Microstructure study of alloy to enhance safety and reduce adverse environmental effects of future fusion power plants

• Nano-metric precipitates through heat treatments in Cr–W–V alloy were formed.
• Metallography studies shows that the microstructure of alloy has been tempered martensite.
• The formation of nano-scale precipitates was confirmed by SEM observations.

Reduced-activation steels were developed to enhance safety and reduce adverse environmental effects of future fusion power plants. Martensitic and bainitic steels were developed during the 1985–90 timeframe, and the feasibility of their use for fusion was investigated in an international collaboration from 1994 to present. This work continues to improve the steels and the formation of very small nano-metric precipitates through standardized heat treatments in Cr–W–V alloy system using the microscopic observations. Metallography studies have revealed that the microstructure of alloy after tempering has been tempered martensite. Also after tempering, the matrix structure of alloy and the formation of nano-scale precipitates on grain and lath boundaries were confirmed by SEM observations. By the application of XRD spectra analysis and TEM electron diffraction patterns, it was shown that the type of precipitates extracted from alloy, would be M23C6 and M7C3that include a cubic and trigonal crystal structure, respectively.