Unravelling Anisotropy Evolution during Spiral Pipe Forming: a Multiscale Approach

Abstract

Spiral forming of bainitic steel coils into large diameter pipes involves a complex deformation history with several strain path changes. These lead to mechanical properties on pipe which are macroscopically different compared to coil. A detailed understanding of the property evolution during spiral pipe forming is crucial to tailor the coil material and to ensure safe pipe operation. However, it has proven difficult to correctly reproduce the anisotropic strength evolution during pipe forming with available phenomenological hardening models. Unravelling the factors contributing to macroscopic anisotropy is inherently a multi-scale problem due to the complex microstructures exhibited by modern bainitic linepipe steels. They promote a large Bauschinger effect, aside from cross loading-effects and more or less pronounced Lüders banding. Here, we present selected experimental and numerical results related to our efforts to predict the mechanical properties of bainitic steel pipes manufactured from hot rolled coils. Across the scales, we consider sources for anisotropy, such as residual stresses, crystallographic texture and grain substructure. A dislocation-based crystal plasticity model incorporated into a computationally efficient hierarchical multi-scale forming simulation is employed to predict texture and strength changes.