Weld Metal Hydrogen Research Articles

Investigations on hydrogen-assisted cold cracking of laser welded AHSS

AbstractThis study aims to investigate the impact of various surface conditions prior to welding on the susceptibility of materials to cold cracking, including an analysis of fracture surfaces. Additionally, a novel method is introduced for quantifying the presence of diffusible hydrogen using thermal desorption analysis (TDA). This method allows for the determination of diffusible hydrogen concentration in thin sheet welded joints without use of welding consumables. Three different cold-rolled Advanced high-strength steel (AHSS) samples with different surface conditions, such as coatings, lubrication, or water, are examined to assess their susceptibility to cold cracking. In addition to measuring the diffusible hydrogen content in both the base material and the coating, the overall hydrogen content of the base material is also measured using the melt extraction (ME) method. The new method for quantifying diffusible hydrogen in weld metal is applied to investigate different welding variations, intentionally introducing hydrogen through coatings and hydrogenous fluids on the sheet surface. By combining the assessment of cracking susceptibility and hydrogen content, a better understanding of critical hydrogen levels leading to hydrogen-assisted cracking (HAC) is achieved. The results of this study demonstrate that the occurrence of cold cracking in specific AHSS samples increases when either lubrication or both coating and water or lubricant are added. Additionally, the presence of diffusible hydrogen in the welds of all materials is found to increase with the introduction of hydrogenous layers to the material. Although a critical hydrogen content is identified, no clear correlation between the amount of hydrogen and cracking susceptibility can be determined. These findings have significant implications for the welding of cold-formed AHSS, particularly in the automotive industry where safety and lightweight design are of paramount importance.

Applying In-Situ Radiography to Study Porosity Formation in Aluminum Welds

In-situ radiographic aluminum welding experiments were set up to observe the porosity formation and movement in aluminum weld pools. Aluminum Alloys 1100, 4047, and 6061 were autogenously gas tungsten arc welded while digitally recording radiograph images of macropores. Hydrogen was added in controlled parts per million through an argon-hydrogen shielding gas. The shielding gas hydrogen varied between 0 and 1000 parts per million of hydrogen, and three travel speeds were tested: 1.69, 2.54, and 3.39 mm/s. The transfer of hydrogen from the arc plasma to the weld pool was characterized using postweld gravimetric measurements to get the total pore volume and calculate weld metal hydrogen content. The amount of hydrogen added through the shielding gas played an important role in macropore volume and growth rate. Welding travel speed likewise played a critical role in hydrogen pickup. Alloy 1100 macropores originated at the bottom of the weld pool and then migrated upward toward the rear of the pool. Macropores in Alloys 4047 and 6061 originated at the leading edge of the weld pool and then moved downward and toward the rear of the pool. It is hypothesized that this difference in behavior is related to Marangoni-controlled fluid flow in Alloys 4047 and 6061.

Study on Hydrogen Diffusion Behavior during Welding of Heavy Plate.

For the multi-layer and multi-pass welding process of the heavy plate, the hydrogen diffusion behavior was numerically simulated to study the effect of solid-state phase transition (SSPT) on the hydrogen diffusion in the thickness direction, and the influence of the residual stress-induced diffusion after SSPT. The calculation results were compared with the experimental results. The comparison shows that the distribution of hydrogen concentration in the direction of thickness was in good agreement. The position with the most severe cold cracking sensitivity was located at a 20–30 mm depth from the top surface in this article. After welding, the hydrogen concentration in this position was kept at a high level for a long time under the effect of the size-constraint effect of the heavy plate and the existence of welding residual stress gradient. In addition, the SSPT reduced the residual stress level of weld metal (WM) significantly, increased that of the heat affected zone (HAZ), and the hydrogen was redistributed under the influence of stress. In the process of phase transformation, the parameters of hydrogen diffusion property of the material changed dramatically in a short time, the hydrogen diffusion coefficient increased in order of magnitude, and the solubility decreased in order of magnitude. This directly led to the upward diffusion of hydrogen in WM, and produced a self-gathering effect. For a welded joint of heavy plate, the self-gathering effect between passes was effective in the short-range and ineffective in the long-range.

