Effect of Bainite to Ferrite Yield Strength Ratio on the Deformability of Mesostructures for Ferrite/Bainite Dual-Phase Steels

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 (σy,B/σy,F) 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 σy,B/σy,F. Inversely, the strain hardening exponent and uniform elongation decrease.

Tailoring Low‐Alloyed Cryogenic Steel Strong and Tough Introduces Fine‐Grained Equiaxed Ferrite by Intercritical Subquenching

“…The two‐phase heat treatment process typically involves a two‐phase quenching step between normal quenching and tempering. Qiao et al [ 17 ] studied the influences of the bainite volume fraction on the tensile properties of ferrite (F)/bainite (B) dual‐phase pipeline steel. The results indicate that strain is predominantly concentrated at the interface between bainite and ferrite.…”

Effect of V Content and Heat Input on HAZ Softening of Deep-Sea Pipeline Steel

“…It is usually necessary to adopt strain-based design for deep-sea pipeline steel, which usually has a dual-phase microstructure with a soft phase and hard phase. Thus, the high strain capacity of steel depends on the soft phase, and the strength depends on the hard phase for support, so as to ensure a good match between strength and plasticity [6,7].…”