The Role of Thermomechanical Processing in Creep Deformation Behavior of Modified 9Cr-1Mo Steel

In this study, to refine the microstructure and enhance the mechanical properties, thermomechanical treatment (TMT) was performed on modified 9Cr-1Mo steel. The creep deformation behavior of TMT processed steel and the steel in its normalized and tempered (NT) state were studied for different stress levels at 923 K (650 degrees C). Transient, secondary, and tertiary creep regimes were analyzed for both conditions of the steel based on the empirical equation epsilon = epsilon(0) + epsilon(t)(1 + e(-rt)) + (epsilon) over dot(S)t + epsilon(L)e(p(tt-tr)). The rate of exhaustion of primary creep (r), r with time to reach the minimum creep rate, minimum creep rate ((epsilon) over dot(min)) ,(epsilon) over dot(min) with time spent in the secondary creep regime, rate of acceleration of tertiary creep (p), p with time to reach the onset of tertiary creep, and creep rate with applied stress exhibited a proportional relationship in both conditions of the steel. This proportionality existence in the transient and tertiary creep deformation obeyed the first-order reaction rate kinetic theory. The enhanced MX (M = V, Nb; X = C, N) precipitation in the TMT steel significantly decreased the creep deformation rate and extended the secondary stages of deformation. TMT processing of modified 9Cr-1Mo steel led to a significant increase in the creep rupture strength through the stable microstructure.