Hydrogen Content In Weld Metal Research Articles

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.

Induction Heating in Underwater Wet Welding-Thermal Input, Microstructure and Diffusible Hydrogen Content.

Hydrogen-assisted cracking is a major challenge in underwater wet welding of high-strength steels with a carbon equivalent larger than 0.4 wt%. In dry welding processes, post-weld heat treatment can reduce the hardness in the heat-affected zone while simultaneously lowering the diffusible hydrogen concentration in the weldment. However, common heat treatments known from atmospheric welding under dry conditions are non-applicable in the wet environment. Induction heating could make a difference since the heat is generated directly in the workpiece. In the present study, the thermal input by using a commercial induction heating system under water was characterized first. Then, the effect of an additional induction heating was examined with respect to the resulting microstructure of weldments on structural steels with different strength and composition. Moreover, the diffusible hydrogen content in weld metal was analyzed by the carrier gas hot extraction method. Post-weld induction heating could reduce the diffusible hydrogen content by −34% in 30 m simulated water depth.

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.

Effects of Fluoride in the Flux on Hydrogen Content in Weld Metal and Operating Behavior in FCAW-S

Effects of Fluoride in the Flux on Hydrogen Content in Weld Metal and Operating Behavior in FCAW-S

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.

셀프실드아크 용접금속의 확산성수소량에 미치는 용접변수의 영향

The effects of the welding parameters, contact tip-to-workpiece distance (CTWD), current, and voltage on the diffusible hydrogen content in weld metal deposited by self-shielded flux cored arc welding were investigated and rationalized by comparing the amount of heat generated in the extension length of the wire. This showed that as CTWD increased from 15mm to 25mm, the amount of heat generated was increased from 71.1J to 174.8J, and the hydrogen content was decreased from 11.3mL/100g to 5.9mL/100 g. Even if little difference was observed in the amount of heat generated, the hydrogen content was increased with an increase in voltage because of the longer arc length. A regression analysis showed that the regression coefficient of voltage in self-shielded flux cored arc welding is greater than that in arc welding. This implies that voltage control is more important in self-shielded flux cored arc welding than in arc welding.

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.

A Predictive Electrochemical Model for Weld Metal Hydrogen Pickup in Underwater Wet Welds

Weld metal hydrogen pickup in underwater wet welding is severe due to the presence and dissociation of water surrounding the welding arc. This undesirable behavior can be minimized, however, with the use of oxidizing-type electrodes. The purpose of this investigation has been placed on the fundamental understanding of the effect of hydrogen pickup by the slag on the weld metal diffusible hydrogen content in direct current, shielded metal arc welding (SMAW) for both electrode-positive polarity (DCEP), and electrode-negative polarity (DCEN). To accomplish this purpose, 20 experimental oxidizing electrodes containing systematic ferric oxide (Fe2O3) additions, ranging from 0 to 70 wt. percent, to the flux coating were investigated. The mole fraction ratio of CaO/SiO2 in the fluxes ranged from 0.05 to 0.35, independent of the ferric oxide additions. Underwater, bead-on-plate welds were deposited on ASTM A36 steel coupons at 0.27 m (city) water depth using a gravity feed system. Welding parameters were held constant throughout the experiments. Weld metal diffusible hydrogen content was determined using the mercury displacement method according to current AWS standard. To correlate weld metal hydrogen content with slag chemistry, the slag hydrogen contents were also determined. The measured diffusible hydrogen contents showed that Fe2O3 was effective in reducing weld metal hydrogen content. Higher hydrogen values were always related to lower Fe2O3 contents initially present in the flux, for instance, 71 mL/100g (DCEP − 0 wt. percent Fe2O3) as compared to 31 mL/100g (DCEP − 36 wt. percent Fe2O3). Amazingly, diffusible hydrogen as low as 13 mL/100g was obtained with the use of DCEN polarity along with 53 wt. percent Fe2O3 in the flux coating. X-ray diffraction (XRD) conducted on different slags showed that the lower diffusible hydrogen values were always associated with the presence of fayalite (2FeO·SiO2). Complementing XRD analysis, Mo¨ssbauer spectroscopy analyses carried out on different slags showed that all ferric (Fe3+) oxide initially present in the slags had transformed to ferrous oxide (FeO), free or combined. Chemical analyses showed that weld metal hydrogen pickup was strongly dependent on the solubility of water in the slag systems. The total and diffusible hydrogen content in the weld metal increased monotonically with increasing slag hydrogen content. Finally, variations in weld metal hydrogen as well as slag hydrogen content with both polarity and iron oxide content in the slag were successfully predicted using an electrochemical model that describes the slag/metal interface equilibrium. In this investigation, the slag/metal interface has been identified as responsible in controlling the weld metal hydrogen pickup. The model assumed that hydrogen was present in the slag as (OH)− ions and that FeO displayed ideal solution behavior.

