The martensitic 9-12% Cr steels like P92, HCM12 types are being introduced as materials for power plants. Their long-term creep properties are somewhat superior to those of the classical steels like X20CrMoV 121 used in the past. Long-time annealing (700 degreesC/ 1000 h) was performed for P92 and HCM12 martensitic steels to simulate the real operating conditions. Characteristic features (particles and subgrains) were discussed on a quantitative and qualitative basis. The results of substructure stability were compared to the results obtained for X20CrMoV121 standard steel after long-time service (about 100 000 h). (C) 2003 Elsevier Science B.V. All rights reserved.