Influence of introduction of carbon and fluorine additives to fluxes made of silicomarganese slag

The authors have carried out the investigations of fluxing agent containing silicomanganese slag with a flux additive based on gas treatment dust of aluminum production. Influence of carbon-fluorine-containing additive introduction on total oxygen and hydrogen content in weld metal has been studied, as well as its influence on impact strength at positive and negative temperatures. For fluxing agent manufacture, silicomanganese slag was used as a base, and aluminum production electrostatic precipitators dust was used as additive. Silicomanganese slag is produced by the West Siberian Electrometallurgical Plant; dust is from aluminum production electrostatic precipitators (carbonfluorine- containing adding) of RUSAL Co. Samples were welded on ASAW-1250 welding tractor. Chemical composition of studied welded samples was investigated according to GOST 10543 – 98 by atomic emission method on DFS-71 spectrometer and by X-ray fluorescence method on XRF-1800 spectrometer. Fractional gas analysis was performed using LECO TS-600 analyzer. Welded samples were tested for impact strength at positive and negative temperatures using impact pendulum-type testing machine according to GOST 9454 – 78. When using a carbon-fluorine-containing flux additive in welding flux based on silicomanganese slag, amount of oxygen and hydrogen in weld metal decreases, while impact strength increases at positive and negative temperatures. Dependences of the amount of oxygen and hydrogen in weld metal and impact strength on the amount of introduced carbonfluorine- containing flux additive were constructed.

Effect of pre-strain on microstructure and hydrogen embrittlement of K-TIG welded austenitic stainless steel

The effects of pre-strain on hydrogen embrittlement of 304L K-TIG welded joint were investigated. As pre-strain of joint increased, fracture location of hydrogen-charged joint changed from weld metal to base metal. In low prestrained joints, fracture may be initiated at the sites of clustered dislocations due to hydrogen in weld metal with a high density of pre-existing dislocations. In high prestrained joints, some regions in base metal suffered severe strain-induced α′ martensitic transformation due to Ni depletion bands and cracking occurred at phase boundaries where may provide more sites for the accumulation of hydrogen atoms and dislocations.

GMAW，FCAWにおける拡散性水素に及ぼす溶接ワイヤ関連因子の影響

It is well-known that diffusible hydrogen strongly influences cold cracking. However, it isn't understood well what kinds of factors in welding consumables affect diffusible hydrogen in weld metal. For example, it is thought that seamed flux cored wire has more amount of diffusible hydrogen than seamless flux cored wire. This study pointed out a misunderstanding of diffusible hydrogen content generated by FCAW. As a result of investigation, there was no correlation between wire structure and diffusible hydrogen content. Furthermore, welding-wire-related factors on GMAW and FCAW were classified clearly into the follows. (a) Surface lubricant, (b) Initial moisture of flux and (c) Moisture absorbed after production. Various welding wires were prepared and measured the diffusible hydrogen content in order to compare the effect of the each factor. As a result, the most influential factor is (b). The second is (c). The effect of (a) is the smallest.

Diffusible hydrogen content in submerged arc welds of a S960 type steel

Abstract Hydrogen induced damage is a dangerous phenomenon affecting the weld quality with regard to construction service life even without visible indication. The determination of diffusible hydrogen in weld metal has been standardized at an international level in ISO 3690:2012. This international standard specifies the sampling and analytical procedure for the determination of diffusible hydrogen in martensitic, bainitic and ferritic steel weld metal which arises from the welding of such steels using arc welding processes with filler metal. In this study, S960QL steel is extensively used in the heavy transport, lifting and mining industry, where mobile or fixed structures have to carry high loads – often in safety critical situations. In order to sustain extreme characteristics of these high strength low alloy steels, it is a must to reduce the manufacturing defects. In the investigations presented in this paper, the influence of arc length on the weld metal hydrogen concentration was studied according to the ISO DIS 3690 in S960QL type steel with submerged arc welding. Measurement of the diffusible hydrogen was carried out by means of carrier gas hot extraction method. The weld seams with different arc length have similar chemical compositions. Maximum hardness values in the range of 410–425 HV1 were measured in the HAZ on both vertical and horizontal rows in welded structure with two mm wire diameter due to recrystallization condition. For four mm wire diameter, the hardness decreasing which is depending on the grain coarsening in the welded samples with two mm was not occurred in the weld seam-HAZ interface. The larger weld pool and the long arc length increased possibility of hydrogen pick-up and absorbing. Because of this reason, the diffusible hydrogen contents in the welded structure increased in accordance with the arc length.

