成果報告書詳細
管理番号20160000000323
タイトル*平成27年度中間年報 水素利用技術研究開発事業 水素ステーション安全基盤整備に関する研究開発 高圧水素ガス用高窒素高強度ステンレス鋼配管の溶接継手に関する研究開発
公開日2016/8/31
報告書年度2015 - 2015
委託先名株式会社エア・リキード・ラボラトリーズ
プロジェクト番号P13002
部署名新エネルギー部
和文要約
英文要約Title: Research and Development on Welded Joints of a High-nitrogen and High-strength Stainless Steel Tube for High-pressure Hydrogen Gas (FY2014-FY2016) FY2015 Annual Report

The purpose of this research is the implementation of welded joints for high-nitrogen and high-strength steel XM19, which is expected to be used in hydrogen refueling station.
(1) Development of welding technique for a high-nitrogen stainless steel
Butt welding of tubes were performed by an automatic TIG welding machine. To keep high strength, optimization of welding parameters and improvement of shielding gas were implemented. As a result of welding tests using various welding parameters, we identified a factor which affects material properties of welded joints. To obtain deeper penetration, hydrogen was added to shielding gases, but it was found that hydrogen can decrease the nitrogen concentration of weld under a specific welding parameter. According to the results, development of weld joints compatible with high strength and good workability will be implemented by optimizing both welding parameters and shielding gases.
(2) Microstructure evaluation of weld metal
Evaluations of weld metal were conducted in terms of distribution of nitrogen concentration, δ ferrite distribution and hardness of δ ferrite. Nitrogen concentration of weld metal decreased up to 0.18 mass%. On the other hand, decrease of nitrogen concentration at HAZ barely occurred, and then it was considered that the decrease of hardness at HAZ was caused by grain coarsening. The microstructure of δ ferrite was visualized by EBSD analysis. To investigate the mechanical properties of the δ ferrite, nanoindentation analysis was performed. The analysis showed that δ ferrite has 10 % higher hardness compared to the austenite in weld metal. It is presumed that the higher hardness of δ ferrite was caused by solid solution strengthening by Cr enrichment.
(3) Evaluation of hydrogen embrittlement of welded tubes
Fatigue tests simulating inner pressure cycle were conducted. To investigate the effect of hydrogen, hydrogen-charging was performed by exposing test specimens to high-pressure hydrogen gas at a pressure of 100 MPa, 270 °C for 72 hours before fatigue tests. Fatigue strength of welded tube was slightly lower than non-welded tube, but there was no effect of hydrogen on the fatigue strengths for both non-welded tube and welded tube. There was also no effect of hydrogen on the fracture surface morphology. Fatigue crack initiation of welded tube was the surface of weld metal, but it was found from precise observation that the fatigue crack was initiated by small defects of weld. It is important to clarify the relationship between the fatigue strength of weld metal and microstructure especially δ ferrite, but it is necessary to prepare test specimens polished after welding. Fatigue tests using the test specimens are planned in FY2016.
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