Hydrogen Embrittlement Susceptibility Of Steel Research Articles

Hydrogen Embrittlement in as-Quenched Martensitic Steels - Application of Incremental Step Loading Technique with Novel Tuning-Fork Test

Hydrogen embrittlement (HE) is a well-known issue, especially with ultrahigh-strength steels (UHSS). Various testing methods are utilised to study HE, but they typically require tensile test equipment, or are impractical due to limited stress control with standard geometries. We have developed a novel Tuning-fork test (TFT) to study HE susceptibility of steels with a new specimen geometry, which can be stressed accurately without tensile test equipment. The test method utilises in situ electrochemical hydrogen charging and constant displacement for stressing of the notched specimens by bending. Crack initiation and propagation are controlled with an isolated tensile stress region, and the failure process is monitored with a loadcell. TFT is a simple and fast testing method, which allows ranking of UHSSs, and to investigate, e.g., microstructural effects on susceptibility to HE and H-induced fracture processes. Here in this study, we present the state-of-the-art with the improved more precise second-generation TFT setup, which benefits from a more sensitive loadcell and a more stable fine-tuneable differential screw adjustment. We extend TFT to testing of martensitic steels with nominal hardness from 400 HBW to 600 HBW with the Incremental step loading technique (ISLT). The results show that TFT with ISLT is well applicable for ranking ultrahigh-strength steels based on their susceptibility to HE. Force-time data from ISLT can also be used for the determination of a material-specific threshold stress level, and the last step for the calculation of a crack initiation-time and time-to-fracture. However, the current manual operation of the loading screw can still limit maximum duration of a test.

A systematic study on the influence of electrochemical charging conditions on the hydrogen embrittlement behaviour of a pipeline steel

Although hydrogen embrittlement (HE) has been the subject of extensive research over the past century, a systematic study on the HE susceptibility of steels under different electrochemical charging conditions has been lacking. This study specifically targets this knowledge gap by evaluating the HE behaviour of a typical pipeline steel X65 after hydrogen-charging in acidic, neutral, and alkaline electrolytes that simulate various industrial environments. Results from a series of experiments show that the HE susceptibility of X65 steel varied significantly with hydrogen-charging electrolytes and, to a smaller extent, with electrochemical charging variables. The highest and lowest HE susceptibilities were found from specimens charged in acidic and alkaline electrolytes, respectively. An increase in yield strength was observed for almost all hydrogen-charged specimens, regardless of the charging conditions. Under severe electrochemical charging conditions, blistering was detected and mechanical properties were substantially decreased. Discussion has been made in comprehending these relationships.

Optimizing the hydrogen embrittlement resistance by tuning the structures of Cu-rich nanoprecipitates in high strength martensite stainless steels

Hydrogen is notoriously known to embrittle high-strength steels, critically endangering the materials service safety. Cu-rich nanoprecipitates can mitigate the hydrogen embrittlement (HE) presumably by imposing hydrogen traps; in the meantime, they may also contribute to strengthening and hence effectively tackle the trade-off between strength and HE resistance. However, as the Cu-rich precipitates grow, they go through sequential transformations, raising a critical question as to exactly which phase of the Cu-rich precipitates prompts the best counter-HE effects. Here, by tuning the structures of the Cu-rich precipitates in a tempered martensitic steel, we find that the HE susceptibility of the steel can be significantly reduced by up to 55.3%, while maintaining roughly the same ultimate tensile strength of the steels. Further, by using high-resolution transmission electron microscopy and hydrogen permeation tests, it is found that, while all Cu-rich precipitates may trap hydrogen and impede hydrogen diffusion, the 9R-structured Cu-rich precipitates (9R-Cu) have the strongest binding with hydrogen and highest trapping capacity. This is further corroborated by first-principles calculations which reveal the precipitates/matrix interface as favorable trapping sites. The findings provide deep insights for remedying the HE susceptibility of high-strength steels through Cu-rich precipitates.

Assesment of ISL, SSRT and CLT techniques for quantification hydrogen embrittlement susceptibility of steels

Assesment of ISL, SSRT and CLT techniques for quantification hydrogen embrittlement susceptibility of steels

Effects of the Addition of Nb and V on the Microstructural Evolution and Hydrogen Embrittlement Resistance of High Strength Martensitic Steels.

