鐵碳合金是非常重要的商業材料，也是在科學和工程界被廣泛研究的材料。鐵碳合金經不同熱處理後，會發生多種形式的相變化，其微觀結構是會伴隨改變。本論文研究含極少量碳的純鐵經不同熱處理後的相變化與對應的熱磁重變化。熱處理方式為將純鐵加熱到1000℃後，以水淬或空冷方式冷卻到室溫，或將經空冷的純鐵做低溫的恆溫處理。經不同熱處理的純鐵於磁熱重分析儀(M-TGA)量測，皆得到相似的M-TGA曲線，尤其是於485℃附近皆有明顯的磁重增加，此現象顯示經不同熱處理的純鐵內皆有類似的結構變化。我們利用同步輻射臨場加熱分析純鐵，於加熱曲線圖確定在485℃附近有相變化的發生；並使用穿透式電子顯微鏡分析純鐵經不同熱處理後的相組成，並據以推斷於485℃附近發生的磁重改變現象，是因為純鐵的肥粒體晶粒於冷卻過程發生的相變化所造成。肥粒體於冷卻過程，肥粒體內發生spinodal相分離，當溫度低於485℃時，則接續有有序化反應的發生。反應機構解釋如下：肥粒體經spinodal相分離而分離成無碳肥粒體(α’)與含碳肥粒體(α”)，其反應式如下：α→α’+α”；含碳之α”相於485℃以下溫度則再經由有序化相變化而轉變為新析出相，反應式為：α”→新析出相。以上高碳鋼經緩慢冷卻後的近似平衡狀態相變化的總反應式為：γ→α→α’+α”→α’+新析出相。

We have studied the phase transformations of pure iron. The methodology of the study of the phase transformations in the pure Fe includes heating the Fe samples to high temperatures 1273 K, and air cooling and/or water quenching. Similar M-TGA curves have been observed for the Fe samples with various heat treatments. Using the synchrotron radiation and TEM study, we have confirmed the occurrence of an ordering reaction at temperature below 758 K after the spinodal decomposition. Upon cooling the Fe from 1273 K, austenite phase (γ) has transformed into ferrite (α) at temperature below 1185 K. Upon further cooling, ferrite has undergone the spinodal decomposition and decomposes into two other low temperature ferrite phases. One is carbon-free ferrite (α’), and the other is carbon-contained ferrite (α”). The spinodal decomposition is shown as follows. α → α’ + α”. At temperature below 758 K, the carbon-contained ferrite has undergone the ordering reaction and transforms into new precipitate, i.e. α” → new precipitate. The overall reactions occurring in the pure Fe upon cooling from high temperature are as follow. γ → α → α’ + α” → α’ + new precipitate.

1. D.A. Porter, K.E. Easterling, Phase Transformations in Metals and Alloys”, 3rd ed., (2008).
2. D.E. Laughlin, Acta Metall., 23, 329 (1975).
3. W.A. Soffa, D.E. Laughlin, Prog. Mat. Sci., 49, 347 (2004).
4. K. Sato, K. Tagawaand, Y. Inoue, Scripta Metall., 22, 899 (1988).
5. K. Sato, K. Tagawaand, Y. Inoue, Mater. Sci. Eng. A, 111, 45 (1989)
6. K. Sato, K. Tagawa, Y. Inoue, Metall. Trans. A, 21, 5 (1990).
7. Y.G. Kim, Y.S. Park, J.K. Han, Metall. Trans. A, 16, 1689 (1985).
8. K.H. Han, Mater. Sci. Eng. A, 197, 223 (1995).
9. W.K. Choo, J.H. Kim, J.C. Yoon, Acta Mater., 45, 4877 (1997)
10. M.C. Li, H. Chand, P.W. Kao, D. Gan, Mater. Chem. Phys., 59, 96 (1999).
11. C.S. Wang, C.N. Hwang, C.G. Chao, T.F. Liu, Scripta Mater., 57, 809 (2007).
12. W.A. Soffa, D. E. Laughlin, Acta Metall., 37, 3019 (1989).
13. R. Oshima, C.M. Wayman, Metall. Trans., 3, 2163 (1972).
14. R.E. Reed-Hill, Physical Metallurgy Principle, 3rd ed., (1992).
15. G.E. Dieter, Mechanical Metallurgy, 132 (1988).
16. L. Cheng, X.L. Wan, K.M. Wu, Mater. Char., 61, 192 (2010).
17. W.F. Smith, “Structure and Properties of Engineering Alloys”, 2nd ed., (1993).
18. T.F. Liu, J.C. Tasy, Scripta Metall., 21, 1213 (1987).
19. D.N. Shackleton, P.M. Kelly, Acta Metall., 15, 979 (1967).
20. C.R. Hutchinson, R.E. Hackenberg, G.J. Shiflet, Acta Mater., 52, 3565 (2004).
21. 羅翊洋，“鐵-13鎵合金之磁彈性與機械性質研究”，國立台灣科技大學，碩士論文 (2014)。
22. 近角聰信，(張煦、李學養譯)，“磁性物理學”，聯經出版事業公司 (1982)。
23. 金重勳，磁性技術手冊，中華民國磁性技術協會出版 (2002).
24. C.N. Hulme-Smith, I. Lonardelli, A.C. Dippel, H.K.D.H. Bhadeshia, Scripta Metall., 69, 409, (2013)
25. J.H. Jang, H.K.D.H. Bhadeshia, D.W. Suh, Scripta Metall., 68, 195, (2013)
26. C. Garcia-Mateo, J.A. Jimenez, H.W. Yen, M.K. Miller, L. Morales-Rivas, M. Kuntz, S.P. Ringer, J.R. Yang, F.G. Caballero, Acta Metall., 91, 162, (2015)
27. J.Y. Yan, A.V. Ruban, Comput. Mater. Sci, 147, 293, (2018)
28. H.K.D.H. Bhadeshia, A.R. Waugh, Acta Metall., 30, 775, (1982)
29. M. Peet, S.S. Babu, M.K. Miller, H.K.D.H. Bhadeshia, Scripta Mater., 50, 1277, (2004)
30. F.G. Caballero, M.K. Miller, S.S. Babu, C. Garcia-Mateo, Acta Mater. 55, 381, (2007)
31. C. Garcia-Mateo, M. Peet, F.G. Caballero, H.K.D.H.Bhadeshia, Mater. Sci. Technol. 20, 814, (2004)
32. F.G. Caballero, M.K. Miller, C. Garcia-Mateo, J. Cornide,J. Alloys Compd, (2012)
33. F.G. Caballero, M.K. Miller, C. Garcia-Mateo, J. Cornide,M.J. Santofimia, Scripta Mater., 67, 846, (2012)
34. E.C. Bain, Trans. AIME., 70, 25, (1924)
35. J.C. Fisher, J.H. Hollomon, D. Turnbull, Metals Trans., 185, 691, (1949)
36. H.K.D.H. Bhadeshia, Bainite in Steels, second ed., Institute of Mat., London, UK, (2001)
37. L.S. Lutterotti, S. Matthies, H.R. Wenk, IUCr-CPD,Newsl., 21, (1999)
38. L. Lutterotti, S. Matthies, H.R. Wenk, A.S. Schultz, J.W. Richardson, J. App. Phys., 21, 594, (1997)
39. J.W. Christian, Mater. Trans. JIM., 33, 208, (1992)
40. J.I. Langford, D. Loue¨r, Rep. Prog. Phys., 59, 131, (1996)
41. H.K.D.H. Bhadeshia, Proc. R. Soc. A., 466, 5, (2010)