Effects of Hydrogen on Fatigue Crack Growth and Stretch Zone of 0.08mass%C Low Carbon Steel Pipe

Oda

2011

JMMP

In order to investigate the brittle-striation formation mechanism of a low carbon steel JIS S10C fatigued in a hydrogen gas environment, fractographic observations of the visualized fracture phenomena during some processes of brittle-striation formation were conducted. The following results were obtained. A striation line is formed during the loading part of the cycle as a trace of blunting by slip. A stable ductile crack then starts growing. These processes are similar to those during the normal ductile fracture from a crack; that is, a ductile tearing process in tension. Based on the experimental results, a brittle-striation formation model, in which hydrogen only enhances the microscopic ductile tearing process just ahead of a crack tip, was proposed. The model rationally explains the peculiar load-frequency effect in the quasi-cleavage range on the fatigue crack growth which reveals a lower growth rate in spite of lowering the load-frequency.

Section: Introductionmentioning

confidence: 99%

Investigation of the Mechanism for Brittle-Striation Formation in Low Carbon Steel Fatigued in Hydrogen Gas (Fractographic Observation on Fracture Processes Visualized by Controlling Load Sequence and Testing Environment)

Oda

2011

JMMP

“…Matsuoka et al [24,25] has explained the formation of this fracture feature in terms of reduced plasticity expansion in the crack-tip region. Based on their model, these striations are the results from slip localization, which is compatible with the HELP mechanism [3,4].…”

Section: H Effect On Fcg Proceduresmentioning

confidence: 99%

Hydrogen-assisted fatigue crack growth in ferritic steels – a fractographic study

et al. 2018

Abstract. Fatigue crack growth (FCG) behavior of a Fe-3wt.%Si ferritic alloy under different environmental conditions using in-situ electrochemical (cathodic) hydrogen (H) charging has been investigated. Three frequencies have been applied. Results clearly show that the FCG rate increased by a factor spanning from 20 to 1000 times, depending on the loading frequencies, when compared to the reference test in air. Lower frequency leads to higher FCG rate. A comprehensive fractographic analysis was carried out: the area fraction of different fracture surface features was measured and taken into statistical analysis. Based on these investigations, the possible mechanisms of H-enhanced FCG are discussed. Similar tests in high-pressure H gas from other studies were also compared and discussed. These results give a preliminary understanding of H effect in fatigue crack propagation procedure in ferritic alloys.

“…The proposed theories described above can be seen as the fundamental mechanisms explaining the influence of hydrogen on deformation processes in the atomic scale which causes hydrogen related deformation mechanisms at the mesoscopic scale e. g. when short crack growth processes are observed. An example of this theoretical approach is the explanation of increased fatigue crack growth rate in the long crack growth regime in carbon steel JIS-SM490B by the hydrogenenhanced successive fatigue crack growth (HESFCG) model [12]. It is proposed that hydrogen accumulates at the crack tip causing a localization of slip deformation due to the HELP mechanism.…”

Section: Introductionmentioning

confidence: 99%

Modeling of hydrogen effects on short crack propagation in a metastable austenitic stainless steel (X2CrNi19-11)

et al. 2018

The experimentally observed short fatigue crack growth rate of an uncharged specimen tested in air is compared with results obtained from specimens tested in 10 MPa hydrogen atmosphere and specimens previously charged with hydrogen. To further discuss the hydrogen related short propagation mechanisms, a simulation approach for predicting short fatigue crack growth is presented. The boundary element method is used for calculating stresses and displacements in an anisotropic elastic solid. The hydrogen concentration is assumed to be homogeneously distributed in the microstructure. Based on this modelling approach, it could be concluded that hydrogen leads to an increasing short fatigue crack growth rate due to increasing irreversible deformation processes at the crack tip and also promotes grain boundary cracking in specimens tested in 10 MPa hydrogen atmosphere.