Slow Strain Rate Tensile Tests of Irradiated Austenitic Stainless Steels in Simulated PWR Environment

For slow strain rate tensile (SSRT) test in hydrogen gas, the degradation in relative reduction in area (RRA) of 300-series austenitic stainless steels is mainly attributed to hydrogen-assisted surface crack growth (HASCG) accompanied by quasi-cleavages. To establish novel criteria for authorizing various austenitic stainless steels for use in high-pressure gaseous hydrogen, a mechanism of the HASCG should be elucidated. At first, this study performed SSRT tests on six types of austenitic stainless steels, Types 304, 316, 316L, 306(hi-Ni), 304N2 and 304(N), in high-pressure hydrogen gas and showed that the RRAs were successfully quantified in terms of a newly-proposed nickel-equivalent equation. Then, to elucidate the microscopic mechanism of the HASCG, elasto-plastic fracture toughness (JIC), fatigue crack growth (FCG) and fatigue life tests on Types 304, 316 and 316L were carried out in high-pressure hydrogen gas. The results demonstrated that the SSRT surface crack grew via the same mechanism as for the JIC and fatigue cracks, i.e., these cracks successively grow with a sharp shape under the loading process, due to local slip deformations near the crack tip by hydrogen. Detailed observations of SSRT surface cracks on Types 304 and 316L were also performed, exhibiting that the onset of the HASCG occurred at the true strain of 0.1 or larger in high-pressure hydrogen gas.

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Modification of the Johnson-cook Model for the Strain Rate Effect On Tensile Properties of 304/316 Austenitic Stainless Steels

Journal of Pressure Vessel Technology ◽

10.1115/1.4050833 ◽

2021 ◽

Author(s):

Jun-Min Seo ◽

Sang-Seop Jeong ◽

Yun-Jae Kim ◽

Jin Weon Kim ◽

Chang-Young Oh ◽

...

Keyword(s):

Plastic Strain ◽

Strain Rate ◽

Tensile Properties ◽

Stainless Steels ◽

Austenitic Stainless Steels ◽

Tensile Tests ◽

Strain Rate Effect ◽

Rate Effect ◽

Strain And Strain Rate ◽

Cook Model

Abstract In this study, tensile tests of 304 and 316 austenitic stainless steels at various strain rate were performed to investigate the strain rate effect on tensile properties. It is shown that the strain rate effect on stress depends not only on the strain rate but also on the plastic strain level. Accordingly, a modification of the existing Johnson-Cook model is proposed to incorporate the interacting effect of plastic strain and strain rate for 304 and 316 austenitic stainless steels. Although improvement is not significant, the proposed modified Johnson-Cook model can reduce the difference from the experimental data at various strain levels, compared to the existing Johnson-Cook model.

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Mechanism of Hydrogen-Assisted Surface Crack Growth of Austenitic Stainless Steels in Slow Strain Rate Tensile Test

Volume 6B: Materials and Fabrication ◽

10.1115/pvp2016-63394 ◽

2016 ◽

Author(s):

Saburo Matsuoka ◽

Junichiro Yamabe ◽

Hisao Matsunaga

Keyword(s):

High Pressure ◽

Strain Rate ◽

Crack Growth ◽

Stainless Steels ◽

Surface Crack ◽

Fatigue Cracks ◽

Austenitic Stainless Steels ◽

Hydrogen Gas ◽

Slow Strain Rate ◽

Surface Crack Growth

Several criteria based on reduction in area (RA) or relative RA (RRA) are proposed for determining the hydrogen compatibility of austenitic stainless steels; however, the mechanism of hydrogen-induced degradation in RA and RRA is not necessarily clear. The degradation in the RA and RRA of the austenitic stainless steels is attributed to hydrogen-assisted surface crack growth (HASCG) accompanied by quasi-cleavages; therefore, a mechanism of the HASCG should be elucidated to establish novel criteria for authorizing various austenitic stainless steels for use in high-pressure gaseous hydrogen. To elucidate the HASCG mechanism, this study performed slow strain rate tensile (SSRT), elasto-plastic fracture toughness (JIC), fatigue crack growth (FCG) and fatigue life tests on Types 304, 316 and 316L in high-pressure hydrogen gas. Experimental results of Type 304 were provided in this paper as a representative of Types 304, 316 and 316L. The results demonstrated that the SSRT surface crack grew via the same mechanism as for the JIC and fatigue cracks, i.e., these crack growths could be uniformly explained on the basis of the hydrogen-induced successive crack growth (HISCG) model, which considers that cracks successively grow with a sharp shape under the loading process, due to local slip deformations near the crack tip by hydrogen. Accordingly, the HIS crack is ductile, not brittle.

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