Effects of a Hydrogen Gas Environment on Fatigue Crack Growth of a Stable Austenitic Stainless Steel

Abstract

In order to clarify the effects of a hydrogen gas environment on the fatigue crack growth characteristics of stable austenitic stainless steels, bending fatigue tests were carried out in a hydrogen gas, in a nitrogen gas at 1.0 MPa and in air on a SUS316L using the Japanese Industrial Standards (type 316L). Also, in order to discuss the difference in the hydrogen sensitivity between austenitic stainless steels, the fatigue tests were also carried out on a SUS304 using the Japanese Industrial Standards (type 304) metastable austenitic stainless steel as a material for comparison. The main results obtained are as follows. Hydrogen gas accelerates the fatigue crack growth rate of type 316L. The degree of the fatigue crack growth acceleration is low compared to that in type 304. The fracture surfaces of both the materials practically consist of two parts; the faceted area seemed to be brittle and the remaining area occupying a greater part of the fracture surface and seemed to be ductile. The faceted area does not significantly contribute to the fatigue crack growth rate in both austenitic stainless steels. The slip-off mechanism seems to be valid not only in air and in nitrogen, but also in hydrogen. Also, the main cause of the fatigue crack growth acceleration of both materials occurs by variation of the slip behaviour. The difference in the degree of the acceleration, which in type 316L is lower than in type 304, seems to be caused by the difference in the stability of the γ phase.

Investigation of Local Hydrogen Distribution Around Fatigue Crack Tip of a Type 304 Stainless Steel with Secondary Ion Mass Spectrometry and Hydrogen Micro-Print Technique

“…The FCG rate was determined as 0.8×10 -6 m/cycle. It is known from our earlier study that FCG rate in hydrogen is 4.0 times as high as in nitrogen under this condition (3) . During the test, FCG behavior was in-situ observed.…”

“…In this HMPT study, a detectable amount of hydrogen was not released from the type 304 stainless steel, in spite of the fact that the FCG rate is accelerated about 4.0 times by hydrogen under this fatigue testing condition (3) .…”

“…The grain sizes are about 30 µm. Figure 1 shows the shape and dimensions of a fatigue specimen (3) . After the mechanical processes, the specimens were ground up to #2000 with abrasive papers and lapped with 0.05 µm γ-alumina dispersed on a micro-cloth to make the surface smooth and the observations easier.…”

“…In order to ensure the safety of components exposed to hydrogen for a long time, it is important to clarify the hydrogen effects on fatigue strength. The authors investigated the effects of a hydrogen gas environment on the fatigue crack growth (FCG) of austenitic stainless steels (1)~ (3) . In the previous studies, it was considered that the hydrogen effect on FCG acceleration in type 304 stainless steel is greater than that in type 316L stainless steel, of which the stability of the γ phase is higher than that of type 304 (3) and the cause of the FCG acceleration is the localization of slip at a fatigue crack tip (1) .…”

“…The authors investigated the effects of a hydrogen gas environment on the fatigue crack growth (FCG) of austenitic stainless steels (1)~ (3) . In the previous studies, it was considered that the hydrogen effect on FCG acceleration in type 304 stainless steel is greater than that in type 316L stainless steel, of which the stability of the γ phase is higher than that of type 304 (3) and the cause of the FCG acceleration is the localization of slip at a fatigue crack tip (1) . Hydrogen sensitivity of austenitic stainless steels in the FCG process is considered to be strongly related to the strain-induced α' martensite as is the case with a static tensile test (4) .…”