Effect of continuous-casting parameters on carbon segregation in SWRH82B high-carbon steel
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摘要: 高碳鋼連鑄生產技術工藝優化是當前連鑄技術研究的主要內容之一。針對國內某鋼廠SWRH82B高碳鋼生產過程中出現碳偏析、網狀滲碳體組織缺陷的問題，采用數值模擬與實驗相結合的方法，利用Fluent軟件建立了八機八流連鑄機凝固傳熱模型，數值模擬計算凝固傳熱特征；研究了八機八流連鑄機在不同澆注速度、過熱度和末端電磁攪拌參數條件下對SWRH82B高碳鋼鑄坯碳偏析和夾雜物的影響；分析了SWRH82B高碳鋼連鑄過程中的主要要素與組織性能之間的關系。研究結果表明：鑄坯中心碳偏析是網狀滲碳體主要誘導因素，通過調整過熱度和澆注速度有利于促進鋼液成分的均勻化，降低夾雜物含量；當過熱度降低至25 ℃，澆注速度提高至2 m·min?1，鑄坯中心平均碳偏析指數由1.17降低為1.11，索氏體化率達到89%，網狀滲碳體級別由四級下降到一級，基本消除C類夾雜物；通過設置末端電磁攪拌參數為電流370 A、頻率7 Hz時，碳偏析指數最低值下降到1.04。通過優化連鑄生產工藝參數，解決了企業SWRH82B高碳鋼生產過程中的缺陷，為高碳鋼的高質量生產提供理論與實踐支撐。Abstract: Optimization of the continuous-casting production technology for high-carbon steel is one of the most important areas of research related to the steelmaking process. This article aims to address the problems of carbon segregation and reticulated cementite defects in the production process of SWRH82B high-carbon steel in a Chinese steel plant. In this study, Fluent software was used to perform a numerical simulation combined with experimentation to establish a heat-transfer model for the solidification of an eight-strand continuous caster. We numerically calculated the heat-transfer characteristics of the solidification and studied the effect of different parameters on the carbon segregation and inclusions of SWRH82B high-carbon steel, including casting speed, degree of superheating, and final-electromagnetic stirring of the eight-strand continuous caster. We also analyzed the relationship between the main elements during the continuous-casting process of the SWRH82B high-carbon steel and its microstructure and properties. The results indicate that carbon segregation in the center of the billet was the main cause of reticulated cementite. The degree of superheating and casting speed were then optimized, which promoted the homogenization of the components of liquid steel and reduced the inclusion content. When the degree of superheating was reduced to 25 ℃ and the casting speed was increased to 2 m·min?1, the carbon segregation index of the billet was reduced from 1.17 to 1.11, the sorbite rate was 89%, the cementite network grade decreased from 4 to 1, and the C inclusions were substantially eliminated. When the end electromagnetic stirring current was set to 370 A and the frequency to 7 Hz, the carbon segregation index decreased to its lowest value of 1.04. The defects occurring in the production process of SWRH82B high-carbon steel were addressed by optimizing the continuous-casting process parameters, which provides theoretical and practical support for the high-quality production of high-carbon steel.
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Key words:
- high-carbon steel /
- continuous casting /
- cementite network /
- center segregation /
- numerical simulation
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圖 1 SWRH82B盤條試樣顯微組織。（a）非金屬夾雜物；（b）索氏體；（c）網狀滲碳體
Figure 1. Microstructures of the SWRH82B wire-rod samples: (a) non-metallic inclusion; (b) sorbate; (c) cementite network
圖 3 八機八流中間包。（a）實體圖；（b）模擬圖
Figure 3. 8-machine 8-strand tundish: (a) photograph; (b) simulation diagram
圖 4 不同拉速對（a）溫度場、（b）夾雜物體積分數含量、（c）流場的影響
Figure 4. Effects of different pulling speeds on (a) temperature field, (b) inclusion content, and (c) flow field
圖 5 不同過熱度對（a）中間包速度場和（b）夾雜物體積分數的影響
Figure 5. Effects of different degrees of superheating on (a) tundish velocity field and (b) inclusion content
圖 6 末端電磁攪拌參數對連鑄坯碳偏析指數的影響
Figure 6. Drill effect of F-EMS parameters on the carbon segregation indexes at the center of the billets
圖 7 工藝參數（a）調整前和（b）調整后的鑄坯低倍圖
Figure 7. Low-magnification maps of slab (a) before and (b) after adjusting process parameters
圖 8 工藝參數（a）調整前和（b）調整后的鑄坯金相圖
Figure 8. Metallography of billet (a) before and (b) after adjusting process parameters
表 1 連鑄機主要參數
Table 1. Main parameters of continuous-casting machine
Caster type Flow number Radius / m Metallurgical length / m Flow spacing / mm Arc 8 10 30.6 1250 Lengths / mm Casting speeds / (m?min?1) Electromagnetic stirring Straightening method Slab cooling mode 6000?12000 3.2 F-EMS Continuous straightening Water-cooling + air-vapor cooling 
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表 2 82B盤條化學成分（質量分數）
Table 2. Chemical composition of 82B wire rods
% C Si Mn S P Cr 0.82 0.23 0.75 0.005 0.016 0.258
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表 3 82B試樣的力學性能
Table 3. Mechanical properties of 82B samples
Sample Tensile strength /
MPaElongation after
fracture / %Area reduction /
%Sample 1 1200 18 41 Sample 2 1230 17 33 Sample 3 1220 19 37 Sample 4 1200 18 34 Sample 5 1210 17 36
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表 4 碳偏析指數
Table 4. Carbon segregation index
Sample Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Segregation index 1.15 1.17 1.18 1.17 1.16
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表 5 標準κ–ε雙方程模型中的經驗系數
Table 5. Empirical coefficient values in the standard κ–ε dual-equation model
Cμ C1 C2 ${\sigma _{\kappa} }$ ${\sigma _{\rm{e}}}$ 0.09 1.44 1.92 1.0 1.3
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