Abstract
In this study, the dependence of the cyclic deformation behavior on the surface morphology of metastable austenitic HSD® 600 TWinning Induced Plasticity (TWIP) steel was investigated. This steel—with the alloying concept Mn-Al-Si—shows a fully austenitic microstructure with deformation-induced twinning at ambient temperature. Four different surface morphologies were analyzed: as-received with a so-called rolling skin, after up milling, after down milling, and a reference morphology achieved by polishing. The morphologies were characterized by X-Ray Diffraction (XRD), Focused Ion Beam (FIB), Scanning Electron Microscopy (SEM) as well as confocal microscopy methods and show significant differences in initial residual stresses, phase fractions, topographies and microstructures. For specimens with all variants of the morphologies, fatigue tests were performed in the Low Cycle Fatigue (LCF) and High Cycle Fatigue (HCF) regime to characterize the cyclic deformation behavior and fatigue life. Moreover, this study focused on the frequency-dependent self-heating of the specimens caused by cyclic plasticity in the HCF regime. The results show that both surface morphology and specimen temperature have a significant influence on the cyclic deformation behavior of HSD® 600 TWIP steel in the HCF regime.
Highlights
High-manganese fully metastable austenitic steels with the alloying concept Mn-Al-Si offer an outstanding combination of formability and strength due to deformation-induced mechanisms like twinning (TWinning Induced Plasticity, TWIP) and phase transformation from γ-austenite to ε-martensite and/or α’-martensite (TRansformation Induced Plasticity, TRIP) [1,2]
Because of the extraordinary mechanical properties of TRIP and TWIP steels, they are suitable e.g., for high energy absorption, components produced by deep drawing and offer new possibilities in lightweight applications [4]
Scanning Electron Microscope (SEM) and Focused Ion Beam (FIB) analyses were carried out with a “GAIA3” dual beam FIB (Tescan s.r.o., Brno, Czech Republic) with a Ga-Ion beam equipped with an Electron Backscatter Diffraction (EBSD) module “Hikari Plus” (Ametek Inc., Berwyn, PA, USA)
Summary
High-manganese fully metastable austenitic steels with the alloying concept Mn-Al-Si offer an outstanding combination of formability and strength due to deformation-induced mechanisms like twinning (TWinning Induced Plasticity, TWIP) and phase transformation from γ-austenite to ε-martensite and/or α’-martensite (TRansformation Induced Plasticity, TRIP) [1,2]. The deformation-induced twins appear as bundles of closely spaced twins with a thickness of a few nanometers which spread across the original grains [7]. They retard the strain localization by acting as strong barriers for dislocation motion, thereby increasing the dislocation density. Because of the extraordinary mechanical properties of TRIP and TWIP steels, they are suitable e.g., for high energy absorption, components produced by deep drawing and offer new possibilities in lightweight applications [4]
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