Refining effect of IF steel produced by RH forced and natural decarburization process
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摘要: 西昌鋼釩廠由于轉爐熱量不足而以轉爐—LF精煉—RH精煉—連鑄工藝生產IF鋼，為探究RH強制脫碳與自然脫碳工藝生產IF鋼精煉效果，采用生產數據統計、氧氮分析、夾雜物自動掃描、掃描電鏡和能譜分析等手段，對不同脫碳工藝對頂渣氧化性以及鋼的潔凈度影響進行了詳細研究。結果表明：（1）與自然脫碳工藝爐次相比，采用強制脫碳工藝的爐次在轉爐結束與RH進站鋼中的平均[O]含量更低；（2）兩種工藝脫碳結束鋼中的[O]含量基本在同一水平；（3）強制脫碳工藝的爐次在RH結束時渣中平均T.Fe的質量分數降低了1.3%。在能滿足RH脫碳效果的前提下，盡量提高轉爐終點鋼液碳含量、降低鋼液氧含量，后續在RH精煉時采用強制吹氧脫碳工藝，適當增大吹氧量來彌補鋼中氧，可顯著降低IF鋼頂渣氧化性。自然脫碳工藝與強制脫碳工藝控制熱軋板T.O含量均比較理想；與自然脫碳工藝相比，強制脫碳工藝可有效降低IF鋼[N]含量，這與強制脫碳工藝真空室內碳氧反應更劇烈所導致的CO氣泡更多和氣液反應面積更大有關。脫碳工藝對IF鋼熱軋板中夾雜物類型、尺寸及數量沒有明顯影響，夾雜物主要由Al2O3夾雜、Al2O3–TiOx夾雜與其他類夾雜物組成，以夾雜物的等效圓直徑表示夾雜物尺寸，以上三類夾雜物平均尺寸分別為4.5、4.4和6.5 μm，且鋼中尺寸在8 μm以下的夾雜物數量占比高于75%。在RH精煉過程中，盡量降低RH脫碳結束鋼中[O]含量，有利于提高鋼液潔凈度。Abstract: Owing to insufficient converter heat, IF steel is produced via the BOF—LF—RH—CC process in the Xichang Steel & Vanadium Co.LTD of Pangang Group, Xichang, China. To explore the refining effect of IF steel produced via the RH forced and natural decarburization process, this work employed standard analysis methods such as production data statistics, total oxygen and nitrogen analysis, automatic scanning electron microscopy, scanning electron microscopy, and energy spectroscopy. The effects of different decarburization processes on the ladle slag oxidability and cleanliness of steel were investigated in detail. Compared with the natural decarburization process heats, results show that the forced decarburization process heats exhibit (1) lower average [O] content in molten steel after BOF and before RH, (2) a similar level of the [O] content in molten steel after decarburization with that of the natural decarburization process, and (3) 1.3% lower average T.Fe mass fraction in the ladle slag after RH treatment. To ensure the RH decarburization effect, the final carbon content increased and molten steel oxygen content reduced in the converter to the maximum extent. The forced oxygen blowing decarburization process was then used to compensate for the molten steel oxygen content during RH refining by increasing oxygen blowing properly, which can significantly decrease the ladle slag oxidability of IF steel. Both the natural decarburization and forced decarburization processes are ideal for controlling the T.O content of a hot–rolled sheet. Compared with the natural decarburization process, the forced decarburization process can effectively reduce the [N] content of IF steel, which is related to a more violent carbon–oxygen reaction in a vacuum chamber, resulting in a high volume of CO bubbles and a large gas–liquid reaction area. The decarburization process has no obvious influence on the type, size, and number of inclusions in the hot–rolled sheet of IF steel that mainly consist of Al2O3, Al2O3–TiOx, and other inclusions. The average sizes of the above three 4.5, 4.4, and 6.5 μm, respectively, according to the equivalent circle diameter of inclusions. In addition, more than 75% of inclusions are within 8 μm. During the RH refining process, reducing the [O] content in molten steel after RH decarburization to the maximum extent is beneficial to improve the cleanliness of molten steel.
