Plastic damage mechanism and grain orientation evolution along the thickness direction in heavy-walled submarine pipelines during the progressive forming process

The progressive forming process (JCOE process) results in the creation of a high-strength submarine pipeline with substantial wall thickness. However, the accumulated of strain during the transverse forming process leads to increased disparities in the microstructure of layers with varying thicknesses, thereby impacting the longitudinal mechanical properties of the pipes. This investigation explores the combination of three-dimensional (3D) simulation and experimental methods allowed for comparison of how the JCOE process impacts the mechanisms of plastic damage and the evolution of longitudinal grain orientation in layers with varying thicknesses in pipes. It was revealed in the findings that the increase in accumulated strain led to a rise in dislocation density within the grain. This exacerbated dislocation pile-up at ferrite boundaries and ferrite/bainite interfaces and raised the level of plastic damage. A reduction in grain size enhanced the strain gradient in the surface layer, resulting in hindered advancement of plastic damage. From the 1/2-thickness layer towards the surface layer, the crystal orientation tended predominantly towards the [110] direction with the accumulation of strain. At a lower level of the accumulated plastic strain, the predominant orientation of the texture in the 1/2-thickness layer was directed towards the α-fibers. As the accumulated deformation progressed into the 1/4-thickness layer, the α-fiber transformed to a {001}<110> type texture under the combined effect of conjugated slip and cross-slip. The transformation of the {001}<110> type texture into the {112}<110> type texture ensued as the accumulated deformation progressed to the surface layer and tended to shift to the {111}<110> type texture. The results of this work guide methods to control the microstructure and properties of heavy-wall dual-phase steel submarine pipelines.