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摘要: 為了進一步研究20CrMo合金鋼在生產過程中夾雜物的演變機理，實現對鋼中非金屬夾雜物的合理控制，保證生產順行，提高產品力學性能，針對“BOF→LF→RH→鈣處理→連鑄→熱軋”工序生產20CrMo合金鋼全流程中非金屬夾雜物的演變規律進行了研究。在LF精煉及RH精煉加鈣前鋼中非金屬夾雜物含有70%以上的Al2O3。鈣處理后，由于過量的鈣加入到鋼液中，夾雜物中CaS質量分數迅速增加至59%，Al2O3質量分數降低至21%。在連鑄過程中由于二次氧化的發生，夾雜物轉變為CaO?Al2O3，其中含有50%的Al2O3、39%的CaO和10%的CaS，并且夾雜物平均尺寸增加。在鋼的冷卻和凝固過程中，CaO質量分數降低至5%，CaS質量分數增加至57%，鋼中夾雜物轉變為Al2O3?CaO?CaS的復合夾雜物，同時含有少量大尺寸的CaO?Al2O3夾雜物。在鋼的軋制過程中，夾雜物中CaO含量進一步降低，CaS含量增加，夾雜物平均尺寸增加，形成了CaO?Al2O3與CaS黏結型的復合夾雜物與Al2O3?CaS復合夾雜物。對CaO-Al2O3與CaS黏結型的復合夾雜物的形成原因進行了討論。Abstract: 20CrMo alloy steel is commonly used to produce high-pressure pipes, gears, automobile parts, etc., and there are stringent requirements for its yield strength, tensile strength, and impact energy. In the actual production process, the existence of nonmetallic inclusions has an important impact on the properties of 20CrMo steel; therefore, studying the evolution of inclusions in the process is necessary. To further examine the evolutionary mechanism of inclusions in the overall production process, the evolution of nonmetallic inclusions in a 20CrMo alloy steel produced via the route of “Basic oxygen furnace (BOF)→Ladle furnace refining (LF)→ Vacuum cycle degassing process (RH)→ calcium treatment→ Continuous casting (CC)→ hot rolling” was studied. This process ensured a smooth production process and improved the mechanical properties of the products. Al2O3 was the main inclusions in the steel during LF and RH refining, which was up to 70%. After calcium treatment, CaS in inclusions increased to 59% and Al2O3 decreased to 21% due to the excessive mixing of calcium into the molten steel. Due to reoxidation during continuous casting, inclusions were transformed to CaO–Al2O3, with 50% Al2O3, 39% CaO, and 10% CaS. And the average diameter of inclusions also increased, which was detrimental to the mechanical properties of the steel. After cooling and solidification of the steel, CaO decreased to 5% and CaS increased to 57%. Inclusions in the steel were transformed into Al2O3–CaO–CaS, and a small amount of large-sized CaO–Al2O3 was also observed. During the rolling process of steel, the CaO content in inclusions further decreased while the CaS content and the diameter of inclusions increased. Moreover, two types of inclusions were observed in the hot-rolled plate, one being Al2O3–CaS compound inclusions, whose size was relatively small, and the other being CaO–Al2O3–CaS compound inclusions. Reasons for the formation of compound inclusions consisting of CaO–Al2O3 and CaS were also discussed.
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Key words:
- alloy steel /
- calcium treatment /
- inclusions /
- reoxidation /
- solidification
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圖 1 精煉及連鑄過程相關元素含量變化。（a）總硫含量、總氧含量、總氮含量；（b）總鈣含量、總鋁含量
Figure 1. Variation of composition in liquid steel: (a) T.S, T.O, and T.N contents; (b) T.Ca and T.Al contents
圖 2 生產過程中夾雜物平均尺寸及數密度變化
Figure 2. Changes in average diameter and number density of inclusions during the production process
圖 4 連鑄坯及軋材中夾雜物成分分布。（a）連鑄坯；（b）熱軋中間坯；（c）熱軋板
Figure 4. Composition distribution of inclusions in slab and rolling plate: (a) slab; (b) hot-rolled intermediate sheet; (c) hot rolling plate
圖 5 生產過程中夾雜物平均成分變化
Figure 5. Changes in the composition of inclusions during the production process of 20CrMo steel
圖 6 鈣處理后及中間包中夾雜物尺寸分布。（a）加鈣后；（b）中間包
Figure 6. Size distribution of inclusions after calcium treatment and in tundish: (a) after Ca addition; (b) tundish
圖 7 隨氧含量增加，鋼中夾雜物變化（溫度: 1823 K）
Figure 7. Change in inclusions with increased oxygen content (Temperature: 1823 K)
圖 9 隨溫度降低夾雜物本身物相轉變
Figure 9. Phase transformation of the inclusion with decreasing temperature
圖 10 隨溫度降低鋼中夾雜物物相轉變
Figure 10. Phase transformation of the inclusions in the steel with decreasing temperature
圖 11 中間包中典型夾雜物形貌。（a）CaO?Al2O3；（b）CaO?Al2O3與CaS復合夾雜物
Figure 11. Morphology of typical inclusions in tundish: (a) CaO?Al2O3; (b) CaO?Al2O3?CaS compound inclusions
圖 12 鑄坯及軋材中典型夾雜物形貌。（a）均相Al2O3?CaO?CaS復合夾雜物；（b）Al2O3?CaO與CaS黏結型夾雜物；（c）CaS夾雜物
Figure 12. Morphology of typical inclusions in slab and plate: (a) homogeneous Al2O3?CaO?CaS inclusions; (b) Al2O3?CaO and CaS compound inclusions; (c) CaS
圖 13 鑄坯中夾雜物尺寸與成分關系
Figure 13. Relationship between the size and composition of inclusions in the slab
圖 14 CaO?Al2O3與CaS黏結型夾雜物形成示意圖
Figure 14. Schematic diagram of the formation mechanism of CaO?Al2O3 and CaS bonded inclusions
表 1 20CrMo合金鋼化學成分（質量分數）
Table 1. Chemical composition of 20CrMo steel
% C Si Mn Cr Mo T.Al T.S T.Ca 0.2 0.21 0.55 0.95 0.2 0.025 <0.003 0.0025 
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