I'm looking for material to build high pressure and high temperature >500degC reactor to work with hydrogen for long time. Popular authentic steel 316 L for example is not enough above 500deg C . Can you suggest any material better than that?
You are really challenging the materials limits. At the moment, I do not think there is a practically economic solutions of metals for you reactor above 500 C and with high pressure of H2. 450 C may be ok with some alloy steel.