Effect of Accelerated Cooling Rate and Finish Rolling Temperature on the Occurrence of Arrowhead Markings in Drop-Weight Tear Test of API 5LX70 Linepipe Nb–V–Ti Steel Plate

Four Nb–V–Ti steel plates of API 5LX70 linepipe were produced with changing accelerated cooling rate and finish rollingtemperature 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 investigatedusing drop-weight tear test at temperatures of 0 °C and − 10 °C. Based on the drop-weight tear test results, an increase in theaccelerated cooling rate, resulting in an increase in the volume fraction of quasi polygonal ferrite, fine polygonal ferrite, andgranular ferrite microstructures, increased the percentage of ductile fracture surface and decreased the percentage of brittlefracture surfaces. Moreover, a reduction in the finish rolling temperature led to similar changes in the ductile fracture surfaceand 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 anddecreasing 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. KCI Citation Count: 0