Liu Shuo, Ba Lingzhi, Li Chengning, Di Xinjie
School of Materials Science and Engineering, Tianjin University, Tianjin 300350, China.
Central Research Institute, Baoshan Iron & Steel Co., Ltd., Shanghai 201900, China.
Materials (Basel). 2022 Nov 2;15(21):7701. doi: 10.3390/ma15217701.
The coarse-grain heat-affected zones (CGHAZs) of X80 girth-welded steel pipelines are prone to embrittlement, which has an extremely adverse effect on their structural integrity. In the present work, the fracture behavior of the CGHAZs of X80 girth welds under the conditions of conventional and ultra-low heat input was studied. The fracture toughness of CGHAZs was evaluated using the crack tip opening displacement (CTOD) test at -10 °C, and the fracture behavior mechanism of CGHAZs were clarified by analyzing microstructural characteristics at prefabricated fatigue cracks containing fracture cloud image, scanning electron microscopy (SEM), and electron back-scatter diffraction (EBSD) figures. The results illustrate that the average fracture toughness (CTOD) value of the ultra-low heat input CGHAZ is 0.6 mm, and the dispersion of CTOD values is small, while the CTOD value of conventional heat input is only 0.04 mm. The ultra-low heat input makes the high-temperature residence time of the coarse-grained region short, reduces the proportion of prior austenite grain boundaries, and inhibits the formation of strip-like bainite and island-like M-A components. The reduction of these deleterious ductile microstructures increases the plastic reserve and deformation capacity of the CGHAZ.
X80 girth焊接钢管的粗晶热影响区（CGHAZs）容易发生脆化，这对其结构完整性有极其不利的影响。在本研究中，研究了X80 girth焊缝在常规热输入和超低热输入条件下粗晶热影响区的断裂行为。通过在-10℃下使用裂纹尖端张开位移（CTOD）试验评估粗晶热影响区的断裂韧性，并通过分析包含断口云纹图像、扫描电子显微镜（SEM）和电子背散射衍射（EBSD）图的预制疲劳裂纹处的微观结构特征，阐明了粗晶热影响区的断裂行为机制。结果表明，超低热输入粗晶热影响区的平均断裂韧性（CTOD）值为0.6mm，CTOD值的分散性小，而常规热输入的CTOD值仅为0.04mm。超低热输入使粗晶区的高温停留时间缩短，降低了原奥氏体晶界的比例，并抑制了带状贝氏体和岛状M-A组元的形成。这些有害韧性微结构的减少增加了粗晶热影响区的塑性储备和变形能力。
