抵抗溶接法の開発(VI) -マルテンサイト系ODS鋼の溶接特性評価試験-

Development of Resistance Welding Process(VI)

河野 秀作; 関 正之; 石橋 藤雄; 平子 一仁*; 塚田 竜也*

Kono, Shusaku; Seki, Masayuki; Ishibashi, Fujio; Hirako, Kazuhiko*; Tsukada, Tatsuya*

マルテンサイト系ODS鋼被覆管の溶接特性評価のために、溶接条件及び熱処理条件の最適化試験を行った。その後に、強度測定評価試験片を製作し、接合部の強度評価試験として引張試験、内圧バースト試験、内圧クリープ試験及び単軸クリープ試験を実施した。(1)溶接特性について 良好な溶接特性を示した。溶接時に懸念された接合開始点に発生する微細剥離等は生じることなく、接合開始点のバラツキも0.05mm以内で均一な接合状態であった。母材自体の組織が均質であったことが、良好な溶接特性を示した一因と考える。(2)端栓材について 端栓材は、被覆管材と共材を用いることにより、接合部近傍における組織、炭化物の析出状態は被覆管材と同等の結果が得られた。(3)熱処理条件の最適化 溶接後に焼きならし(1050C)と焼き戻し(780C-10分)処理を兼用することにより、接合部近傍の組織は転位密度の低い等軸粒の組織となった。また、炭化物の析出状態についても母材と同等の分布を示した。溶接時の残留応力も緩和できることから、溶接後の熱処理(焼きならし(1050)と焼き戻し(780C-10分))は必須条件となる。(4)接合強度 すべての強度試験において、接合部の強度は、被覆管母材と同等の強度が得られた。そのため、マルテンサイト系ODS鋼の溶接技術開発は完結したと考える。

The welding condition and the heat-treatment condition were optimized to evaluate welding properties of the martensitic ODS steel cladding tube. The test pieces for evaluation of strength properties of the welded zone were produced by the optimized welding condition. In order to evaluate the strength of the welded zone, the internal creep rapture test, the single axis creep rapture test, the burst test and the tensile test were conducted. Following results were obtained in these tests. (1) Weld ability. An excellent welding characteristic was observed. The micro cracks, etc. were not served at the joint starting point. The joint starting poonts were connected uniformly with errors less than 0.05mm. It is considered that an excellent welding characteristic was result of homogeneous micro structure of cladding material. (2) End plug material. In case of the material of end plug was martensitic ODS steel as same as that of cladding tube, the micro structure and the precipitation state carbide near the welded zone were found to be almost same as that of cladding tube. (3) Optimization of heat-treatment condition. The heat treatments of normalizing (10501C) and tempering (780C) were performed after welding and the micro structure near the welded zone was the isometric structure with low dislocation density, the precipitation state of carbide was uniform as same as that of cladding tube. These heat treatments can relax the residual stress accumulated when welding; it is considered that these heat treatments after welding are indispensable. (4) Strength of welded zone. The strength of the welded zone was found to be equal to that of cladding tube in all the strength tests. Therefore, it is concluded that the welding technology for the martensitic ODS steel is completed.