Microstructure and precipitation behavior of advanced RAFM steels for high-temperature applications on fusion reactors

The composition of new eigth 9% Cr reduced activation ferritic/martensitioc steels (RAFMs) has been finely tuned in order to increase the amount of fine MX precipitates and reduce coarse M23C6 carbides through the application of thermomechanical treatments. The microstructural investigations by TEM/STEM and EELS have shown M23C6, M2X (Cr2N), and MX (Ta, V, and Ti-rich) precipitates after tempering at 750 degrees C/2 h. Higher N contens (0.04-0.03 wt%) seems to favored M2X precipitation over MX with V contents round 0.2 wt%. MX-Ti rich presents sizes larger than MX (Ta or V rich). EELS anlysis have shown that the MX (Ta, V and Ti rich) precipitated after tempering at 750 degrees C/2 h are mainly carbo-nitrides. Composition, size, number density and carbon and nitrogen content on MX and M2X is discussed in terms of the composition of each Alloy.

Automated summary

The composition of new 8%Cr reduced activation ferritic/martensitic steels have been finely tuned to increase fine MX precipitates and reduce coarse M23C6 carbides through thermomechanical treatments. The study shows that higher nitrogen content favors M2X precipitation over MX, with vanadium contents around 0.2 wt%. MX-Ti rich precipitates are larger in size than MX (Ta or V rich). EELS analysis indicates that the precipitates of MX (Ta, V and Ti rich) after tempering at 750 degrees C/2 h are mainly carbo-nitrides. Discussions are held on the composition, size, number density, carbon, and nitrogen content of MX and M2X in relation to each alloy.