Hydrogen embrittlement in different materials: A review

Effect of hydrogen on the fracture behavior of high strength steel during slow strain rate test

The first direct observation of hydrogen trapping sites in TiC precipitation-hardening steel through atom probe tomography

The susceptibility to hydrogen embrittlement (HE) of martensitic steels has been examined by means of a delayed-fracture test and hydrogen thermal desorption analysis. The intensity of a desorptionrate peak around 50 °C to 200 °C increased when the specimen was preloaded and more remarkably so when it was loaded under the presence of hydrogen. The increment appeared initially at the low-temperature region in the original peak. As hydrogen entry proceeded, the increment then appeared at the high-temperature region, while that in the low-temperature region was reduced. The alteration occurred earlier in steels tempered at lower temperatures, with a higher embrittlement susceptibility. A defect acting as the trap of the desorption in the high-temperature region was assigned to large vacancy clusters that have higher binding energies with hydrogen. Deformation-induced generation of vacancies and their clustering have been considered to be promoted by hydrogen and to play a primary role on the HE susceptibility of high-strength steel.

Hydrogen Thermal Desorption Relevant to Delayed-Fracture Susceptibility of High-Strength Steels

The design of atomic-scale microstructural traps to limit the diffusion of hydrogen is one key strategy in the development of hydrogen-embrittlement–resistant materials. In the case of bearing steels, an effective trapping mechanism may be the incorporation of finely dispersed V-Mo-Nb carbides in a ferrite matrix. First, we charged a ferritic steel with deuterium by means of electrolytic loading to achieve a high hydrogen concentration. We then immobilized it in the microstructure with a cryogenic transfer protocol before atom probe tomography (APT) analysis. Using APT, we show trapping of hydrogen within the core of these carbides with quantitative composition profiles. Furthermore, with this method the experiment can be feasibly replicated in any APT-equipped laboratory by using a simple cold chain.

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Direct observation of individual hydrogen atoms at trapping sites in a ferritic steel

Hydrogen trapping and de-trapping behavior was investigated for steels with and without V. The de-trapping of hydrogen is very slow while the trapping presumably proceeds rapidly for steels containing VC precipitates. The activation energy for de-trapping is in the range of 33 to 35 kJ/mol. The trapped-hydrogen content and diffusible-hydrogen content in the steady state increase with increasing hydrogen entry rate into the steel. The density of hydrogen trapping sites decides the maximum trapped-hydrogen content; 9 ppm for 1 % V steel tempered at peak secondary hardening temperature. Analysis of hydrogen embrittlement cracking tests in terms of hydrogen contents such as the critical hydrogen content should be performed on the specimens with uniform hydrogen distribution and must consider the nature of hydrogen whether it is trapped or diffusible.

Hydrogen Trapping Behavior in Vanadium-added Steel

Evaluation Method of Delayed Fracture Property of High Strength Steels

Provided is a steel wire for low-temperature annealing which comprises, by mass%, C: 0.10% to 0.60%, Si: 0.01% to 0.40%, Mn: 0.20% to 1.50%, P: 0% to 0.040%, S: 0% to 0.050%, and N: 0.0005% to 0.0300%, and further comprises one or more selected from Cr: 0.03% to 0.4%, V: 0.03% to 0.2%, and Mo: 0.03% to 0.2%, with Fe and inevitable impurities as the remainder. The volume percent of pearlite structure is between 1.40 × (C%) × 100% and 100%, the volume percent of proeutectoid ferrite is between 0% and (1 - 1.25 × (C%)) × 50%, and the volume percent of bainite structure is between 0% and 40%. The tensile strength is between 480 + 850 × Ceq.MPa and 580 + 1130 × Ceq.MPa.

Steel wire for low-temperature annealing and method for producing the same

A plated steel wire for PWS excelling in torsion property comprising, by mass, 0.8 to 1.1% C, 0.8 to 1.3% Si, 0.3 to 0.8% Mn, 0.001 to 0.006% N and 0.0004 to 0.0060% B provided that B in the state of solid solution is 0.0002% or more, and further comprising either 0.005 to 0.1% Al or 0.005 to 0.1% Ti or both with the balance composed of Fe and unavoidable impurities. In the plated steel wire, the areal ratio of non-pearlite structure is 10% or below in the zone from its surface layer to a depth of 50 μm and 5% or below in the whole cross section thereof, and the surface thereof is provided with a zinc plating at a plating weight of 300 to 500 g/m2.

Plated steel wire for pws excelling in torsion property and process for producing the same

Synopsis : The evaluation methods of the delayed fracture properties of high strength steels and the methods which improve the delayed fracture resistance of steels have been reviewed. The evaluation method which is crucial for the development of steels with high strength has yet to be authorized. However, a new evaluating method which adopts the critical hydrogen concentration for fracture and the hydrogen concentration which is absorbed from the environment as parameters has been proposed. It was verified that evaluation using this method showed good agreement with exposure tests of bolts in the service environment, and this method is being applied not only to delayed fracture but to other hydrogen embrittlement problems. To improve the delayed fracture properties of steels, the hydrogen trapping phenomenon in alloy carbides such as VC, Mo2C and TiC, and the TMCP process have been researched extensively. By using these methods, the development of high strength steels with excellent hydrogen embrittlement resistance has progressed.

Shingo Yamasaki

Papers

Hydrogen Trapping Behavior in Vanadium-added Steel

Evaluation Method of Delayed Fracture Property of High Strength Steels

Steel wire for low-temperature annealing and method for producing the same

Plated steel wire for pws excelling in torsion property and process for producing the same

Evaluation Method of Delayed Fracture Property and Overcoming Techniques of Delayed Fracture of High Strength Steels