Evolution of oxide–CaS complex inclusions during protective atmosphere electroslag remelting
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摘要: 利用掃描電鏡分析了自耗電極和電渣重熔鋼中夾雜物的特征，結合熱力學計算，分析了氧硫復合夾雜物在電渣重熔過程中的轉變機理。結果表明，電渣重熔采用氣氛保護結合脫氧操作可以將自耗電極全氧質量分數由0.0017%降低至0.0008%。電渣重熔之后鋼中小于3 μm夾雜物的比例顯著增加。自耗電極中的夾雜物為CaS與含質量分數3%和11%左右MgO的CaO–Al2O3–SiO2–MgO結合的兩類復合夾雜物。電渣過程未被去除的氧化物夾雜中的SiO2被鋼液中酸溶鋁還原，保留至電渣錠中。電渣錠中含約1%MgO和2%SiO2且成分均勻的CaO–Al2O3–SiO2–MgO是在電渣過程中新生的夾雜物。自耗電極中的CaS通過分解為鋼液中溶解Ca和S，以及通過與液態氧化物夾雜中Al2O3反應的途徑在電渣過程被去除。電渣錠中低熔點氧化物夾雜周圍環狀CaS是鋼液凝固過程中溶解S、酸溶鋁Al與氧化物夾雜中CaO的反應產物，高熔點氧化物夾雜周圍環狀CaS是鋼液凝固過程中Ca和S偏析后反應新生的夾雜物。復合夾雜物中補丁狀CaS是在電渣重熔鋼液冷卻過程中由復合夾雜物熔體中析出的。Abstract: The inclusions in the consumable steel electrode and electroslag remelted steel were characterized using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). The evolution mechanism of oxide–sulfide complex inclusions during electroslag remelting (ESR) was elucidated based on inclusion experimental identification and thermodynamic calculation. The results show that the combination of protective atmosphere and deoxidation operation during ESR lowers the total oxygen content from 0.0017% in the electrode to 0.0008% in the ingot. The number proportion of the inclusions smaller than 3 μm in the steel greatly increases after ESR. The inclusions in the steel electrode are two oxide–sulfide complex types of CaS+CaO–Al2O3–SiO2–MgO containing about 3% MgO and CaS+CaO–Al2O3–SiO2–MgO containing about 11% MgO. SiO2 in the original oxide inclusions that had not been removed in ESRR process was reduced by soluble aluminum in liquid steel, and the products remain in the ESR process until in remelted ingot. The CaO–Al2O3–SiO2–MgO inclusions with uniform elements distribution, which contain about 1%MgO and about 2%SiO2, in the ingot are newly formed oxide inclusions in the ESR. CaS inclusions in the steel electrode were removed during the ESR through dissociating into soluble calcium and sulfur in liquid steel, and in the way of reacting with Al2O3 in liquid oxide inclusions. The shell-type CaS around low-melting-temperature oxide inclusion generated as a result of the reaction between CaO in the oxide inclusion and dissolved aluminum and sulfur in liquid steel during solidification of liquid steel in the ESR process. The shell-type CaS around high-melting-temperature oxide inclusion is the reaction products of enriched soluble Ca and S during solidification of liquid steel. Patch-type CaS in the oxide–sulfide complex inclusion precipitated from the complex inclusion melt during the cooling of liquid steel in the ESR process.
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Key words:
- non-metallic inclusion /
- sulfide /
- electroslag remelting /
- ultralow oxygen /
- sulfide capacity
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圖 1 自耗電極和電渣錠中夾雜物的尺寸分布
Figure 1. Size distribution of inclusions in the consumable steel and remelted steel
圖 2 自耗電極中典型夾雜物的元素面分布（a,b,c）和EDS譜圖（d,e）（圖（d）和（e）中的EDS譜圖分別對應圖（a）和（c）中夾雜物的EDS點分析）
Figure 2. Element mappings (a,b,c) and EDS spectra (d,e) of complex inclusions in the consumable steel electrode (EDS spectra in (d) and (e) correspond to the inclusions shown in (a) and (c), respectively).
