Showing papers on "Submerged arc welding published in 1994"

SUBMERGED ARC WELDING METHOD FOR HIGH STRENGTH Cr-Mo STEEL

Abstract: A submerged arc welding method for a high strength (2.25%-3%)Cr-3%Mo-V steel, to obtain a weld metal excellent in strength at room temperature and high temperature, toughness, and creep strength, after SR, temper brittleness resistance, cold crack resistance and SR crack resistance. The Cr-Mo steel contains: 2.00 to 3.25% of Cr, 0.90 to 1.20% of Mo, and V as essential components, and Nb, Ti, B and Ca as needed. A welding heat input is in the range of from 20 to 50 kJ/cm. The solid wire contains 0.09 to 0.19% of C, 0.30% or less of Si, 0.50 to 1.40% of Mn, 2.00 to 3.80% of Cr and 0.90 to 1.20% of Mo. The bonded flux contains 5 to 20% of SiO₂, 20 to 40% of MgO, 2.4 to 12% of a metal fluoride (F-converted value) and 3 to 12% of a metal carbonate (CO₂-converted value). A weld metal contains 0.08 to 0.15% of C, 0.05 to 0.30% of Si, 0.50 to 1.20% of Mn, 0.030 to 0.060% of O, 0.10 to 0.50% of V and 0.005 to 0.035% of Nb. P and Ti in the weld metal are restricted to 0.010% or less and 0.012% or less, respectively. The components of C, Si, Mn, O, P, Ti are added from the solid wire and the bonded flux, and the components of V and Nb are added from at least one of the wire and the bonded flux. Moreover, the welding is performed such that Ps is 3.50 to 5.50, Ps being expressed by Ps = 10×[C] D + 10×[Si] D + [Mn] D + 50×[P] D + 20×[O] D where [X] D is wt% of the component X in weld metal.

Cooling induced segregation of impurity elements to grain boundaries in Fe-3 wt%Ni alloys, 214wt%Cr-1 wt%Mo steel and submerged arc weld metal

Abstract: Previous theoretical and experimental studies demonstrate that small bulk concentrations of impurity and solute elements can segregate to grain boundaries in ferritic steels during cooling from high temperatures. This results from solute-vacancy pair formation and their subsequent diffusion to the grain boundary sinks. The grain boundary segregation which results from cooling at three different rates from fixed temperatures of 1273 and 1323 K respectively, have been measured on ferritic Fe-3 wt%Ni alloys and 2 1 4 wt % Cr -1 wt % Mo steels containing additions of either P or Sn. In addition, a CMn submerged arc weld metal subject to a complex thermal cycle has been investigated. The composition of the grain boundaries have been measured on thin foil specimens using both conventional and high resolution STEM-EDS X-ray microanalysis techniques. Segregations of both P and Sn have been observed in the Fe-3 wt% Ni alloys and 2 1 4 wt % Cr -1 wt % Mo steels and P segregations in the weld metal. The measured grain boundary segregations of both P and Sn are discussed with respect to previous theoretical predictions for the cooling rates investigated and the interactive role of other elements present.

Welding method for rotatable shafts

Abstract: An improved welding method is provided for repairing broken rotors. The welding method preferably employs a 2.25Cr-1.0Mo-0.3V-type filler metal, preferably deposited using a narrow groove welding technique. The broken pieces are aligned end to end. A narrow groove is formed to substantially remove the end surfaces. The groove is preheated, filled with the welding filler metal, and postheated, resulting in a strong, high temperature resistant, long lasting weld.

Influence of chromium on the mechanical properties and microstructure of weld metal from a high-strength SMA electrode

Abstract: In the present work, the influence of Cr on mechanical properties and microstructure of weld metal from a high-strength SMA electrode is analyzed by considering 12 experimental low-alloy low-hydrogen iron powder AWS E10018, E11018, E12018-M type covered electrodes. These electrodes were manufactured to obtain in the weld deposits Cr contents ranging from 0 to 1.8%, with two different Mn levels for each Cr content, maintaining the amount of other elements at a fixed value. All-weld-metal specimens and production type single V-groove welds were mechanically tested in the as-welded and stress-relieved conditions, and a metallographic study was conducted. Chromium was found to be deleterious to toughness with only a minor influence due to Mn variations. A postweld heat treatment led in all cases to a reduction of toughness. Increasing Cr content in the welds produced a higher proportion of acicular ferrite and a general refinement of the microstructure.