Determination of hydrogen input in welded joints of press-hardened 22MnB5 steel

Over the last decades, press hardening or hot forming has become all pervasive for automotive body-in-white design. Press-hardened boron-microalloyed steels are widely used in modern body structure for high safety standard and lightweight achievement. Considering the welding of press-hardened components, some special considerations have to be taken into account compared to conventional deep-drawing steel grades. The welding process results in a significant hardness drop in the heat-affected zone (HAZ) which may lead to a change in failure mode or premature failure. Furthermore, the mechanical properties of the welded joints are influenced by the weld metal hydrogen content. Hydrogen pickup of press-hardened steel may result from the heat treatment or the welding process. Due to the martensitic microstructure and the high strength level, a critical hydrogen content may cause hydrogen embrittlement or hydrogen-assisted cold cracking (HACC). This paper contributes to the determination of the diffusible hydrogen content in resistance spot-welded and gas metal arc-welded joints of press-hardened boron-microalloyed steel. It also promotes the understanding of the effect of diffusible hydrogen on the mechanical properties of those joints. Hydrogen was deliberately introduced during welding by wetting of the sheet surface with hydrogenated fluids. The hydrogen content in the weld metal was quantified by thermal desorption mass spectrometry (TDMS) technique. Finally, the influence on the mechanical properties of the welded joints was determined based on a simple component test. A GMA-welded component was set under a constant static load and evaluated for delayed hydrogen-assisted cracking.

Diffusible Hydrogen Content Depending on Welding and Cooling Parameters

Safety of welded components made from high-strength materials is assured above all by the avoidance of hydrogen-assisted cold cracking which occurs during fabrication and may have effects during service. In this context, continuous advancement of the procedures and standards for hydrogen analysis is required. Exact determination of the weld metal diffusible hydrogen according to ISO DIS 3690 is therefore highly relevant as regards the welding and cooling parameters to be maintained. In the investigations presented in this paper, the influence of the welding process parameters and of the cooling parameters on the diffusible hydrogen content was examined and the procedures and parameters specified in ISO DIS 3690 for the weld specimen preparation were checked. The influence of cooling conditions, arc length and contact tube distance (CTD) on the weld metal hydrogen concentration was studied for a high-strength flux cored wire electrode and a high-strength solid wire electrode. Measurement of the diffusible hydrogen was carried out by means of carrier gas hot extraction using a sensitive and long-term stable thermal conductivity detector (TCD).

Comparing of the Welding Atmosphere Moisture Effect on Hydrogen Distribution in TI-6AL-4V, Pure Commercial Titanium and TI-15V-3CR-3SN-3AL Weld Joints

Welding-titanium and titanium alloys must be performed with special precautions because these materials are very reactive to contamination from atmosphere gases. One of the important technological considerations in welding titanium and its alloys is protection of the molten weld pool and HAZ from atmospheric gases such as nitrogen, oxygen, carbon dioxide and moisture and contamination. Absorption of the atmospheric gases affects the mechanical and metallurgical properties and may cause embrittlement, lake of fatigue strength and hydrogen cracking of titanium welds. In this paper, the effect of welding atmosphere moisture on hydrogen absorption and distribution in Ti-6Al-4V, pure titanium and TI-15V-3CR-3SN-3AL TIG welds has been studied. The experimental results indicated that hydrogen distribution which was symmetrical with respect to the weld axis had maximum and minimum points. It was also observed that heat treating the joints after welding resulted in reduction of the magnitude of the maximum and minimum points as well as redistributed the hydrogen in the welds in such a way that the distance of the maximum and minimum points got farther from the weld axis. This distribution is affected by type of titanium alloy and degree of annealing .in this investigation we used vacuum welding chamber with TIG welding apparatus and a special metal sampling and composition detecting systems for joining the samples and detecting the amount of hydrogen in the weld metal .the aim of this investigation was to increase the level of our knowledge about harmful effect of diffusion the hydrogen in the different titanium alloys. Introduction

