Effect of strain rate and temperature on the serration behavior of SA508-III RPV steel in the dynamic strain aging process

Dynamic strain aging (DSA) effect on SA508-III reactor pressure vessel (RPV) steel was investigated. The SA508-III RPV steel was subjected to tension tests at different strain rates (1.1 × 10⁻⁵ s⁻¹ and 6.6 × 10⁻⁵ s⁻¹) and different temperatures (500 and 550 °C) to evaluate the influence of strain rate and temperature on the serrated flow behavior, which is the repetitive and discontinuous yielding phenomenon on the stress–strain curves. The higher temperature leads to the higher density of precipitates, M₂₃C₆ carbides and needle-like Mo₂C carbides. It was found that the samples under tension test of 6.6 × 10⁻⁵ s⁻¹ and 500 °C possess superior mechanical properties and mainly show A-type serrations on the tension test curves. Then, the local regress method was used to filter the DSA curves, thus to show the real trend of the curves. It has been found that the less time of interaction between dislocations and precipitates under higher strain rates leads to a higher strength of the sample. The more tiny-stress drops on the 550 °C serration curve can be attributed to the hardening phase, M₂₃C₆ carbides and needle-like Mo₂C carbides. The higher percentage of the small stress drops on the serration curves represents the higher mechanical strength.