Triggered vacuum anodic arc

Abstract: An anodic vacuum arc deposition system for rapidly depositing a high quality, small grain size, coating on a workpiece. The anodic vacuum arc deposition system includes an arc initiator and an anodic electrode having a continuous feed. The anodic vacuum arc deposition system may be configured with a coaxial anode and cathode. A plurality of coaxial electrodes may used to deposition-coat a large area and/or to sequentially deposit a series of layers each of a different material. In one embodiment, a low current triggered anodic vacuum arc with a continuous wire feed mechanism provides the user with a self-contained high differential metal plasma spray. This apparatus provides coatings with properties similar to coatings from a basic anodic arc deposition source but can be self-ignited, continuously run, and made highly mobile for greater coverage control. An alternative embodiment of this device incorporates a cathodic arc source which supplies ions to both ignite the anodic arc and to enhance the ion population of the anodic arc metal flux for greater control over the deposition process via substrate biasing and magnetic focusing, and the degree of ionization at the substrate.

Heat input and dilution effects in microalloyed steel weld metals

Abstract: The sensitivity of weld metal microstructure and mechanical properties to variations in both heat input (i.e., cooling rate) and weld dilution in submerged arc (SA) welding of microalloyed steel was examined. Weldments were prepared with weld metal dilutions of approximately 40% and 70% at heat inputs of 2.0, 3.3, 4.6, and 5.3 kJ/mm, using two commercial welding wires and a basic commercial flux. The high dilution welds, which were ordinary bead-on-plate welds, resulted in microstructures that ranged from ferrite with aligned second phase at low heat inputs to acicular ferrite at high heat inputs. Special over-welding techniques were used to make the low dilution welds, allowing use of the same welding parameters as those for the high dilution welds. The technique involved remelting of weld metal to simulate the effect of multipass welding. The microstructure of these welds was predominantly acicular ferrite, independent of heat input. As a consequence, the low dilution welds had superior toughness compared to the high dilution welds.

Plasma parameters near a small anode in a high-pressure arc (gas metal arc welding)

Abstract: The size of the arc attachment at the anode of gas metal are welding (GMAW) is small compared to the arc column. The small anode attachment results in a high current density and high Joule heating near the anode. It is believed that this is the reason why the voltage in such an arc rises with current which is in contrast to an almost current-independent V-I characteristic in the case of a large anode. The equation to describe the distribution of plasma parameters near a small are anode is presented. Calculations have been performed for an atmospheric pressure arc in argon in the 50 A to 500 A current range and for the anode sizes of 0.5 mm to 2 mm. Calculations showed that: (1) the voltage drop across the anode layer rises with the current, and (2) there is an electron temperature maximum close to the anode. The calculated volt-ampere characteristic of the anode layer is in agreement with experimental data. The calculated heat flux to the anode is slightly higher than that measured. It is believed that this difference is due to anode vaporization. The thermal balance of the anode is discussed.

Pipe making welding method of clad stainless steel pipe

Abstract: PURPOSE: To provide a welding method of a seam weld zone in the case of production of a clad stainless steel pipe by a method, such as UOE, from a clad steel consisting of an austenitic stainless steel having excellent corrosion resistance as a base metal on an inside surface side and a low alloy steel having excellent strength as a base metal on an outside surface side. CONSTITUTION: The seam part 3 of the clad steel is subjected to edge prepn. of a double Vee shape of which the depth of the groove 4 on the inside surface side is 80 to 130% of the thickness of a cladding metal 2, the angle is 60 to 80°, the route thickness is 3 to 5mm and the angle on the outside surface side is 60 to 80°. The groove part 5 on the outside surface side is subjected to tack welding with a welding wire for the low alloy steel; thereafter, the inside and outside surfaces are subjected to submerged arc welding with one pass. As a result, the inside surface weld zone free from the defects occurring in component dilution is obtd. COPYRIGHT: (C)1995,JPO

