Evolution of inclusions in IF steel during continuous casting process
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摘要: 针对某厂生产的IF钢连铸过程中间包钢液和铸坯取样，采取T.O、[N]含量分析和ASPEX扫描电镜-能谱仪等方法，并结合热力学计算分析了连铸过程钢中夹杂物的演变行为。结果表明，连铸过程钢中T.O含量整体呈现下降趋势，但中间包开浇阶段钢液受到覆盖剂或耐材的二次氧化，应适当调整覆盖剂成分或炉衬成分，铸坯中T.O含量为12×10−6，[N]含量为21×10−6，符合IF钢控制要求。夹杂物数量密度的变化趋势与T.O一致，铸坯中夹杂物数量密度增加是因为凝固冷却过程中有大量TiN析出。整个中间包过程注流区钢液中夹杂物的数量密度低于浇注区，但平均尺寸更大。随着浇注进行，中间包钢液夹杂物中MgO的含量逐渐升高，且与尺寸呈现负相关关系，大于10 μm的夹杂物集中分布在Al2O3含量高的区域。热力学计算结果表明1600 ℃时，钢液中稳定存在的夹杂物相只有Al2O3，然而试验结果中发现了较多的Al2O3-TiOx夹杂物，这是由于RH精炼过程加钛合金后，造成局部Ti浓度过高，为TiOx和Al2O3-TiOx的形成提供了条件。铸坯中存在TiS类夹杂物，包含纯TiS夹杂物和Al2O3-TiS及TiS-TiN的复合夹杂物，此类夹杂物的尺寸随着TiS质量分数的增大而减小。Abstract: The evolution of inclusions in steel of the continuous casting process of IF steel produced by a plant was studied by systematically sampling including molten steel and casting billet. The methods of analysis mainly include analysis of total oxygen and nitrogen content, ASPEX scanning electron microscope-spectrometer and thermodynamic calculations. The results show that the content of total oxygen in steel during continuous casting process presents a total decreasing trend. But there is a secondary oxidation of molten steel by covering agent or resistant material at the opening stage of tundish. The composition of covering agent or lining should be adjusted appropriately, so as to make the content of T.O and [N] in casting slab is 12×10−6 and 21×10−6, respectively, which meet the control requirements of IF steel. The trend of the number density of inclusions in steel during the continuous casting process is consistent with the trend of total oxygen content. The increase of the number density of inclusions in slab is subject to TiN precipitation during solidification and cooling. The number density of inclusions in the molten steel in the tundish injection area is lower than that in the pouring area during the entire tundish process, whose size is larger. With the pouring, the content of MgO of inclusions in the molten steel of tundish gradually increases, and shows a negative correlation with the size, and the inclusions larger than 10 μm are concentrated in the area with high Al2O3 content. Thermodynamic calculation results show that the stable inclusion phase in the molten steel at 1 600 °C is only Al2O3, but some Al2O3−TiOx inclusions are found in the experimental results, which is due to the addition of titanium alloys in the RH refining process causing the local Ti concentration to be too high, which provides conditions for the formation of TiOx and Al2O3−TiOx. There are TiS-containing inclusions in slab, including pure TiS inclusions and composite inclusions of Al2O3−TiS and TiS-TiN, and the size of such inclusions decreases with the increase of mass fraction of TiS.
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Key words:
- IF steel /
- continuous casting /
- non-metallic inclusions /
- evolution /
- thermodynamic calculation
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图 1 连铸过程钢中T.O、[N]含量的变化
Figure 1. Variation of T.O and [N] content in steel during continuous casting process
图 2 连铸过程钢中夹杂物数量密度和平均尺寸变化
Figure 2. Variation of number density and average size of inclusions in steel during continuous casting process
图 3 RH出站和中间包钢液及铸坯中夹杂物的尺寸分布对比
Figure 3. Comparison of the size distribution of inclusions in molten steel of RH outbound and tundish and inclusions in slab
图 4 1600 ℃时不同氧含量下IF钢中Al-Ti-O平衡相图
Figure 4. Al-Ti-O equilibrium phase diagram of IF steel under different oxygen contents at 1 600 ℃
图 5 连铸过程钢中夹杂物平均成分变化
Figure 5. Variation of the average composition of inclusions in steel during continuous casting process
图 6 中间包钢液中夹杂物尺寸和成分的关系
Figure 6. Relationship between the size and composition of the inclusions in molten steel in tundish
图 7 中间包浇注区钢液中夹杂物的成分和尺寸
Figure 7. Composition and size of inclusions in molten steel in the tundish pouring area
图 8 中间包钢液中Al2O3夹杂物的典型形貌
（a）球状；（b）块状；（c）不规则状；（d）条状；（e）聚合状；（f）球拍状；（g）簇群状；（h）花瓣状；（i）树枝状
Figure 8. Typical morphologies of the Al2O3 inclusions in molten steel in tundish
图 9 中间包钢液中Al2O3-TiOx夹杂物的典型形貌
（a）Al-Ti均匀分布；(b)Al-Ti包裹Al；（c）Al包裹Al-Ti
Figure 9. Typical morphologies of Al2O3-TiOx inclusions in molten steel in tundish
图 10 IF钢冷却过程中夹杂物物相变化
Figure 10. Changes in the phase of inclusions during the cooling of IF steel
图 11 铸坯中TiN夹杂物的典型形貌
（a）长方形状；（b）三角形状；（c）不规则状
Figure 11. Typical morphologies of TiN inclusions in slab
图 12 铸坯中Al2O3-TiN夹杂物的典型形貌
（a）完全包裹的长方形状；（b）完全包裹的不规则状；（c）不完全包裹的不规则状
Figure 12. Typical morphologies of Al2O3-TiN inclusions in slab
图 13 铸坯中含TiS类夹杂物的典型形貌
（a）纯TiS夹杂物；（b）TiS-TiN复合夹杂物；（c）Al2O3-TiS复合夹杂物
Figure 13. Typical morphologies of inclusions containing TiS in slab
图 15 铸坯中夹杂物尺寸和成分的关系
Figure 15. Relationship between the size and composition of inclusions in slab
表 1 IF钢化学成分
Table 1. Chemical compositions of IF steel
% 工序 C Si Mn P S Als T.Al T.Ti RH出站 0.001 0.0018 0.13 0.007 0.007 0.035 0.038 0.063 成品值 0.0018 0.002 0.13 0.007 0.007 0.026 0.027 0.056 
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表 2 连铸中间包钢液中不同类型夹杂物的比例
Table 2. Proportion of different types of inclusions in molten steel of continuous casting tundish
% 工序 Al2O3 Al2O3-TiOx 其他 RH出站 55.2 32.7 12.1 中间包前期注流区 67.3 24.4 8.3 中间包前期浇注区 75.5 17.9 6.6 中间包中期注流区 46.6 33.3 20.1 中间包中期浇注区 68.3 22.7 9 中间包后期注流区 65.6 23.6 10.8 中间包后期浇注区 72.2 16.4 11.4
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表 3 铸坯中不同类型夹杂物的比例
Table 3. Proportion of different types of inclusions in slab
% Al2O3 Al2O3-TiOx TiN Al2O3-TiN 含TiS类 MnS 11.1 24.4 28.7 19.7 15.5 0.6
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