Hydrogen Absorption And Diffusion in different welded Duplex Steels

In this study, hydrogen absorption and diffusion were investigated for various high-alloyed ferritic-austenitic duplex steels. On account of the specific transformation and solidification behaviour, respectively, of duplex steels as compared to single-phase ferritic and austenitic steels, special conditions have to be considered concerning hydrogen absorption which may ultimately lead to microstructure-dependent hydrogen-assisted weld metal cracking. Hydrogen absorption during welding may occur via the shielding gas, moisture from Qthe surroundings or via the welding filler material. As a contribution to the interpretation and prediction of “ hydrogen-induced cracking in welded duplex steels, the actual hydrogen absorption via the arc as well as the weld metal hydrogen diffusion was investigated for the first time in a duplex steel DS (1.4462), a super duplex steel SDS (1.4501) and in a lean duplex steel LDS (1.4162). Isothermal heat treatment using carrier gas hot extraction enabled quantification of the amounts of hydrogen trapped in the respective microstructure areas. The hydrogen diffusion coefficients were determined by analytical and numerical calculation. The total hydrogen concentrations and the diffusion coefficients were found to be nearly identical. Trapped hydrogen was however observed to be dependent on the material and on the microstructure condition. The influence of hydrogen on the mechano-technological properties of the weld metal was characterized with the help of tensile tests. In addition, the hydrogen embrittlement effect was detected in scanning electron microscopic analyses

Hydrogen absorption of different welded duplex steels

In this study, hydrogen absorption and storage was investigated for various high-alloyed ferritic–austenitic duplex stainless steels. On account of the specific transformation and solidification behaviour, respectively, of duplex stainless steels as compared to single-phase ferritic and austenitic steels, special conditions have to be considered concerning hydrogen absorption which may ultimately lead to microstructure-dependent hydrogen-assisted weld metal cracking. Hydrogen absorption during welding may occur via the shielding gas, moisture from the surroundings or via the welding filler material. As a contribution to the interpretation and prediction of hydrogen-induced cracking in welded duplex stainless steels, the actual hydrogen absorption via the arc as well as the weld metal hydrogen diffusion was investigated in a duplex stainless steel DSS (1.4462) and in a lean-duplex stainless steel LDS (1.4162). Isothermal heat treatment using carrier gas hot extraction enabled quantification of the amounts of hydrogen trapped in the respective microstructures. The total hydrogen concentrations were found to be nearly identical. Trapped hydrogen was however observed to be dependent on the material and on the microstructure condition. The influence of hydrogen on the mechanical properties of the weld metal was characterized with the help of tensile tests. In addition, hydrogen embrittlement was detected in scanning electron microscopic analyses.

Method for the quantitative assessment of transverse weld metal hydrogen cracking

Diffusible hydrogen introduced during the welding process can drastically reduce the toughness and ductility of welds in steel structures. In welds experiencing high levels of longitudinal residual stress (such as upper passes in multipass thick sections), transverse weld metal cracking can occur. While there are methods available for assessing susceptibility of heat affected zones in the parent material to hydrogen cracking, there are few that are applicable to the deposited weld metal, and none that are quantitative in relation to transverse cracking. Therefore, the current work was undertaken to develop a test that isolates and quantitatively assesses the effects of diffusible hydrogen on transverse cracking in the weld metal. The test method was based on four point bending of as-deposited weld metal with controlled levels of diffusible hydrogen. It is proposed that such a test configuration allows quantitative assessment of the relationship between applied stress/strain, hydrogen content, microstructural characteristics and the fracture behaviour. There were two variations on the test method; the first involved rectangular specimens machined from bead on plate welds providing a geometrically regular specimen with low variability in test results, and the second involved an as-welded bead on plate specimen (un-machined) which inherently has a higher level of variability due to greater irregularity in the specimen geometry, but which has the potential for industrial application due to the much simplified sample preparation and handling required. The method shows a high level of reproducibility and shows great potential for future application for both assessment of susceptibility of weld metals to hydrogen embrittlement, as well as more fundamental studies of the physico-chemical mechanisms underlying hydrogen embrittlement phenomena.

