Effect of La on non-metallic inclusions in FeCrAl alloy
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摘要: 为研究稀土La对FeCrAl合金中夹杂物类型及分布的影响，在热力学分析的基础上，借助SEM-EDS观察分析了夹杂物三维形貌及其成分，统计分析了夹杂物尺寸及数量。结果表明，1600 ℃时FeCrAl合金中只存在单一Al2O3夹杂。凝固过程中，随着体系中固相率的增大，AlN在凝固前沿析出。加入质量分数为0.0093%的La后，Al2O3被变质为LaAlO3。La添加量为0.0378%时，主要夹杂物类型为LaAlO3+La2O2S，夹杂物数量明显增多，且随着保温时长的增加， La2O2S比例逐渐增加。La添加量为0.0964%时，La2O2S比例进一步增加，保温60 min后，钢中只有单一La2O2S夹杂稳定存在。夹杂物聚合特性对夹杂物粒径影响显著。1600 ℃下保温60 min，仅含单一LaAlO3的试样中，LaAlO3在保温前期呈现较强的聚合趋势，夹杂物平均粒径先由2.34 μm增大至3.31 μm，随后减小至1.93 μm。La2O2S聚合趋势较弱，含有La2O2S的试样中，夹杂物平均粒径较小且变化稳定，在保温前期，夹杂物平均粒径稳定在1.8～2.0 μm。Abstract: In order to study the influence of rare earth La addition on the type and distribution of inclusions in FeCrAl alloys, based on thermodynamic analysis, the three-dimensional morphology and composition of inclusions were observed and analyzed by SEM-EDS, and the size and quantity of inclusions were statistically analyzed. The results show that single Al2O3 only inclusion exists in FeCrAl alloy at 1600 ℃. During the solidification process, with the increase of the solid fraction in the system, AlN precipitates at the solidification front. After adding 0.0093% La, Al2O3 transforms into LaAlO3. When the addition amount of La is 0.0378%, the type of inclusions is LaAlO3+La2O2S, and the number of inclusions increases significantly. As holding time prolongs, the proportion of La2O2S gradually increases. When the addition amount of La is 0.0964%, the proportion of La2O2S is further increased. After 60 min of heat preservation, single La2O2S only inclusion exists stably in the steel. The particle size of the inclusions is significantly affected by the aggregation properties of the inclusions. In the samples containing single LaAlO3 only at 1600 ℃ for 60 min, LaAlO3 shows a strong tendency to aggregate in the early stage of the incubation, and average particle size of the inclusions firstly increases from 2.34 μm to 3.31 μm, and then decreases to 1.93 μm. The tendency of La2O2S to aggregate is weak. In the samples containing La2O2S, average particle size of inclusions is small and uniform, in the early stage of heat preservation, average particle size of inclusions remains in the range of 1.8−2.0 μm.
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Key words:
- FeCrAl alloy /
- La /
- inclusions /
- AlN precipitates /
- agglomeration
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图 1 16Cr5Al中夹杂物平衡析出示意
Figure 1. Equilibrium precipitation diagram of inclusions in 16Cr5Al
图 2 16Cr5Al中Al-N平衡析出（1873 K）
Figure 2. Al-N equilibrium precipitation diagram in 16Cr5Al（1873 K）
图 3 Fe-16Cr-5Al-0.005N体系中AlN析出曲线(1800 K)
Figure 3. Thermodynamics of AlN formation in the Fe-16Cr-5Al-0.005N at 1800 K
图 4 不含稀土试样中典型夹杂物形貌及能谱分析结果
(a)AlN；(b)Al2O3
Figure 4. Morphology and energy spectrum analysis results of typical inclusions in steel without RE addition
图 5 不含稀土试样中典型夹杂物三维形貌
(a) AlN；(b) Al2O3
Figure 5. Three-dimensional morphology of typical inclusions in steel without RE addition
图 6 典型稀土夹杂物形貌及能谱分析结果
(a) LaAlO3；(b) La2O2S
Figure 6. Typical rare earth inclusion morphology and energy spectrum analysis results
图 7 典型稀土夹杂物三维形貌
(a)、(b) La2O2S；(c)、(d) LaAlO3
Figure 7. Three-dimensional morphology of typical rare earth inclusions
图 9 稀土夹杂物存在状态及数密度变化
Figure 9. Existence state and number density change of rare earth inclusions in steel under different conditions
图 10 稀土夹杂物粒径统计
Figure 10. Statistics of particle size of rare earth inclusions in steel under different conditions
表 1 试验钢化学成分
Table 1. Chemical compositions of experimental steels
% 编号 Cr Al La C N S O [O]1 [O]2 1# 15.96 5.07 0.0093 0.156 0.0052 0.0005 0.0019 0.0030 ＜0.0001 2# 16.03 4.96 0.0378 0.132 0.0068 0.0007 0.0023 0.0055 ＜0.0001 3# 15.92 5.05 0.0964 0.128 0.0046 ＜0.0005 0.0013 0.0056 ＜0.0001 
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表 2 溶质元素的平衡分配系数及扩散系数
Table 2. Equilibrium partition coefficient and diffusion coefficient of solute elements
溶质元素 $ {k}^{\delta /L} $ $ {D}_{\mathrm{s}} $/（m2·s−1） Al 0.96 5.9×10−4×exp(−241417/RT) Cr 0.95 2.4×10−4×exp(−239785/RT) N 0.25 8×10−7×exp(−79078/RT)
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表 3 钢中元素相互作用系数
Table 3. Coefficient of interaction of elements in steel
$ {e}_{{\rm{Al}}}^{{\rm{Al}}} $ $ {r}_{{\rm{Al}}}^{{\rm{Al}}} $ $ {e}_{{\rm{Al}}}^{{\rm{Cr}}} $ $ {r}_{{\rm{Al}}}^{{\rm{Cr}}} $ $ {e}_{{\rm{Al}}}^{{\rm{N}}} $ $ {r}_{{\rm{Al}}}^{{\rm{N}}} $ $ {e}_{{\rm{N}}}^{{\rm{Al}}} $ $ {r}_{{\rm{N}}}^{{\rm{Al}}} $ $ {e}_{{\rm{N}}}^{{\rm{Cr}}} $ $ {r}_{{\rm{N}}}^{{\rm{Cr}}} $ $ {e}_{{\rm{N}}}^{{\rm{N}}} $ $ {r}_{{\rm{N}}}^{{\rm{N}}} $ 0.043 −0.001 0.0122 0 0.033 0 0.017 0 −0.06 0.0007 0 0
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表 4 试样中不同夹杂物类型
Table 4. Different inclusion types in steel samples
编号 夹杂物类型 不同稀土处理时间夹杂物类型变化 5 min 10 min 20 min 30 min 60 min 1# AlN √ √ √ √ √ Al2O3 √ √ √ LaAlO3 √ √ √ √ √ La2O2S 2# AlN √ √ √ √ √ Al2O3 √ √ LaAlO3 √ √ √ √ √ La2O2S √ √ √ √ √ 3# AlN √ √ √ √ √ Al2O3 √ √ LaAlO3 √ √ √ √ La2O2S √ √ √ √ √
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