Effect of welding parameters on microstructure and mechanical properties of a friction stir welded 11Cr-ferritic/martensitic steel

摩擦攪拌接合した11Crフェライト/マルテンサイト鋼の組織と強度に及ぼす接合パラメータの影響評価

佐藤 裕*; 粉川 博之*; 矢野 康英  ; 関尾 佳弘  

Sato, Yutaka*; Kokawa, Hiroyuki*; Yano, Yasuhide; Sekio, Yoshihiro

高速増殖炉用に開発された11Crフェライト/マルテンサイト鋼(PNC-FMS)に先進的固相接合方法である摩擦攪拌接合(FSW)を適用し、強度と組織に及ぼす接合パラメーターの影響を評価した。なお、本研究の一部は、文部科学省原子力基礎基盤戦略研究イニシアチブにより実施された「摩擦攪拌接合によるNa高速炉炉心材料の新たな接合技術に関する研究」の成果である。

PNC-FMS is a newly developed 11Cr-ferritic/martensitic steel with good swelling resistance, designed for the wrapper tubes of fast reactors. In this study, friction stir welding (FSW) was attempted as a welding process of PNC-FMS because fusion welding of this steel significantly reduced mechanical properties through formation of brittle microstructure. FSW was applied to PNC-FMS at 100 to 300 rpm using Q60 tool, and defect-free welds were obtained. The stir zones had fine microstructure with ferrite and martensite, and the grain size and fraction of martensite increased with rotational speed. Since all welds were overmatched, all transverse tensile specimens were broken at the base material region. The tensile test of the stir zone clarified that the stir zone produced at 100 rpm exhibited higher strengths and elongation than the base material. This study showed that FSW at lower rotational speed produced the stir zone having better mechanical properties in PNC-FMS.