic equilibrium diagrams among Mg, Al, Ti, and O. The calculated results show the relation among the state of MgO, MgAl2O4, and Al2O3 are closed to the equilibrium contents of Mg, Al, and O in the liquid steel. In the experimental process, different amounts of magnesium were added to the original SM570 samples, and then all the samples are analyzed.
Experimental results show that as long as adding a small amount of magnesium to the SM570 under the current chemical composition, the modification of the inclusions can be achieved. After the magnesium addition, the average particle size of the inclusions are decreased effectively. And with the increase of the magnesium addition, the path of the modification for inclusion is: Al2O3 → Spinel (Al2O3•MgO) → MgO.
Finally, considering the smallest average particle size of the inclusions, the most number of the inclusions contained in the unit area, and the generation of the small size Spinel, it shows that with the 5.45ppm magnesium addition , the best modified results of the inclusions can be achieved under the current chemical composition of SM570 steel.

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