本論文主要所探討的為鐵-8.1錳-3.8鋁-0.7碳(wt.%)之合金鋼經過不同溫度時效熱處理後的相變化行為。合金首先經過鎔鑄、均質化處理、熱鍛成板狀並切成小塊的試片後封進真空石英管後經過1100 ℃持溫一小時的固溶處理後再以每50 ℃為間隔進行1000 ℃至500 ℃的低溫熱處理。最後對做完熱處理後的試片以各種不同的儀器進行分析，以觀察其相變化過後的顯微組織。
鐵錳鋁合金在1100 ℃持溫一小時的固溶處理與1000 ℃至750 ℃的恆溫熱處理經由分析後發現為沃斯田體相為主，並可在晶界上觀察到冷卻過程中產生的不連續之介穩態的M23C6碳化物。在700 ℃時，波來體會以晶界上的不連續之M23C6碳化物為核種開始長進晶粒內，其組成為肥粒體(α)與碳化物(M23C6)。650 ℃時可觀察到波來體持續長進晶粒內，此溫度下的成核驅動力夠大足以形成M3C碳化物，其波來體組成為α + M3C。600 ℃至500 ℃熱處理後為完全波來體組織，其組成為α + M3C。經由能量散布光譜儀(EDS)分析後得知M23C6與M3C為富錳碳且貧鋁，而其中M23C6的鋁較M3C多約3.5 %。

關鍵字:鐵錳鋁合金、波來體、M23C6、M3C

Phase transformation of an Fe-8.1 Mn-3.8 Al-0.7 C (wt.%) alloy has been studied after solution and subsequent isothermal heat treatments at various aging temperatures and holding time. The alloy was first casted, homogenized, hot forged and then sectioned into specimens. The specimens were then sealed in quartz tubes under vacuum conditions and then subjected to solid solution treatment at 1100 ℃ for 1 hour, and then quenched to room temperature before further subjecting them to isothermal treatment at temperatures ranging from 1100 ℃ to 500 ℃ at 50 ℃ intervals. Microstructural analysis was done by various testing instruments.
Upon solid solution treatment at 1100 ℃ for 1 hour and isothermal treatment ranging from 1000 ℃ to 750 ℃, the Fe-Mn-Al alloy was found to have mostly austenite phase as equilibrium phase, and discontinuous M23C6 carbide along the grain boundaries as metastable phase. At 700 ℃, pearlite was observed to nucleate from the M23C6 carbides along the grain boundaries and then grow into the grains. The pearlite is composed of ferrite (α) and carbide (M23C6). At 650 ℃, the pearlite has grown more into the austenite grains and the driving force of nucleation is strong enough to form M3C carbide, with composition being α + M3C. At 600 ℃ to 500 ℃, microstructure of the alloy was observed to be wholly composed of pearlite structure and its composition is α + M3C. The M23C6 and M3C carbides are rich in manganese and carbon, and lean in aluminum, in which the aluminum in M23C6 is 3.5 % higher than that in M3C.

