MICROSTRUCTURE AND DEFORMATION RATE DURING LONG-TERM CYCLIC CREEP OF THE MARTENSITIC STEEL X22CRMOV12-1

The microstructure of three specimens of the martensitic steel X22CrMoV12-1 which had been subjected to long-term cyclic creep at 873 K with intermittent phases of unloading (stress ratio R = 0) and compression (R = -1) was quantified by electron microscopy with regard to carbides, dislocations and pores. The laws of time dependent coarsening of carbides and strain controlled growth of subgrains found for monotonic creep hold also for cyclic creep. The longer time it takes cyclic creep to reach a given strain leads to a growth advantage of carbides compared to monotonic creep. The microstructural model of plastic deformation previously developed for monotonic creep on X20(22)CrMoV12-1 allows to calculate the cyclic creep acceleration due to this advantage in carbide growth.