Header menu link for other important links
Effect of interspersed hold at peak load on the high-temperature fatigue crack growth rate response of SS 316 L(N) stainless steel
, M. Thomas
Published in ASTM International
Volume: 9
Issue: 5
Low-carbon, nitrogen-enhanced austenitic stainless steels (316 L(N)) are often used in the construction of power plant components, such as heat transport systems that operate at elevated temperatures. Some of these components may be subjected to a combination of creep and fatigue loads during the high-temperature operating conditions, and the synergistic action leads to accelerated failure life. The present study aims to assess the effect of interspersed hold at peak load on the fatigue crack growth rate in SS 316 L(N) at test temperatures of 823 K (550°C), 873 K (600°C), and 923 K (650°C). The fatigue hold-time experiments were conducted using repeated blocks of 1,500 cycles of constant amplitude cyclic loading at a stress ratio of 0.1 followed by a hold-time waveform at the peak load with a dwell period of 600 s. In some experiments, the dwell time was set as 900 or 1,200 s. The results indicate a marginal slowdown in the crack growth rate with dwell time testing at 550°C compared with continuous cycling at high temperatures. This could be due to increased crack tip plasticity, crack tip blunting due to hold time, and associated crack closure during subsequent cycles of fatigue loading. Crack length estimated by unloading compliance technique prior to and after hold time suggested a crack length increase after hold period for the first unloading cycle, but upon subsequent cycling, the crack growth rate appeared to slow down. It is presumed that there is a competition between crack closure due to enhanced plastic zone sizes (due to creep) and crack extension due to creep during hold time. It is noted that SS 310 L(N) is a creepresistant alloy and exhibits dynamic strain aging at the test temperatures. The scanning electron microscopy fractographs in general indicated evidence of conjoint damage due to fatigue (through striations) and creep. The presence of both transgranular and intergranular modes of fracture could be seen. Formation of the triple-point crack as a result of grain boundary sliding was observed from the electron fractography in addition to void nucleation along the grain boundaries, indicating the damage accumulation during the creep. © 2020 ASTM International. All rights reserved.
About the journal
JournalData powered by TypesetMaterials Performance and Characterization
PublisherData powered by TypesetASTM International
Impact FactorNo
Citation Styleunsrt