Session: MF-02-05 Materials for Hydrogen Service-High Alloy Materials 2

Paper Number: 123293

123293 - Effects of Temperature and Hydrogen on Fatigue Properties of Austenitic Stainless Steels 

The design of liquid hydrogen tanks requires a thorough understanding of the factors influencing fatigue crack initiation and propagation at cryogenic temperatures on materials used in hydrogen environments. In the case of austenitic stainless steels, it is well-established that hydrogen embrittlement (HE) is characterized by a loss of ductility in tension, with maximum embrittlement occurring at approximately 190 K, with this effect vanishing at very low temperatures [1-2]. However, is the amount of literature on the impact on high cycle fatigue strength is much more limited. Therefore, the work presented here aims to assess the high-cycle fatigue resistance of austenitic stainless steels in a hydrogen environment within the temperature range of 190 K to 300 K.

Two grades of austenitic stainless steels were selected, namely 304L and 316L. Due to differences in stacking fault energy, these two grades are expected to present varying proportions of martensitic transformation at low temperatures under fixed loading conditions [3], which may in turn influence the sensitivity to HE.

The first step of this work consisted in the determination of the fatigue resistance of these grades in air at different temperature. High cycle fatigue strengths are investigated at -83°C, 25°C and 100°C under a positive (R=0,1) load ratio. The preliminary results indicate that a significant ratchetting occurs during fatigue loading. The amount of ratchetting depends on the steel grade and temperature, with an increase of ratchetting strain with test temperature. In addition, the analysis of fatigue life shows that the lower the temperature, the higher the fatigue life is for a given stress amplitude. Note that the overall temperature sensitivity of the two materials seems to be close.

The second step was concerned with the influence of hydrogen gas on the fatigue strength at various temperatures. The analyses are performed at room temperature under hydrogen pressure of 1,5 MPa. The preliminary results suggest the absence of any hydrogen effect on the ratchetting deformation and the fatigue life at room temperature under a hydrogen pressure of 1,5 MPa. However, fracture surface analysis shows significant differences between specimen tested in air and in hydrogen environment, the depths and widths of stable propagation of the main crack appear to be different for both expositions. Phenomena occurring at temperatures above and below the maximum embrittlement temperature will be investigated so as to identify the role of various factors (martensitic transformation and hydrogen diffusivity).

Presenting Author: Romain Chochoy Institut Pprime

Presenting Author Biography: I hold a engineering degree's in materials mechanics from the Polytech Paris-Saclay engineering school, and I am currently pursuing a doctoral thesis at the Pprime Institute. This thesis focuses on studying the effect of hydrogen on the low-temperature fatigue properties of austenitic stainless steel.

Authors:

Romain Chochoy Institut Pprime
Pierre Osmond CETIM
Denis Bertheau Institut Pprime
Guillaume Benoit Institut Pprime
Daniella Guedes Sales CETIM
Gouenou Girardin CETIM
Gilbert Hénaff Institut Pprime