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Key words:
- IF steel /
- RH refining /
- ladle slag oxidability /
- cleanliness /
- inclusions /
- decarburization process
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圖 2 不同RH脫碳工藝鋼中[O]含量和RH結束渣中T.Fe含量分布
Figure 2. Distribution of [O] content in molten steel and T.Fe content in the ladle slag after the RH treatment in different RH decarburization processes
圖 3 不同吹氧量時各工序鋼中[O]和RH結束渣中T.Fe變化
Figure 3. Changes of [O] content in molten steel of the different processes and T.Fe content in the ladle slag after the RH treatment for different oxygen blowing conditions
圖 4 不同脫碳工藝爐次鋼中T.O和[N]含量變化。（a）自然脫碳；（b）強制脫碳
Figure 4. Total oxygen and nitrogen changes in different decarburization process heats: (a) natural decarburization process; (b) forced decarburization process
圖 5 自然脫碳工藝爐次1鋼中夾雜物的典型形貌。（a）Al2O3夾雜物；（b）Al2O3?TiOx夾雜物；（c）CaO?Al2O3?TiOx、MgO?Al2O3、MgO?Al2O3?TiOx夾雜物
Figure 5. Typical morphologies of inclusions in the natural decarburization process of Heat 1：(a) Al2O3 inclusions; (b) Al2O3–TiOx inclusions; (c) CaO–Al2O3–TiOx, MgO–Al2O3–TiOx, and MgO–Al2O3 inclusions
圖 6 強制脫碳工藝爐次4鋼中夾雜物的典型形貌。（a）Al2O3夾雜物；（b）Al2O3?TiOx夾雜物；（c）CaO?Al2O3?TiOx、CaO?Al2O3、CaO?Al2O3?TiOx夾雜物
Figure 6. Typical morphologies of inclusions in the forced decarburization process of Heat 4: (a) Al2O3 inclusions; (b) Al2O3–TiOx inclusions; (c) CaO–Al2O3–TiOx, CaO–Al2O3, and CaO–Al2O3–TiOx inclusions
圖 7 夾雜物的能譜面掃圖。（a）Al2O3夾雜物；（b）Al2O3–TiOx夾雜物；（c）MgO–Al2O3–TiOx夾雜物；（d）CaO–Al2O3–TiOx夾雜物
Figure 7. Elemental mapping of inclusions: (a) Al2O3; (b) Al2O3–TiOx; (c) MgO–Al2O3–TiOx; (d) CaO–Al2O3–TiOx
圖 8 不同脫碳工藝各類夾雜物尺寸分布箱型圖
Figure 8. Size changes and distribution of inclusions in different decarburization processes
圖 9 不同脫碳工藝爐次各類夾雜物數量密度變化。（a）自然脫碳；（b）強制脫碳
Figure 9. Number density changes of inclusions in different decarburization process heats: (a) natural decarburization process; (b) forced decarburization process
圖 10 RH脫碳結束鋼中[O]與鋼中夾雜物的數量關系
Figure 10. Relationship between the number of inclusions and [O] content in molten steel after RH decarburization
表 1 試驗爐次RH過程工藝參數
Table 1. Process parameters of experimental heats during the RH treatment
Decarburization process Heats Oxygen
blowing/
m3[C] content in
steel after
decarburization/
10?6[O] content in
steel after
decarburization/
10?6Natural decarburization 1 0 18 277 2 0 11 284 3 0 15 290 Forced decarburization 4 15 13 285 5 10 10 262 6 60 10 306 
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表 2 自然脫碳與強制脫碳工藝脫碳效果比較
Table 2. Comparison of the decarburization effects between the natural and forced decarburization processes
Decarburization process [C]ave content in steel
after BOF/10?6[C]ave content in steel
before RH/10?6[C]ave content in steel
after decarburization/10?6RH decarburization time/min RH treatment time/min Natural decarburization 420 305 11.1 20 32 Forced decarburization 490 344 11.8 21 33 Note: The subscript ave represents the average content in this work.
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