Hydrogen embrittlement can easily occur in high strength martensitic steel, manifesting itself as a sudden failure or fracture without warning and greatly threatening the safety of automotive applications. Optimizing the composition of the alloy can be performed by matching heat treatment processing methods and controlling the precipitation amounts to form hydrogen traps. In doing so, the hydrogen embrittlement susceptibility of steel can be effectively delayed, reducing the risk of hydrogen-induced delayed cracking. In this study, four kinds of 1500 MPa strength grade martensitic steel were selected for testing and supplemented with different loadings of Nb and V, respectively. Their grains, phases, and precipitations were compared by optical microscopy (OM), electron backscattered diffraction (ESBD), and transmission electron microscopy (TEM) analyses. After the addition of Nb and V, the microstructure was refined, the residual austenite content increased, and the hydrogen embrittlement resistance was significantly improved.

Influence of microstructure on the high-pressure hydrogen SSRT properties of Cr-Mo steel

In a high pressure hydrogen gas environment, there is a risk of "hydrogen embrittlement (HE)" by hydrogen entered to the steels. Therefore, many experiments of steels in high pressure hydrogen gas have been conducted such as tensile, fatigue and so on. However, there are little knowledge of influence of the material microstructure on HE. There is a possibility of HE susceptibility of steels depending on the material microstructure. Therefore, objective of this development is clarification of the microstructure to excellent HE resistance. As a result of Slow Strain Rate Tensile (SSRT) test under hydrogen environment, tempered martensite structure with finely cementite dispersed was most excellent in HE resistance. The reason for this is considered that the generation of micro voids, which is the initiation of surface cracks affecting ductility of SSRT, was suppressed.

Dependence of hydrogen embrittlement on annealing time in medium-Mn steels

PurposeThe purpose of this paper is to investigate the effect of the soft annealing time on the microstructure and hydrogen embrittlement (HE) of Fe-0.22C-11.54Mn-2.05Al steels.Design/methodology/approachSteels A and B with different morphologies were prepared by cold rolling after warm rolling, long/short softening annealing and finally annealing at 700 °C for 30 min. Uncharged and charged samples were subjected to tensile, and HE behavior was studied by electron backscattered diffraction, scanning electron microscopy and X-ray diffraction.FindingsThe two samples exhibited similar tensile strengths. The homogeneous equiaxed microstructure of steel B was found to be more conducive to relieve its HE sensitivity. Steel A exhibited bimodal-grained microstructures – blocky and lath. The formation of crack in the blocky grains of steel A resulted in a significant reduction in its plasticity and tensile strength.Originality/valueThe high HE susceptibility of steel A is mainly connected with the inhomogeneity of martensite transformation.

Numerical simulation of the hydrogen trapping effect on crack propagation in API 5CT P110 steel under cathodic overprotection

The possibility of the development of hydrogen embrittlement processes increases in cathodic protection systems when cathodic overprotection occurs, and large amounts of hydrogen are produced. Additionally, the hydrogen embrittlement susceptibility of steel depends on solubility, diffusivity, and hydrogen trapping. This paper presents a numerical simulation of the reversible and irreversible hydrogen trapping effects on crack propagation in API 5CT P110 steel using a model based on a synthesis of fracture mechanics and continuum damage mechanics, in which the trapping term of the diffusion equation was replaced by the trapping terms of other more complete model. The simulation was performed with using a C(T) specimen loaded in the tensile opening mode, in the linear elastic regime, in plane strain state, under the action of a static mechanical loading and the effect of hydrogen. The simulations showed that the material degradation ahead of the crack tip increases with increases in hydrogen concentration at the crack tip due to the hydrogen trapping effect. Furthermore, the process of onset and crack growth in material with irreversible traps is slower than that in material with reversible traps. These results are consistent with macroscopic observations of the trapping effect, providing a better understanding of the hydrogen embrittlement in structural steels.