Weld metal hydrogen assisted cracking in 50 mm TMCP steel plate with SAW process

The transverse crack, a type of cold crack, occurs perpendicular to the welding direction. From experience, preheating and interpass temperature are important factors in cold crack occurrence. Transverse cracks were detected in the specimen welded with 70°C preheat and an interpass temperature below 30°C; cracks were detected 9·5–14 mm away from the weld surface. Hardness values of preheating 70°C and interpass temperatures below 30°C were higher than those of preheating 70°C and interpass temperatures 100–120°C in the deposited weld metal. The residual stress values for the specimen welded with 70°C preheat and an interpass temperature below 30°C were higher than those of the specimen welded at preheating 70°C and interpass temperatures 100–120°C. The weld cracks were detected in the area of the maximum residual stresses.

Internal Friction by Hydrogen in Super Duplex Stainless Steel Weld Metal

The internal friction behavior by hydrogen in the 329J4L super duplex stainless weld metal was examined. Two internal friction peaks at low temperature in the weld metal were observed after hydrogen charging. These peaks appear to be caused by stress-induced diffusion of hydrogen in sigma and austenite. These peaks gradually increased with hydrogen charging time and were unique to duplex stainless steel.A sharp peak of significant strength occurred at 245K for a frequency of 1.5Hz in as-welded condition. The activation energy of this peak after 7.2ks charging is approximately 38.7kJ/mol which compares favorably with the hydrogen diffusion energy for austenitic stainless steel. This peak is associated with the stress-induced motion of hydrogen in an interstitial-substitutional pair.On the other hand, the sigma (s) phase precipitation suppressed this peak and showed slightly broader peak, providing a strong indication of hydrogen trapping into the sigma phase. After peak separating calculation using theoretical internal friction curve, two peaks were observed after hydrogen charging. One of the peaks observed at 245K exhibited an activation energy of 38.7kJ/mol. A broad peak at 225K is interpreted as a stress-induced motion of hydrogen in tetragonal sigma phase. The activation energy of peak by hydrogen in sigma phase was estimated to 36.7kJ/mol. Consequently, a broad peak by hydrogen in sigma phase was observed at 225K in the hydrogenated weld metal precipitating sigma phase. It is apparent from these results that hydrogen can easily diffuse in the sigma phase as compared to austenite.

Cold Cracking in Weldments of Steel S 690 QT

The cold cracking process in shielded metal arc and gas metal arc welding of steel S 690 QT is investigated by Tekken test. The conditions for cold cracking are varied by changing the specimens’ thickness, heat input, initial weld metal hydrogen concentration and preheating temperature. The kinetics of initiation and propagation of cracking is monitored by acoustic emission equipment. It is found out that the crack’s propagation path shifts from weld metal to fusion line and HAZ with decreasing initial weld metal hydrogen concentration and increasing hardness of HAZ. In the investigated range of cold cracking conditions the magnitude of cracking is mainly controlled by the preheating temperature and heat input. The acoustic emission signal provides valuable information about the factors controlling the kinetics of crack initiation and propagation and the intensity of cold cracking. The initial hydrogen concentration in weld metal controls the incubation period’s duration and affects the cracking intensity at higher heat inputs. The preheating temperature does not influence the incubation period, but significantly affects the kinetics of crack propagation. The heat input has a complex influence on the cracking kinetics and intensity. This is related to the contradictive effects of heat input on the initial hydrogen concentration per unit length of weld metal and on the behaviour of hydrogen during cooling. The obtained results provide a basis for combined experimental — modelling investigations on the cold cracking phenomenon in weldments of higher strength structural steels, aiming at quantitative evaluation of the influence of the main controlling factors.

Prevention of Weld Metal Hydrogen Cracking in High-Strength Multipass Welds

Welding modern high-strength steel with low carbon and impurity contents, preheat may be dictated by cracking sensitivity of the weld metal instead of the HAZ. Standard EN 1011 does not provide the user with any unified methodology for the calculation of safe preheat for weld metal. The few calculation formulae that apply to multipass welds can give greatly varying predictions. This article studies controlling factors that govern transverse hydrogen cracking in high-strength multipass weld metal. The experiments comprised heavily restrained Y- and U-groove multipass cracking tests of SMAW and SAW welds. The objectives were the assessment of hydrogen cracking risk by defining the Crack — No Crack boundaries in terms of safe line description giving the desired lower-bound estimates, and to derive predictive equations capable of giving reliable estimates of the required preheat/interpass temperature T0/Ti for the avoidance of cracking. Equations were derived to assess the weld critical hydrogen content Hcr corresponding to the Crack — No Crack conditions as a function of either weld metal Pcm, yield strength Rp0.2 or maximum hardness HV5(max). For the calculation of safe T0/Ti estimates, a formula incorporating weld metal strength as linear functions of either CET or weld HV5(max), weld build-up thickness aw in the form of tanh expression and weld diffusible hydrogen Hd in terms of combined [In / powerlaw] expression, was found descriptive.

