Abstract
The strength and plasticity balance of F/B dual-phase X80 pipeline steels strongly depends on deformation compatibility between the soft phase of ferrite and the hard phase of bainite; thus, the tensile strength of ferrite and bainite, as non-negligible factors affecting the deformation compatibility, should be considered first. In this purely theoretical paper, an abstract representative volume elements (RVE) model was developed, based on the mesostructure of an F/B dual-phase X80 pipeline steel. The effect of the yield strength difference between bainite and ferrite on tensile properties and the strain hardening behaviors of the mesostructure was studied. The results show that deformation first occurs in ferrite, and strain and stress localize in ferrite prior to bainite. In the modified Crussard-Jaoul (C-J) analysis, as the yield strength ratio of bainite to ferrite () increases, the transition strain associated with the deformation transformation from ferrite soft phase deformation to uniform deformation of ferrite and bainite increases. Meanwhile, as the uncoordinated deformation of ferrite and bainite is enhanced, the strain localization factor (SLF) increases, especially the local strain concentration. Consequently, the yield, tensile strength, and yield ratio (yield strength/tensile strength) increase with the increase in . Inversely, the strain hardening exponent and uniform elongation decrease.
Highlights
With the rapid increase in demand for clean energy, such as natural gas, long-distance gas transportation pipelines are developing towards larger diameters and higher operating pressures to maximize transport efficiency, promoting the rapid development of highstrength pipeline steel
Our research has shown that the mechanical properties andstrainhardening behavior of the F/B dual-phase X80 pipeline steel are independent of the volume fraction of bainite [16] and dependent on the morphology and distribution of bainite [17]
This is because the deformation ofthe low-strength ferrite occurs more during plastic deformation; concomitantly, strain and stress concentration occurs at the F/B interface, and the plastic deformation occurs in bainite to accommodate the high deformation properties of ferrite when the stress concentration near the F/B interface is higher than the yield strength of bainite [18]
Summary
With the rapid increase in demand for clean energy, such as natural gas, long-distance gas transportation pipelines are developing towards larger diameters and higher operating pressures to maximize transport efficiency, promoting the rapid development of highstrength pipeline steel. Our research has shown that the mechanical properties andstrainhardening behavior of the F/B dual-phase X80 pipeline steel are independent of the volume fraction of bainite [16] and dependent on the morphology and distribution of bainite [17] This is because the deformation ofthe low-strength ferrite occurs more during plastic deformation; concomitantly, strain and stress concentration occurs at the F/B interface, and the plastic deformation occurs in bainite to accommodate the high deformation properties of ferrite when the stress concentration near the F/B interface is higher than the yield strength of bainite [18]. This work aims to reveal the mechanism by which the difference in tensile strength between ferrite and bainite affects the deformation compatibility in the mesostructure and to help optimize the microstructure of the F/B dual-phase pipeline steels to obtain strength and deformability balance
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