連鑄控流模式對大方坯及棒材組織結構與宏觀偏析影響

王璞; 鐵占鵬; 肖紅; 張壯; 唐海燕; 苗紅生; 張家泉

doi:10.13374/j.issn2095-9389.2021.01.27.007

連鑄控流模式對大方坯及棒材組織結構與宏觀偏析影響

doi: 10.13374/j.issn2095-9389.2021.01.27.007

王璞¹,
鐵占鵬^{1, 2},
肖紅^{1, 3},
張壯¹,
唐海燕¹,
苗紅生²,
張家泉^1, ,

1.
北京科技大學冶金與生態工程學院，北京 100083
2.
西寧特殊鋼股份有限公司，西寧 810005
3.
湖南中科電氣股份有限公司磁電研究院，岳陽 414000

基金項目: 國家自然科學基金資助項目（U1860111, 51874033）；國家重點研發計劃資助項目（016YEB0601302）；湖南省科技計劃資助項目（2019RS2065）

詳細信息

通訊作者:
E-mail：jqzhang@metall.ustb.edu.cn

中圖分類號: TF777.2
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出版歷程
- 收稿日期: 2020-01-27
- 網絡出版日期: 2021-03-08
- 刊出日期: 2021-08-25

Macrostructure and macrosegregation behavior of bloom products under various flow control modes of the casting process

1.
School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China
2.
Xining Special Steel Co., Ltd., Xining 810005, China
3.
Magnetoelectric Research Institute, Hunan Zhongke Electric Co., Ltd., Yueyang 414000, China

More Information

Corresponding author: E-mail: jqzhang@metall.ustb.edu.cn

摘要

摘要: 以中碳結構鋼大方坯及其熱軋棒材為研究對象，通過對鑄坯和軋材進行低倍侵蝕和成分分析，揭示了連鑄控流模式對大方坯凝固組織與宏觀偏析分布特征的影響及其鑄軋遺傳性。研究表明：常規直通水口澆注模式下，結晶器電磁攪拌(Mold electromagnetic stirring, M-EMS)電流由0增加到800 A，鑄坯等軸晶率由6.06%僅可增加到11.71%，難以有效避免大方坯常見的中心縮孔缺陷與突出的中心線偏析。采用新型五孔水口澆注模式，即使不開啟M-EMS，鑄坯中心等軸晶率仍可達23.1%，大方坯中心縮孔級別可降至1.0級以下，滿足后續熱軋大棒材探傷要求。同時發現，五孔水口澆注模式下，大方坯鑄態組織中往往會出現較為明顯的柱狀晶到等軸晶轉變(Columnar to equiaxed transition, CET)區，鑄坯斷面碳偏析指數呈M型分布，表現為斷面1/4位置CET區域碳偏析指數最高。大棒材軋制基本改變不了鑄坯斷面宏觀偏析的分布形態，且可能導致中心線偏析指數增加。同時指出，基于連鑄控流模式的作用規律和鑄?軋遺傳性特征，以及特殊鋼長材熱加工對中心致密度和偏析分布與程度的要求，實際生產中應從連鑄工藝源頭合理地控制鑄態組織與宏觀偏析分布形態。
- 水口注流模式 /
- 電磁攪拌 /
- 拉速 /
- 凝固組織形態 /
- 碳偏析分布 /
- 鑄軋遺傳性
Abstract: Owing to the large cross-section and wide solidification-temperature zone, bloom castings of medium- and high-carbon steels are prone to severe central shrinkage and macrosegregation defects. Flow control technologies such as nozzle injection mode and electromagnetic stirring, together with the casting speed, play a key role in the as-cast macrostructure and macrosegregation distribution in bloom castings achieving soundness and compositional homogeneity of the final as-rolled products. Based on the production process of a medium-carbon-steel bloom casting and its heavy section bars, various flow control modes have been adopted in the casting production to study their effects on the semiproduct solidification structure and the carbon distribution across the bloom section and the following rolled bars. The conventional nozzle with a single straight port shows that the equiaxed crystal ratio in the casting process can only increase from 6.06% to 11.71% with the M-EMS intensity changes from 0 to 800 A, in which a shrinkage cavity and macrosegregation exist along the centerline on the strand casting. While the novel five-port nozzle has been adopted, the equiaxed crystal ratio can reach 23.1% even with the M-EMS power off, and the center cavity index drops down to grade 1.0 or below, meeting the requirement of microvoid flaw detection for the bar products. Additionally, the carbon segregation across the bloom cross-section is observed to resemble an M-shaped curve with a maximum carbon segregation index in the columnar to equiaxed transition zone instead of the popular center region. For the heavy section bars rolled from bloom casting, a similar carbon distribution pattern as the cast is observed after hot working but with an even higher centerline segregation index. Therefore, considering the special quality requirements for the subsequent hot processing, the macrostructure and pattern and intensity of macro-segregation should be regulated from the beginning of casting with a reasonable flow control mode as mentioned in the study.
- nozzle injection modes /
- electromagnetic stirring /
- casting speed /
- pattern of macrostructure /
- carbon segregation distribution /
- cast-rolling heredity

