Heat-to-Heat Variation in Creep Properties of Types 304 and 316 Stainless Steels

Abstract

A wide variation in creep-rupture and long-term creep properties of 20 heats of type 304 and seven heats of type 316 stainless steel was observed. The observed variation in 1000-hr creep-rupture strength, SRt , has been related to the corresponding ultimate tensile strength variation, Sur , by a relationship of the form: SRt = α exp (β Sur), where α and β are material constants. This relationship between creep-rupture strength and ultimate tensile strength was further extended for minimum-expected 105 -hr creep-rupture strength data reported in the literature. The heat-to-heat variation in ultimate tensile strength for both types 304 and 316 stailness steel was explained in terms of carbon plus nitrogen content and grain intercept, d, by a relationship of the form Sur = A(C + N)−1/2 + B, where A and B are constants for a given temperature. The time to onset of third-stage creep for various heats of type 304 and 316 stainless steel was related to time to rupture by relationships that are independent of test temperature, for test times reaching 22,622 hr.