Diffusible Hydrogen Content Research Articles

Prevention of cold cracking by the welding process for reducing diffusible hydrogen in high-tensile thick plate welding

ABSTRACT Cold cracking sensibility is a severe problem in the welding fabrication of large-scale steel structures. It is well known that diffusible hydrogen content in the weld metal strongly influences this cracking. In recent years, a novel welding process using a special welding torch was researched and developed. By using this process, the amount of hydrogen content in the weld metal can be greatly reduced than the conventional process. In this study, the effect of cold cracking prevention and required preheating temperature reduction by new welding process were confirmed. The window type restraint weld cracking test was applied. Both base metal and welding material were 780 MPa class high-tensile steel. During the test, the preheat and interpass temperatures were controlled strictly. Moreover, the temperature level was changed from 50°C to 0°C. As a result, cold cracking (transverse crack) occurred with the conventional method in which the temperature was kept under 50°C. In contrast, there is no crack with the developed one under 50°C and 25°C. When the controlled temperature was lowered to 0°C, many cracks were observed with the developed process. From the above, the effect of cold cracking prevention by the novel welding process for reducing diffusible hydrogen was confirmed and about 50°C preheating temperature reduction effect was demonstrated. These test results confirmed the consistency with past research results. A very good agreement was obtained when comparing the test results and the past research results of cold cracking control indexes in terms of root cracking and multi-pass weld transverse cracking. Therefore, the validity of this study was demonstrated.

Microstructure and mechanical properties of FCTIG-welded DH36 steel with rutile-type and basic-type flux cored wires

Using basic-type flux cored wires significantly improve the toughness of weld joints, but the addition of fluoride decreases the weld-ability of the metal. In this paper, the flux cored tungsten inert gas (FCTIG) process was used to weld DH36 steel with a basic-type flux cored wire and a rutile-type flux cored wire. The microstructure and mechanical properties of the wires were investigated as well as the diffusible hydrogen content in the different weld joints. The results indicated that the FCTIG process using a basic-type flux cored wire has more technological advantages and produces lower amounts of fume during welding compared with flux cored arc welding (FCAW). The presence of large amounts of alloying elements in the rutile-type flux cored wire promoted the formation of acicular ferrite (AF) in the weld bead, which enhanced the micro-hardness and strength of the bead. The generation of fluoride with the basic-type flux cored wire reduced the diffusible hydrogen content (DHC) in the weld joint, with the lowest DHC value being 3.18 mL/100 g. The toughness of the weld joint made with the basic-type flux cored wire was improved, and the highest impact energy measured was 264.8 J.

Delayed Fracture in Automotive Advanced High Strength Steel: A New Investigation Approach

Nowadays Al–Si coated boron steels (that are Advanced High Strength Steels, AHSS) are largely used in vehicle bodies. If on one hand they offer great mechanical performances, on the other hand they are susceptible to hydrogen delayed fracture. As this phenomenon brings to the reject of the component during production or even worse the failure during operation, diffusible hydrogen absorbed in the component needs to be monitored during plant process. A simple procedure, by means of a solid‐state innovative sensor, is developed to check diffusible hydrogen concentration during laboratory experiments and manufacturing process. The behavior of an Al–Si coated boron steel after hydrogen absorption is investigated by means of slow strain rate mechanical tests (SSRT) and correlated to the diffusible hydrogen content. Finally, in manufacturing process an extensive plant test campaign is performed on semi‐manufactured vehicle parts in order to verify the laboratory's results. These tests confirmed the possibility to approach the evaluation of diffusible hydrogen content in semi‐products during car manufacturing by means of an easy procedure based on a robust sensor.

