Hydrogen In High Strength Steel Research Articles

Influence of temperature and alloying on the apparent diffusivity of hydrogen in high strength steel

In the present study, apparent hydrogen diffusivities in 2.25Cr–1Mo and mild steel in the temperature range of 25–400 °C were determined from the hydrogen evolution profiles from specimens, electrochemically charged with hydrogen to saturation. These profiles were generated by measuring the volume of hydrogen diffused out from a specimen using a hot extraction-gas chromatography technique. The diffusivity values agree well with the literature data on apparent diffusivity of hydrogen in steel. Results from this study along with apparent diffusivity of hydrogen in 9Cr–1MoVNbN steel obtained from an earlier study are compared to reveal the effects of alloying on diffusivity of hydrogen in steel. The results indicated that the apparent hydrogen diffusivity in steel decreases with alloy content of steel. It is also shown that the activation energy for apparent diffusion of hydrogen in steel increases with increase in alloy content. Based on these, it is also shown that for the same amount of hydrogen charged into different steels; the hydrogen diffused out for a given time will be less for alloyed steel than for the unalloyed steels. Practical implications of these results in the diffusible hydrogen measurements in steel welding consumables and choosing the post-heating during welding of steels are discussed.

Characterization of Hydrogen-Induced Contact Fracture in High-Strength Steel

This study investigated the hydrogen embrittlement (HE) cracking behavior produced by local contact loading of high-strength steel. When a spherical impression was applied to a hydrogen-absorbed high-strength steel, HE induces contact fracture, where radial cracks are initiated and propagated from the indentation impression. The length of the radial crack was found to be dependent on the hydrogen content in the steel as well as the applied contact force. A combined experimental/computational investigation was conducted in order to clarify the mechanism of hydrogen-induced contact fracture. In the computation, crack propagation was simulated using a cohesive zone model (CZM) in finite element method (FEM), in order to elucidate stress criterion of the present HE crack. It was found that the normal tensile stress was developed around impression, and it initiated and propagated the HE crack. It was also revealed that the hydrogen content enhanced contact fracture damage, especially the resistance of crack propagation (i.e., threshold stress intensity factor, Kth). The findings may be useful for countermeasure of contact fracture coupled with hydrogen in high-strength steel. Such phenomenon is potentially experienced in various contact components in hydrogen environment.

Internal reversible hydrogen embrittlement leads to engineering failure of cold drawn wire

1. IntroductionHydrogenembrittlementisverycommontypeofphenomenonthatcausesindustrialfailureofsteelmaterial.Ithasbeenobserved that embrittlement may also take place due to interfacial segregation of hydrogen in high strength steel, whichleads to delamination or decohesion. Cold drawn high carbon steel wires are amenable to being weaker along thelongitudinal planes compared to the transverse planes due to fibre-like deformation of pearlitic phases in the longitudinaldirection. Hydrogen embrittlement is prone to cause spontaneous splitting in cold drawn wire. Generally, atomic hydrogenis absorbed initially by the metal surface and transforms to molecular hydrogen when the concentration reaches highervalue.Themolecularhydrogenaccumulatesinvoids,poresandinterfacesamongmanyotherdefectsites.Ifthesedefectsarenot present in the vicinity of the high hydrogen areas, blisters or hair line cracks are formed to release the high pressure.Experimentally it was found that the segregation of molecular hydrogen generates 10

Influence of activation energy and sensitivity to hydrogen embrittlement on fatigue strength degradation by irreversible hydrogen in high-strength steels

Fatigue tests were conducted for cold-drawn eutectoid steels having different activation energies for irreversible hydrogen trap sites and sensitivities to hydrogen embrittlement; the purpose was to investigate the mechanism of fatigue strength degradation by irreversible hydrogen. The fatigue strength of a sample with low activation energy was decreased by irreversible hydrogen in the material, whereas the fatigue strength of a sample with high activation energy was not. When the activation energies for irreversible hydrogen were almost equal, a higher sensitivity to hydrogen embrittlement induced fatigue strength degradation by irreversible hydrogen. Therefore, fatigue strength degradation by irreversible hydrogen depends on the activation energy for irreversible hydrogen trap sites and sensitivity to hydrogen embrittlement.

