Showing papers on "Shielded metal arc welding published in 1997"

Welding of nickel-base superalloys having a nil-ductility range

Abstract: An article made of a nickel-base superalloy having a nil-ductility range from the solidus temperature of the alloy to about 600° F. below the solidus temperature is welded, as for example in the weld repair of surface cracks, by removing foreign matter from the area to be welded, first stress relieving the article, adjusting the temperature of the article to a welding temperature of from about 1800° F. to about 2100° F., welding a preselected area in an inert atmosphere at the welding temperature, and second stress relieving the article. Welding is preferably accomplished by striking an arc in the preselected area so as to locally melt the alloy in the preselected area, providing a filler metal having the same composition as the nickel-based superalloy of the article, and feeding the filler metal into the arc so that the filler metal is melted and fused with the article to form a weldment upon solidification.

Influence of Mn and Ni on the microstructure and toughness of C-Mn-Ni weld metals

Abstract: A systematic investigation has been carried out to study the microstructure and toughness of C-Mn-Ni low-alloy shielded metal arc (SMA) weld metals. The manganese and nickel concentrations were progressively changed to determine their influence on weld microstructure and mechanical properties as well as to identify their interactions. The results obtained showed that manganese and nickel have considerable effect on the weld metal microstructure, and both Mn and Ni affect the microstructure in a similar way, i.e., promoting acicular ferrite at the expense of proeutectoid ferrite (grain boundary ferrite and ferrite sideplates). The results in the top bead also showed that there is an optimum composition range that produces an optimum balance of weld metal microstructures. For optimum toughness, a combination of 0.6-1.4% manganese and 1.0-3.7% nickel is suggested. Additions beyond this limit promotes the formation of martensite and other microstructural features, which may be detrimental to weld metal toughness.

Effect of CO/sub 2/ shielding gas on metal droplet formation in arc welding

Abstract: We have developed a unified arc electrode model that enables us to make predictions of the time development of molten drops from the welding wire in gas metal arc welding. The wire is taken as the positive electrode, and the effects of surface tension, magnetic pinch forces, and convection within the drop are taken into account to predict drop detachment for any given arc current. For pure argon, we have previously predicted the sharp transition that is observed experimentally at about 300 A between globular transfer at low current, when drop diameters are larger than the wire diameter, and spray transfer, for currents above 300 A, when drop diameters are smaller than the wire diameter. In this paper, we predict that addition of 25% of CO/sub 2/ to the argon leads to an increase in the transition current to more than 325 A, also in agreement with published experimental results. For pure CO/sub 2/, we find a significantly different drop behavior due to the more constricted arc. Both small and large drops are produced, with many very small drops being produced successively between each large drop.

Method of welding wallpaper alloy and arc welder modified to practice same

Abstract: A method of and welder for welding a corrosion resistant, wallpaper alloy to the inside surface of a vessel wall formed from a corrosion susceptible steel sheet after the wallpaper alloy has been affixed to the inside to provide an exposed seam of wallpaper alloy extending in a given path wherein the method and welder comprising moving a welding wire toward the seam, melting and depositing the welding wire onto the seam along the path by a short circuit arc welding process of the type having a welding cycle with a short condition and an arcing condition, which arcing condition constitutes a plasma boost portion with a set peak current level followed by a plasma portion with a current decreasing from said peak current level toward a set background current level with a given time between the plasma boost portion and the short condition andsetting the length of time of the plasma portion of the arcing condition to a value greater than 25% of the given time or greater than 2.0 ms.

CO2 laser beam welding of 6061-T6 aluminum alloy thin plate

Abstract: Laser beam welding is an attractive welding process for age-hardened aluminum alloys, because its low heat input minimizes the width of weld fusion and heat-affected zones (HAZs). In the present work, 1-mm-thick age-hardened Al-Mg-Si alloy, 6061-T6, plates were welded with full penetration using a 2.5-kW CO2 laser. Fractions of porosity in the fusion zones were less than 0.05 pct in bead-on-plate welding and less than 0.2 pct in butt welding with polishing the groove surface before welding. The width of a softened region in the-laser beam welds was less than 1/4 times that of a tungsten inert gas (TIG) weld. The softened region is caused by reversion of strengthening β″ (Mg2Si) precipitates due to weld heat input. The hardness values of the softened region in the laser beam welds were almost fully recovered to that of the base metal after an artificial aging treatment at 448 K for 28.8 ks without solution annealing, whereas those in the TIG weld were not recovered in a partly reverted region. Both the bead-on-plate weld and the butt weld after the postweld artificial aging treatment had almost equivalent tensile strengths to that of the base plate.