Investigation of diffusible hydrogen content in drawn arc stud weld metal

The fully mechanized drawn arc stud welding is a welding procedure for joining pin-shaped elements. In particular, it is an established joining technique for large studs in steel construction. The process is characterized by its high heat input due to high current and a weld pool protection realized by a ceramic ferrule holding the metal vapor as a shielding gas. Turbulences inside the ferrule during welding cause contaminations with atmospheric humidity. Furthermore, a high cooling rate results in a locally strongly hardened heat-affected zone and a considerable residual stress state in the parent material. Thus, there is a risk of enhanced hydrogen cracking susceptibility, especially for stud welding on high strength steels or under adverse welding conditions. An analysis procedure for determination of diffusible hydrogen content in drawn arc stud weld metal is presented in this article. This novel method is based on carrier gas hot extraction according to ISO 3690.

Research on impact toughness of 105SS drill pipe in wet H2S environment

In order to investigate the corrosion behavior and impact toughness of 105SS drill pipe steel in the wet H2S environment, the impact and corrosion testing were carried out. The results show that the diffusible hydrogen concentration is mainly influenced by the morphology of the corrosion scales and the dynamic fracture toughness loss of 105SS drill pipe steels increases with the increase of diffusible hydrogen concentration. However, when hydrogen was released, the impact energy increases. The area of quasi-cleavage features on the fracture surfaces increases with the increase of hydrogen concentration.

On the role of hydrogen in stress corrosion cracking of magnesium and its alloys: Gas-analysis study

One of the main challenges impeding wider uptake of magnesium alloys by the industry is their poor resistance to general corrosion and stress-corrosion cracking (SCC), the nature of which is not fully understood. Although SCC is generally associated with hydrogen embrittlement, the experimental data on the possible hydrogen state, concentration and distribution in Mg is scarce, and its role in SCC is unclear. These issues are addressed in the present study using as-cast technically pure Mg as well as wrought ZK60 and AZ31 alloys slow-strain rate tensile tested in air and in corrosive media before and after prestraining. Hydrogen concentration and extraction curves have been obtained and analyzed for the specimens tested in corrosive media. It is found that most part of hydrogen is contained in the corrosion products while the concentration of diffusible hydrogen in the matrix is negligible for all the materials studied. On the basis of fractographic observations combined with gas-analysis and mechanical testing data, it is suggested that SCC of the ZK60 and AZ31 alloys results from brittle cracking of a surface hydride film, while SCC of pure Mg is likely associated with adsorbed hydrogen facilitating ductile fracture.

The influence of the welding environment on the properties of Tekken joints made from S355J2C+N steel

There are three main methods of underwater welding: dry, wet and intermediate between them, by using the local dry chamber. Due to low costs, the most common method is the wet welding with the use of covered electrodes. Water as a welding environment carries out a lot of problems. The first is limited visibility and instability of the welding arc. The biggest problem during underwater welding is high susceptibility to cold cracking, resulting from the increased diffusible hydrogen content in deposited metal and high stress values.In the work, Tekken joints from S355J2C+N steel were made in air and in water environment. The joints were subjected to non-destructive visual (VT) and penetrant (PT) tests. Then, macroscopic tests and hardness measurements were performed. The results confirm the literature reports that the water environment causes an in-crease in hardness in the heat affected zone (HAZ), which promotes the formation of cracks in welding joints.

Effects of Drawn Strain and Aging Temperature on Critical Diffusible Hydrogen Content and Absorbed Hydrogen Content in Pearlitic Steel Wires

Effects of Drawn Strain and Aging Temperature on Critical Diffusible Hydrogen Content and Absorbed Hydrogen Content in Pearlitic Steel Wires

Effect of Prestrain on Hydrogen Embrittlement Susceptibility of EH 36 Steels Using In Situ Slow-Strain-Rate Testing

Hydrogen can provide pure and clean energy; however, to use it as an energy source, facilities such as hydrogen carriers and recharging stations need to be constructed. Structural steels are affected by hydrogen embrittlement (HE), and their susceptibility to this needs to be investigated prior to their use in construction. Most structural steels are normally fabricated using thermomechanical controlled processing, which produces a large dislocation density to increase strength. This study investigated the prestrain effect on HE susceptibility of EH 36 steels using thermal desorption spectroscopy (TDS) and in situ slow-strain-rate testing. Hydrogen was electrochemically charged into specimens, and the reversible hydrogen content and that relating to trap sites were measured using TDS. With an increase in prestrain, there was increase in the diffusible hydrogen content; furthermore, with hydrogen charging, there was a drastic reduction in total elongation with an increase in prestrain. In addition, there was an increase in HE susceptibility with an increase in prestrain compared to when an air condition was employed. Specifically, there was an abrupt increase in HE sensitivity at a prestrain value between 10 and 15%; strain hardening was more dominant below a prestrain value of 10%; and HE was more dominant above a prestrain value of 15% for EH 36 steels.

