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Austenitic stainless steels (ASS) offer attractive characteristics for use in hydrogen service, such as low hydrogen diffusivity and high solubility. The role of the production process is, however, still unclear. Especially the effect of additive manufacturing (AM) on the hydrogen interaction is not extensively researched yet. The present work compares the hydrogen embrittlement sensitivity of conventional (cold rolled and annealed) and additive manufactured 316L ASS and evaluates the possible advantage of performing a heat treatment and/or reducing the surface roughness post printing. AM increases the hydrogen solubility but the hydrogen diffusivity was only slightly reduced. The heat treatment reduced the hydrogen solubility of the AM materials and significantly increased the hydrogen diffusivity. Despite these observations, the conventional 316L ASS shows a higher hydrogen embrittlement (HE) sensitivity compared to AM316L. This is linked to the increased hydrogen-assisted cracking sensitivity of conventional 316L ASS. The heat treated microstructure behaves similarly as the as-built material in terms of HE sensitivity, while a major improvement is observed when the surface oxide layer formed during the heat treatment is maintained since this reduces hydrogen absorption. Surface polishing intensifies the HE sensitivity which is linked to a higher surface hydrogen concentration leading to more crack initiation. [Display omitted] • Additive manufactured 316L ASS showed specific microstructural features. • Embrittlement sensitivity was lower for AM specimens compared to conventional one. • AM parts showed a reduced sensitivity to martensitic transformations with hydrogen. • Heat treatment resulted in an overall reduced embrittlement sensitivity. • Surface treatment increased the sensitivity due to more hydrogen at the surface. [ABSTRACT FROM AUTHOR]

The present study evaluates thermal desorption spectroscopy (TDS) data measured for UNS S32205 duplex stainless steel. Variations in the TDS spectra are obtained by electrochemical hydrogen charging for different times and by applying different heating rates for desorption to evaluate the desorption activation energy. Good agreement is found when comparing the experimental TDS curves with the desorption flux based on a numerical diffusion model using a homogeneous average hydrogen diffusion coefficient for the two-phase (ferrite-austenite) duplex microstructure. Trapping cannot be distinguished from the experimental TDS data since hydrogen diffusion in austenite is the rate-determining process during desorption. An average diffusion activation energy of 43.4 kJ/mol is determined from the experiments. Moreover, similar findings are obtained with a finite-element model that includes the heterogeneous hydrogen-related properties of the two phases of this duplex stainless steel. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract The hydrogen induced damage of generic Fe-C-Ti and Fe-C-V ferritic alloys was investigated to assess the influence of precipitates on the hydrogen sensitivity of a material. The precipitates, formed during heat treatment, were evaluated by scanning transmission electron microscopy (STEM). The hydrogen/material interaction was evaluated by: 1) melt and hot extraction to determine the total and diffusible hydrogen content, respectively, 2) permeation experiments to calculate the diffusion coefficient, 3) thermal desorption spectroscopy to determine the hydrogen trapping characteristics of the materials. Furthermore, two different types of hydrogen induced damage were evaluated, i.e. hydrogen assisted cracking and blistering, resulting from electrochemical hydrogen charging with and without the application of an external load, respectively. Evaluation of the hydrogen induced damage and the role of the precipitates was performed by combining optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). An important though divertive role of diffusible hydrogen is observed in both damage mechanisms for the investigated microstructures. On the one hand, a large amount of diffusible hydrogen compared to strongly trapped hydrogen promotes hydrogen assisted cracking of materials, while on the other hand, the blistering phenomenon is delayed under such conditions. Highlights • Hydrogen induced damage is studied in Fe-C-Ti and Fe-C-V ferritic alloys. • Fe-C-Ti is less susceptible to hydrogen embrittlement than Fe-C-V. • Fe-C-V is less susceptible to blistering than Fe-C-Ti. • The role of diffusible hydrogen depends on the damage mechanism. [ABSTRACT FROM AUTHOR]