Method of welding

Abstract: A process for buttwelding metal workpieces (12) having bevelled joint preparations using an automatic GTAW welder (20) using filler wire (32) includes preparing the bevelled workpieces (12) with bevelled joint areas having minimal land thickness at the root extremities; placing the prepared workpiece joint sections together with an open gap between their adjacent root extremities, the gap having a minimum dimension that avoids harmful compression stress between the workpieces due to weld shrinkage and a maximum dimension that avoids filler wire penetration of the gap; fusion welding the open root area of the adjacent workpieces (12) with a root pass weld using an automatic GTAW welder (20) supplied with filler wire (32) and a shield gas including 1 to 10 % hydrogen and the balance inert gas; and then promptly overlaying the root pass weld with at least one additional filler weld pass using an automatic GTAW welder (20) supplied with filler wire (32) and hydrogen-free shield gas.

Exposure of welders and other metal workers to ELF magnetic fields.

Abstract: This study assessed exposure to extremely low frequency (ELF) magnetic fields of welders and other metal workers and compared exposure from different welding processes. Exposure to ELF magnetic fields was measured for 50 workers selected from a nationwide cohort of metal workers and 15 nonrandomly selected full-time welders in a shipyard. The measurements were carried out with personal exposure meters during 3 days of work for the metal workers and 1 day of work for the shipyard welders. To record a large dynamic range of ELF magnetic field values, the measurements were carried out with ‘‘high/low’’ pairs of personal exposure meters. Additional measurements of static magnetic fields at fixed positions close to welding installations were done with a Hall-effect fluxmeter. The total time of measurement was 1273 hours. The metal workers reported welding activity for 5.8% of the time, and the median of the work-period mean exposure to ELF magnetic fields was 0.18mT. DC metal inert or active gas welding (MIG/MAG) was used 80% of the time for welding, and AC manual metal arc welding (MMA) was used 10% of the time. The shipyard welders reported welding activity for 56% of the time, and the median and maximum of the workday mean exposure to ELF magnetic fields was 4.70 and 27.5mT, respectively. For full-shift welders the average workday mean was 21.2 mT for MMA welders and 2.3 mT for MIG/MAG welders. The average exposure during the effective time of welding was estimated to be 65 mT for the MMA welding process and 7 mT for the MIG/MAG welding process. The time of exposure above 1mT was found to be a useful measure of the effective time of welding. Large differences in exposure to ELF magnetic fields were found between different groups of welders, depending on the welding process and effective time of welding. MMA (AC) welding caused roughly 10 times higher exposure to ELF magnetic fields compared with MIG/MAG (DC) welding. The measurements of static fields suggest that the combined exposure to static and ELF fields of MIG/MAG (DC) welders and the exposure to ELF fields of MMA (AC) welders are roughly of the same level.Bioelectromagnetics 18:470-477, 1997. q 1997 Wiley-Liss, Inc.

Weldability and toughness assessment of Ti-microalloyed offshore steel

Abstract: The present study has been carried out to investigate the coarse-grained heat-affected zone (CGHAZ) microstructure and crack tip opening displacement (CTOD) toughness of grade StE 355 Ti-microalloyed offshore steels. Three parent plates (40-mm thick) were studied, two of which had Ti microalloying with either Nb + V or Nb also present. As a third steel, conventional StE 355 steel without Ti addition was welded for comparison purposes. Multipass tandem submerged arc weld (SAW) and manual metal arc weld (SMAW) welds were produced. Different heat-affected zone (HAZ) microstructures were simulated to ascertain the detrimental effect of welding on toughness. All HAZ microstructures were examined using optical and electron microscopy. It can be concluded that Ti addition with appropriate steel processing, which disperses fine TiN precipitates uniformly, with a fine balance of other microalloying elements and with a Ti/N weight ratio of about 2.2, is beneficial for HAZ properties of StE 355 grade steel.

