The standard EN 10222-2 is entitled Steel forgings for pressure purposes - Part 2: Ferritic and martensitic steels with specified elevated temperature properties. Grade X10CrMoVNb9-1 would be considered a high alloy steel, not a stainless steel, since the Cr content is only 8-9.5% The microstructure that develops upon normalizing is a mixture of ferrite and bainite. The tempering operation causes fine M23C6 precipitates to nucleate on prior Nb(C,N) particles.