Abstract

Four Nb–V–Ti steel plates of API 5LX70 linepipe were produced with changing accelerated cooling rate and finish rolling temperature using thermomechanical controlled process. The changes in ductile fracture surface, brittle fracture surfaces, including initial cleavage fracture and inverse fracture, arrowhead marking surfaces, and delamination were investigated using drop-weight tear test at temperatures of 0 °C and − 10 °C. Based on the drop-weight tear test results, an increase in the accelerated cooling rate, resulting in an increase in the volume fraction of quasi polygonal ferrite, fine polygonal ferrite, and granular ferrite microstructures, increased the percentage of ductile fracture surface and decreased the percentage of brittle fracture surfaces. Moreover, a reduction in the finish rolling temperature led to similar changes in the ductile fracture surface and brittle fracture surfaces due to an increase in the volume fraction of aciculae ferrite. Arrowhead markings surfaces, caused by the presence of banded structures, their percentage was reduced by increasing the accelerated cooling rate and decreasing the finish rolling temperature at the temperature of 0 °C. Furthermore, as the accelerated cooling rate increased, the number, length, thickness, and depth of delaminations were reduced at temperatures of 0 °C and − 10 °C.

Graphic Abstract

中文翻译：

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API 5LX70管线钢Nb–V–Ti钢板落重撕裂试验中加速冷却速率和终轧温度对箭头标记出现的影响

摘要

使用热机械控制工艺生产了四块API 5LX70管线管的Nb-V-Ti钢板，它们具有变化的加速冷却速率和精轧温度。使用滴落撕裂试验在0°C和− 10°C的温度下研究了延性断裂表面，脆性断裂表面（包括初始解理断裂和反断裂），箭头标记表面和分层的变化。根据落锤撕裂试验结果，加速冷却速率增加，导致准多边形铁素体，细多边形铁素体和粒状铁素体微结构的体积分数增加，延性断裂表面的百分比增加，而降低脆性断裂面的百分比。此外，终轧温度的降低由于球状铁素体的体积分数增加而导致延性断裂面和脆性断裂面发生类似变化。由于带状结构的存在，箭头标记表面会通过提高加速冷却速率和降低0°C温度下的终轧温度来降低其百分比。此外，随着加速冷却速率的提高，在0°C和-10°C的温度下，分层的数量，长度，厚度和深度减小。通过提高加速冷却速率和降低0°C温度下的终轧温度来降低它们的百分比。此外，随着加速冷却速率的提高，在0°C和-10°C的温度下，分层的数量，长度，厚度和深度减小。通过提高加速冷却速率和降低0°C温度下的终轧温度来降低它们的百分比。此外，随着加速冷却速率的提高，在0°C和-10°C的温度下，分层的数量，长度，厚度和深度减小。

图形摘要