An unconventional hydrogen effect that suppresses thermal formation of the hcp phase in fcc steels

Iron and steels are extensively used as structural materials, and have three primary phase structures: Body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal closed-packed (hcp). Controlling phase stabilities, especially by the use of interstitials, is a universal method that provides a diverse variety of functional and mechanical properties in steels. In this context, hydrogen, which can act as an interstitial species in steels, has been recognized to promote phase transformation from fcc to hcp. However, we here report a dramatic effect of interstitial hydrogen that suppresses this hcp phase transformation. More specifically, the fraction of hcp phase that forms during cooling decreases with increasing diffusible hydrogen content. This new finding opens new venues for thermodynamics-based microstructure design and for development of robust, strong, and ductile steels in hydrogen-related infrastructures.

Microstructural evaluation of hydrogen embrittlement and successive recovery in advanced high strength steel

Advanced high strength steels (AHSS) have high susceptibility to hydrogen embrittlement, and are often exposed to hydrogen environments in processing. In order to study the embrittlement and recovery of steel, tensile tests were conducted on two different types of AHSS over time after hydrogen charging. Concentration measurements and hydrogen microprinting were carried out at the same time steps to visualize the hydrogen behavior during recovery. The diffusible hydrogen concentration was found to decay exponentially, and empirical relations were found for both types of steel. Hydrogen concentration decay rates were determined to be -0.355 /hr in TBF-980, and -0.225 /hr in DP-980. Hydrogen concentration thresholds for embrittlement were found to be 1.04 mL/100 g for TBF, and 0.87 mL/100 g for DP steel. TBF steel is predicted to recover from embrittlement within 4.2 h, compared to 7.2 h in DP steel. A two-factor method of evaluating recovery from embrittlement, requiring hydrogen concentration threshold and decay rate, is explained for use in predicting recovery after exposure to hydrogen. Anisotropic hydrogen diffusion rates were also observed on the surface of both steels for a short time after charging, as hydrogen left the surface through <001> and <101> grains faster than grains with <111> orientations. This could be explained by differences in surface energies between the different orientations.

Effect of Weld Consumable Conditioning on the Diffusible Hydrogen and Subsequent Residual Stress and Flexural Strength of Multipass Welded P91 Steels

P91 steel weld joint was prepared using the shielded metal arc welding process and four different conditions of weld consumable that provide the different levels of diffusible hydrogen in deposited metal. In the present research, the effects of diffusible hydrogen content on the flexural strength, lower critical stress, and tensile strength of P91 steel welds were also determined with respect to different electrode conditions. To investigate the effect of diffusible hydrogen on multipass welding, top and root side flexural tests were performed. The residual stresses (axial stress and transverse stress) were also measured using the blind hole drilling method for different conditions of welding consumable. The peak value of residual stresses was measured at the center of the weld fusion zone. The maximum value of transverse stress was measured to be 355 MPa for case II (6.21 mL/100 g of diffusible hydrogen), while the maximum axial stress was about 218 MPa for case IV (12.43 mL/100 g of diffusible hydrogen). A three-dimensional finite element simulation was also performed to predict the residual stress distribution and thermal profile along the welded joint. The experimentally determined residual stresses correlated well with the numerically estimated residual stresses. The diffusible hydrogen content was not observed to have any significant effect on the residual stresses. The corrected residual stress values were also predicted by considering the plasticity-induced error. However, the flexural performance of the welded joint was affected by the diffusible hydrogen content. The top and root flexural strength was measured to be optimum for the low level of diffusible hydrogen content, and the values decreased with an increase in diffusible hydrogen content.

