Macroscopic results of long-term creep on a modified 9Cr–1Mo steel (T91)

Modified 9Cr–1Mo steel specimens were subjected to creep tests at temperatures ranging from 500 to 600 °C. One test at 500 °C ruptured after approximately 160,000 h and another at 600 °C ruptured after approximately 94,000 h. Two tests at 500 and 600 °C are still under creep having not ruptured after more than 170,000 h. These tests show that the Monkman–Grant relationship between minimum creep rates and time to fracture holds for a wide range of temperatures and applied stresses. It is also observed that there is a clear change in creep mechanism from power-law creep to viscous creep as well as a transition from significant reduction of area to virtually no reduction of area during creep at 500, 600 and 625 °C as it is mentioned in the literature for the higher temperatures.