The hydrogen embrittlement sensitivity of three twinning-induced plasticity steels is investigated. A reference TWIP steel (18Mn-0.6C) is compared to an aluminium added TWIP steel (18Mn-0.6C-1.5Al) and a TWIP steel with an increased manganese content (24.5Mn-0.6C), exhibiting an identical stacking fault energy as the aluminium added material. As such, the importance of the stacking fault energy in the reduction of the hydrogen embrittlement sensitivity with aluminium addition is evaluated, which is considered as one of the possible underlying mechanisms. Through thermal desorption spectroscopy analysis, it is shown that both aluminium and manganese addition increase the hydrogen solubility while the hydrogen diffusivity is increased by manganese addition and decreased by aluminium addition. These effects can be considered as the bulk effects of both alloying additions on the hydrogen properties. With respect to the mechanical properties, aluminium addition leads to the expected increased resistance to hydrogen while manganese addition reduces the hydrogen resistance, despite the equal stacking fault energy. The aluminium added TWIP steel shows increased resistance to hydrogen-assisted crack initiation and propagation suppressing intergranular fracture in the presence of hydrogen. On the contrary, the increased manganese content increases the tendency for intergranular cracking in the presence of hydrogen. The critical hydrogen concentration might therefore be higher with the addition of aluminium. [ABSTRACT FROM AUTHOR]

The present study evaluates the active hydrogen trapping sites of three martensitic Fe C alloys with a carbon content of 0.2 wt%, 0.4 wt% and 1.1 wt% by thermal desorption spectroscopy (TDS). The absence of additional alloying elements reduces the microstructural complexity and allows focussing on the carbon effects only. The TDS spectra are extrapolated towards cryogenic temperatures, enabling to deconvolute the desorption spectrum in Gaussian curves corresponding with H detrapping from lattice positions, dislocations, high angle grain boundaries and cementite. The activation energy for hydrogen desorption and the amount of H trapped at each site is further profoundly evaluated. It is found that the carbon content controls the amount of hydrogen trapped at dislocations and its activation energy for detrapping decreases with increasing carbon content. The trap density of the high angle grain boundaries is controlled only by the prior austenitic grain size and the corresponding activation energy for H desorption is independent of the carbon content. Hydrogen trapping at cementite was only detected in the samples with the highest carbon content (Fe-1.1C). • Interaction between hydrogen and martensitic Fe C steels is investigated by TDS. • The main hydrogen trapping sites are dislocations and high angle grain boundaries. • C content strongly influences the H trapping characteristics at dislocations. • Amount of H trapped at HAGBs merely depends on the prior austenitic grain size. • H trapping at cementite is only relevant for hypereutectoid compositions. [ABSTRACT FROM AUTHOR]

[Display omitted] • In-situ constant crosshead displacement rate tensile tests on 304L stainless steel. • Hydrogen embrittlement increased with decreasing strain rate. • Pre-straining increased hydrogen diffusion in thermal desorption spectroscopy. • Hydrogen increase and temperature restriction led to martensitic transformation. • A competition exist between hydrogen embrittlement and enhanced martensite. In-situ tensile testing of electrochemically hydrogen charged 304L stainless steel at different crosshead displacement rates results in a largely different elongation at fracture compared to the corresponding test in air. At slow engineering strain rates (below 1E-2 s−1), large ductility losses are observed and the alloy suffers from clear hydrogen embrittlement (HE). The HE increases with decreasing strain rate due to the increased time that is given for hydrogen to diffuse and accumulate. However, at higher engineering strain rates (above 1E-2 s−1), the ductility increases with hydrogen charging. Due to intense martensitic transformations triggered by a combined temperature and hydrogen effect, the strain hardening of the alloy improves and necking is postponed. The temperature effect is restricted by reference testing in solution showing that HE still prevails. The enhanced martensitic transformations with hydrogen open opportunities for the creation of hydrogen resistant materials where the balance between HE and enhanced martensitic transformations can be optimized for the required application. Furthermore, tensile pre-straining results in an increased HE susceptibility due to the presence of stress concentrations and α'-martensite. [ABSTRACT FROM AUTHOR]

The present work evaluates hydrogen-assisted cracking in 2205 duplex stainless steel by performing electron backscatter diffraction (EBSD) on in-situ hydrogen charged tensile tested specimens. The hydrogen embrittlement sensitivity increases with the electrochemical hydrogen charging time. The hydrogen presence results in deformation-induced martensite formation in the austenite during in-situ tensile straining, which starts immediately after yielding. Hydrogen-assisted cracking starts at a later stage in the tensile test and the cracks mainly initiate in austenite. The deformation-induced martensite is not vulnerable for crack initiation, neither is its interface with the austenite matrix. The presence of hydrogen-assisted cracks depends on the strain level reached in the specimen and is therefore most pronounced in the necked region. Crack propagation occurs through austenite, ferrite and their interface and is mainly governed by strain fields. Finally, propagation also occurs by coalescence of several smaller cracks. [ABSTRACT FROM AUTHOR]

