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摘要
In order to take into account the dual-phase ferrite/pearlite microstructures of the X65 steel in the simulations of the U- and O forming steps of the production of a gas pipeline tube, a multi-scale approach based on a two-level homogenization scheme([1]) is applied. Three different scales are introduced: the nano-scale of a ferrite-cementite bi-lamella of pearlite, the pearlite/ferrite microstructure and the macro-scale. Firstly, homogenization is applied to a bi-lamella representative volume element (RVE) of pearlite. Secondly, pearlite is treated at the micro-scale as an effective phase with an anisotropic flow curve in an elasto-plastic ferrite matrix. The predicted flow curves of the X65 steel are in a rather good agreement with experimental stress-strain curves in rolling and transverse directions, respectively. The cooling step produces in the steel sheet different microstructures in the center and at its skins. The surficial microstructure has slightly less pearlite content, reduced lamella spacing and a lower residual dislocation density. The effective flow behavior at the sheet skins is determined and the impact of the different microstructure features is quantified. At the macro-scale, 2D plane strain FE simulations of the U-O forming steps are then performed twice: once with the reference flow curve and once with different flow curves in the sheet center and at its skins. Thus, the accuracy increase due to locally different flow curves is outlined. Eventually, the most critical local macro-stress/strain state of the O forming step is extracted and applied as boundary condition on the corresponding microstructure in order to evaluate the micro-stresses and strains and to locate its critical areas.
- 出版日期2014-6