Keywords: Fe-Mn-Al alloy, Pearlite, M23C6, M3C

[1] J.L. Ham, R.E. Cairns, “Manganese joins aluminum to give strong stainless” Product Engineering (1958): 51-52.
[2] D.J. Schmatz, “Structure and properties of austenitic alloys containing aluminum and silicon” Trans. ASM 52 (1960): 898.
[3] K. Ishida, “Phase equilibria in Fe-Mn-Al-C alloys” ISIJ 30 (1990): 680-686.
[4] S. Chen, “Current state of Fe-Mn-Al-C low density steels” Progress in Materials Science 89 (2017): 345-391.
[5] D.A. Porter and K.E. Easterling, “Phase Transformation in Metals and Alloys”, 2/e, (2001).
[6] Hull, FREDERICK C., and ROBERT F. Mehl. “The structure of pearlite.” Trans. ASM 30 (1942): 381-424.
[7] P.R. Howell, J.V. Bee, R.W.K. Honeycombe, “The crystallography of the austenite-ferrite /carbide transformation in Fe-Cr-C alloys.” Metall. Trans A10 (1979): 1213-1222.
[8] K.H. Kuo and C.L. Jia, “Crystallography of M23C6 and M6C precipitated in a low alloy steel.” Acta Metallurgica 33.6 (1985): 991-996.
[9] M.H. Lewis, and B. Hattersley, “Precipitation of M23C6 in austenitic steels.” Acta metallurgica 13.11 (1965): 1159-1168.
[10] D.N. Shackleton, and P.M. Kelly, “The crystallography of cementite precipitation in the bainite transformation.” Acta Metallurgica 15.6 (1967): 979-992.
[11] D.S. Zhou, and G.J. Shiflet, “A new orientation relationship between austenite and cementite in an Fe-C-Mn steel.” Scripta metallurgica et materialia 27.9 (1992): 1215-1218.
[12] 張育仁，“鐵-30錳-1.7鋁-1.0碳合金之時效相變化研究”，碩士論文，國立台灣科技大學，台北(2009)。
[13] Atlas of isothermal Transformation Diagrams, American Society for Metals, (1977)
[14] W.F. Smith, “Structure and properties of engineering alloys.” McGraw-Hill Book Co., illustrated, (1981).
[15] G. Spanos, “Morphology, crystallography and mechanism of sympathetic nucleation of proeutectoid cementite plates.” Scripta metallurgica et materialia 22 (1988): 1537-1542.
[16] Z.F. Xu, “Characterization of M23C6 carbides precipitating at grain boundaries in 100Mn13 steel.” Metallurgical and Materials Transactions A 47 (2016): 4862-4868.
[17] 宋元聖，“錳鋁鋼中形成κ波來體的共析反應研究”，碩士論文，國立台灣科技大學，台北(2011)。
[18] 呂宣萱，“鐵-8錳-0.8碳合金鋼內形成麻田散體之臨界錳含量研究”，碩士論文，國立台灣科技大學，台北(2022)。
[19] J. Chu, “Kinetic study of Mn vacuum evaporation from Mn steel melts.” Separation and Purification Technology 255 (2021): 117698.
[20] https://sppic-r.ntust.edu.tw/ (台科大貴重儀器中心)。
[21] C.J. Altstetter, “Processing and properties of Fe-Mn-Al Alloys.” Material Science and Engineering 82 (1986): 13-25.
[22] S.A. Hackney and G.J. Shiflet, “The pearlite-austenite growth interface in an Fe-0.8 C-12 Mn alloy.” Acta Metallurgica 35.5 (1987): 1007-1017.
[23] W. Pitsch, “Der Orientierungszusammenhang zwischen Zementit und Austenit.” Acta Metallurgica 10.9 (1962): 897-900.
[24] W.T. Denholm, “Crystallization studies in the aluminum-rich corner of the aluminum-iron-manganese system.” Metallurgical Transactions A 15 (1984): 1311-1317.
[25] J.C. Benz and H.W. Leavenworth, Jr. “An assessment of Fe-Mn-Al alloys as substitutes for stainless steels.” Journal of metals (1985): 36-39.
[26] J. Charles and A. Berghezan, “Nickel-free austenitic steels for cryogenic applications: The Fe-23%Mn-5%Al-0.2%C alloys.” Cryogenics 21.5 (1981): 278-280.
[27] X.J Liu, S.M. Hao, L.Y. Xu, Y.F. Guo and H. Chen, “Experimental study of the phase equilibria in the Fe-Mn-Al system” Metallurgical and Materials Transactions A 27 (1996): 2429-2465.
[28] W.C. Cheng, “Observing the D03 phase in Fe-Mn-Al alloys” Materials science and Engineering A337 (2002): 281-286.
[29] W.C. Cheng, “Observing the massive transformation in an Fe-Mn-Al alloy” Materials science and Engineering A335 (2002): 82-88.
[30] W.C. Cheng, “The formation of austenite annealing twins from the ferrite phase during aging in an Fe-Mn-Al alloy” Materials science and Engineering A341 (2003): 106-111.