Experimental and numerical study of multi-phase medium-Mn TWIP-TRIP steel: influences of strain rate and phase constituents
William E. Luecke, Y. Liu, Jake T. Benzing, X. Zhang, A. Dutta, D. Ponge, C. Oksay, D. Raabe, J.E. Wittig
The present work investigates the room temperature tensile properties of a Fe-12Mn-3Al-0.05C (weight %) twinning- and transformation-induced plasticity (TWIP-TRIP) steel from quasi-static to low-dynamic strain rates ( ̇ = 10-4 /s to ̇ = 102 /s). The resulting multi-phase microstructure, analyzed with electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), consists of coarse-grained recovered '-martensite, ultrafine-grained ferrite and ultrafine-grained austenite. Servo-hydraulic tension testing results yield a positive strain-rate sensitivity of yield and ultimate tensile strengths, indicating the flow stress predominantly depends on respective short-range barriers in the multi-phase microstructure. Thermal imaging and digital image correlation allow for in situ measurements of temperature and local strain in the gage section during tensile testing. Lüders bands and Portevin Le Chatalier (PLC) bands are not observed. Bright-field TEM, dark-field TEM and selected area electron diffraction provide insight into the deformation mechanisms. A two-scale finite element model uses empirical evidence and constitutive equations to dissect the microstructural influences (for each phase) on tensile properties. Calibration of macro-scale tensile properties is conducted to capture the strain rate sensitivity of the multi-phase TWIP-TRIP steel and is used to provide a parametric analysis of variables relevant for advanced high strength steel design. A 3D crystal plasticity finite element model uses a microstructure reconstructed from 3D EBSD measurements to study grain interactions and morphological effects on the micro-scale.