Influence of thermal history on precipitation of hardening phases in tempered martensite 10%Cr-steel X12CrMoWVNbN 10-1-1

Precipitation of hardening phases was studied in the cast and the forged version of a tempered martensitic 10% Cr-steel by EDX-analysis of extracted precipitates in the scanning transmission electron microscope. It was found that the type of V-rich precipitates varies with thermal history. Tempering of the martensitic structure at temperatures ≤690 and ≥730 °C produces M2X and MX, respectively, as major V-rich phases (M: metallic elements, X: C, N) with M2X being lower in V-content and smaller in size than MX. Creep for 7.7 kh at 650 °C changes the major V-rich phase from M2X to MX and also leads to local appearance of relatively large particles of modified V-containing Z-phase. The evolution from M2X to MX and Z-phase is expected to be accompanied with decrease in creep resistance.