Sensors and control systems in arc welding

Abstract: Part 1: General review. Introduction to sensing systems and their application in arc welding processes. State-of-the-art review of sensors and their application in welding processes. Control system. Basis for welding process control. Sensor techniques and welding robots. Analysis of questionnaire results on sensor application to welding processes. Future aspects and subject. Part 2: Collected papers on applications of sensors to welding processes. Groove tracking control by laser sensing method. Development of automatic multi-layer welding system applying laser sensing technique. Online visual sensor system for arc-welding robot. Welding robot with visual seam tracking sensor. An arc-welding robot with a compact visual sensor. Development of robot for three-dimensional multi-layer welding with vision sensor. Visual arc sensor (ARC-EYE). Fuzzy control of CO2 short-arc welding. Application of fuzzy neural network to welding line tracking. Magnetic control of arc in high speed TIG welding. Adaptive control of welding condition using visual sensing. Automatic welding system with laser optical sensor for heavy-wall structures. Group-control system of narrow-gap MIG welding. Automatic control technique for narrow gap GMA welding. A study on automatic control system of one-side submerged arc welding by flux copper backing. Touch sensor and arc sensor for arc welding robots. Application of arc sensor to robotic seam tracking. Dynamic analysis of arc-length and its application to arc-sensing. Robot welding with arc sensing. Arc sensing method by fuzzy control. Development and application of arc sensor control with high speed rotating arc process. Groove tracking control by arc welding current. Automatic seam tracking and bead height control by arc sensor. Through-the-arc sensing control of welding speed for one-sided welding. Some kinds of wire ground sensors. Application of touch sensor to arc welding robot. Automatic welding for LNG corrugated membrane. Welding process monitoring by arc sound. Vibrating reed sensor for tracing the centre of narrow groove. Development of ultra heat-resistant electro-magnetic sensing system for automatic tracking of welding joint. Motion generation of an off-line programming system of an arc-welding robot. Application of an off-line teaching system for arc welding robots. Development and availability of IC-card welding system for automatic welding. Development of remote-controlled circumferential TIG welding system. In-process control system in one side SAW. Application of arc sensor and visual sensor on arc welding robots. Intelligent arc welding robot and simultaneous control of penetration depth and bead height. NC welding robot for large structures. Development of fully automatic pipe welding system.

Cracking characteristics of A516 steel weldment in H2S containing environments

Abstract: Sulfide stress cracking (SSC) and hydrogen-induced cracking (HIC) are two well-known phenomena that take place in steels situated in H 2 S containing environments. This investigation presents the cracking characteristics of A516 pressure vessel steel weldments prepared by submerged arc welding, under various welding heat inputs (15, 30 and 45 kJ cm −1 ), following immersion in NACE TM-01-77 solution (5 wt.% NaCl + 0.5 wt.% CH 3 COOH) saturated with H 2 S gas. The results of slow strain rate testing, performed at a strain rate of 5 × 10 −7 s −1 , reveal the presence of SSC, HIC, and quasi-cleavage fracture in the base metal. Metallographic examination of the fractured specimens reveals that HIC initiates and/or propagates in both the ferrite and pearlite phases and along the ferrite/pearlite interface in the base metal. An increase in the welding heat input causes increases in the amount of grain boundary ferrite and Widmanstatten ferrite in the weld metal and heat-affected zone (HAZ), respectively, and subsequently results in decreases in the cracking resistances of the weld metal and HAZ n H 2 S containing environments.

Plasma welding process

Abstract: In a plasma welding process, a voltage is applied between an electrode and an object to be welded so as to generate a plasma arc with a plasma gas directed through a torch to surround the electrode, and welding is performed using the plasma arc as a heat source. The process cyclically varies energy contained in the plasma arc by cyclically varying a plasma gas flow rate.

Workpiece cleaning during variable polarity plasma arc welding of aluminum

Abstract: Variable Polarity Plasma Arc welding has proved to be extremely successful in welding aluminum alloys despite their adherent refractory oxide. This success has been attributed to removal of the oxide during the reverse polarity cycle. In situ optical spectroscopy is used to measure the amount of hydrogen and oxygen in the plasma arc with a minimum detectable limit of less than 100 ppm. It was found that the amount of contamination is independent of surface preparation and torch speed. Using this information, it is proposed that the predominant mechanism for reverse polarity cleaning in aluminum is dielectric breakdown of the surface oxide ahead of the torch rather than by ion sputtering.

