Mineralogical phase and formation mechanism of titanium-bearing protective layers in a blast furnace hearth
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摘要: 基于高爐破損調查取樣分析, 借助X射線熒光分析、X射線衍射分析、電子探針分析、掃描電子顯微鏡結合能譜分析等手段分析了高爐爐缸、爐底不同部位形成的含鈦保護層化學成分、物相組成和微觀形貌, 并建立正規溶液熱力學模型對Ti (C, N)形成的熱力學條件進行分析, 然后針對高爐的實際工況, 明晰高爐爐缸TiC0.3N0.7形成的條件.結果表明, 高爐爐缸側壁最薄處炭磚殘余厚度僅為200 mm; 爐缸爐底炭磚表面普遍存在含鈦保護層, 保護層平均厚度在300~600 mm左右, 高爐爐缸不同部位形成的保護層中Ti(C, N)主要以TiC0.3N0.7形式存在, 并與Fe相聚集在一起.Ti (C, N)固溶體實際混合摩爾生成吉布斯自由能顯著低于標準混合摩爾生成吉布斯自由能和理想混合摩爾生成吉布斯自由能.在不同溫度條件下, TiC和TiN在固溶體中存在的比例不同, 高溫時以析出TiC為主, 低溫時以析出TiN為主.Ti (C, N)固溶體的形成與高爐熱力學狀態條件直接相關, TiC0.3N0.7在該高爐爐缸中的形成溫度為1423℃.Abstract: In theory and practice, TiO2-bearing iron ores are the preferred raw materials for prolonging blast furnace times due to their protection of the refractory lining of the hearth. Currently, however, a lack of detailed understanding of the mineralogical composition, formation mechanism, and ratio of C to N in the Ti(C, N) solid solution leaves the blast furnace operator unable to employ a scientific and effective measure to deal with abnormal hearth erosion. As a result, frequent hearth breakouts might occur, causing great financial loss to steel companies. In the present work, in an attempt to clarify the essence of longevity blast furnaces, investigations were conducted into blast furnace hearth damage together with dissection analyses, to derive the mineralogical composition and microstructure of titanium-bearing protective layers. The results show that the exact chemical composition of the TiCxN1-x which formed in the blast furnace is TiC0.3N0.7. Based on thermodynamic analysis, the standard Gibbs free energy of the formation of Ti(C, N) decreases at first, then increases with increasing TiC content. At different temperatures, the proportion of TiC and TiN in the solid solution is different, i.e., more TiC at higher temperatures but more TiN at lower temperatures. At 1423℃, the TiC0.3N0.7 is formed in the hot-side of the investigated blast furnace hearth, and the thickness of the titanium-bearing protective layer varies with smelting intensity, temperature, and circulation strength of hot metal. This paper classifies the protective layer into various types based on formation mechanism. Finally, a comprehensive regulatory scheme is presented to act as a basis for extending the lifespan of the blast furnace hearth.
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Key words:
- blast furnace /
- hearth /
- titanium-bearing protective layer /
- phase composition /
- TiC0.3N0.7 /
- precipitation temperature
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圖 1 高爐爐缸爐底保護層宏觀形貌. (a) 1號試樣; (b) 2號試樣; (c) 3號試樣
Figure 1. Macroscopic morphology of the protective layer in blast furnace hearth: (a) sample 1; (b) sample 2; (c) sample 3
圖 2 高爐爐缸爐底三類保護層試樣X射線衍射檢測結果. (a) 1號試樣; (b) 2號試樣; (c) 3號試樣
Figure 2. XRD results of three types of protective layers in the blast furnace hearth: (a) sample 1; (b) sample 2; (c) sample 3
圖 3 高爐爐缸不同部位保護層試樣的微觀形貌. (a) 1號試樣; (b) 2號試樣; (c) 3號試樣
Figure 3. Microscopic appearance of the protective layer of different parts in the blast furnace hearth: (a) sample 1; (b) sample 2; (c) sample 3
圖 4 Ti(C, N)固溶體生成吉布斯自由能隨TiC物質的量的變化(1400 ℃)
Figure 4. Change of Gibbs free energy of Ti(C, N) solid solution with TiC content (1400 ℃)
圖 5 不同溫度下Ti(C, N)固溶體生成吉布斯自由能隨TiC物質的量的變化
Figure 5. Change of Gibbs free energy with TiC content in Ti(C, N) at different temperatures
圖 6 TiC和TiN在固溶體TiCN中的活度(a)及活度系數(b)
Figure 6. Activity (a) and the activity coefficients (b) of TiC and TiN in the solid solution of Ti(C, N)
圖 7 TiC在固溶體Ti(C, N)中的物質的量隨溫度的變化
Figure 7. Variation in the content of TiC in the solid solution of Ti(C, N) with temperature
圖 8 高爐爐缸TiC在Ti(C, N)固溶體中的物質的量隨溫度的變化
Figure 8. Variation in the content of TiC in the solid solution of Ti(C, N) with temperature in the BF hearth
表 1 保護層試樣X射線熒光分析法成分分析(質量分數)
Table 1. XRF analysis of the protective layer samples ?
% 試樣 TiO2 Fe2O3 CaO SiO2 Al2O3 MgO C Na2O K2O 1號試樣 31.72 14.04 15.94 14.39 10.19 6.03 2.08 0.5 0.84 2號試樣 45.07 19.17 0.61 3.05 14.27 0.04 12.89 0.32 0.34 3號試樣 54.21 17.66 0.38 8.49 2.28 0.11 15.15 0.34 0.64 高爐渣 10.01 31.99 27.21 14.36 10.39 
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表 2 高爐爐缸爐底保護層試樣的電子探針分析結果
Table 2. EPMA analysis of the protective layer samples in blast furnace hearth bottom
元素 質量分數/% 原子數分數/% 摩爾比(Ti∶C∶N) Ti 65.858 49.648 C 5.198 14.869 1.000∶0.300∶0.715 N 16.872 35.483 總計 87.928 100.000
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