Welding method and welding material

Abstract: A welding method for two members adapted to be welded and formed of a low-alloy steel for structural purposes causing the weld metal to develop martensite transformation during cooling after welding, so that the weld metal becomes expanded to a greater degree at room temperature than at a temperature at which the martensite transformation initiates. The welding material comprises a ferrous alloy containing C, Cr, Ni, Si, Mn, Mo and Nb, all of which meet substantially with the contents of the following equation (1): ##EQU1##

Welding of gamma titanium aluminide alloys

Abstract: An article made of a gamma titanium aluminide alloy is welded, as for example in the weld repair of surface cracks, by removing foreign matter from the area to be welded, first stress relieving the article, cooling the entire article to a welding temperature of from about 1000° F. to about 1400° F., welding a preselected region in an inert atmosphere at the welding temperature, and second stress relieving the article. Welding is preferably accomplished by striking an arc in the preselected region so as to locally melt the alloy in the preselected region, providing a filler metal having the same composition as the gamma titanium aluminide alloy of the article, and feeding the filler metal into the arc so that the filler metal is melted and fused with the article to form a weldment upon solidification.

Process for coating or welding easily oxidised materials and plasma torch for carrying out this process

Abstract: A process for coating or welding easily oxidised materials is carried out by applying weld metal powder by a plasma powder welding process with an alternating current or with a direct current and a superimposed alternating current as welding current to generate a plasma arc for the powder welding process For this purpose, one base of the plasma arc is produced in a spherical recess (34) of an electrode (32)

Flux-cored wire for gas shielded metal-arc welding

Abstract: PROBLEM TO BE SOLVED: To extend the range of the welding condition and to improve the welding work efficiency by adding water glass as an arc stabilizer in a wire and kneading the mixture, and adding fired sodium titanate and potassium titanate of a specified quantity. SOLUTION: Water glass is added as an arc stabilizer to the composition of a flux-cored wire for the gas shield metal arc welding having a butted part, the mixture is kneaded, and one or two of fired sodium titanate and potassium titanate is added by 0.2-2% to the total wt.% of the wire. Excellent moisture absorption resistance is ensured thereby. In addition, the total amount of hydrogen is regulated to be <=70 ppm. In this flux-cored wire, the arc condition is stable also in the CO2 gas shield gas welding, spatters are small and generated only in a small amount. Firing after adding water glass and kneading is preferably performed at 150 deg.C or over. The outer steel shell is preferably formed of mild steel from the viewpoint of the drawability after the flux is filled.

Weld metal microstructure calculations from fundamentals of transport phenomena in the arc welding of low-alloy steels

Abstract: In recent years, significant progress has been made toward understanding the development of the weld pool shape and size from the numerical calculations of heat transfer and fluid flow in the weld pool. Although such calculations have provided detailed information about the welding processes, no efforts have been made to understand the development of fusion zone microstructures from the fundamentals of transport phenomena. The aim of this work is to address this. Heat transfer and fluid flow during manual metal arc welding of low-alloy steels containing different concentrations of vanadium and manganese were investigated by solving the equations of conservation of mass, momentum and energy in three-dimensional transient form. The computed microstructures are found to be in good agreement with the experimentally observed microstructures. The agreement indicates significant promise for predicting weld metal microstructure from the fundamentals of transport phenomena.

Consumable electrode type arc welding method and device

Abstract: Provided is a consumable electrode type arc welding method and device in which stable welding can be performed at a high speed for a welding gap greater than a thickness of a base metal and the like, and welding conditions are automatically changed according to the welding gap along a welding line to perform the stable welding. A first base metal extended vertically and a second base metal which has an upper end positioned in a middle portion of the first base metal and is provided along the first base metal are welded together. The first and second base metals have a thickness of 2.8 mm, and an arc is generated toward an upper end portion of the second base metal from obliquely above on a side opposite to the first base metal. The second base metal is melted to be a part of a weld metal. An amount of the second base metal to be melted is increased or decreased according to a welding gap detected by a laser sensor.

