Comparative Assessment for Static Creep and Tension-Tension Cyclic Creep Behaviors of Modified 9Cr-1Mo Steel

Cyclic creep (CC) tests were performed with the magnitudes of the stress range of constant stress ratio (R=0.1) under continuous tension-tension loading cycles at a hold time of 10 minute at 600oC for normalized and tempered modified 9Cr-1Mo steel. Cyclic strain-time curves were obtained from the controlled cyclic creep tests, and the cyclic creep behavior was investigated and compared with the static creep (SC) behavior. In the present test conditions, the results of creep rupture time and creep rate showed retardation behaviour when compared with those of the static creep. Creep rupture ductility decreased with a decrease in stress, and the ductility was almost the same for the CC and SC. In the fracture micrographs, the CC showed typical ductile fracture preceded by many dimples which occurred in the equi-axed core. The dimple size and area decreased with a decrease in the stress ranges. The precipitates formed in the CC test specimens were more coarsened than those in CC ones.