| AVS 62nd International Symposium & Exhibition | |
| Atom Probe Tomography Focus Topic | Monday Sessions |
| Session AP+AS-MoA |
| Session: | Current and New Research Fields for Applications of Atom Probe Tomography |
| Presenter: | Mattias Thuvander, Chalmers University of Technology, Sweden |
| Authors: | M. Thuvander, Chalmers University of Technology, Sweden J. Odqvist, KTH Royal Institute of Technology, Sweden P. Hedström, KTH Royal Institute of Technology, Sweden |
| Correspondent: | Click to Email |
Ferrite containing more than a few percent chromium is susceptible to embrittlement when subjected to elevated temperatures for sufficiently long periods of time. The phenomenon is often called '475°C embrittlement', indicating the temperature at which the effect is most rapid. The embrittlement is an issue for several important types of steel, including corrosion resistant ferritic steel, duplex stainless steel, cast austenitic steel and austenitic weldments, and limits their maximum service temperature (to about 300°C). The volume fraction of ferrite ranges from 100% in ferritic steel, to about 50% in duplex steel, down to 5-25% in austenitic castings and weldments (for which the presence of some ferrite is needed to avoid solidification cracking). The reason behind the embrittlement is the phase separation into two bcc-phases, Cr-rich α' and Fe-rich α, as can be seen in the binary Fe-Cr phase diagram. The phase separation results in an increase in strength and hardness but a decrease in ductility. Depending on Cr-content and temperature, the phase separation occurs by nucleation and growth (typically for low Cr contents) or by spinodal decomposition (typically for high Cr contents). Spinodal decomposition is an interesting phenomenon in physical metallurgy and it has been extensively studied for a long time. The phase separation occurs on the nanometer scale and during the early stages the concentration variations are subtle. Therefore, it is a challenging mechanism to study experimentally. Atom probe tomography (APT) is a well-suited technique, as small concentration variations on a small scale can be measured, also in the case when the phase separation has a complex 3D-structure, which is the case for spinodal decomposition. In this presentation, APT methodology for studying spinodal decomposition will be discussed. Also, results from several investigations concerning phase separation kinetics will be presented. For example, the influence of stress on spinodal decomposition in duplex steels, the influence of homogenization temperature on spinodal decomposition in binary Fe-Cr and the behavior of different ternary Fe-Cr-X systems will be addressed.