Multi-purpose, multi-transfer, multi-position shielding gas for arc welding

Abstract: A shielding gas composition and method of using the shielding gas in gas metal arc welding of flux cored are welding, or composite cored arc welding The gas is a mixture of argon, helium and carbon dioxide blended to facilitate metal transfer in any position for all the named processes

Consumable electrode type gas shielded metal arc welding method

Abstract: PROBLEM TO BE SOLVED: To provide a joined part having the performance of a sound weld joint free from blow holes SOLUTION: In a method to perform the consumable electrode type gas shielded metal-arc welding using the high-nitrogen stainless steel welding material, nitrogen gas, argon gas or helium gas up to 98vol%, or the mixture gas of argon gas, helium gas and nitrogen gas is used as the shield gas The stainless steel welding material is preferably the austenitic stainless steel welding material containing, by weight, 60-300% Ni, 160-300% Cr, and 015-045% N as the main alloy composition, or the two-phase stainless steel welding material containing, by weight, 30-90% Ni, 160-300% Cr, 015-045% N as the main alloy composition COPYRIGHT: (C)1998,JPO

Process and apparatus for reducing the emission of ozone produced during a gas shielded arc welding operation

Abstract: Reducing the emission of ozone products during an electric arc welding operation under a protective gas (F1,26) comprises using a gas (F2,38) sheathing the electric arc, the gas being at a temperature greater than 100 degrees C immediately upstream of the root of the electric arc. Also claimed is the device for the above process.

Shielded metal arc welding method for high tensile strength steel

Abstract: PROBLEM TO BE SOLVED: To provide a low hydrogen type shielded metal arc welding method by which low temperature crack resistance of the weld metal is improved and weld metal having excellent tensile strength and toughness is obtained in shielded metal arc welding of high tensile strength steel of 880-1180 MPa in tensile strength. SOLUTION: When high tensile strength steel of ≤0.16 wt.% C, of 0.50-0.70 wt.% Ceq which is formularized as Ceq=C+Mn/6+(Cr+Mo+V)+(Ni+Cu)/15 and of 880-1180 MPa in tensile strength is welded with a low hydrogen type shielded metal arc welding electrode, an electrode whose steel core wire of ≤0.02 wt.% C is coated with coating flux containing <0.5 wt.% Mn, and whose whole constituent is ≤0.35 wt.% C, 0.5-2.5 wt.% Si, 0.5-2.5 wt.% Mn, 1.0-3.0 wt.% Ni, 0.2-1.2 wt.% Cr and 0.2-1.0 wt.% Mo, and whose Y value is adjusted to be between -0.1 and 0.1, is used. Where, Y=Ceq-TS/1300, TS is the tensile strength of the steel in MPa, Ceq=C+Mn/6+(Cr+Mo+V)+(Ni+Cu)/15, and Ceq is of the deposited metal obtained by welding of 10-40 kJ/cm in heat input. COPYRIGHT: (C)1999,JPO

Welded joint excellent in fatigue strength and welding method therefor

Abstract: PROBLEM TO BE SOLVED: To provide a welded joint excellent in fatigue strength by controlling preheating temp., weld heat input, and cooling velocity after welding, respectively, and forming retained austenite in the joint, at the time of welding a structural steel. SOLUTION: A structural steel with 590-950MPa tensile strength, having a composition containing, by weight ratio, 0.10-0.45% C, 0.5-3.0% Si, 0.2-2.5% Mn, and other proper alloying elements, such as Ni, Cr, and Mo, is welded. At this time, a joint, in which the structure of the heat-affected zone heated to a temp. not lower than the Ac1 transformation point and lower than the melting point consists of 5=20vol.% of retained austenite and the balance one or >=2 kinds among ferrite, pearlite, bainite, and martensite, is formed. Moreover, this structure can be obtained by preheating the weld seam of a steel material to 350-500 deg.C, applying shielded metal arc welding or gas-shielded metal- arc welding at (3000 to 20000)J/cm heat input, and then performing air cooling for >=15sec after the completion of welding or water cooling at a rate of (40 to 100) deg.C/S after 15sec-15min from the completion of welding.