The role of titanium and vanadium based precipitates on hydrogen induced degradation of ferritic materials

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.

Effect of intercritical annealing time on hydrogen embrittlement of warm-rolled medium Mn steel

The susceptibility to hydrogen embrittlement (HE) of warm-rolled medium Mn steel (0.2C-5Mn-0.6Si-3Al) with different microstructure characteristics obtained by changing intercritical annealing time at 750 °C was investigated by carrying out slow strain rate test and hydrogen thermal analysis on electrochemically hydrogen charged samples. The results show that the increase in intercritical annealing time leads to an increase of the susceptibility to HE regardless of the decrease of both strength and diffusible hydrogen content. Unlike that of typical ductile fracture characteristic of uncharged sample, the hydrogen-charged sample shows a mixed fracture characteristic of ductile intragranular and brittle interface decohesion fracture mode in the crack initiation region. The susceptibility to HE was correlated mainly to the mechanical stability of retained austenite. These results suggest that suitable intercritical annealing treatment should be performed to ensure safety service of components made of this kind steel besides obtaining excellent combination of strength and ductility.

The effect of hydrogen content and welding conditions on the hydrogen induced cracking of the API X70 steel weld

The self-restraint testing was used to investigate the influence of hydrogen content, preheating, and post-heating on the sensitivity of welding of API X70 pipeline steel to hydrogen induced cracking (HIC). The variation of hydrogen content was applied using a low hydrogen electrode E8018-G and a high hydrogen (cellulosic) electrode E8010-P1. Diffusible hydrogen of these electrodes was measured by mercury displacement method. The average diffusible hydrogen content of cellulosic electrode E8010-P1 and low hydrogen electrode E8018-G were 43.6 and 1.1 ml/100 g of weld metal, respectively. The results of visual inspection, penetrant test, and macroscopic examination showed that welding with cellulosic electrode leads to cracking unless both preheating and post-heating are applied. However, in the case of low hydrogen electrode, cracking occurs only if no preheating or post-heating is applied. The microstructure of the welded specimens in different conditions by optical and scanning electron microscopy (SEM) showed that the dominant phase in the weld zone of all specimens is bainite. The microhardness profile displayed that hardness limitation (350 HV) cannot predict the sensitivity to cold cracking; therefore, other parameters such as hydrogen content should also be considered.

Evaluation of Corrosion Rate and Diffusible Hydrogen Content of High Tensile Steel under Loading with Corrosion Environment

Evaluation of Corrosion Rate and Diffusible Hydrogen Content of High Tensile Steel under Loading with Corrosion Environment

Effect of Buffer System on the Sulfide Stress Cracking Susceptibility of Low-Alloy Steel

The effects of a buffer system in test solution and CO2 partial pressure on sulfide stress cracking (SSC) susceptibility of low-alloy steel were investigated under pH 4.0 at 0.03 MPa H2S partial pressure. A double cantilever beam test was used to quantitatively evaluate SSC susceptibility. The corrosion rates and absorbed diffusible hydrogen concentration were also evaluated. Acetic acid/sodium acetate (acetate buffered solution) and carbonic acid/bicarbonate (bicarbonate buffered solution) buffered solutions were used as buffer systems in this study. From the results, in atmospheric pressure tests, KISSC values in bicarbonate buffered solutions were equivalent to or lower than those in acetate buffered solutions. In high CO2 partial pressure conditions, KISSC values in bicarbonate buffered solutions were much higher than those in acetate buffered solutions. At a high CO2 partial pressure and H2S partial pressure (pCO2/pH2S) ratio condition, hydrogen entry is considered to be greatly prevented by corrosion products probably containing amorphous iron carbonate. Presence of the corrosion product with high protectiveness produced in the high pCO2/pH2S ratio condition suggests the possibility that conventional test conditions using acetate buffered solutions are conservative or are equivalent test conditions for actual field conditions.