A Chart Method to Determine Necessary Preheat Temperature in Steel Welding.

Preheating is carried out to avoid cold cracking in steel welding. The occurrence of cold cracking is considered to be governed by accumulating diffusible hydrogen, welding residual stresses and hardness at the crack initiation site. The hydrogen accumulating at the crack site depends on the initial diffusible hydrogen content in weld metal, the weld heat input and the wall thickness. The local residual stress is governed by the weld metal yield strength, the joint restraint and the notch stress concentration factor. The HAZ hardness is influenced by the steel chemical composition, the weld heat input and the plate (wall) thickness.These influential factors affect cold cracking independenly or in an interacted manner. It must be, thus, difficult to predict the necessary preheat temperature by a theoretical method or simple formulae. The method presently proposed is completely based on the empirical results by y-groove weld cracking tests. The present method determines the necessary preheat temperature through the charts describing the following respective effects : 1) steel composition ; 2) diffusible hydrogen content of weld metal ; 3) weld heat input ; 4) wall thickness ; 5) weld metal yield strength ; 6) joint restraint. As to the steel composition, this method uses CEN carbon equivalent that preferably assesses weldability of a wide variety of steels. Also, this method considers a logarithmic dependence of the weld metal hydrogen and the analysis of hydrogen diffusion in a weld has proved that the hydrogen effect on cold cracking must be logarithmic.

Brittle failure resistance of steels and weld metals for pressure vessels of light‐water reactors

The influence of the hydrogen effect during welding of great thicknesses of steels induced into welded joints particularly by moisture contained in the filler material used, is followed up in this paper. The results are compared with the effect of hydrogen induced into the weld metal by controlled cathodic hydrogenization, i. e. by simulation of service conditions. The development of cracks was observed by their propagation in both the undercladding area and surface weld deposit. In the paper the dependence of the crack propagation rate on the stress intensity factor range is expressed. It was found that even if the effect of metallurgically induced hydrogen has no unfavourable consequences on mechanical properties, it is necessary to minimize the hydrogen content in weld metal and avoid subcladding initiations and crack formation and protective cladding overlay reduction. Undercladding initiations and surface defects are the intercepting spots for the hydrogen diffusion, where damaging or substantial reduction of cohesive strength between grains appears.

Sol-gel fluxes for flux cored welding consumables

The feasibility of producing high purity homogeneous welding fluxes by the solgel process and the effects that these fluxes have on the welding process were determined. Reagent grade solgel welding fluxes were produced by making systematic variations of the SiO2-CaO-TiO2-l pct Na2O flux system. The resulting fluxes were made into flux cored wires and used to make bead on plate welds on a niobium microalloyed HSLA steel. Solgel fluxes were shown to have excellent homogeneity, low residual hydrogen content, and no apparent water adsorption. The welding behavior of the solgel fluxes was shown to have superior arc stability compared to a commercial flux cored wire and very low weld metal hydrogen content. The chemical behavior of this flux system was characterized with respect to elemental transfer. The weldments exhibited a primarily acicular ferrite microstructure. Analysis of nonmetallic inclusion size distributions was compared to previous investigations and found to be consistent with the formation of high toughness weld metal microstructure.

エレクトロスラグ溶接における水素の反応機構

The reaction mechanism of hydrogen transfer in electroslag welding is presented.The effects of baiscity of flux and water vapour pressure of atmopshere on hydrogen contents of deposited weld metal in copper moulds with electroslag welding using a consumable nozzle have been investigated.It has been found that Sievert's law does not hold in the relation between the hydrogen content of weld metal and water vapour pressure but a linear relation does.This relation may hold under the assumption that the water dissolves in slag as hydroxyl combined with silicate networks and free hydroxyl ions and that only hydroxyl ions react with metal.The partition coefficient and the reaction rate constant of hydrogen is reversely proportional to the basicity of flux. The former is almost same as the value so far reported in electroslag ramelting and the latter is three to nine times as high as that.

