Contents lists available at ScienceDirect Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea Developing fuel cladding Fe-25Cr-22Ni stainless steels with high microstructural stabilities via Mo/Nb/Ti/Ta/W alloying D.H. Wen a , Q. Wang a, ⁎ , B.B. Jiang a , C. Zhang a , X.N. Li a , G.Q. Chen a , R. Tang b , R.Q. Zhang b , C. Dong a , P.K. Liaw c a Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China b Science and Technology on Reactor Fuel and Materials Laboratory, Nuclear Power Institute of China, Chengdu 610213, China c Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996, USA ARTICLE INFO Keywords: Austenitic stainless steels Minor-alloying Microstructural stability Precipitation behavior Mechanical property ABSTRACT In order to improve the microstructural stability of high Cr/Ni austenitic stainless steels (ASSs) at high tem- peratures, the present work investigated the effects of minor-alloying elements (Mo, Nb, Ti, Ta, and W) on the microstructural evolution and mechanical properties of Fe-25Cr-22Ni (wt%) ASS systematically. The designed alloy ingots were hot-rolled, solid-solutioned at 1423 K for 0.5 h, stabilized at 1173 K for 0.5 h, and then aged at 973 K for different hours. It was found that these minor-alloying elements make different contributions to the microstructural stabilities of alloys. Only a small amount of harmful σ particles exists after 408 h-aging in W/Ta- modified alloys, which indicates W and Ta can improve the microstructural stability effectively. Whereas Ti should be forbidden since it accelerates the phase precipitation of Cr 23 C 6 and σ remarkably. Excessive Mo can also promote the formation of σ phase and the transformation of Cr 23 C 6 to σ during aging. The influences of the precipitated phases on mechanical properties of alloys were then studied. Thermal calculations were also per- formed to analyze the phase precipitation caused by minor-alloying. The Fe-25Cr-22Ni-0.046C-0.73Mo-0.18Nb- 0.34Ta (wt%) exhibits excellent mechanical property due to its higher microstructural stability at 973 K, which has great potential for fuel cladding application. 1. Introduction Fuel-cladding materials are of great importance for developing super-critical water reactors (SCWRs) due to the severe environment of the super-critical water (SCW) state at 923 K / 25 MPa, which requires the cladding materials with a good combination of creep-resistant strength, high corrosion-, oxidation-, and neutron irradiation-resistant properties [1,2]. Although zirconium alloy cladding materials exhibited outstanding comprehensive performances in commercial reactors op- erated below 623 K, their corrosion resistance could be deteriorated sharply in the SCW circumstance [3,4]. Ferrite/Martensite dual-phase stainless steels (SSs) suffer from severe oxidation under the SCW con- dition and exhibit poor creep-resistance at high temperatures (HTs) [5]. The prominent mechanical properties and corrosion-resistance of Ni- based superalloys at HTs could not balance out the radiation-induced fragility because of the large thermal neutron absorption coefficient of the base Ni [6–8]. In contrast, the austenitic stainless steels (ASSs) containing high Cr and Ni contents ((20–25)Cr-(20–25)Ni, the numbers in front of elements present the weight percent, wt%), such as 310S (Fe- 25Cr-20Ni-0.08C), HR3C (Fe-25Cr-20Ni-0.4Nb-0.1C-0.2N), and NF709 (Fe-20Cr-25Ni-1.5Mo-0.3Nb-0.1Ti-0.15N-0.08C), are candidate mate- rials to be applied into the SCWRs, since they exhibit prominent com- prehensive properties and relatively-lower irradiation sensitivity [9,10]. However, one underlying issue for this kind of high-Cr/Ni ASSs is their microstructural stability during the long-term exposure to the SCWRs coolant at high temperatures. In other words, some coarse harmful brittle phases, like Cr 23 C 6 (cF-C 6 Cr 23 type) and σ-FeCr (tP-CrFe type) particles, are always precipitated from the austenitic matrix after a long-term aging at 873–1173 K. Ultimately, it would result in a sig- nificant loss in both the ductility and toughness due to the chain-like distribution of these brittle phases on grain boundaries (GBs) as a path for crack propagation [11–15]. These GB precipitates could also result in a Cr depletion in the matrix and an increased susceptibility to the intergranular corrosion [12,16,17]. Therefore, it is necessary to im- prove the microstructural stability of ASSs at HTs for the guarantee of https://doi.org/10.1016/j.msea.2018.02.020 Received 9 December 2017; Accepted 6 February 2018 ⁎ Corresponding author. E-mail address: wangq@dlut.edu.cn (Q. Wang). Materials Science & Engineering A 719 (2018) 27–42 Available online 07 February 2018 0921-5093/ © 2018 Elsevier B.V. All rights reserved. T