近年來現代建設朝高層化、大跨距發展，因此需要高強度與高厚度的結構鋼板。此外，在接合過程中為了提高銲接效率，必須在銲接時，導入大量的熱量，但高入熱量銲接熱影響區會導致晶粒粗大，鋼中晶粒粗大是造成韌性及強度下降的主要原因，透過介在物與基底微結構的改質，可提升鋼鐵其強度及韌性。
利用介在物增加熱影響區(HAZ)鋼鐵的韌性，主要有兩個方式:1.抑制沃斯田鐵晶粒成長，2.促進晶內(針狀)肥粒鐵的形成。第一在鋼中控制介在物的尺寸及數量，在高溫銲接過程中，沃斯田鐵晶粒成長，介在物會限制晶界移動，達到晶粒細化的效果。第二針狀肥粒鐵可在介在物異質成核成長，在晶中形成針狀肥粒鐵，達到晶內細化的效果，來提升鋼鐵中韌性及強度。
本研究實驗主軸分為兩部分，其一藉由模擬銲接過程的熱影響區，計算出沃斯田鐵晶粒尺寸與時間之關係，其二模擬不同冷卻速率，來觀測針狀肥粒鐵微結構及計算析出的比例。
取熱處理後試片以OM做微結構初步觀察，以場發射式SEM-EDS做介在物成分分析，搭配Electron Back Scattering Diffraction (EBSD)與OIM軟體中的KAM數值分析針狀肥粒鐵差排密度與IQ(Image quality)計算針狀肥粒鐵相比例。
實驗結果，熱處理條件為T1400-A與T1200-A的兩種試片的針狀肥粒鐵體積分率分別為26%與17%。T1400沃斯田鐵晶粒尺寸為105μm，T1200為26μm。綜合上述，沃斯田鐵晶粒尺寸增加，針狀肥粒鐵的生成也會增加。使用EBSD技術做Kernel average misorientation 數值分析，針狀肥粒鐵為0.35，肥粒鐵為0.2;並做介面間匹配度鑑定，結果顯示含Al及Si的介在物與針狀肥粒鐵間為不連續整合介面。

The study is divided into two parts experiment, first one is simulation of the heat affected zone of welding process and calculate the equation of austenite grain size and holding time. Second, simulate the different cooling rate and observe the acicular ferrite and calculate the volume proportion of each phase. The heat treatment process was designed to get the proper microstructure. OM analysis was checked the AF structure. EDS analysis identify the inclusion type. EBSD reconfirm the AF structure. By heat treatment experiment to simulate HAZ and observe growth of austenite grain size, we can construct the austenite grain growth equation of austenite grain size v.s holding time. Simulating various cooling rates, we can find that most appropriate cooling rate for the formation of acicular ferrite is air cooling. AF has a characteristic that the value of KAM will be relatively large, and the peak value at around 0.4.

[1] 羅新傑, "結構用鋼胚中介在物之研究," 國立成功大學材料科學及工程學系碩士論文, 2012.
[2] H. Flower and T. Lindley, "Electron backscattering diffraction study of acicular ferrite, bainite, and martensite steel microstructures," Materials Science and Technology, vol. 16, pp. 26-40, 2000.
[3] Y. M. Kim, H. Lee, and N. J. Kim, "Transformation behavior and microstructural characteristics of acicular ferrite in linepipe steels," Materials Science and Engineering: A, vol. 478, pp. 361-370, 2008.
[4] M. Nikravesh, M. Naderi, and G. Akbari, "Influence of hot plastic deformation and cooling rate on martensite and bainite start temperatures in 22MnB5 steel," Materials Science and Engineering: A, vol. 540, pp. 24-29, 2012.
[5] M.-C. Zhao, Y.-Y. Shan, F.-R. Xiao, and K. Yang, "Acicular ferrite formation during hot plate rolling for pipeline steels," Materials science and technology, vol. 19, pp. 355-359, 2003.
[6] 黃文星, 付建勛, "鋼鐵冶煉之二次精煉與氧化物冶金," 台灣台南:合記圖書, 2012.
[7] Z. Ma, "Control of nonmetallic inclusions in continuously cast steels in view of macro-cleanliness, castability, precipitation modification and grain refinement," Materials Science and Materials Technology, TU Bergakademie Freiberg, 2001.
[8] 刘中柱, 桑原守, "氧化物冶金技术的最新进展及其实践," 炼钢, vol. 23, pp. 7-13, 2007.
[9] L. Sin-Jie, Y. H. F. Su, L. Muh-Jung, and K. Jui-Chao, "EBSD analysis of magnesium addition on inclusion formation in SS400 structural steel," Materials Characterization, vol. 82, pp. 103-112, 2013.
[10] O. Grong and D. K. Matlock, "Microstructural development in mild and low-alloy steel weld metals," International Materials Reviews, vol. 31, pp. 27-48, 1986.
[11] D. Abson and R. Pargeter, "Factors influencing as-deposited strength, microstructure, and toughness of manual metal arc welds suitable for C-Mn steel fabrications," International Metals Reviews, vol. 31, pp. 141-196, 1986.
[12] T.-K. Lee, H. Kim, B. Kang, and S. Hwang, "Effect of inclusion size on the nucleation of acicular ferrite in welds," ISIJ international, vol. 40, pp. 1260-1268, 2000.
[13] 余圣甫, 雷毅, 黄安国, 谢明立, 李志远, "氧化物冶金技术及其应用," 材料导报, vol. 18, pp. 50-52, 2005.