The Effect of Water Temperature on Underbead Cracking of Underwater Wet Weldments

Abstract: : Specifications for Underwater Welding have not yet addressed the effect of water temperature on weldment microstructure. The environmental effects on Underwater Wet Welding using a shielded metal arc welding (SMAW) process are severe with higher quenching rates, porosity, slag inclusions and diffusible hydrogen levels. One of the problems associated with these high quenching rates and high diffusible hydrogen levels is the increased likelihood of underbead cracking in the heat affected zone (HAZ), particularly with steel weldment which have a higher carbon equivalent (approximately greater than 0.3). In this work, the underbead cracking resulting in three underwater test welds made on ASTM 516 grade 70 steel three different water temperatures (2.8 deg C, 10 deg C and 31 deg C) was investigated. This was done by optical and scanning electron microscopy (SEM) and by making microhardness measurements. HAZ underbead cracking was observed in all three weldments, but was much less prevalent in the 31 deg C sample and could only be seen at high magnifications in the optical microscope. The cracking in this weldment only appeared to occur in isolated regions where head tempering had been ineffective for some reason. The weldments made at 10 deg C and 2.8 deg C both showed extensive evidence of underbead HAZ cracking typical of that associated with rapid cooling rates, high diffusible hydrogen levels and hard microstructures. SEM studies of the surfaces of these cracks showed evidence for transgranular failure with secondary cracking, both of which are typical of hydrogen induced cracking. This work highlights the importance of water temperature, quenching and diffusible hydrogen levels in underwater wet welding. This is an issue of critical importance in the future wet welding structural repair of Naval ships.

Susceptibility to and occurrence -of HAZ liquation cracking in rail steels: Study of rail welding with high-C welding materials (4th Report)

Abstract: Sitmmary: The conventional enclosed manual metal arc welding process used for field welding rails has the disadvantage that liquation cracks are likely to occur at the boundaries of coarsened austenite grains in the heat affected zone. This paper describes an investigation% of the HAZ liquation crack susceptibility of rails and -the causes of cracking. Experiments have been conducted to determine 1. the critica1.C content of the weld metal and critical welding conditions necessary to avoid cracks by use of electrodes with various C contents. Synthetic tests involving HAZ liquation cracks being simulated have also been conducted to compare crack susceptibility and causes of cracks in rail steels with the corresponding behaviour of general structural steels. The experimental results obtained may be summarised as follows: 1 The crack incidence increases with a decreasing weld metal C content when the difference in the C content between the weld metal and rail steel is 0.3% or more. Cracking is prevented when this difference is less than 0.2%. The crack susceptibility increases with an increasing electrode diameter and welding current or welding heat input. The HAZ liquation crack susceptibility of presently marketed rail steels is equivalent to that of mild steel not facing a HAZ liquation cracking problem in terms of steel chemistry. The principal cause of HAZ liquation cracking in rails welded by the manual metal arc welding process is the large difference in the liquidus and solidus temperatures due to the difference in C content between the weld metal and base metal. 2 3

The effect of magnesium content on the arc stability of SMAW E7016-C2L/8016-C2 covered electrodes

Abstract: The influence of magnesium powder additions to the coating of basic, low hydrogen AWS E7016-C2L/8016-C2 electrodes on the arc stability was studied, as well as the effects of the welding current type and the coating thickness. Overall, it was found that the magnesium content, the coating thickness and the welding current type affected the mechanisms of both metal transfer and electric charge transfer. It was concluded that magnesium additions to the coating, with alternating current (AC) welding, improved both the electric charge and the metal transfers. For direct current electrode positive (DCEP) welding, this effect appeared to be less significant. An increase in the coating thickness made both types of transfer difficult. Finally, with AC welding, for the same arc column length, the metal transfer became easier and the root mean square (rms) voltage value lower than for DCEP welding.

How to Perform Welding in Duplex Stainless Steels to Obtain Optimum Weld Metal Properties

Abstract: Summary Welding of duplex grades, e.g. 2205, has been carried out using SMAW, GTAW and SAW. The most sensitive area, with frequent problems, is the root side in single-side GTA-welded joints. In this case the duplex filler in the exposed area should either be over-alloyed or, in the case of GTAW, the filler material should be welded with a nitrogen-bearing shielding/purging gas. The impact strength of the weld metal obtained with SMAW is normally lower than that of GTA welds. By using basic covered electrodes—or electrodes which give low oxygen or inclusion contents in the welds—acceptably high impact strength at low temperatures can be obtained. Contrary to expectations, the use of nickel base filler for root runs can strongly reduce the notch toughness.