Abstract
Hot forming processes are extensively used to produce semi-finished and finished components. At elevated temperatures, dynamic recovery and recrystallization processes occur that enable large shape changes at low forming forces. In steel, non-metallic inclusions cannot be avoided during metallurgical processes. They may induce damage in the same way as at room temperature, but the softening of the matrix due to dynamic recrystallization may be used to control the initiation and progression of damage. Damage models do not take into account that dynamic recrystallization reduces the local stresses at the interface of matrix–inclusion. The purpose of the presented study is to analyze the interaction between dynamic recrystallization and damage initiation. Using representative volume elements, the influence of dynamic recrystallization on damage initiation is studied at different temperatures, strain rates, and stress states. Based on this study, a damage model is devised that couples dynamic recrystallization and damage on the macro level and hence can be used in macroscopic process simulations.
Highlights
Hot forming processes are widely used in the industry to form semi-finished products and components
The damage initiation and growth are driven by the deformation-induced local build-up of stresses at the matrix–inclusion interface
The results show two key outcomes: (i) the increasing inclusion size in a fixed size representative volume elements (RVE) induces higher total damage in the material, i.e. the notch effect scales with inclusion size, and (ii) the influence of DRX in comparison with no DRX decreases for small inclusions
Summary
Hot forming processes are widely used in the industry to form semi-finished products and components. Elevated temperatures lower the forming forces, allow for large deformation, and for transforming the microstructure from the inhomogeneous, coarse state after casting into a dense, worked microstructure. Apart from the grain structure inhomogeneities, segregations, voids, and second phase particles (e.g. non-metallic inclusions) are the main source of microstructural inhomogeneities that stem from the casting process. The presence of non-metallic inclusions may lead to additional damage. Non-metallic inclusions are inevitable in industrially processed steels. Depending on their type, inclusion can plastically deform with the matrix or behave in a rigid manner. Hard inclusions may promote decohesion of the matrix–inclusion interface and initiate damage
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