Effect of Structure on Creep Strength of a Low-Alloy Cr-Mo-V Steel

Abstract

The published data on the creep and rupture strength of low-alloy ferritic steels are critically examined and it is concluded that there is no evidence that maximum strength accrues from a fully upper bainite structure. The creep strength, over a range of stress, of samples of one cast of low-alloy Cr-Mo-V steel in various structural conditions has been examined. It is shown that there is no gain in strength (primary creep strain or secondary-creep rate) to be obtained by increasing the bainite content above ∼20% at 11 hbar and 575°C (848 K). At higher stresses, creep strength improves up to ∼60% bainite. The stress-dependence of creep is structure-sensitive and its variation indicates that at itresses <∼11 hbar material containing ∼20–30 % bainite will have a lower secondary-creep rate than fully bainitic structures.