Solidification microstructure of high borated stainless steels with rare earth and titanium additions
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Rare Met. https://doi.org/10.1007/s12598-019-01247-w
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Solidification microstructure of high borated stainless steels with rare earth and titanium additions Yong-Wang Li, Hai-Tao Liu* , Zhao-Jie Wang, Zhi-Heng Zhang, Wei-Ting Li, Hui-Ying Shen, Xiao-Ming Zhang, Guo-Dong Wang
Received: 4 February 2018 / Revised: 16 April 2018 / Accepted: 12 March 2019 Ó The Nonferrous Metals Society of China and Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract To study the effects of rare earth (RE) and Ti on the solidification microstructure of high borated stainless steels, 1.6 wt% B stainless steel doped with RE and 2.1 wt% B stainless steel doped with Ti were prepared by ingot casting, respectively. The solidification microstructure of researched steels was characterized in detail. The modification mechanism was clarified based on the heterogeneous nucleation theory and the thermodynamic calculation. The solidification microstructure of 1.6 wt% B and 2.1 wt% B stainless steels was characterized by the continuous and network-like eutectic borides around the matrix grains. It was found that the fine RE compounds could act as the heterogeneous nuclei for both borides and austenite during solidification. Thus, the eutectic borides were more dispersed in the modified steel. Moreover, lots of fine ‘eutectic cells’ were formed in the matrix regions. As a result of the preferential formation of TiB2 during solidification, the amount of the eutectic borides in the steel modified with Ti was significantly decreased. Besides, the continuity of the eutectic borides network was weakened. In a word, the present work provides a promising method to modify the solidification microstructure for high borated stainless steels. Keywords Borated stainless steels; Solidification microstructure; Rare earth; Titanium
Y.-W. Li, H.-T. Liu*, Z.-J. Wang, Z.-H. Zhang, W.-T. Li, H.-Y. Shen, X.-M. Zhang, G.-D. Wang State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China e-mail: [email protected]
1 Introduction In the nuclear-fuel-reprocessing systems, the demands for high borated stainless steels (modified austenitic stainless steel with 0.20 wt%–2.25 wt% boron, which was defined by ASTM A887-89) used as the container materials to store and transport spent fuel are increasing due to their excellent properties of thermal neutron absorption and anti-corrosion [1–3]. With the boron content in the steels increasing, an improvement in thermal neutron absorption property would be obtained. However, the limited solubility of boron in stainless steel would induce a large number of continuous and network-like eutectic M2B-type borides in the steels which were prepared by ingot casting [4, 5]. These eutectic borides revealed a considerable difference in mechanical properties with matrix grains, severely deteriorating the workability of ingots [5–7]. The workability would be greatly improved if finer and more dispersed borides could be obtained for high borated stainless steel
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