Abstract
Austenite mechanical stability, i.e., retained austenite volume fraction (RAVF) variation with strain, and transformation behavior were investigated for two third-generation advanced high-strength steels (3GAHSS) under quasi-static uniaxial tension: a 1200 grade, two-phase medium Mn (10 wt pct) TRIP steel, and a 980 grade, three-phase TRIP steel produced with a quenching and partitioning heat treatment. The medium Mn (10 wt pct) TRIP steel deforms inhomogeneously via propagative instabilities (Lüders and Portevin Le Châtelier-like bands), while the 980 grade TRIP steel deforms homogenously up to necking. The dramatically different deformation behaviors of these steels required the development of a new in situ experimental technique that couples volumetric synchrotron X-ray diffraction measurement of RAVF with surface strain measurement using stereo digital image correlation over the beam impingement area. Measurement results with the new technique are compared to those from a more conventional approach wherein strains are measured over the entire gage region, while RAVF measurement is the same as that in the new technique. A determination is made as to the appropriateness of the different measurement techniques in measuring the transformation behaviors for steels with homogeneous and inhomogeneous deformation behaviors. Extension of the new in situ technique to the measurement of austenite transformation under different deformation modes and to higher strain rates is discussed.
| Original language | English |
|---|---|
| Pages (from-to) | 2583-2596 |
| Number of pages | 14 |
| Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
| Volume | 49 |
| Issue number | 7 |
| DOIs | |
| State | Published - Jul 1 2018 |
| Externally published | Yes |
Funding
This study was supported, in part, by the U.S. Department of Energy (DOE) under Cooperative Agreement Number DE-EE0005976, with the United States Automotive Materials Partnership LLC (USAMP). The DOE program name is ‘‘Integrated Computational Materials Engineering Approach to Development of Lightweight 3GAHSS Vehicle Assembly.’’ This research used resources of the Advanced Photon Source (APS), a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Oak Ridge National Laboratory is operated by UT-Battelle, LLC, for the U.S. DOE under Contract DE-AC05-00OR22725. Pacific Northwest National Laboratory is operated by Bat-telle Memorial Institute for the U.S. DOE under Contract No. DE-AC06-76RL01830. R. Spence kindly assisted the authors with the diffraction measurements at APS Beam line 11-ID-C. W. Poling kindly provided the authors with Figure 1(a). D. Matlock and J. Speer offered their expert assistance with development and manufacture of the 10 wt pctMn TRIP steel test specimens. BAO Steel in China provided the Q&P980 material with the support of J. Wang of the GM China Science Lab.
| Funders | Funder number |
|---|---|
| DOE Office of Science | |
| United States Automotive Materials Partnership LLC | |
| U.S. Department of Energy | DE-EE0005976 |
| Argonne National Laboratory | DE-AC05-00OR22725 |