Abstract
Characteristic damage parameters were investigated for modified 9Cr-1Mo steel used in high efficiency fossil-fired power plants as hot section components. Microstructural observations and mechanical tests were carried out for base metal and welded joint after ageing, creep and fatigue tests at elevated temperatures. The precipitation of Laves phase caused the decrease in toughness. The creep damage in base metal corresponded to the decrease in hardness. Recovery of dislocation structure was related to decrease of hardness. The fatigue damage in base metal correlated to the maximum crack length among micro-cracks initiated during fatigue cycles. In the welded joint, the creep fracture occurred by the formation and growth of voids in the fine grained HAZ near base metal. The creep damage was associated with the increase in area fraction of voids.