[14] J. Gregg and H. Bhadeshia, "Solid-state nucleation of acicular ferrite on minerals added to molten steel," Acta materialia, vol. 45, pp. 739-748, 1997.
[15] W. Yan, Y. Shan, and K. Yang, "Effect of TiN inclusions on the impact toughness of low-carbon microalloyed steels," Metallurgical and Materials Transactions A, vol. 37, pp. 2147-2158, 2006.
[16] K. Inoue, I. Ohnuma, H. Ohtani, K. Ishida, and T. Nishizawa, "Solubility product of TiN in austenite," ISIJ international, vol. 38, pp. 991-997, 1998.
[17] S. Kimura, Y. Nabeshima, K. Nakajima, and S. Mizoguchi, "Behavior of nonmetallic inclusions in front of the solid-liquid interface in low-carbon steels," Metallurgical and Materials Transactions B, vol. 31, pp. 1013-1021, 2000.
[18] S. Kimura, K. Nakajima, and S. Mizoguchi, "Behavior of alumina-magnesia complex inclusions and magnesia inclusions on the surface of molten low-carbon steels," Metallurgical and Materials Transactions B, vol. 32, pp. 79-85, 2001.
[19] A. Kojima, A. Kiyose, R. Uemori, M. Minagawa, M. Hoshino, T. Nakashima, K. Ishida, H. Yasui, "Super high HAZ toughness technology with fine microstructure imparted by fine particles," Shinnittetsu Giho, pp. 2-5, 2004.
[20] G. Thewlis, "Classification and quantification of microstructures in steels," Materials Science and technology, vol. 20, pp. 143-160, 2004.
[21] D. S. Sarma, A. Karasev, and P. Jonsson, "On the role of non-metallic inclusions in the nucleation of acicular ferrite in steels," ISIJ international, vol. 49, pp. 1063-1074, 2009.
[22] H. K. D. H. Bhadeshia, Bainite in steels: Inst. of Metals, 1992.
[23] J. Gregg and H. Bhadeshia, "Bainite nucleation from mineral surfaces," Acta metallurgica et materialia, vol. 42, pp. 3321-3330, 1994.
[24] C. Wayman, "Shape memory and related phenomena," Progress in materials Science, vol. 36, pp. 203-224, 1992.
[25] S. S. Babu, "The mechanism of acicular ferrite in weld deposits," Current opinion in Solid state and Materials Science, vol. 8, pp. 267-278, 2004.
[26] E. Menon and H. Aaronson, "Overview no. 57 Morphology, crystallography and kinetics of sympathetic nucleation," Acta Metallurgica, vol. 35, pp. 549-563, 1987.
[27] I. Madariaga and I. Gutierrez, "Role of the particle–matrix interface on the nucleation of acicular ferrite in a medium carbon microalloyed steel," Acta materialia, vol. 47, pp. 951-960, 1999.
[28] B. L. Bramfitt, "The effect of carbide and nitride additions on the heterogeneous nucleation behavior of liquid iron," Metallurgical Transactions, vol. 1, pp. 1987-1995, 1970.
[29] J.-S. Byun, J.-H. Shim, Y. Cho, and D. Lee, "Non-metallic inclusion and intragranular nucleation of ferrite in Ti-killed C–Mn steel," Acta Materialia, vol. 51, pp. 1593-1606, 2003.
[30] W. Huang, "An assessment of the Fe-Mn system," Calphad, vol. 13, pp. 243-252, 1989.
[31] T. B. Massalski, H. Okamoto, P. Subramanian, and L. Kacprzak, Binary alloy phase diagrams: ASM international, 1990.
[32] C. Liu and S. Bhole, "Fracture behavior in a pressure vessel steel weld," Materials & design, vol. 23, pp. 371-376, 2002.
[33] L. Saraf, "Kernel Average Misorientation Confidence Index Correlation from FIB Sliced Ni-Fe-Cr alloy Surface," Microscopy and Microanalysis, vol. 17, pp. 424-425, 2011.
[34] A. J. DeArdo, C. Garcia, K. Cho, and M. Hua, "New method of characterizing and quantifying complex microstructures in steels," Materials and Manufacturing Processes, vol. 25, pp. 33-40, 2010.
[35] R. Farrar and P. Harrison, "Acicular ferrite in carbon-manganese weld metals: an overview," Journal of materials science, vol. 22, pp. 3812-3820, 1987.
[36] 蘇保鳴, "熱軋低碳鋼之相變態數學模型," 國立成功大學材料科學及工程學系碩士論文, 2011.
[37] C. Garcıa de Andrés, M. J. Bartolomé, C. Capdevila, D. San Martın, F. Caballero, and V. López, "Metallographic techniques for the determination of the austenite grain size in medium-carbon microalloyed steels," Materials characterization, vol. 46, pp. 389-398, 2001.
[38] R. Grange, "The rapid heat treatment of steel," Metallurgical transactions, vol. 2, pp. 65-78, 1971.
[39] M. Zhang, L. Li, R. Fu, D. Krizan, and B. De Cooman, "Continuous cooling transformation diagrams and properties of micro-alloyed TRIP steels," Materials Science and Engineering: A, vol. 438, pp. 296-299, 2006.
[40] 李國光, "沃斯回火球墨鑄鐵切削性之研究," 國立台灣科技大學機械工程學系碩士論文, 2006.
[41] J. Nutting, "Metallography of Phase Transformations," International Materials Reviews, vol. 18, pp. 37-37, 1973.