隨著全球對氣候變遷的關注日益升高，鋼鐵業作為能源密集型產業，其減碳需求日益迫切。面對碳稅與永續轉型的政策壓力，低碳高爐技術逐漸導入高還原度的熱壓還原鐵（Hot Briquetted Iron, HBI）以取代傳統燒結礦，期望有效降低碳排放。然而，HBI 相較於傳統礦料具有更高的含鐵率與孔隙度，其物理與化學性質差異顯著，投入高爐後可能影響熔融行為與軟熔帶（cohesive zone）的位置與厚度，進而干擾爐內氣體流動與熱交換機制。因此，亟需釐清 HBI 在高爐履歷條件下的氧化、還原與滲碳行為，以及其對軟熔特性的潛在影響。
本研究以模擬中鋼高爐升溫速率與還原氣氛（40% CO / 60% N₂）為基礎，系統探討 HBI 與純鐵樣品於 600 °C 至 1400 °C 溫度範圍內的相變化、組織演化與碳濃度變化。實驗觀察顯示，900 °C 以下以氧化反應為主，其中 HBI 因孔隙結構導致內部氧化比例高達 50%；900 °C 以上則轉為還原與滲碳反應，HBI 最終碳含量達 0.45 wt%，滲碳深度達 10 mm，遠高於純鐵之表面吸碳行為。熱力學計算與 XRD 分析進一步證實 Fe₃C（cementite）相於高溫時具穩定生成潛力，並推估其擴散與相變化行為。此外，藉由 FACTSage 熱力模擬本研究比較不同還原程度下 HBI 的熔渣生成與軟熔起始溫度變化。結果指出：若 HBI 滲碳後仍保留一定比例的氧化鐵（如 15–51 wt.% FeO），其與爐料中 Ca–Si–Al 成分反應生成低熔點氧化物（如 MeO），將提前引發熔渣生成與軟化行為，使軟熔帶軟熔起始溫度可降低至約 1120–1150 °C。此行為對高爐氣流通透性與操作穩定性具有潛在正面影響，惟必須兼顧還原度控制以避免過早熔化造成阻氣。本研究整合實驗分析與熱力學模擬，提供鋼廠於高爐實務操作中評估 HBI 添加比例與還原條件之技術依據，對於提升減碳效率、優化與穩定軟熔帶行為具有重要參考價值。

With increasing global attention to climate change, the steel industry, as an energy-intensive sector, is facing growing pressure to reduce carbon emissions. In response to carbon tax policies and sustainable transformation goals, low-carbon blast furnace technologies are progressively adopting highly reduced Hot Briquetted Iron (HBI) to replace traditional sinter as a burden material. However, HBI exhibits significant differences from conventional iron ores in terms of chemical composition and physical structure, including higher iron content and greater porosity. These characteristics may influence its melting behavior and shift the position and thickness of the cohesive zone in the blast furnace, potentially disturbing gas flow and heat transfer. Therefore, it is critical to clarify the oxidation, reduction, and carburization behavior of HBI under blast furnace conditions, as well as its effect on softening–melting phenomena.
In this study, a series of experiments were conducted simulating the heating rate and reducing atmosphere (40% CO / 60% N₂) of China Steel Corporation’s blast furnace. The phase transformation, microstructural evolution, and carbon concentration profile of HBI and pure iron were systematically investigated over a temperature range from 600 to 1400 °C. The results showed that oxidation dominated below 900 °C, with HBI exhibiting severe internal oxidation covering up to 50% of the cross-sectional area due to its porous structure. Above 900 °C, reduction and carburization became dominant. HBI achieved a maximum carbon content of 0.45 wt% and a carburization depth of up to 10 mm, significantly higher than the surface-limited carburization in pure iron. Thermodynamic calculations and XRD analysis confirmed the potential formation of Fe₃C (cementite) at elevated temperatures and suggested favorable conditions for carbon diffusion and carbide stabilization.
Furthermore, FACTSage simulations were employed to assess slag formation and softening onset temperatures under varying FeO contents. When HBI retained a moderate amount of unreduced Wüstite (e.g., 15–51 wt.% FeO) after carburization, it reacted with Ca–Si–Al compounds in the burden to form low-melting-point slag phases such as MeO. This led to earlier slag generation and softening, with cohesive zone onset temperatures potentially reduced to 1120–1150 °C. This behavior may improve gas permeability and burden descent uniformity if properly managed. However, it also highlights the importance of controlling the reduction degree to avoid premature softening that could hinder furnace operation.