Hydrogen Embrittlement in Advanced High Strength Steels and Ultra High Strength Steels: a new investigation approach

In order to reduce CO2 emissions and fuel consumption, and to respect current environmental norms, the reduction of vehicles weight is a primary target of the automotive industry. Advanced High Strength Steels (AHSS) and Ultra High Strength Steel (UHSS), which present excellent mechanical properties, are consequently increasingly used in vehicle manufacturing. The increased strength to mass ratio compensates the higher cost per kg, and AHSS and UHSS are proving to be cost-effective solutions for the body-in-white of mass market products.In particular, aluminized boron steel can be formed in complex shapes with press hardening processes, acquiring high strength without distortion, and increasing protection from crashes. On the other hand, its characteristic martensitic microstructure is sensitive to hydrogen delayed fracture phenomena and, at the same time, the dew point in the furnace can produce hydrogen consequently to the high temperature reaction between water and aluminum. The high temperature also promotes hydrogen diffusion through the metal lattice under the aluminum-silicon coating, thus increasing the diffusible hydrogen content. However, after cooling, the coating acts as a strong barrier preventing the hydrogen from going out of the microstructure. This increases the probability of delayed fracture. As this failure brings to the rejection of the component during production, or, even worse, to the failure in its operation, diffusible hydrogen absorbed in the component needs to be monitored during the production process.For fast and simple measurements of the response to diffusible hydrogen of aluminized boron steel, one of the HELIOS innovative instruments was used, HELIOS II. Unlike the Devanathan cell that is based on a double electrochemical cell, HELIOS II is based on a single cell coupled with a solid-state sensor. The instrument is able to give an immediate measure of diffusible hydrogen content in sheet steels, semi-products or products, avoiding time-consuming specimen palladium coating with a guided procedure that requires virtually zero training.Two examples of diffusible hydrogen analyses are given for Usibor®1500-AS, one before hot stamping/ quenching, and one after hot stamping, suggesting that the increase in the number of dislocations during hot stamping could be the main responsible for the lower apparent diffusivity of hydrogen.

Influence of welding parameters on diffusible hydrogen content in high-strength steel welds using modified spray arc process

In order to satisfy the growing requirements towards lightweight design and resource efficiency in modern steel constructions, e.g., mobile cranes and bridges, high-strength steels with typical yield strength ≥ 690 MPa are coming into use to an increasing extent. However, these steels require special treatment in welding. The susceptibility for degradation of the mechanical properties in the presence of hydrogen increases significantly with increasing yield strength. In case of missing knowledge about how and the amount of hydrogen that is uptaken during welding, hydrogen-assisted cracking (HAC) can be a negative consequence. Moreover, modern weld technology like the modified spray arc process enables welding of narrower weld seams. In this context, a reduced number of weld beads, volume, and total heat input are technical and economical benefits. This work presents the influence of welding parameters on the diffusible hydrogen content in both (1) single-pass and (2) multi-layer welds. Different hydrogen concentrations were detected by varied contact tube distance, wire feed speed, arc length, and varied arc type (transitional arc and modified spray arc). The results show that all welding parameters have significant influence on the diffusible hydrogen concentration in the single-pass welds. By increasing the number of weld beads in case of multi-layer welding, the hydrogen concentration has been reduced. Whereby, differences in hydrogen concentrations between both arc types are present.

Influence of hydrogen on electrochemical behavior of Ni-based superalloy 718

Numerous studies have shown that Ni-based superalloy 718 may be sensitive to hydrogen embrittlement and have highlighted the dominant roles played by the hydrogen solubility and the hydrogen trapping. Samples were hydrogenated by cathodic polarization in molten salts under different conditions to vary the diffusible hydrogen content and to saturate the different hydrogen traps present in the microstructure strengthened by precipitation. Open circuit potential and galvanic coupling measurements were conducted in order to characterize the effect of diffusible and trapped hydrogen on electrochemical behavior and to discuss the possibility of galvanic coupling between zones with different hydrogen contents.