高強度鋼の疲労き裂進展下限界条件に及ぼすき裂寸法，応力比および水素の影響

The effects of crack size, stress ratio and absorbed hydrogen on the fatigue crack propagation characteristics of high strength steel were studied near threshold regime. The test material was SCM440H low alloy steel. The material was quenched in vacuum and tempered at low temperature to achieve high strength and to lower the initial content of hydrogen of the material. The effects of crack size and stress ratio on the fatigue crack propagation rate and threshold stress intensity factor were investigated in air at first. These data offered a baseline as a reference. The effect of absorbed hydrogen was examined using a material in which hydrogen was introduced by cathodic charging. It was verified that the absorbed hydrogen in high strength steel affected the high cycle fatigue crack propagation characteristics. The fatigue crack propagation rate near threshold region was accelerated and ΔKth was lowered. The concentration of about 1ppm hydrogen caused 20% reduction of ΔKth. Since absorbed hydrogen has an influence even on high cycle fatigue crack propagation, it should be taken into account in the evaluation of defect of hydrogen utilization machine.

Elastic recoil detection analysis of hydrogen in high strength steel

Elastic recoil detection analysis of hydrogen in high strength steel

Analysis of Surface Hydrogen in High-Strength Steels

Hot-extraction thermal conductivity method, secondary ion mass spectrometry (SIMS) and anodic dissolution and the reaction of the liberated hydrogen with nitroxyl free radical method were used in the determination of surface enriched hydrogen in AISI 1062 and 4037 steels. The data support the hypothesis that hydrogen embrittlement originates in the thin outer surface layers of these steels. Résumé On a utilisé la méthode de conductivité thermique par extraction à chaud, la spectrométrie de masse des ions secondaires (SIMS), la dissolution anodique et la méthode de réaction de l'hydrogene libéré avec les radicaux libres nitroxyles, pour déterminer l'enrichissement des surfaces en hydrogene des aciers AISI 1062 et 4037. Les résultats supportent l'hypothese que la fragilisation par l'hydrogéne s'initie dans une fine couche à la surface de ces aciers.

Evaluation of threshold stress intensity in high strength hydrogen charged steel in low strain rate tension tests

AbstractThe fracture ductility of high strength steel is strongly influenced by the presence of hydrogen, although hydrogen does not significantly affect the yield strength. The deterioration of fracture ductility is particularly evident in low strain rate tension tests, but less pronounced at conventional crosshead speeds. Low concentrations of hydrogen in high strength steels do not substantially affect the fracture toughness, but result in the appearance of a threshold stress intensity. The threshold values can be obtained from low strain rate tension tests at a crosshead speed of 0·1 mm min−1. These values are practically the same as those obtained from hydrogen charged peripherally notched pre cracked specimens subjected to a constant static load in a delayed failure test. Microfractographic investigations of fracture surfaces of hydrogen charged steel from low strain rate tension tests indicate that the growth and the coalescence of voids in the final stages of the fracture process are partly assist...

Studies on the analysis of hydrogen in high strength steels

Studies on the analysis of hydrogen in high strength steels

Influence of Grinding Fluids on the Introduction of Hydrogen in High Strength Steel

Abstract The objective of this study was to determine if chemical reactions with machining fluids or their breakdown during a preselected machining operation can be a significant source of entrapped hydrogen in 4340 high strength [260 to 280 ksi (175 to 200 kg/mm2)] steel. Specimens were subjected to a specified schedule to low stress and abusive milling and grinding operations using oil base (neutral, chlorinated, and sulfurized) and water miscible oil emulsion (neutral, chlorinated, and sulfurized) machining fluides. It was found that significantly high levels of hydrogen are introduced in the steel specimens as a result of the breakdown of machining fluids during the grinding operations. On a relative basis, among the fluids used, sulfurized fluids appeared to have introduced the highest level of hydrogen in the test specimens.