End Closure Joining of Ferritic-Martensitic and Oxide-Dispersion Strengthened Steel Cladding Tubes by Magnetic Pulse Wel
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INTRODUCTION
FERRITIC-MARTENSITIC (FM) steels have been demonstrated as a long-life fuel pin cladding material for advanced fast reactors, owing to their good thermal conductivity, low thermal expansion, low corrosion rate, and excellent swelling resistance.[1,2] More recently, attention has focused on the FM steels strengthened by finely dispersing oxide particles such as Y2O3, socalled ‘‘oxide-dispersion strengthened (ODS) steels’’, in order to increase the working temperature of the materials up to 923 K (650 C) and maybe up to 973 K (700 C).[3,4] The finely dispersing oxide particles offer a superior resistance to the creep of this class of steels at high irradiation temperatures, since they do not coagulate and do not dissolve in the matrix at temperatures of up to 1573 K (1300 C).[5]
JUNG-GU LEE, formerly Senior Researcher with the Nuclear Materials Development Division, Korea Atomic Energy Research Institute (KAERI), Yuseong, Daejeon 305-353, Republic of Korea, is now Assistant Professor with the School of Materials Science and Engineering, University of Ulsan, Nam-gu, Ulsan 680-749, Republic of Korea. Contact e-mail: [email protected] JIN-JU PARK, MIN-KU LEE, CHANG-KYU RHEE, and TAE-KYU KIM, Principal Researchers, are with the Nuclear Materials Development Division, Korea Atomic Energy Research Institute (KAERI). Contact e-mail: [email protected] ALEXEY SPIRIN, Researcher, VASILIY KRUTIKOV, Junior Researcher, and SERGEY PARANIN, Senior Researcher, are with the Institute of Electrophysics of the Ural Branch of Russian Academy of Sciences (IEP), 620016, Yekaterinburg, Russian Federation. Manuscript submitted September 25, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
A joining method for FM-ODS steels is one of the primary concerns in fabricating fuel pins using these materials.[6,7] The conventional fusion welding techniques significantly degrade the mechanical properties of FM steels at the weld region, by introducing unwanted microstructural heterogeneity and residual stress, which causes brittle fracture and hydrogen embrittlement.[8] The local melting of ODS steels at the weld region also leads to adverse microstructural changes such as agglomeration and coarsening of the oxide particles and disruption of a fine-scaled microstructure.[9] More practically, post-joining heat treatment of a fuel pin cladding is basically impossible without detrimental effects on the fuel, and fuel pins with defective joints should be reopened and the contents inside recuperated. Thus, any joining technology applied to fuel pin fabrication requires high reliability and simplicity of operation. Bearing in mind the above aspects, a magnetic pulse welding (MPW) technique has come into consideration in the current study as a substitutive joining process for fuel pin fabrication using FM-ODS steels. MPW is a solid-state impact joining method,[10,11] which uses the power of a high-energy magnetic field to accelerate a metal piece onto another stationary one and to create a metallic bonding there between. The joining occurs on
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