Abstract
The quantitative characterization of the microstructure evolution in high-Mn steel during deformation is of great importance to understanding its strain-hardening behavior. In the current study, in situ high-energy synchrotron X-ray diffraction was employed to characterize the microstructure evolution in a Fe-17Mn-1.5Al-0.3C steel during a tensile test. The microstructure at different engineering strain levels—in terms of ε-martensite and α’-martensite volume fractions, the stacking fault probability, and the twin fault probability—was analyzed by the Rietveld refinement method. The Fe-17Mn-1.5Al-0.3C steel exhibits a high ultimate tensile strength with a superior uniform elongation and a high strain-hardening rate. The remaining high strain-hardening rate at the strain level about 0.025 to 0.35 results from ε-martensite dominant transformation-induced-plasticity (TRIP) effect. The increase in the strain-hardening rate at the strain level around 0.35 to 0.43 is attributed to the synergetic α’-martensite dominant TRIP and twinning-induced-plasticity (TWIP) effects. An evaluation of the stacking fault energy (SFE) of the Fe-17Mn-1.5Al-0.3C steel by the synchrotron measurements shows good agreement with the thermodynamic calculation of the SFE.
Highlights
In the last three decades, the requirement for advanced high-strength steels (AHSS) has been highlighted in the automobile industry to reduce automobile weight and fuel consumption, as well as to improve passenger safety [1]
When the stacking fault energy (SFE) is below ~20 mJ/m2, the high-Mn steels are deformed by dislocation slip and ε-/α’-martensitic transformation, and the TRIP
Based on the results tensile deformation confirms the mixture of TRIP and TWIP mechanisms during tensile deformation obtained in the present study, the microstructure evolution and strengthening mechanisms in the in the studied material
Summary
In the last three decades, the requirement for advanced high-strength steels (AHSS) has been highlighted in the automobile industry to reduce automobile weight and fuel consumption, as well as to improve passenger safety [1]. To obtain an excellent combination of high strength and superior ductility has become the top issue in the modern AHSS design for automotive applications. The high-Mn steels with austenitic microstructure manifest both high strength and outstanding ductility. Stacking fault energy (SFE) plays a decisive role in controlling the mechanical properties and strain-hardening behavior in the high-Mn austenitic steels. When the SFE is below ~20 mJ/m2 , the high-Mn steels are deformed by dislocation slip and ε-/α’-martensitic transformation, and the TRIP effect is the dominant deformation mechanism [9,10,11]. High-Mn steels with a SFE in the range of
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