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摘要: 通過工業試驗對202不銹鋼進行系統取樣，分析試樣中夾雜物的變化特征，結合熱力學計算，研究了202不銹鋼中非金屬夾雜物的形成機理。在進行硅錳脫氧后，LF精煉過程中鋼液內以球型Ca?Si?Mn?O夾雜物為主。對于硅錳脫氧鋼，鋼液中殘余鋁質量分數為1×10?5時，可以擴大Mn?Si?O相圖的液相區，但鋁質量分數超過3×10?5會導致鋼中容易形成氧化鋁夾雜物并減小液相區。在連鑄坯中以Mn?Al?O類夾雜物為主，相較于LF精煉過程試樣，連鑄坯試樣中夾雜物的MnO和Al2O3含量明顯增加，CaO和SiO2含量明顯減小，夾雜物個數則由LF出鋼試樣的5.5 mm?2增加到11.3 mm?2。結合熱力學計算發現，凝固過程中會有Mn?Al?O夾雜物形成，這也使其成為連鑄坯中主要的夾雜物類型。Abstract: Non-metallic inclusions generally deteriorate the quality of stainless steel products, such as skin laminations or line defects on the rolled strip in stainless steel. Thus, the formation mechanism of non-metallic inclusions in 202 stainless steel was investigated with industrial trials and thermodynamic calculation. Steel samples were analyzed by scanning electron microscopy and energy dispersive spectroscopy. Compositions of the steel samples were determined by inductively coupled plasma-optical emission spectrometer. After Si?Mn deoxidation, the main inclusions were spherical Ca?Si?Mn?O inclusions during LF refining process. The liquid phase region of the Mn?Si?O phase diagram was affected by the residual aluminum content in Si?Mn deoxidized stainless steel. 1×10?5 mass fraction of aluminum in steel enlarged the liquid phase region of the Mn?Si?O phase diagram. However, more than 3×10?5 mass fraction of aluminum led to the formation of alumina inclusions and the reduction of the liquid phase region of the Mn?Si?O phase diagram. After the continuous casting process, the main inclusions in the steel were changed from Ca?Si?Mn?O to Mn?Al?O. Compared with the steel sample taken during the LF refining process, the MnO and Al2O3 content of inclusions in the continuous casting samples increased significantly, while the content of CaO and SiO2 decreased significantly. At the same time, the amount of inclusions increased from 5.5 mm?2 to 11.3 mm?2 after continuous casting. Combined with thermodynamic calculations, it was found that Mn?Al?O inclusions were formed during solidification, which became the main type of inclusion after continuous casting. In addition, the effect of aluminum content on the formation of oxide inclusions during continuous casting was discussed. Thermodynamic calculation indicated that the alumina inclusions were formed in the steel containing more than 3×10?5 mass fraction of aluminum during continuous casting. High aluminum content promoted the formation of alumina and inhibited the formation of Mn?Al?O inclusions during solidification.
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Key words:
- stainless steel /
- Si?Mn deoxidation /
- continuous casting /
- inclusion /
- thermodynamic calculation
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圖 2 202不銹鋼試樣中典型夾雜物形貌. (a) 試樣1；(b) 試樣2；(c) 試樣3
Figure 2. Morphology of inclusions in steel samples: (a) sample 1; (b) sample 2; (c) sample 3
圖 3 202不銹鋼試樣中典型夾雜物成分分布情況. (a) 試樣1；(b) 試樣2；(c) 試樣3
Figure 3. Distribution of main elements in inclusions: (a) sample 1; (b) sample 2; (c) sample 3
圖 4 夾雜物在CaO?SiO2?MnO相圖中的分布情況
Figure 4. Composition distributions (mass fraction) of inclusions in CaO?SiO2?MnO phase diagrams. Solid lines represent the boundary line of different phases at 1873 K
圖 5 夾雜物在Al2O3?SiO2?MnO相圖中的分布情況
Figure 5. Composition distributions (mass fraction) of inclusions in Al2O3?SiO2?MnO phase diagrams. Solid lines represent the boundary line of different phases at 1873 K
圖 7 不同尺寸夾雜物中各氧化物質量比例. (a) 試樣1；(b) 試樣2；(c) 試樣3
Figure 7. Mass ratio of main compositions in inclusions of different sizes: (a) sample 1; (b) sample 2; (c) sample 3
圖 8 1600 ℃202不銹鋼Si?Mn?O平衡相圖
Figure 8. Phase diagram of the Si?Mn?O system with iso-oxygen contours in Fe?15Cr?4Ni steel at 1600 ℃
圖 9 1600 ℃不同鋁含量202不銹鋼Si?Mn?O平衡相圖. (a) Fe?15Cr?4Ni?0.001Al鋼液；(b) Fe?15Cr?4Ni?0.003Al鋼液
Figure 9. Phase diagram of the Si?Mn?O system with iso-oxygen contours: (a) Fe?15Cr?4Ni?0.001Al steel; (b) Fe?15Cr?4Ni?0.003Al steel at 1600 ℃
圖 10 202不銹鋼平衡析出相圖. (a) 1×10?5 Al; (b) 3×10?5 Al; (c) 6×10?5 Al; (d) 1×10?4 Al
Figure 10. Equilibrium precipitation of inclusions during continuous casting of sample 3 with different Al contents: (a) 1×10?5 Al; (b) 3×10?5 Al; (c) 6×10?5 Al; (d) 1×10?4 Al
表 1 202不銹鋼主要成分
Table 1. Chemical composition of 202 stainless steel
試樣號 取樣位置 質量分數/% C Si Mn S Cr Ni Al O 1# LF進站 0.036 0.50 7.34 0.0110 14.77 3.95 0.0004 0.0029 2# LF出站 0.036 0.49 7.40 0.0095 15.03 3.97 0.0005 0.0024 3# 連鑄坯 0.041 0.45 7.31 0.0033 14.73 3.98 0.0009 0.0022 
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