By integrating experimental results with thermodynamic modeling, this study provides technical insight for optimizing HBI utilization in blast furnace operations. The findings offer valuable guidance for improving decarbonization efficiency, refining burden design, and maintaining cohesive zone stability under future low-carbon ironmaking strategies.

1. Heikkilä, A., et al., Reduction of Iron Ore Pellets, Sinter, and Lump Ore under Simulated Blast Furnace Conditions. steel research international, 2020. 91(11).
2. Babich, A., Blast furnace injection for minimizing the coke rate and CO2 emissions. Ironmaking & Steelmaking, 2021. 48(6): p. 728-741.
3. Geerdes, M., et al., Modern Blast Furnace Ironmaking: An Introduction, 4th ed., IOS Press, Amsterdam, 2020.
4. Abu Tahari, M.N., et al., Influence of hydrogen and carbon monoxide on reduction behavior of iron oxide at high temperature: Effect on reduction gas concentrations. International Journal of Hydrogen Energy, 2021. 46(48): p. 24791-24805.
5. Zhang, X., et al., A review on low carbon emissions projects of steel industry in the World. Journal of Cleaner Production, 2021. 306: p. 127259.
6. Schütze, W.R., HBI – Hot Briquetting of Direct Reduced Iron: Technology and Status of Industrial Application. Maschinenfabrik Köppern GmbH & Co. KG, Hattingen, Germany, 2002.
7. European Commission, Ensuring a future for steel in Europe. Press Memo (MEMO/13/523), Brussels, 11 June 2013. Available from: https://ec.europa.eu/commission/presscorner/detail/en/memo_13_523
8. Kuang, S., Z. Li, and A. Yu, Review on Modeling and Simulation of Blast Furnace. steel research international, 2017. 89(1).
9. Chen, Y. and H. Zuo, Review of hydrogen-rich ironmaking technology in blast furnace. Ironmaking & Steelmaking, 2021. 48(6): p. 749-768.
10. Chen, M., et al., High Temperature Softening Behaviours of Iron Blast Furnace Feeds and their Correlations to the Microstructures, in 6th International Symposium on High‐Temperature Metallurgical Processing. 2015. p. 67-74.
11. Ohno, K.-i., et al., Effect of Pre-reduction Degree on Softening Behavior of Simulant Sinter Iron Ore. ISIJ International, 2020. 60(7): p. 1520-1527.
12. Thurnhofer, A., et al., Iron Ore Reduction in a Laboratory-scale Fluidized Bed Reactor—Effect of Pre-reduction on Final Reduction Degree. ISIJ International, 2005. 45(2): p. 151-158.
13. Matinde, E. and M. Hino, Dephosphorization Treatment of High Phosphorus Iron Ore by Pre-reduction, Mechanical Crushing and Screening Methods. ISIJ International, 2011. 51(2): p. 220-227.
14. Kaushik, P. and R.J. Fruehan, Behavior of direct reduced iron and hot briquetted iron in the upper blast furnace shaft: Part I. Fundamentals of kinetics and mechanism of oxidation. Metallurgical and Materials Transactions B, 2006. 37(5): p. 715-725.
15. Yang, Y., K. Raipala, and L. Holappa, Ironmaking, in Treatise on Process Metallurgy, Elsevier, Oxford, pp. 2–88, 2014.
16. Durnovich, D., Hot briquetted iron: the multi-purpose metallic. Midrex Commentary (Direct from Midrex), 2021. Available from: https://www.midrex.com/commentary/hot-briquetted-iron-the-multi-purpose-metallic/
17. Wu, S., et al., New Evaluation Methods Discussion of Softening–Melting and Dropping Characteristic of BF Iron Bearing Burden. steel research international, 2014. 85(2): p. 233-242.
18. Gavel, D.J., et al., Characterization of the burden behaviour of iron ore pellets mixed with nut coke under simulated blast furnace conditions. Ironmaking & Steelmaking, 2020. 47(2): p. 195-202.
