Abstract
This study aims to discover the stress-state dependence of the dynamic strain aging (DSA) effect on the deformation and fracture behavior of high-strength dual-phase (DP) steel at different deformation temperatures (25–400°C) and reveal the damage mechanisms under these various configurations. To achieve different stress states, predesigned specimens with different geometric features were used. Scanning electron microscopy was applied to analyze the fracture modes (e.g., dimple or shear mode) and underlying damage mechanism of the investigated material. DSA is present in this DP steel, showing the Portevin-Le Chatelier (PLC) effect with serrated flow behavior, thermal hardening, and blue brittleness phenomena. Results show that the stress state contributes distinctly to the DSA effect in terms of the magnitude of thermal hardening and the pattern of blue brittleness. Either low stress triaxiality or Lode angle parameter promotes DSA-induced blue brittleness. Accordingly, the damage mechanisms also show dependence on the stress states in conjunction with the DSA effect.
Highlights
The dynamic strain aging (DSA) effect has been widely investigated since the middle of the 20th century because it strongly affects mechanical properties, including the strength and ductility of metals [1−5]
This study aims to discover the stress-state dependence of the dynamic strain aging (DSA) effect on the deformation and fracture behavior of high-strength dual-phase (DP) steel at different deformation temperatures (25–400°C) and reveal the damage mechanisms under these various configurations
DSA is present in this DP steel, showing the Portevin–Le Chatelier (PLC) effect with serrated flow behavior, thermal hardening, and blue brittleness phenomena
Summary
The dynamic strain aging (DSA) effect has been widely investigated since the middle of the 20th century because it strongly affects mechanical properties, including the strength and ductility of metals [1−5]. Hong and Lee [16] concluded that the fast crack propagation rate could be related to the enhanced work hardening rate, which is often a result of the DSA Another feature revealed by crack growth tests is periodic crack jumps [18] or the alternate tension–tear process [19] at the crack tip zone, indicating a repeated crack tip blunting and tearing. Stress state has a considerable influence on the ductile fracture for metallic materials, as revealed by microstructure-level damage mechanisms [39−41] and the observed mechanical tests [42−44]; the focused stress state for DSA-related case is typically uniaxial tensile or compression tests under either monotonic or cyclic loading. The results could provide information on microstructure features at damage initiation
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