Interaction solid solution hardening in 2.25Cr-1Mo steel

Abstract

The creep behavior of annealed 2.25Cr-1Mo steel—a low-alloy ferritic steel—is complicated by the metallurgical processes that occur in the steel. These processes, which involve both solid solution and precipitation effects, give rise to creep curves that differ from a classical three-stage creep curve in that two steady-state stages occur. During the first steady-state stage, the creep rate is controlled by the motion of dislocations that contain atmospheres of carbon and molybdenum atom clusters, a process termed interaction solid solution hardening. Eventually, the precipitation of Mo 2C removes molybdenum and carbon from solution, and the creep rate increases to a new steady state where the creep rate is controlled by atmosphere-free dislocations moving through a precipitate field. These nonclassical curves occur at intermediate stresses. As the stress decreases, the first steady-state stage disappears because the dislocation velocity decreases and the molybdenum-carbon atmosphere will be able to diffuse with the dislocations. At high stresses a classical curve occurs when the creep rate is controlled by a combination of processes that operate in the two steady-state stages of the nonclassical curves.