Microstructural characterization of 5 to 9 pct Cr-2 pct W-V-Ta martensitic steels
- Univ. of Pittsburgh, PA (United States). Dept. of Materials Science and Engineering
- Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.
The microstructure of 9Cr-2W-0.25V-0.1C (9Cr-2WV), 9Cr-2W-0.25V-0.07Ta-0.1C (9Cr-2WVTa), 7 Cr-2W-0.25V-0.07Ta-0.1C (7Cr-2WVTa), and 5Cr-2W-0.25V-0.07Ta-0.1C (5Cr-2WVTa) steels (all compositions are in wt pct) have been characterized by analytical electron microscopy (AEM) and atom probe field ion microscopy (APFIM). These alloys have potential applications in fusion reactors because they exhibit reduced neutron activation in comparison to the conventional Cr-Mo steels. The matrix in all four alloy was 100 pct martensite. The precipitate type in the steels depended primarily on the chromium level in the alloy. In the two 9Cr steels, the stable phases were blocky M{sub 23}C{sub 6} and small spherical precipitates previously identified as MC. The two lower-chromium steels contained blocky M{sub 7}C{sub 3} and small needle-shaped carbonitrides in addition to M{sub 23}C{sub 6}. The AEM and APFIM analyses revealed that, in the steels containing tantalum, the majority of the tantalum was in solid solution. With the exception of a few of the small spherical precipitates in low-number densities in the 9Cr-2WVTa, none of the other precipitates contained measurable tantalum. The experimentally observed phases were in agreement with those predicted by phase equilibria calculations using the ThermoCalc software. However, a similar match between the experimental and predicted values of the phase compositions did not occur in some instances. Atom probe analyses directly confirmed the crucial role of trace amounts of nitrogen in the formation of vanadium-rich carbonitrides as predicted by thermodynamic equilibrium calculations.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 634635
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 6 Vol. 29; ISSN 1073-5623; ISSN MMTAEB
- Country of Publication:
- United States
- Language:
- English
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