Misorientation, grain boundary, texture and recrystallization study in X90 hot bend related to mechanical properties

In the present study, electron backscattering diffraction (EBSD) was used to study the relationship between misorientation, grain boundary, texture, recrystallization and the mechanical properties for API (American Petroleum Institute) X90 hot induction bend. The experimental results show that the yield strength of the parent pipe is 748 MPa, while it reduced about 40 MPa after hot induction bending. The strength in the inner arc side is similar along the longitudinal and transverse direction, but it is anisotropic in the outer arc side. The texture of {113} <110> components and {112} <110> components are the main reason for anisotropy. After hot induction bending, the deformed and elongated grains exist in the bend zone of X90 bend, and the sub-grain boundaries exist in the grains. The grains in the neutral axis are equiaxed and without lath-like structure and sub-structure. A large fraction of lath bainite (LB) boundaries and Σ3 boundaries in the outer arc side resulted in a high strength and low impact toughness. Moreover, the deformed region and the recrystallization region have the same tendency for the tested specimens, the neutral axis of X90 bend has a lower stored energy in the grains that could resist the cracks propagation effectively.