Effect of Accelerated Cooling Rate and Finish Rolling Temperature on the Occurrence of Arrowhead Markings in Drop-Weight
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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 N. Amirjani1 · M. Ketabchi1 · M. Eskandari2 · M. Hizombor3 Received: 4 June 2020 / Accepted: 30 July 2020 © The Korean Institute of Metals and Materials 2020
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. Keywords Drop-weight tear test · Thermo-mechanical controlled process · High-strength low-alloyed steel · Arrowhead markings · API 5LX70
1 Introduction Among various methods for transporting oil and gas, the use of linepipe is the most cost-effective and convenient procedure [1]. Thus, due to the increasing demand for lightweight and inexpensive pipes with large diameters to transport more oil and gas at high pressures, along with application in special conditions such as polar regions and sour environments, which is the greatest challenge for piping at present and
* N. Amirjani [email protected] 1
Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, Tehran 15875‑4313, Iran
2
Department of Materials Science and Engineering, Faculty of Engineering, Shahid Chamran University of Ahvaz, Ahvaz 83151‑61357, Iran
3
Metallurgy and Manufacturing Processes Organization, Khouzestan Oxin Steel Company, Ahvaz 61788‑13111, Iran
future, the considerable need for high-strength and toughness pipes has increased [2, 3]. Thermomechanical controlled process (TMCP), which includes controlled rolling and controlled cooling, is known as a modern procedure for producing steel plates, beside high-strength low-alloyed steel (microalloyed steel), a particular group of steels with a carbon content of less than 0.1%, and
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