Hydrogen Entry into Steel Exposed in an Outdoor Environment

Introduction In recent years, high-strength steels have been widely used in many engineering fields such as automobiles and construction. However, hydrogen embrittlement (HE) of high-strength steels has been a great concern because HE susceptibility of steels strongly relates to the strength of them. Especially, high-strength steels are often used in atmospheric corrosion environments and hydrogen atoms are generated by corrosion reaction. Some of the generated hydrogen atoms are absorbed into steel and they relate to occurrence of HE. In atmospheric corrosion environments, steel corrosion proceeds with forming iron rust on the surface. The rust layer may affect hydrogen entry behavior into the steel. Therefore, it is needed to investigate the effect on rust layer on hydrogen entry behavior into steel. In this study, hydrogen entry behavior into steel exposed in an outdoor environment is discussed based on the results of hydrogen permeation current and corrosion potential. Experimental Hydrogen permeation current for steel exposed in an outdoor environment was measured by Devanathan-Stachurski method1. A sheet of plain carbon steel (0.020%C, 0.01%Si, 0.18%Mn, 0.015%P, 0.007%S, bal. Fe) was used as a material. The steel sheet was exposed at Choshi exposure test and research center (Chiba, Japan). The exposure test started at August, 2016 and the exposure period was changed from 1 to 6 months. After the exposure test, the steel sheet was cut into a small coupon of 25 mmw x 25 mml x 0.8 mmt. The exposed steel surface was washed with Milli-Q water (18 MΩ•cm). One side of the steel surface facing to the air was used as a hydrogen-entry side and the opposite surface of the steel was used as a hydrogen-withdrawal side for hydrogen permeation tests. The hydrogen-withdrawal side was polished and electroplated with Pd ca. 400 nm in thickness before hydrogen permeation test. A 30 μL of Milli-Q water was placed on steel to measure hydrogen permeation current. During drying of the water droplet, corrosion potential for the steel was measured with a Kelvin probe simultaneously with hydrogen permeation current. Results and Discussion In this study, hydrogen entry into steel exposed in an outdoor environment was investigated with hydrogen permeation current and corrosion potential measurements. It was found from the results of hydrogen permeation current and corrosion potential that hydrogen entry into steel after the exposure test was observed during drying of a water droplet. Therefore, hydrogen absorption reaction into the exposed steels occurs with corrosion. Figure shows change of the amount of hydrogen entry for the exposed steels in the test environment. The amount of absorbed hydrogen into steel was calculated by time-integral of hydrogen permeation current during drying of the water droplet. The plots at 0 month are obtained from the hydrogen permeation data for a bare steel. As shown in the figure, the amount of hydrogen entry into the exposed steel decreases significantly after one-month exposure and then it keeps almost constant independent of exposure period. After one-month exposure, the steel surface was wholly covered with iron rust. These results indicate that the formation of iron rust affected the amount of hydrogen entry into steel. Reference M. A.V. Devanathan, A. Stachurski, Proc. Roy. Soc., A270, 910 (1962). Figure 1

Alloy and composition dependence of hydrogen embrittlement susceptibility in high-strength steel fasteners.

High-strength steel fasteners characterized by tensile strengths above 1100 MPa are often used in critical applications where a failure can have catastrophic consequences. Preventing hydrogen embrittlement (HE) failure is a fundamental concern implicating the entire fastener supply chain. Research is typically conducted under idealized conditions that cannot be translated into know-how prescribed in fastener industry standards and practices. Additionally, inconsistencies and even contradictions in fastener industry standards have led to much confusion and many preventable or misdiagnosed fastener failures. HE susceptibility is a function of the material condition, which is comprehensively described by the metallurgical and mechanical properties. Material strength has a first-order effect on HE susceptibility, which increases significantly above 1200 MPa and is characterized by a ductile--brittle transition. For a given concentration of hydrogen and at equal strength, the critical strength above which the ductile-brittle transition begins can vary due to second-order effects of chemistry, tempering temperature and sub-microstructure. Additionally, non-homogeneity of the metallurgical structure resulting from poorly controlled heat treatment, impurities and non-metallic inclusions can increase HE susceptibility of steel in ways that are measurable but unpredictable. Below 1200 MPa, non-conforming quality is often the root cause of real-life failures.This article is part of the themed issue 'The challenges of hydrogen and metals'.

Hydrogen Embrittlement of Steels for Prestressing Concrete: The FIP and DIBt Tests

Abstract Two tests, the International Federation of Prestressed Concrete (FIP) and the Deutsches Institut fur Bautechnik (DIBt) tests, are currently used for ascertaining the hydrogen embrittlement susceptibility of steels for prestressing concrete. Both tests have advantages and drawbacks and further research is needed. With this goal, two types of eutectoid cold-drawn steel wires, one more susceptible to hydrogen embrittlement than the other, were tested according to FIP and DIBt recommendations. Based on the obtained experimental results and on the analysis of the mentioned references, some conclusions have been deduced, among others that the FIP test is suited for quality control of a given type of steel (and for comparison purposes) of different grades of the same steel. Also, significant correlation was found between times to rupture in both tests and residual longitudinal stresses.