The Mechanism of Dynamic Strain Aging for Type a Serrations in Tensile Curves of a Medium-Mn Steel

The mechanical properties after tempering and intercritical annealing of medium manganese steels with 4 wt% Mn for forging applications are presented. After forging with subsequent air cooling, heat treatments were performed, specifically tempering from 250 and 450 °C and intercritical annealing between 600 and 675 °C. Tensile properties, Charpy V‐notch impact toughness, and hardness were determined and compared with microstructural features characterized by metallography and synchrotron measurements, leading to the classification of six different heat treatment stages for medium manganese steels. Furthermore, the effects of different alloying additions (boron 0.0016–0.0057 wt%, molybdenum 0.2 wt%, and aluminum 0.5 wt%) are discussed with respect to the mechanical properties. It is shown that boron increases the impact toughness more effectively in the tempering regime, while the molybdenum alloyed samples exhibit higher toughness after intercritical annealing. Most of the materials and heat treatment states follow the inverse relationship between toughness and strength, while the aluminum alloyed samples show a superior toughness after tempering.

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Tempering and Intercritical Annealing of Air‐Hardening 4 wt% Medium Manganese Steels

Gramlich

Bleck

2021

steel research int.

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Interpretation of Dynamic Strain Aging in an Intercritical Annealed Steel by Dislocation Multiplication Induced by Martensitic Transformation

Gong

Zeng

et al. 2021

Metall Mater Trans A

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To elucidate the dynamic strain aging (DSA) mechanism that causes serrated flow in the tensile curves of an intercritical annealed steel with retained austenite (RA) and intercritical ferrite, the multi-aspect microstructural characterization and micromechanical deformation behavior were systematically investigated in this study. Our results demonstrate that the DSA phenomenon is dependent on the strain rate, deformation temperature, and strain. This is accompanied by deformation-induced martensitic transformation (DIMT) and the generation of crystallographic defects in nucleating and propagating Portevin-Le Chatelier bands. An increase in the deformation temperature and strain rate leads to an increase in the stacking fault energy of RA. This inhibits the growth of martensitic embryos and retards the kinetics of martensitic transformation of RA, consequently decreasing or suppressing the DSA phenomenon. Furthermore, neither the long-range diffusion model of carbon atoms nor the short-range diffusion model on the reorientation of C-Mn complexes could reasonably explain the DSA phenomenon in this study. Based on the in situ synchrotron X-ray diffraction results and established mathematical models stemming from the dislocation multiplication theory, the DSA could be attributed to the periodic instantaneous dislocation multiplication in constituent phases caused by burst DIMT.

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Discontinuous Yielding Mechanisms in Tempered Hierarchical Duplex Phase Steel with High-Density Dislocations

Gong

Liu

et al. 2022

Metall Mater Trans A

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The Mechanism of Dynamic Strain Aging for Type a Serrations in Tensile Curves of a Medium-Mn Steel

Cited by 26 publications

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Tempering and Intercritical Annealing of Air‐Hardening 4 wt% Medium Manganese Steels

Tempering and Intercritical Annealing of Air‐Hardening 4 wt% Medium Manganese Steels

Interpretation of Dynamic Strain Aging in an Intercritical Annealed Steel by Dislocation Multiplication Induced by Martensitic Transformation

Discontinuous Yielding Mechanisms in Tempered Hierarchical Duplex Phase Steel with High-Density Dislocations

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