Shuai Kangxin, Liu Haixiao, Li Ming, Yin Shubiao, Li Ba, Wang Bing, Liu Qingyou, Jia Shujun
Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650031, China.
Engineering Steel Institute, Central Iron and Steel Research Institute, Beijing 100081, China.
Materials (Basel). 2024 Nov 27;17(23):5818. doi: 10.3390/ma17235818.
With the rapid development of hydrogen pipelines, their safety issues have become increasingly prominent. In order to evaluate the properties of pipeline materials under a high-pressure hydrogen environment, this study investigates the hydrogen embrittlement sensitivity of X70 welded pipe in a 10 MPa high-pressure hydrogen environment, using slow strain rate testing (SSRT) and low-cycle fatigue (LCF) analysis. The microstructure, slow tensile and fatigue fracture morphology of base metal (BM) and weld metal (WM) were characterized and analyzed by means of ultra-depth microscope, scanning electron microscope (SEM), electron backscattering diffraction (EBSD), and transmission electron microscope (TEM). Results indicate that while the high-pressure hydrogen environment has minimal impact on ultimate tensile strength (UTS) for both BM and WM, it significantly decreases reduction of area (RA) and elongation (EL), with RA reduction in WM exceeding that in BM. Under the nitrogen environment, the slow tensile fracture of X70 pipeline steel BM and WM is a typical ductile fracture, while under the high-pressure hydrogen environment, the unevenness of the slow tensile fracture increased, and a large number of microcracks appeared on the fracture surface and edges, with the fracture mode changing to ductile fracture + quasi-cleavage fracture. In addition, the high-pressure hydrogen environment reduces the fatigue life of the BM and WM of X70 pipeline steel, and the fatigue life of the WM decreases more than that of the BM as well. Compared to the nitrogen environment, the fatigue fracture specimens of BM and WM in the hydrogen environment showed quasi-cleavage fracture patterns, and the fracture area in the instantaneous fracture zone (IFZ) was significantly reduced. Compared with the BM of X70 pipeline steel, although the effective grain size of the WM is smaller, WM's microstructure, with larger Martensite/austenite (M/A) constituents and MnS and Al-rich oxides, contributes to a heightened embrittlement sensitivity. In contrast, the second-phase precipitation of nanosized Nb, V, and Ti composite carbon-nitride in the BM acts as an effective irreversible hydrogen trap, which can significantly reduce the hydrogen embrittlement sensitivity.
随着氢气管道的快速发展，其安全问题日益突出。为了评估管道材料在高压氢气环境下的性能，本研究采用慢应变速率试验（SSRT）和低周疲劳（LCF）分析方法，研究了X70焊接管在10 MPa高压氢气环境下的氢脆敏感性。通过超景深显微镜、扫描电子显微镜（SEM）、电子背散射衍射（EBSD）和透射电子显微镜（TEM）对母材（BM）和焊缝金属（WM）的微观结构、慢拉伸和疲劳断口形貌进行了表征和分析。结果表明，高压氢气环境对BM和WM的抗拉强度（UTS）影响最小，但显著降低了断面收缩率（RA）和伸长率（EL），WM的RA降低幅度超过BM。在氮气环境下，X70管道钢BM和WM的慢拉伸断口为典型的韧性断口，而在高压氢气环境下，慢拉伸断口的不均匀性增加，断口表面和边缘出现大量微裂纹，断口模式转变为韧性断口+准解理断口。此外，高压氢气环境降低了X70管道钢BM和WM的疲劳寿命，WM的疲劳寿命降低幅度也大于BM。与氮气环境相比，氢气环境下BM和WM的疲劳断口试样呈现准解理断口模式，瞬时断裂区（IFZ）的断裂面积显著减小。与X70管道钢的BM相比，WM虽然有效晶粒尺寸较小，但其具有较大的马氏体/奥氏体（M/A）组分以及MnS和富铝氧化物的微观结构导致其脆化敏感性增强。相反，BM中纳米尺寸的Nb、V和Ti复合碳氮化物的第二相析出物作为有效的不可逆氢陷阱，可显著降低氢脆敏感性。
