Comparison of primary creep regeneration and anelastic recovery behaviour of 316H austenitic and 10%Cr martensitic steels

Abstract

ABSTRACT Primary creep regeneration (PCR), i.e. re-occurrence of the primary creep stage for a material loaded under stress-varying creep conditions, is an important consideration for the design and assessment of high-temperature components operating under cyclic loading conditions. This study reviews observations from a comprehensive creep experiment program aiming to understand the PCR behaviour of two high-temperature steels with very different metallurgical-microstructural characteristics at their respective application temperatures; namely 316H austenitic stainless steel at 650°C and a 10%Cr martensitic steel at 600°C. The program included twelve (stress-varying) creep tests for each steel which were systematically designed to characterise the PCR and anelastic recovery response of the steels under various loading scenarios. The experimental observations showed that the PCR behaviour of both steels is similarly sensitive to the parameters of the loading profile and PCR is more pronounced for e.g. larger reverse-loading magnitudes or longer reverse-loading durations. Detailed analysis however showed that the early PCR response is different for the two steels and the 10%Cr steel showed significantly higher creep rates immediately after a stress-transient. Similarly, it was found that although the anelastic recovery response of both steels shares similar sensitivity to the parameters of the prior-loading profile, the extent of anelastic recovery is less significant for the 316H steel. The observed PCR and anelastic recovery behaviour of the two steels have been interpreted based on their dislocation-structure and microstructural features.