Effect of strain rate on low cycle fatigue of 316LN stainless steel with varying nitrogen content: Part-II fatigue life and fracture

A tailored-for-purpose environmental fatigue testing facility was previously developed to perform direct strain-controlled tests on stainless steel in simulated PWR water. Strain in specimen mid-section is generated by the use of pneumatic bellows, and eddy current measurement is used as a feedback signal. The procedure conforms with the ASTM E 606 practice for low cycle fatigue, giving results which are directly compatible with the major NPP design codes. Past studies were compiled in the NUREG/CR-6909 report and environmental reduction factors Fen were proposed to account for fatigue life reduction in hot water as compared to a reference value in air. This database exclusively contained non-stabilized stainless steels, mainly tested under stroke control. The applicability of the stainless steel Fen factor for stabilized alloys was already challenged in past papers (PVP2013-97500, PVP2014-28465). The results presented in this paper follow the same overall trend of lower experimental values (4.12–11.46) compared to those expected according to the NUREG report (9.49–10.37). In this paper results of a dual strain rate test programme on niobium stabilized AISI 347 type stainless steel are presented and discussed in the context of the NUREG/CR-6909 Fen methodology. Special attention is paid to the effect of strain signal on fatigue life, which according to current prediction methods does not affect the value of Fen.

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Influence of the Strain Rate on the Low Cycle Fatigue Life of an Austenitic Stainless Steel with a Ground Surface Finish in Different Environments

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.891-892.1320 ◽

2014 ◽

Vol 891-892 ◽

pp. 1320-1326 ◽

Cited By ~ 2

Author(s):

Thibault Poulain ◽

José Mendez ◽

Gilbert Hénaff ◽

Laurent de Baglion

Keyword(s):

Stainless Steel ◽

Fatigue Life ◽

Austenitic Stainless Steel ◽

Strain Rate ◽

Surface Finish ◽

Power Plants ◽

Low Cycle Fatigue ◽

Total Strain Amplitude ◽

Cycle Fatigue ◽

Pressurized Water

This paper focuses on the influence of strain rate in Low Cycle Fatigue (LCF) of a 304L austenitic stainless steel at 300 °C in different environments (secondary vacuum, air and Pressurized Water Reactor (PWR) water environment). Moreover test samples are ground to obtain a surface finish rougher than all that could be found in nuclear power plants. Different strain rates (4x10-3, 1x10-4and 1x10-5s-1) are studied, with a triangular waveform at a total strain amplitude of ±0.6%. The influence of strain rate on cyclic stress-strain behavior and fatigue life is firstly analyzed in secondary vacuum, considered as a non-active environment. Then, interactions between stain rate and environmental effects in Air and in PWR environment are presented. In all environments, a decrease in strain rate leads to a negative strain rate dependence of the stress response and a reduction in fatigue life. Finally, SEM observations of fatigue striations in PWR environment indicate a crack propagation rate enhancement when the strain rate is decreased.

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