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圖 1 大方坯鑄機和兩種水口示意圖

Figure 1. Schematic diagram of the bloom casting machine and the two kinds of nozzles

下載: 全尺寸圖片幻燈片

圖 2 大方坯鑄坯（a）與熱軋棒材（b）截面取樣及鉆屑示意圖

Figure 2. Schematic diagram for section sampling and drilling of the as-cast bloom (a) and hot-rolled bar (b)

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圖 3 結晶器不同控流模式下大方坯橫截面低倍情況。（a）115-S3B；（b）115-S3Z；（c）536-S1B

Figure 3. Macrostructure of the bloom cross-section under different flow control modes in the mold: (a) 115-S3B；(b) 115-S3Z；(c) 536-S1B

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圖 4 結晶器不同控流模式下鑄坯等軸晶率

Figure 4. Equiaxed crystal ratios under different flow control modes in the mold

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圖 5 不同F-EMS參數下大方坯低倍情況。（a）578-S2A鑄坯橫截面；（b）578-S2A鑄坯縱截面；（c）579-S1A鑄坯橫截面；（d）579-S1A鑄坯縱截面

Figure 5. Macrostructure of bloom castings under different parameters of the F-EMS: (a) cross-section of 578-S2A；(b) longitudinal section of 578-S2A；(c) cross-section of 579-S1A；(d) longitudinal section of 579-S1A

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圖 6 不同F-EMS參數下熱軋圓棒低倍情況。（a）578-S2A軋材橫截面；（b）578-S2A軋材縱截面；（c）579-S1A軋材橫截面；（d）579-S1A軋材縱截面

Figure 6. Macrostructure of hot-rolled bars under different parameters of the F-EMS: (a) cross-section of 578-S2A；(b) longitudinal section of 578-S2A；(c) cross-section of 579-S1A；(d) longitudinal section of 579-S1A

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圖 7 不同拉速下大方坯低倍形貌。（a）579-S3B鑄坯橫截面；（b）579-S3B鑄坯縱截面；（c）579-S2B鑄坯橫截面；（d）579-S2B鑄坯縱截面

Figure 7. Macrostructure of bloom castings under different casting speeds: (a) cross-section of 579-S3B；(b) longitudinal section of 579-S3B；(c) cross-section of 579-S2B；(d) longitudinal section of 579-S2B

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圖 8 五孔水口組合控流模式下不同拉速鑄坯等軸晶率

Figure 8. Equiaxed crystal ratios under different casting speeds with combined flow control modes

下載: 全尺寸圖片幻燈片

圖 9 兩種控流模式下大方坯縱截面低倍及碳偏析指數分布。（a）115-S3Z；（b）536-S2B

Figure 9. Macrostructure and carbon segregation index in the bloom longitudinal sections under two flow control modes: (a) 115-S3Z；(b) 536-S2B

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圖 10 鑄態枝晶組織特征與CET區正偏析形成機理

Figure 10. Schematic illustration of the as-cast macrostructure and location of the CET zone

1—chilled layed；2—columnar zone；3—CET zone；4—solid-liquid zone of euqiaxed；5—liquid-solid zone of equiaxed

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圖 11 鑄坯（左）與軋材（右）鉆屑取樣及其局域點狀偏析分布特征示意圖

Figure 11. Schematic illustration of sample drilling and local spot segregation distribution in the bloom casting and rolled bar

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圖 12 碳偏析指數分布特征。（a）鑄坯；（b）軋材

Figure 12. Distribution of the carbon segregation index: (a) as-cast bloom；(b) hot-rolled bar

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表 1 大方坯連鑄機及生產工藝基本參數

Table 1. Bloom continuous casting machine and its basic production parameters

Number of castings	Spacing of each strand/ mm	Cross-section/ （mm×mm）	Radius of continuous caster/m	Mold length/ mm	Maximum metallurgical length/m	Electromagnetic stirring technology
3 strands	2200	410×530	16.5	780	34	M-EMS+F-EMS

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表 2 45鋼主要化學成分（質量分數）

Table 2. Chemical composition of 45 steel %

C	Si	Mn	Cr	Ni	S	P
0.42–0.50	0.17–0.37	0.5–0.8	≤0.25	≤0.25	≤0.035	≤0.035

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表 3 試樣編號及澆鑄試驗工況

Table 3. Sample numbers and casting conditions

Sample number	Injection mode	Superheat degree/℃	Casting speed/ (m·min^?1)	(Current intensity/A) \ (Frequency/Hz)
Sample number	Injection mode	Superheat degree/℃	Casting speed/ (m·min^?1)	M-EMS	F-EMS
115-S3B	Normal nozzle	20	0.38	0\0	700\7.5
115-S3Z	Normal nozzle	20	0.38	800\1.5	700\7.5
536-S1B	Five-port nozzle	33	0.38	0\0	700\7.5
536-S2B	Five-port nozzle	33	0.38	300\1.5	700\7.5
578-S2A	Five-port nozzle	28	0.38	500\1.5	660\7.5
579-S1A	Five-port nozzle	28	0.38	500\1.5	800\5
579-S3B	Five-port nozzle	28	0.40	500\1.5	800\5
579-S2B	Five-port nozzle	28	0.42	500\1.5	800\5

下載: 導出CSV

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