Spectroscopic measurement of hydrogen contamination in weld arc plasmas

The introduction of hydrogen into metals during welding is known to cause hydrogen assisted cracking and embrittlement in certain situations. It has been shown that the weld metal hydrogen content is directly related to hydrogen concentration in the weld arc plasma. In this paper we describe a simple spectroscopic technique for measuring the arc plasma hydrogen concentration in real time when an argon shield gas is used. This technique is based on the fact that the intensity ratio of the hydrogen Balmer Alpha emission line at 6563 Å and an argon emission line at 6965 Å was observed to be an approximately linear function of hydrogen concentration in the weld arc plasma. This technique was experimentally verified under a variety of welding conditions for gas metal arc welding and found to have an error of less than 10% when measuring hydrogen concentrations in the arc plasma as low as 0.25% by volume. This method of hydrogen measurement is also applicable when welding with shield gases not containing argon so long as a suitable ratioing line is available.

鋼材の溶接遅れ割れの研究(第3報)

In the previous reports, the authors studied the effects of various factors on the occurence of cold cracks including root cracks, toe cracks and under-bead cracks in the heat-affected zones of base metals. They proposed the preheating temperatures necessary for the prevention of these cold cracks as a function of the chemical composition of steel, the groove shape, the restraint and the hydrogen content in weld metal.There have arised cases where not only base metal cracking but also weld metal cracking must be considered in the selection of the preheating temperature, especially for the welding of steels with lower carbon contents. A number of cold cracking tests have thus been conducted in order to find the necessary preheating and inter-pass temperature, θpr*, for preventing cold cracking in multi-run weld metals.The θph* is given by the following empirical equation as:θph*(°C)=120+120 log (HJIS/3.5)+5(hω-20)+8(σB-83)where, HJIS is the diffusible hydrogen content in weld metal by the JIS method (0.1 to 40 ml/100gr), hw the weld metal thickness (15 to 40 mm) and σB the tensile strength of weld metal (60 to 90 kgf/mm2).

水カーテン式水中ＭＩＧアーク溶接 ＩＩ 溶接金属の性質および強さに与える水圧の影響

The effect of water pressure on chemical compositions and non-diffusible hydrogen content in weld metal was studied by use of high water. pressure simulator. The water curtain type MIG arc welding method was applied to the butt welding of mild steel under high pressure levels corresponding to water depth of 50 m and 90 m. The results obtained are as follows.1) In case the pure argon was used as a shielding gas, silicon, manganese and carbon content in weld metal were not affected with water depth. On the other hand, when oxygen was added to argon, these elements decreased with increasing of oxygen content and arc length under the constant water pressure and also decreased with increasing of water pressure under the constant oxygen content and the constant arc length.2) Non-diffusible hydrogen content in weld metal was not affected so much with increasing of water pressure and was in the range of 2.2-3.5 cc/100 g, which was very low level compared with the other wet welding method.3) Effect of root gap was dissimilar in plate thickness. For the single pass butt welding of 6 mm thick plate, the appropriate gap was 0 mm or 2-3 mm.4) The hardness in welds was not affected with water pressure. The hardness in weld metal decreased with increasing of oxygen content which affected the increase of molten metal and decrease of deoxidizes elements.5) Single pass and multi-pass butt welds, welded in down hand position under high water pressure, included no defect and passed not only in tensile test but also in 180°bending test.6) Good results were obtained in Charpy V-notch impact test of deposited metal welded. under water depth of 50 m. Oxygen addition to shielding gas was available for increasing the impact value.

高張力鋼のサブマージアーク溶接における溶接割れの研究 ＩＩ ルート割れについて

In the previous study, the welding condition for preventing the transverse weld cracking in submerged-arc welding of HT-80 were determined.In the present study, y-groove cracking tests were employed for determining the root cracking condition.The root cracking characteristics depend on the PCM of base metal or weld metal, whichever is higher, diffusible hydrogen content of weld metal and cooling time of weldment.The critical conditions to prevent the transverse cracking are severer than the ones to prevent the root cracking. It is concluded, therefore, that an adoption of the welding conditions to prevent the transverse cracking generally guarantees both the root and the transverse crack-free weldments in submergedarc welding of HT-80 steels.