Welding current effect on diffusible hydrogen content in flux cored arc weld metal

The application of flux cored arc welding (FCAW) has increased in manufacturing and fabrication. Even though FCAW is well known for its good capability in producing quality welds, few reports have been published on the cause of the relatively high diffusible hydrogen content in the weld metal and its relation with the ingredients used in the wire production and with the welding parameters (mainly welding current). This paper describes experiments where data obtained from weld metal diffusible hydrogen analysis, metal droplet collection, and high-speed recording of metal droplet transfer were used to evaluate the effect of welding current on diffusible hydrogen content in the weld metal. The results from gas chromatography analysis showed that weld metal hydrogen content indeed increased with welding current. A polynomial regressional analysis concluded that hydrogen increase with current was better described by a linear function with proportional constant of approximately 0.7 or 70%. Different from the GMA welding transfer behavior, statistical analysis showed only a small increase in metal droplet size with increasing current. The metal transfer mode remained in the globular range for currents between 100 and 150 A. The most surprising findings were with the high-speed cinematography recording. Observing the high speed movies, it was possible to see that at low current, "unmelted" flux sporadically touched the weld pool but at higher current, the flux remained touching the weld pool during the whole time of droplet formation and transfer. It is believed that since the flux has ingredients that contain hydrogen, hydrogen passes through the arc undisturbed, going to the weld bead intact and increasing the hydrogen content in the weld metal. Another important observation is regarding to droplet size. Droplet size increased with increasing current because forces from decomposed gases from the flux could sustain the droplets, retarding their transfer and allowing them to grow.

Hydrogen trapping in ferritic steel weld metal

A brief overview is given of the role of hydrogen trapping in hydrogen management of steel welding. The concept of hydrogen trapping is introduced in conjunction with efforts in reducing hydrogen cracking in steel welding. Appropriate selection of hydrogen traps offers the potential to control the content and distribution of hydrogen in steel weldments. The effectiveness of hydrogen traps through selective alloying in reducing the concentration of diffusible hydrogen during welding thermal cycles is evaluated, particularly in its use as a substitute for costly weld heat treatment practices. The relationship of weld metal microstructure and hydrogen contents to the effective use of hydrogen trapping elements is discussed. The fundamental aspects which control hydrogen content as well as hydrogen distribution in steel are discussed, such as the statistical thermodynamics and the transport of hydrogen in steel containing traps. As tools for investigating potential hydrogen traps, several experimental methods are discussed in relation to their applicability to characterise the physical nature of hydrogen traps. These methods include the hydrogen permeation technique and hydrogen thermal desorption analysis. Recent efforts to prevent hydrogen cracking in steel weldments through numerical computations require consideration of hydrogen trapping in the weld microstructure, and hence knowledge of applicable data of hydrogen trapping parameters is necessary for welding engineers to improve hydrogen management in steel welding.

Uso del ensayo de implante y la técnica de emisión acústica para estudiar el agrietamiento asistido por hidrógeno en la zona fundida en la soldadura de un acero HSLA-80

Weld metal hydrogen assisted cracking was studied using two flux cored wire (AWS E 70T-5 and AWS E 120 T5-K4) and a mixture gas of CO 2 + 5% H 2 to induce high values of diffusible hydrogen in high strength low alloy steel (HSLA-80) weldments. An Acoustical Emission Measurement System (AEMS) RMS voltmeter was coupled to the implant test (NF 89-100) apparatus to determine energy, amplitude and event numbers of signal. All cracks were initiated in the partially melted zone and propagated into the coarse-grained region of the heat affected zone when E 70 T5 consumable was used, and the quasi-cleavage fracture mode was predominant. When E 120 T5 K4 consumable was used the cracks propagated vertically across the fusion zone, and a mixed fracture mode was the most important. A significant relationship between acoustic emission parameters and fracture modes was found.