Creep-fatigue interaction in heat resistant austenitic alloys

Abstract

Abstract. This work includes an investigation of two commercial austenitic steels: UNS S21500 (Esshete 1250) and UNS S31035 (Sandvik Sanicro TM 25). The materials were exposed to isothermal strain controlled fatigue with load controlled dwell time at maximum strain. The testing temperature used was 700°C and the test cycles were performed in tension. Mechanical test data were obtained and analysed in order to define creep-fatigue damage diagrams at failure for the investigated austenitic alloys. During the given conditions, Sanicro 25 showed superior creep-fatigue life, suffered less amount of creep elongation for the same amount of strain amplitude and dwell times compared to Esshete 1250. Both alloys showed creep-fatigue interaction damage for specific test configurations.

Microstructural evolution during high temperature dwell-fatigue of austenitic stainless steels

“…Previous studies that have investigated the mechanical response during high temperature dwell-fatigue conditions agree that the susceptibility for creep and the interaction of creep and fatigue are found to be the most important life limiting properties [10,12,13,17]. The dwellfatigue performance focusing on the creep resistance during the dwell time of the two investigated materials are summarised in Fig.…”

“…3, with strain controlled cyclic part (black dotted line) and load controlled dwell part (black solid line). All the evaluated conditions from [10] can be viewed in Table 2. The number of cycles to failure (N f ) was defined as the point where the maximum stress range (Δσ) decreases 10%, as specified in [16].…”

“…The number of cycles to failure (N f ) was defined as the point where the maximum stress range (Δσ) decreases 10%, as specified in [16]. More details regarding the dwell-fatigue experiment are given in [10].…”

“…Test data is plotted as creep life fraction and fatigue life fraction and by drawing lower bound lines to the data inputs, the parameters for safe design can be computed [9]. For the austenitic stainless steels Sanicro 25 and Esshete 1250 such a diagram was generated and evaluated using the principal cases of Hales [8] and Plumbridge [4], in a previous publication by Wärner et al [10], but no microstructural investigations were considered. In that study it was found that both materials suffered from creep-fatigue interaction damage that limited the amount of cycles to failure, Esshete 1250 showed more creep elongation and Sanicro 25 suffered higher maximum stresses but in general still showed superior CF life compared to Esshete 1250.…”

“…The investigations were performed after the specimens had been exposed to high temperature isothermal dwell-fatigue in order to determine the creep-fatigue interaction behaviour and damage mechanisms. The mechanical response has partly been evaluated in a previous study [10].…”