高圧水素環境におけるV添加析出強化型高Mnオーステナイト鋼のき裂進展加速機構

• Published in: 鉄と鋼 p. TETSU-2024-093
• Main Authors: 三浦, 滉大, 髙桑, 脩, 佐治, 篤, 舘, 幸生, 岩野, 竜也
• Format: Journal Article
• Language: Japanese
• Published: 一般社団法人 日本鉄鋼協会 01.12.2024
• Subjects: austenitic steel; fatigue crack growth; fracture toughness; high-pressure gaseous hydrogen; hydrogen embrittlement; precipitation strengthening
• ISSN: 0021-1575; 1883-2954
• DOI: 10.2355/tetsutohagane.TETSU-2024-093

To verify the crack growth resistance of the V-added precipitation-strengthened high-Mn austenitic steel subject to a static and dynamic loading in a hydrogenated environment, the fracture toughness test and two types of fatigue crack growth (FCG) test, i.e., stress intensity factor range ΔK-increasing and ΔK-constant tests were performed under high-pressure gaseous hydrogen environment under the pressure of 95 MPa. The fracture toughness dramatically decreased from 95 to 35 MPa･m1/2 by hydrogen occlusion. The fracture surface consists of intergranular fracture aspects in gaseous hydrogen despite being covered by the dimples tested in air. The FCG acceleration was also pronounced: more acceleration emerged as the ΔK became higher. When changing the loading frequency f as 1, 0.1, 0.01, and 0.001 Hz under constant ΔK of 30MPa･m1/2, the relative FCG rate in gaseous hydrogen to that in air became higher as f decreased, i.e., the dependency of FCG acceleration on the crack opening time. However, the acceleration did not completely depend on the crack opening time, which means a part of FCG acceleration was dominated by crack tip plasticity under cyclic loading. The scanning electron microscopy (SEM) characterization, including the electron-channeling contrast (ECC) imaging and the electron backscatter diffraction (EBSD) analysis, demonstrated that the crack preferentially propagates along grain boundary in the hydrogenated environment. The micro-void and/or micro-crack ahead of the primary FCG crack initiated at the M23C6 carbides precipitated at the grain boundary, which triggered the dramatic acceleration of FCG under 95 MPa gaseous hydrogen.