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摘要: 通过工业试验对202不锈钢进行系统取样，分析试样中夹杂物的变化特征，结合热力学计算，研究了202不锈钢中非金属夹杂物的形成机理。在进行硅锰脱氧后，LF精炼过程中钢液内以球型Ca−Si−Mn−O夹杂物为主。对于硅锰脱氧钢，钢液中残余铝质量分数为1×10−5时，可以扩大Mn−Si−O相图的液相区，但铝质量分数超过3×10−5会导致钢中容易形成氧化铝夹杂物并减小液相区。在连铸坯中以Mn−Al−O类夹杂物为主，相较于LF精炼过程试样，连铸坯试样中夹杂物的MnO和Al2O3含量明显增加，CaO和SiO2含量明显减小，夹杂物个数则由LF出钢试样的5.5 mm−2增加到11.3 mm−2。结合热力学计算发现，凝固过程中会有Mn−Al−O夹杂物形成，这也使其成为连铸坯中主要的夹杂物类型。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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图 2 202不锈钢试样中典型夹杂物形貌. (a) 试样1；(b) 试样2；(c) 试样3
Figure 2. Morphology of inclusions in steel samples: (a) sample 1; (b) sample 2; (c) sample 3
图 3 202不锈钢试样中典型夹杂物成分分布情况. (a) 试样1；(b) 试样2；(c) 试样3
Figure 3. Distribution of main elements in inclusions: (a) sample 1; (b) sample 2; (c) sample 3
图 4 夹杂物在CaO−SiO2−MnO相图中的分布情况
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
图 5 夹杂物在Al2O3−SiO2−MnO相图中的分布情况
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
图 7 不同尺寸夹杂物中各氧化物质量比例. (a) 试样1；(b) 试样2；(c) 试样3
Figure 7. Mass ratio of main compositions in inclusions of different sizes: (a) sample 1; (b) sample 2; (c) sample 3
图 8 1600 ℃202不锈钢Si−Mn−O平衡相图
Figure 8. Phase diagram of the Si−Mn−O system with iso-oxygen contours in Fe−15Cr−4Ni steel at 1600 ℃
图 9 1600 ℃不同铝含量202不锈钢Si−Mn−O平衡相图. (a) Fe−15Cr−4Ni−0.001Al钢液；(b) Fe−15Cr−4Ni−0.003Al钢液
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 ℃
图 10 202不锈钢平衡析出相图. (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不锈钢主要成分
Table 1. Chemical composition of 202 stainless steel
试样号 取样位置 质量分数/% C Si Mn S Cr Ni Al O 1# LF进站 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# 连铸坯 0.041 0.45 7.31 0.0033 14.73 3.98 0.0009 0.0022 
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