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Acta Metall Sin  2017, Vol. 53 Issue (8): 927-936    DOI: 10.11900/0412.1961.2017.00055
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Microstructure, Ordered Structure and Warm TensileDuctility of Fe-6.5%Si Alloy with Various Ce Content
Xuan YU1, Zhihao ZHANG2(), Jianxin XIE1,2
1 Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing, Beijing 100083, China
2 Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China
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Fe-6.5%Si (mass fraction) alloy is an important soft magnetic material due to its excellent magnetic properties. However, the existence of ordered structure in a great amount is the fundamental cause of poor ductility of the alloy, which restricts the application of the alloy seriously. To modify the microstructure and crystal structure of Fe-6.5%Si alloy by rare earth micro-alloying is one of the significant methods to reduce brittleness and improve plastic deformation ability of the alloy. Whereas, there still lack of elaborate studies on order degree reduction mechanism, ductility improvement evaluation and its connections to a varying microstructure, rare earth distribution, etc., caused by rare earth doping, which restricts a deep understanding on rare earth micro-alloying mechanism and its application in this alloy. In this work, influences of Ce content (mass fraction) on microstructure, ordered structures and warm tensile property of the as-cast alloy were investigated, and the ductility improvement mechanism of the alloy caused by Ce micro-alloying was analyzed. The results indicate that, there is no evident variation of as-cast microstructure when Ce content is below 150×10-6, while the obvious microstructure refinement is observed when Ce content exceeds 210×10-6. Ce addition reduces the alloy's order degree significantly and thus improves its warm tensile ductility obviously. Compared with Ce undoped specimens, average tensile elongation to failure at 400 ℃ increases from 7.4% to 10.1%, 19.3% and 23.0% by 62×10-6, 150×10-6 and 210×10-6 Ce doping, respectively. Inter-granular brittle fracture characteristic occurs in fractured tensile specimens due to the obvious Ce enrichment at grain boundary when Ce content increases to 260×10-6 and 790×10-6, hence the average tensile elongation to failure at 400 ℃ reduces to 15.5% and 14.2%. A reasonable Ce content is within the range of (150~210)×10-6 to improve effectively the ductility of Fe-6.5%Si alloy.

Key words:  Fe-6.5%Si alloy      rare earth element      ordered structure      ductility      intermetallics     
Received:  22 February 2017     
ZTFLH:  TG11  
Fund: Supported by National Basic Research Program of China (No.2011CB606300) and High Technology Research and Development Program of China (No.2012AA03A505)

Cite this article: 

Xuan YU, Zhihao ZHANG, Jianxin XIE. Microstructure, Ordered Structure and Warm TensileDuctility of Fe-6.5%Si Alloy with Various Ce Content. Acta Metall Sin, 2017, 53(8): 927-936.

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Sample Ce Si S P O C Fe
Ce-0 0 6.56 0.0057 0.0071 0.0005 0.023 Bal.
Ce-62 0.0062 6.62 0.0056 0.0063 0.0008 0.021 Bal.
Ce-150 0.0150 6.40 0.0049 0.0084 0.0004 0.026 Bal.
Ce-210 0.0210 6.52 0.0014 0.0068 0.0007 0.021 Bal.
Ce-260 0.0260 6.54 0.0014 0.0064 0.0006 0.020 Bal.
Ce-790 0.0790 6.57 0.0009 0.0072 0.0006 0.017 Bal.
Table 1  Chemical compositions of the Fe-6.5% Si alloy ingots with different Ce contents (mass fraction / %)
Fig.1  OM images of the Fe-6.5%Si alloy samples of Ce-0 (a), Ce-62 (b), Ce-150 (c), Ce-210 (d), Ce-260 (e) and Ce-790 (f)
Fig.2  SEM image (a) and EPMA maps of Ce (b), S (c), O (d) and C (e) elements in Ce-210 sample nearby the grain boundary (Ce-rich phases are marked by arrows)
Fig.3  SEM image (a) and EPMA maps of Ce (b) and S (c) elements in Ce-790 sample (Ce-rich phases are marked by arrows)
Fig.4  XRD spectra of the Fe-6.5%Si alloy with different Ce contents
Fig.5  DSC curves of the Fe-6.5%Si alloy with various Ce contents (a) and average relative peak area of B2 to A2 transformation, taking the average area of Ce undoped samples as 1.0 (b)
Fig.6  {100} superlattice spot dark field TEM images and SAED patterns (insets) of <001> zone axis of samples Ce-0 (a), Ce-62 (b), Ce-150 (c) and Ce-210 (d) (APB—antiphase boundary)
Fig.7  Schematic of ordered structure formation characteristics in the Fe-6.5%Si alloy with Ce undoped and doped
Fig.8  Engineering stress-strain curves (a) and average plastic elongation to failure and average ultimate tensile stress curves (b) of the Fe-6.5%Si alloy tested at 400 ℃ (Inset in Fig.8a shows the macrophotograph of original and tested specimens)
Fig.9  Fracture morphologies of the Fe-6.5%Si alloy at 400 ℃ (Insets in Figs.9b~d are the local magnifications)

(a) Ce-0 (b) Ce-62 (c) Ce-150 (d) Ce-210 (e) Ce-260 (f) Ce-790

Fig.10  Schematic of microscopic characteristics and warm tensile ductility in the Fe-6.5%Si alloy with different Ce contents
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