Hydrogen-induced cracking in 4340-type steel: Effects of composition, yield strength, and H2 pressure (original) (raw)
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Materials Science and Engineering: A, 2015
The purpose of this paper is to reveal the dominant factors affecting tensile fracture under a hydrogen gas atmosphere. Tensile tests were conducted in hydrogen gas with circumferentially-notched specimens of a commercial tempered martensitic steel. Two specimens were exposed to hydrogen gas for 48 h before tensile testing; the other two specimens were not pre-charged. Longitudinal cracks along the loading direction and a transverse crack perpendicular to the loading direction were observed on a cross section of the non-charged specimen, but there was only one small crack on a cross section of the precharged specimen. Electron back scatter diffraction, energy dispersive X-ray spectrometry and finite element method analyses were applied to clarify the relationships among the longitudinal crack, Mn segregation, microstructures of martensitic steel and hydrogen. As a result, it has been demonstrated that Mn segregation and MnS promote hydrogen-assisted cracking in the tempered martensitic steel, causing the longitudinal cracking which is a mechanically non-preferential direction in homogeneous situations. More specifically, we have shown that the role of the Mn segregation is to promote the hydrogen-enhanced decohesion effect (HEDE), which is particularly important for crack propagation in the present case. These considerations indicate that the presence of Mn is crucially important for hydrogen-assisted cracking associated with hydrogen-enhanced localized plasticity (HELP) as well as HEDE.
Influence of hydrogen on plasticity around the crack tip in high strength steels
Engineering Fracture Mechanics, 2017
Fracture mechanics concepts applied to tests in aggressive environments are a challenge for integrity analysis. Specifically about hydrogen, the concentration of this element in defects or in trapping sites can cause unexpected failure. The present paper presents results showing the influence of hydrogen in the reduction of fracture toughness and a discussion about how to deal with it in high strength alloys. The results show that the hydrogen reduces the plasticity and consequently the applications of CTOD concepts are questionable for the studied materials.
Strength, Fracture and Complexity, 2018
Hydrogen-Induced Cracking (HIC) is one of several related mechanisms whereby absorbed hydrogen atoms can compromise the integrity of components manufactured of low strength steels. A "low strength steel" is defined as having a maximum hardness of 22 HRC (249 HV). The corresponding maximum tensile strength is of the order of 800 MPa (116 ksi). Steels having localized areas with microhardness in excess of 22 HRC are particularly vulnerable to the development of HIC damage. HIC is a term applied to phenomena which occurs at low temperatures (typically less than about 90°C), and must not be confused with high temperature hydrogen attack of low strength carbon-manganese and low alloy steels exposed to hot hydrogen gas-containing environments. This review will highlight main factors that affect HIC development or failure by considering the following: (i) Metallurgical factors (effect of materials and microstructures), and (ii) Environmental exposure factors.
Effect of Hydrogen on Fracture of Austenitic Fe-Mn-Al Steel
ISIJ International, 1994
Bombay 400 076, India. / 993) In this investigation a stable high manganese austenitic steel, 0.45C-1 7Mn-2.8Al, has been studied for hydrogen embrittlement using cathodically precharged specimens. Tensile testing of axisymmetric and p[ane strain specimens precharged with hydrogen show an appreciable loss of 8-100/o reduction in area (RA) whereasthe loss in o/o elongation is lesser. Thetrue fracture strain decreased from 0.88 to O.73 for axisymmetric and from O.79 to 0.60 for plane strain specimens, Hydrogen precharging is observed to result in decrease of CTOD at crack initiation by about 0.07 mm and a decrease in crack tip fracture strain for crack initiation from O.53 to 0.34. The greater effect of hydrogen precharging thus observed is attributed to existence of higher stress triaxiality in CTOD and plane strain tensile testing in comparison to axisymmetric one. OnSEM examination of fracture surfaces the uncharged tensile specimensshowedon]y dimpled fracture, the precharged specimensshowedtransition from dimpled to quasicleavage and intergranular fracture near the surface. Regions close to the pre-fatigue tip in CTOD specimens depict intergranular fracture. The fractographic changes are attributed to the combined role of stress intensity and hydrogen concentration variation arising out of hydrogen transport inside the specimen.
Effect of hydrogen on the properties and fracture characteristics of TRIP 800 steels
Corrosion Science, 2011
The paper describes effect of hydrogen on the properties and fracture characteristics of two variants of TRIP 800 C–Mn–Si steels. The effect of hydrogen was studied by means of tensile tests on specimens previously charged by hydrogen. Hydrogen provoked embrittlement in both variants but only for very high hydrogen content. Hydrogen embrittlement manifested itself mainly by a loss of plasticity.
Hydrogen embrittlement (HE) of TM210 maraging steel was studied by slow strain rate tensile and constant load tests. The over-aged sample exhibited the best resistance to HE, since HE susceptibility of the maraging steel does not depend on the strength, but rather on the reverted austenite content. The hydrogen concentration, observed by scanning Kelvin probe force microscopy, was enriched in the reverted austenite at the grain boundaries and martensite lath boundaries, resulting in hydrogeninduced cracks propagating along the grain boundaries and martensite lath boundaries.
The influence of hydrogen flux on crack initiation in martensitic steels
Understanding hydrogen transport and trapping phenomena is a key feature to revisit the hydrogen embrittlement (HE) models proposed in the literature. Both aspects can be affected by stress-strain states at different microstructural scales. Elastic distortion and plastic strain are both aspects of the mechanical states associated with defects (vacancies, dislocations), metallurgical elements (grain boundaries, precipitates), internal stresses and applied stresses, which can modify the diffusion and solubility of hydrogen. In the present work we first explore the effects of a tensile stress applied on martensitic steel membrane on the hydrogen concentration and mobility. In a second part, we analyse the impact of mobile and trapped hydrogen on HE using local approach of fracture under hydrogen flux.
Effect of hydrogen on the fracture behavior of high strength steel during slow strain rate test
Corrosion Science, 2007
The effect of hydrogen on the fracture behavior of the quenched and tempered AISI 4135 steel at 1450 MPa has been investigated by means of slow strain rate tests on smooth and circumferentiallynotched round-bar specimens. Hydrogen was introduced into specimens by electrochemical charging and its content was measured by thermal desorption spectrometry (TDS) analysis. Results showed that the steel had high hydrogen embrittlement susceptibility. For both smooth and notched specimens, the fracture mode was changed from microvoid coalescence (MVC) to brittle intergranular (IG) fracture after the introduction of a small amount of diffusible hydrogen. Fracture initiated in the vicinity of the notch root for notched specimens, while it started from around the center in smooth specimens. The fracture stress decreased with increasing diffusible hydrogen content, and the decreasing trend was more prominent for specimens with a higher stress concentration factor. Taking into account the stress-driven hydrogen diffusion and accumulation in the vicinity of the notch root, the local diffusible hydrogen concentration and local fracture stress in notched specimens have been calculated. According to numerical results, the relationship between the local fracture stress and local diffusible hydrogen concentration was independent of stress concentration factor, which could account for the effect of hydrogen on the fracture stress of the steel.