Creep deformation behaviour of thermomechanically treated India specific reduced activation ferritic martensitic steel

Abstract

In the present work, the influence of thermomechanical treatment (TMT) on microstructural evolution and creep deformation behaviour of India specific reduced activation ferritic martensitic (INRAFM) steel was investigated. Firstly, the TMT was carried out on INRAFM steel by reducing its thickness to 25% at warm rolling temperature (973 K), followed by tempering for 90 min at 1033 K. The resultant microstructural characteristics were compared with those attained in normalized and tempered (N+T) condition. TMT treated steel shows a refinement in lath structure with an increment in population of finer M23C6 precipitates along the hierarchal PAG/packet/block boundaries and MX carbonitrides in the intralath region. After TMT, creep tests were performed on the steel over the stress range of 200–300 MPa at temperature of 823 K. The rupture time of the steel significantly increased upon TMT, due to refinement in microstructural features that enhanced the creep resistance. Dependence of minimum creep rate on applied stress obeys Norton's power law and the stress exponent values indicated the deformation mechanism as dislocation creep. Modified Monkman-Grant relation shows a good relation between rupture time/strain to failure with minimum creep rate. Thereafter, the effect of TMT on the transient, secondary and tertiary creep behaviour was also examined and presented in this work. The TMT treated steel shows lower rate of exhaustion, higher threshold stress and prolonged tertiary region.