Applicability of empirical formulas and fractography for assessment of creep life and creep fracture modes of tempered martensitic 9%Cr steel

Abstract

In this study, the creep behaviour of P92 steel in as-received condition and after longterm isothermal ageing was investigated at 600 and 650°C using uniaxial tension creep tests. The creep testing was carried out in the power-law creep region. The analyses of creep data indicate that creep behaviour of the steel under investigation obeys both Monkman-Grant and modified Monkman-Grant empirical formulas and provides high values of creep damage factor λ. The tertiary creep was examined in terms of the variations of the time to onset of tertiary creep tot with the time to fracture tf . To assess the effect of damage process on the loss of creep strength, most creep tests were followed by fractographic investigations. It was observed that the large Laves phase particles, which coarsened during creep exposure, served as preferred sites for creep cavity nucleation. The fractography of creep ruptured specimens revealed a dominant transgranular fracture mode by necking at the highest stresses, and a mixture of transgranular and intergranular fracture modes at medium and low-stress regions.