Effect of Cooling Rate and Finish Rolling Temperature on Structure and Strength of API 5LX70 Linepipe Steel Plate
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JMEPEG https://doi.org/10.1007/s11665-020-04961-0
Effect of Cooling Rate and Finish Rolling Temperature on Structure and Strength of API 5LX70 Linepipe Steel Plate N. Amirjani, M. Ketabchi, M. Eskandari, and M. Hizombor (Submitted October 10, 2019; in revised form May 28, 2020) The present study has investigated the effect of changes in accelerated cooling (ACC) and finish rolling temperature (FRT) on the mechanical properties of high-strength low-alloy (HSLA) Nb-V-Ti steel plate of non-sour API 5LX70 linepipe during the thermomechanical controlled process (TMCP). Tensile test results showed that increasing ACC or reducing FRT enhanced yield and tensile strengths of the subject steel, which was also confirmed by the Vickers hardness test. Microstructure examinations demonstrated that increasing ACC and reducing FRT resulted in a lower volume fraction and a finer size of pearlite. Moreover, an increase in the ACC enhanced the formation of granular ferrite (GF) and fine polygonal ferrite (FPF), while a decrease in the FRT mostly affected the formation of acicular ferrite (AF). In all microstructures, banded structures and particles with a size of approximately 6 lm were observed due to segregation during solidification, where changing the parameters did not affect their formations. Keywords
API 5LX70, banded structures, ferrite-pearlite, high-strength low-alloyed steel, pipeline integrity management, thermomechanical controlled process
1. Introduction Among various modes for transporting oil and gas from upstream production fields to downstream industries, pipeline transmission is by far the most cost-effective and safest one (Ref 1). Due to this decisive role and with the annual market of the multi-billion dollar, the pipeline role with complicated multidisciplinary concepts such as design, construction, operation, maintenance, and repair has been recognized as an industry, not just a simple means of transportation. This industry is now facing many challenges, such as increasing pipe diameter and internal pressure due to the jump in global consumption, determining how to transfer poor-quality, contaminated, and corrosive oil and gas from production fields in harsh and remote terrains, maintaining existing aged pipelines and also establishing an integrated management system capable of maintaining the pipeline sustainable, reliable, safe, and ecofriendly while being wholly cost-effective (Ref 2, 3). To overcome the challenges, the pipeline management should provide line pipe free of defects, having high strength, toughness, ductility, and formability, resistant to corrosive N. Amirjani and M. Ketabchi, Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, Tehran, Iran; M. Eskandari, Department of Materials Science and Engineering, Faculty of Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran; and M. Hizombor, Metallurgy and Manufacturing Processes Organization, Khouzestan Oxin Steel Company, Ahvaz, Iran. Contact e-mails: [email protected], [email protected], m.eskandari@scu.
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