Microstructure evolution and deformation mechanism along the thickness of heavy-wall ferrite-bainite dual-phase offshore pipelines by the progressive forming process

• Published in: Journal of materials processing technology Vol. 326; p. 118355
• Main Authors: Xu, Ling-zhi, Qiao, Gui-ying, Lu, Xin-xin, Gu, Yu, Xu, Kai, Chen, Xiao-wei, Xiao, Fu-ren
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2024
• Subjects: Ferrite-bainite dual-phase steel; Mechanical properties; Offshore pipeline; Plastic damage; Progressive forming process; Mechanical properties; Progressive forming process; Ferrite-bainite dual-phase steel; Plastic damage; Offshore pipeline
• ISSN: 0924-0136
• DOI: 10.1016/j.jmatprotec.2024.118355

The progressive forming process of J-forming, C-forming, O-forming, and expansion (JCOE process) is an effective approach for manufacturing high-strength and high-strain offshore pipelines. However, the difference in microstructure of each layer along the thickness increases due to the strain accumulation and deformation direction during pipe forming, which affects the properties. In this study, the effects of the JCOE process on the microstructure evolution and deformation mechanism of heavy-wall ferrite-bainite dual-phase offshore pipeline steel along the thickness were investigated using a combination of simulation and experiment. The results revealed that the higher accumulated strains in the outer and inner layers increased localized microstrain and ferrite hardening and improved the overall strength. However, the pile-up of many dislocations at the ferrite-bainite interface promoted the generation of cleavage facets, increasing the plastic damage. The outer layer had a consistent deformation direction in the JCOE process, promoting dislocations to slip toward the phase interface. Dislocations in the inner layer slipped and annihilated in the opposite direction by back stress due to reverse deformation. The work-hardening behavior of each layer after JCOE process was divided into two stages and decreased with the increase of accumulated strain. Furthermore, the cyclic plastic deformation reduced the plastic damage and ensured the deformation capacity. This work is valuable for the development and control of microstructural characterization and forming fabrication of high-strength, high-strain offshore pipelines. [Display omitted] •Evolutionary patterns of cumulative strain and microstructure during JCOE.•The increase in accumulated strain facilitates the promotion of cleavage facets.•The deformation direction of each layer affects the distribution of dislocations.•The work-hardening capacity decreases with increasing accumulated strain.•Cyclic plastic strain reduces plastic damage and ensures deformability.