In this study, the fracture behavior of 2205 duplex stainless steel (DSS) under in-situ hydrogen charging is evaluated. For this purpose, fracture toughness tests are performed on single-edge notched bending specimens, in which hydrogen is introduced electrochemically in-situ , using an acid and a saline electrolyte at different current densities. The hydrogen content of both electrochemically and gaseous pre-charged specimens is measured to assess the influence of the aggressiveness of the environment. Three environments are evaluated: realistic, severe and highly severe. As the microstructure of DSS is characterized by the presence of ferrite and austenite bands, the influence of directionality on fracture toughness is also studied. For this purpose, specimens are machined in two directions, being crack growth parallel to the bands in one case, while crack growth is perpendicular to the bands in the other case. Fracture toughness was found to decrease with increasing current density and in a more aggressive environment, and to increase when crack growth was perpendicular to the bands. The fracture surface was also evaluated, revealing splits in the direction of the bands in all in-situ tests. The origin and propagation of these splits were studied using electron backscatter diffraction scans, concluding that splits propagated through the ferrite-austenite interface. • Hydrogen promotes embrittlement in DSS2205 under in-situ fracture toughness tests. • Hydrogen damaged was pronounced in acid media. • Hydrogen accumulation in ferrite/austenite bands promotes decohesion. • Ferrite/austenite bands parallel to the crack propagation enhances embrittlement. [ABSTRACT FROM AUTHOR]

A comparative study of the active deformation mechanisms in duplex stainless steel is performed during straining with and without hydrogen charging. Interrupted tensile tests at an equal strain level clearly show that hydrogen influences how plastic deformation is accommodated. Slip planarity and martensite formation in austenite is observed for the hydrogen charged condition while dislocation multiplication and cross-slip take place for the uncharged condition. Three possibilities are put forward to explain the change: the reduction in stacking fault energy by hydrogen, a shift with respect to what phase accommodates most of the plastic strain and hydrogen pinning edge dislocations and thus restraining them to shift to the screw dislocation type and cross-slip. • Duplex stainless steel suffered a large ductility loss under hydrogen presence. • In the austenitic part, homogeneous dislocation slip changed to planar slip. • Martensitic transformations occurred in the austenite phase. • The martensite transformations happened in correspondence to established mechanisms. [ABSTRACT FROM AUTHOR]

The goal of this work is to propose a general mechanism for hydrogen induced crack initiation in steels based on a microstructural study of multiple steel grades. Four types of steels with strongly varying microstructures are studied for this purpose, i.e. ultra low carbon (ULC) steel, TRIP (transformation induced plasticity) steel, Fe-C-Ti generic alloy, and pressure vessel steel. A strong dependency of the initiation of hydrogen induced cracks on the microstructural features in the materials is observed. By use of SEM-EBSD characterization, initiation is found to always occur at the hard secondary phase particles in the materials. [ABSTRACT FROM AUTHOR]

Background Cutaneous squamous cell carcinoma (SCC) is the most frequent skin cancer after organ transplantation. Currently, the pre-identification of transplant patients at increased risk for non-melanoma skin cancer remains difficult. Objective To investigate the Hp polymorphism as a marker for the identification of a subset of patients with an increased susceptibility to develop SCC/Bowen's disease. Methods Haptoglobin phenotyping was performed with haemoglobin-supplemented starch gel electrophoresis in 300 kidney transplant patients. High-performance gel permeation chromatography was used in case of low serum haptoglobin concentration. Results Cox regression analysis (adjusted for age, gender and Mediterranean origin) showed a significant association of the Hp 1-1 phenotype with a higher risk of SCC/Bowen's disease ( P = 0.035) and multiple primary SCCs ( P = 0.002). No significant difference between the Hp phenotypes was found for the development of Bowen's disease and SCCs in the first 10 years following renal transplantation. However, after a follow-up of >10 years, a significant association between the Hp 1-1 phenotype and the occurrence of Bowen's disease and SCC was reported ( P = 0.002 and P = 0.001 respectively). Conclusions This study shows an increased risk for the development of (multiple) SCCs in kidney transplant patients with the Hp 1-1 phenotype. This finding points to the role of Hp 1-1 phenotype as an important predictor in identifying a subset of patients with an increased need for preventive measures and is in agreement with the decreased anti-inflammatory capacity of this phenotype. [ABSTRACT FROM AUTHOR]