Abstract
There is a need worldwide to develop materials for advanced power plants with steam temperatures of 700°C and above that will achieve long-term creep-rupture strength and low CO2 emissions. The creep resistance of actual 9-12Cr steels is not enough to fulfil the engineering requirements above 600°C. In this paper, the authors report their advances in the improvement of creep properties of this type of steels by the microstructural optimization through nano-precipitation using two methodologies. 1) Applying a high temperature austenitization cycle followed by an ausforming step (thermomechanical treatment, TMT) to G91 steel, to increase the martensite dislocation density and, thus, the number density of MX precipitates (M = V,Nb; X = C,N) but at the expense of deteriorating the ductility. 2) Compositional adjustments, guided by computational thermodynamics, combined with a conventional heat treatment (no TMT), to design novel steels with a good ductility while still possessing a high number density of MX precipitates, similar to the one obtained after the TMT in G91. The microstructures have been characterized by optical, scanning and transmission electron microscopy, EBSD and atom probe tomography. The creep behaviour at 700°C has been evaluated under a load of 200 N using small punch creep tests.
| Original language | English |
|---|---|
| Article number | 2118082 |
| Journal | European Journal of Materials |
| Volume | 3 |
| Issue number | 1 |
| DOIs | |
| State | Published - 2023 |
Funding
Authors acknowledge financial support to Agencia Estatal de Investigación (AEI) in the form of Coordinate Projects MAT2016-80875-C3-1-R and PID2019-109334RB-C31. J. Vivas acknowledges financial support in the form of a FPI Grant BES-2014-069863. D. De-Castro acknowledges financial support in the form of a FPI Grant BES-C-2017-0090. APT was conducted at ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. DOE Office of Science User Facility. European Regional Development Fund through the Agencia Estatal de Investigaci?n;Spanish Ministry of Science and Innovation. The authors would like to thank James Burns for assistance in performing APT sample preparation and running the APT experiments. The authors are grateful for the dilatometer tests by Phase Transformation laboratory and for the SEM microscopy by the Microscopy Lab at CENIM-CSIC. This work contributes to the Joint Programme on Nuclear Materials (JPNM) of the European Energy Research Alliance (EERA).
Keywords
- Creep resistant steels
- ausforming
- creep fracture behaviour
- microstructural degradation
- small punch creep tests
- thermomechanical treatment