圖 3 自耗電極中氧化物夾雜在CaO–Al2O3–SiO2三元相圖中的成分分布。（a）3%MgO；（b）11%MgO
Figure 3. Composition distribution of oxide inclusions in steel electrode on the CaO–Al2O3–SiO2 phase diagram: (a) 3%MgO; (b) 11%MgO
圖 4 電渣錠中典型夾雜物的元素面分布（a,b,c,d）和EDS譜圖（e,f）（圖（e）和（f）中的EDS譜圖分別對應圖（a）和（d）中夾雜物的EDS點分析）
Figure 4. Element mappings (a,b,c,d) and EDS spectra (e,f) of complex inclusions in the remelted ingot (EDS spectra in (e) and (f) correspond to the inclusions shown in (a) and (d), respectively)
圖 5 電渣錠中氧化物夾雜在CaO–Al2O3–SiO2三元相圖中的成分分布。（a）3%MgO；（b）11%MgO
Figure 5. Composition distribution of oxide inclusions in the remelted ingot on the CaO–Al2O3–SiO2 phase diagram: (a) 3%MgO; (b) 11%MgO
圖 6 氧化物夾雜中SiO2與酸溶鋁[Al]s反應的吉布斯自由能變化值隨溫度的變化
Figure 6. Gibbs free energy change for the reaction between SiO2 in the oxide inclusion and dissolved aluminum in liquid steel against the temperature
圖 7 氧化物夾雜中MgO與酸溶鋁[Al]s反應的吉布斯自由能變化值隨溫度的變化
Figure 7. Gibbs free energy change for the reaction between MgO in the oxide inclusion and dissolved aluminum in liquid steel against the temperature
圖 8 CaO–Al2O3–SiO2–MgO夾雜物的硫化物容量隨溫度的變化
Figure 8. Dependence of the sulfide capacity of CaO–Al2O3–SiO2–MgO inclusion on temperature
表 1 自耗電極的化學成分（質量分數）
Table 1. Chemical composition of the consumable electrode and remelted ingot
% C Si Mn S Ni Cr V Mo Ca T.O Al Mg N 0.39 1.15 0.42 0.0022 0.16 5.67 0.97 1.47 0.0008 0.0017 0.0150 0.0003 0.0083 
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表 2 電渣錠的化學成分（質量分數）
Table 2. Chemical composition of the remelted ingot
% C Si Mn S Ni Cr V Mo Ca T.O Al Mg N 0.39 1.06 0.42 0.0016 0.16 5.67 0.97 1.47 0.0005 0.0008 0.0160 0.0002 0.0088
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表 3 采用的一階活度相互作用系數數據[11, 21–22]
Table 3. First-order interaction parameters
$\mathop e\nolimits_i^j $ used in the present calculation$\mathop e\nolimits_i^j $ C Si Mn S Ni Cr V Ca O Al N Al 0.091 0.056 0.0035 0.035 –0.029 0.0096 — –0.047 –1.98 0.045 –0.058 Si 0.18 0.11 0.002 0.056 0.005 –0.0003 0.025 –0.067 –0.23 0.058 0.09
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表 4 采用的一階活度相互作用系數
$e_i^j$ [20, 22, 29]Table 4. First-order interaction parameters
$e_i^j$ used in the present study[20, 22, 29]$\mathop e\nolimits_{\rm{i}}^j $ C Si Mn S Ni Cr V Mo Ca O Al Ca –0.34 –0.096 –0.0156 –140 –0.044 0.014 — — –0.002 –9000 –0.072 S 0.111 0.075 –0.026 –0.046 — –0.0105 –0.019 0.0027 –110 –0.27 0.041 Mg 0.15 –0.096 — — –0.012 0.022 — — — 560 –0.27
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表 5 ξ的計算參數
Table 5. Parameters used for calculating ξ
Unary reaction ξi MgO 9573.07326 Al2O3 157705.276 SiO2 168872.847 CaO –3.3099425×104 Binary reaction ξmix Al2O3–CaO ${y_{{\rm{A}}{{\rm{l}}^{{\rm{3 + }}}}}} \cdot {y_{{\rm{C}}{{\rm{a}}^{{\rm{2 + }}}}}} \cdot \left[ {98282.7968 + 55.07340941T} \right]$ Al2O3–SiO2 ${y_{{\rm{A}}{{\rm{l}}^{{\rm{3 + }}}}}} \cdot {y_{{\rm{S}}{{\rm{i}}^{{\rm{4 + }}}}}} \cdot \left[ {186850.468} \right]$ CaO–SiO2 ${y_{{\rm{C}}{{\rm{a}}^{{\rm{2 + }}}}}} \cdot {y_{{\rm{S}}{{\rm{i}}^{{\rm{4 + }}}}}} \cdot \left[ {97271.7695 + 72.874T} \right]$ MgO–SiO2 ${y_{{\rm{M}}{{\rm{g}}^{{\rm{2 + }}}}}} \cdot {y_{{\rm{S}}{{\rm{i}}^{{\rm{4 + }}}}}} \cdot \left[ {69740.322 - 224.084556T} \right]$ Ternary reaction ξmix Al2O3–MgO–CaO ${y_{{\rm{A}}{{\rm{l}}^{{\rm{3 + }}}}}} \cdot {y_{{\rm{M}}{{\rm{g}}^{{\rm{2 + }}}}}} \cdot {y_{{\rm{C}}{{\rm{a}}^{{\rm{2 + }}}}}} \cdot \left[ {4165955.5 - 1066.5663T - {\rm{3040801}}{\rm{.89}}{y_{{\rm{A}}{{\rm{l}}^{{\rm{3 + }}}}}}} \right]$ Al2O3– SiO2–CaO ${y_{{\rm{A}}{{\rm{l}}^{{\rm{3 + }}}}}} \cdot {y_{{\rm{S}}{{\rm{i}}^{{\rm{4 + }}}}}} \cdot {y_{{\rm{C}}{{\rm{a}}^{{\rm{2 + }}}}}} \cdot \left[ { - 2035792.64 + {\rm{686}}{\rm{.044695}}T} \right]$ Al2O3–SiO2–MgO ${y_{{\rm{A}}{{\rm{l}}^{{\rm{3 + }}}}}} \cdot {y_{{\rm{S}}{{\rm{i}}^{{\rm{4 + }}}}}} \cdot {y_{{\rm{M}}{{\rm{g}}^{{\rm{2 + }}}}}} \cdot \left[ {{\rm{156192}}{\rm{.588}} - {\rm{290}}{\rm{.498555}}T{\rm{ + 949447}}{\rm{.247}}{y_{{\rm{A}}{{\rm{l}}^{{\rm{3 + }}}}}}} \right]$ SiO2–MgO–CaO ${y_{{\rm{M}}{{\rm{g}}^{{\rm{2 + }}}}}} \cdot {y_{{\rm{S}}{{\rm{i}}^{{\rm{4 + }}}}}} \cdot {y_{{\rm{C}}{{\rm{a}}^{{\rm{2 + }}}}}} \cdot \left[ { - {\rm{1526497}}{\rm{.71 + 625}}{\rm{.662842}}T{\rm{ + 1485255}}{\rm{.98}}{y_{{\rm{C}}{{\rm{a}}^{{\rm{2 + }}}}}}} \right]$
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