板厚方向の溶接われ感受性に関する研究

The effects of several factors on the weld cracking susceptibility in the through-thickness direction were investigated by oblique Y-groove cracking test, Heel cracking test and Insert window type weld cracking test.The results obtained are summarized as follows:(1) The cracking susceptibility in the through-thickness direction increases as sulphur content and Pct value of steel plate increase.(2) Sulphur content is thought to indicate inclusion content, and total length of inclusion increases as sulphur content increases. Therefore, spherizing of inclusion improves greatly cracking susceptibility in the through-thickness direction.(3) The cracking susceptibility in the through-thickness direction is affected also by the diffusible hydrogen content in weld metal. For the prevention of the cracking in the through-thickness direction, it is effective to reduce the diffusible hydrogen content.(4) New formula PL for evaluation of the cracking susceptibility in the through-thickness direction was obtained.

厚板溶接部の溶接割れ防止の研究 Ｉ 溶接金属中の拡散性水素の分布と後熱処理によるその変化

This paper deals with the diffusible hydrogen in multilayer weldment with plate thickness 100 mm to 200 mm.The hydrogen distribution in thick weldment are examined by the experiment. The following facts were clarified.(1) Diffusible hydrogen content in weld metal is raised with an increase of the number of welding layer. The maximum position of diffusible hydrogen content in thickness direction exists at just under the last layer and its distribution can be shown as Fig. 5 and Fig. 7. The hydrogen contents of maximum position was raised with an increase of the number of welding layer.(2) Maximum hydrogen contents, above mentioned, is reduced about 30 per cent with locally postheating for 0.5 hr at 300°C, and diffusible hydrogen is almost removed with furnace annealing for 2 hr at 625°C.(3) Diffusible hydrogen remains for a long period in thick weldment, for example, it remains over 60 days in 100 mm thick weldment of A 387 Gr D steel (2 1/4Cr-1 MO Steel).

アーク溶接過程における水素の拳動(第3報)

Studies are made to determine the sources of hydrogen in shielded metal arc weld metal.First, by assuming that dissolution of hydrogen in molten metal obeys Sieverts'law, an equation is theoretically derived which is able to distinguish between the effects of humidity in the ambient atmosphere and those of moisture from the electrode coating.Next, the coefficients involved in the equation are determined experimentally.Finally, a formula which can predict the diffusible hydrogen content in the weld metal of HT50-HT100 steels is proposed.The results are summarized as follows:1) Evaporation of water from coating flux of low hydrogen type electrode occurs in two stages; one is the evaporation of moisture up to about 200°C and the other is that of bound water with a peak temperature at 750°C.2) The effects of slag covering and its basicity in weld puddle on the diffusible hydrogen content are negligible in the case of low hydrogen type electrode.3) Moisture evaporated from the coating of electrode at elevated temperatures contributes as the cause of the diffusible hydrogen in weld metal much more than that evaporated at relatively low temperatures.4) The diffusible hydrogen content [H]D in weld metal in ml/100g is given by[H]D=(A+12a+0.64b)1/2-1.8, where A is a material constant of electrode which depends mainly on the evaporation of moisture at elvated temperatures in ml/100g, a being moisture content in the coating in wt.% and b the partial pressure of vapour in the ambient atmosphere in mmHg.5) The above equation gives the practical information to control the diffusible hydrogen content in weld metal.

アーク溶接過程における水素の挙動(第1報)

Studies are made to determine the sources of hydrogen in shielded metal arc weld metal.First, by assuming that dissolution of hydrogen in molten metal obeys Sieverts'law, an equation is theoretically derived which is able to distinguish between the effects of humidity in the ambient atmosphere and those of moisture from the electrode coating.Next, the coefficients involved in the equation are determined experimentally.Finally, a formula which can predict the diffusible hydrogen content in the weld metal of HT50-HT100 steels is proposed.The results are summarized as follows:1) Evaporation of water from coating flux of low hydrogen type electrode occurs in two stages; one is the evaporation of moisture up to about 200°C and the other is that of bound water with a peak temperature at 750°C.2) The effects of slag covering and its basicity in weld puddle on the diffusible hydrogen content are negligible in the case of low hydrogen type electrode.3) Moisture evaporated from the coating of electrode at elevated temperatures contributes as the cause of the diffusible hydrogen in weld metal much more than that evaporated at relatively low temperatures.4) The diffusible hydrogen content [H]D in weld metal in ml/100g is given by[H]D=(A+12a+0.64b)1/2-1.8, where A is a material constant of electrode which depends mainly on the evaporation of moisture at elvated temperatures in ml/100g, a being moisture content in the coating in wt.% and b the partial pressure of vapour in the ambient atmosphere in mmHg.5) The above equation gives the practical information to control the diffusible hydrogen content in weld metal.