19. de Alencar, J.P.S.G., V.G. de Resende, and L.F.A. de Castro, Effect of Temperature on Morphology of Metallic Iron and Formation of Clusters of Iron Ore Pellets. Metallurgical and Materials Transactions B, 2016. 47(1): p. 85-88.
20. Tuo, B., et al., Influence of Coke Reactivity on Softening-Melting Dropping Behavior of Iron-Bearing Burden. steel research international, 2015. 86(9): p. 1028-1036.
21. Guo, W.T., et al., Microstructure evolution during softening and melting process in different reduction degrees. Ironmaking & Steelmaking, 2016. 43(1): p. 22-30.
22. Pan, Y.-Z., et al., Effect of reduction degree on cohesive zone and permeability of mixed burden. Ironmaking & Steelmaking, 2020. 47(3): p. 322-327.
23. Song, Q., Effect of nut coke on the performance of the ironmaking blast furnace. Ph.D. Thesis, Delft University of Technology, Delft, 2013. DOI: 10.4233/uuid:c774c99c2f40-48bb-852a-c8cb4e77d7d2.
24. Liu, X., et al., Influence of High Temperature Interaction between Sinter and Lump Ores on the Formation Behavior of Primary-slags in Blast Furnace. ISIJ International, 2014. 54(9): p. 2089-2096.
25. Elliott, J.F., Phase Equilibria in Iron Alloys, Addison-Wesley, Reading, MA, 1983.
26. Turkdogan, E.T., Fundamentals of Steelmaking, Institute of Materials, London, 1996.
27. 盧科妙, et al., 鋼廠集塵灰回收為高爐原料之冶金性質調查. 鑛冶：中國鑛冶 工程學會會刊, 2021. 65(4): p. 7-15.
28. Hornby, S., J. Madias, and F. Torre, DRI/HBI – exploding the myths. Steel Times International, 2016. 40(1): p. 42–49 (Jan/Feb).
29. Sammt, F.L. and R.L. Hunter, Handling & Shipping of DRI/HBI – Will It Burn? Steel Times International, 2000. 24(3): p. 42–43.
30. Mueller, H., The growing importance of DRI. Steel Times International, 2014. 38(8): p. 39–41 (Nov/Dec).
31. Daghagheleh, O., et al., Long-Term Reoxidation of Hot Briquetted Iron in Various Prepared Climatic Conditions. steel research international, 2023. 94(1): p. 2200535.
32. Scarnati, T., High-carbon DRI – getting the most value from iron ore. Steel Times International, 2008. 32(1): p. 30–32 (Jan/Feb).
33. Kaushik, P. and R. Fruehan, Mixed burden softening and melting phenomena in blast furnace operation Part 1–X-ray observation of ferrous burden. Ironmaking & steelmaking, 2006. 33(6): p. 507-519.
34. Kaushik, P. and R.J. Fruehan, Mixed burden softening and melting phenomena in blast furnace operation Part 2 – Mechanism of softening and melting and impact on cohesive zone. Ironmaking & Steelmaking, 2006. 33(6): p. 520-528.
35. Kaushik, P. and R.J. Fruehan, Mixed burden softening and melting phenomena in blast furnace operation Part 3 – Mechanism of burden interaction and melt exudation phenomenon. Ironmaking & Steelmaking, 2007. 34(1): p. 10-22.
36. Hwang, H.-S., et al., Carburization of iron using CO−H2 gas mixture. Metals and Materials International, 2004. 10(1): p. 77-82.
37. Bhadeshia, H.K.D.H., Cementite. International Materials Reviews, 2020. 65(1): p. 1-27.
38. Okamoto, T. and H. Matsumoto, Precipitation of Ferrite from Cementite. Metal Science, 1975. 9(1): p. 8-12.
39. 張, 興., et al., CO-CO<SUB>2</SUB>雰囲気における固体鉄への浸炭速度. 鉄と鋼, 1997. 83(5): p. 299-304.
40. Colpaert, H., Equilibrium Phases and Constituents in the Fe–C System. Metallography, Microstructure, and Analysis, 2017. 6(5): p. 443-457.
41. Callister Jr, W.D. and D.G. Rethwisch, Materials Science and Engineering: An Introduction, John Wiley & Sons, Hoboken, NJ, 2020.
42. Chipman, J., Thermodynamics and phase diagram of the Fe-C system. Metallurgical and Materials Transactions B, 1972. 3: p. 55-64.