A Study of Mechanical Stress Relief (MSR) Treatment of Residual Stresses for One-Pass Submerged Arc Welding of V-Grooved Mild Steel Plate:

Abstract: The heat-transfer and thermal stress distributions in one-pass submerged arc welding (SAW) were numerically determined using the finite element method (FEM) for a V-grooved rectangular steel plate in which the weld preparation was filled during welding. A two-dimensional non-linear heat-transfer analysis was performed for a transverse section of the plate. This was followed by a thermo-elasto-plastic transient thermal stress analysis, assuming plane strain to be constant for the same model section. The same stress model was used to simulate a mechanical stress relief (MSR) treatment of the plate. This has frequently been used in the fabrication of large pressure vessels instead of post-weld heat treatment (PWHT). In this way its effect in reducing the residual stress in the welded plate was investigated. MSR was simulated by enforcing a constant displacement loading in the welding direction.The solution of the thermal stress analysis showed that it was possible for the residual stress around the weld cent...

Sulfide Stress Corrosion Cracking in Welded Joints of Welded Linepipes

Abstract: The sulfide stress cracking (SSC) behavior of welded linepipes has been studied using some SSC tests, such as tensile SSC test (NACE-TM 0177-90 Method A), full thickness SSC tests, four points bending SSC tests and full scale SSC tests. Detailed metallographic examinations have been performed in order to understand the influences of steel chemistries and heat inputs in welding on the SSC resistance of the heat affected zone. The effects of the geometry of the SSC specimen and hydrogen concentration on the SSC have also been investigated. The results have indicated that homogenized bainitic ferrite microstructure, which can be attained by reducing carbon content and by applying accelerated cooling after controlled rolling in plate rolling process, improves the resistance of steel plates to the SSC. Meanwhile, most specimens from submerged arc welding welded joints fail at the heat affected zone, regardless of differences in the microstructures of base materials, and they tend to show nearly the same level of the ratio of threshold stress to yield strength in the tensile SSC test. Specimen geometry and the quantity of hydrogen concentration in steel affect on the threshold stress, and hence reducing the hydrogen concentration improves the SSC resistance of the welded joints especially in lower hardness heat affected zone. Relations between the results of the laboratory tests and full scale tests are also discussed.

The interfacial microstructure of weld overlay of corrosion resistant alloys

Abstract: For reasons of economy, hydrogenation pressure vessels of heavy wall sections are fabricated by cladding with one or more layers of austenitic stainless steel on the inside of the vessel wall. Submerged Arc Welding with strip-electrode technology is used in this process because of its ability to combine excellent deposit properties and controllable penetration with high deposition rates. However, hydrogen-related disbonding of the clad-overlay is a problem remaining in the use of the composite pressure vessels in petrochemical industries. One of the major factors contributing to the disbonding is the microstructure developed during solidification of the weld metal. It is unclear what kind of microstructure is most susceptible to disbonding and how the microstructure develops. Marshall and Lazor et al. believed that martensitic structures were the culprit for the initiation of disbonding. Ohnishi et al. concluded from their investigation that a layer of martensite adjacent to the fusion line would reduce the disbonding. Recently, Godden et al. found that a so-called Type 2 grain boundary was the most susceptible structure to the disbonding, but the mechanism is not clear. This study investigated the microstructures along the interface between overlays and base steel and established the mechanism of the formation ofmore » crack-susceptible microstructures.« less

Method for welding clad steel pipe

Abstract: PURPOSE:To provide a method for welding a clad steel pipe with excellent strength, toughness and crack resistance by permitting application of a low-alloy steel wire in welding of particularly the outside surface side on premise of effective utilization of an existing UOE stage CONSTITUTION:Submerged arc welding is executed under conditions under which a butt groove shape 4 of a clad steel consisting of a low-alloy steel 1 on the outside surface side and a stainless steel basically composed of components, such as Ni, Cr and Mo, or a higher alloy steel on the inside surface side is specified to 80 to 130% of the cladding metal thickness in the groove depth on the inside surface side, an angle to 60 to 80 deg, the root face thickness to 1 to 3mm and the angle on the outside surface side to 60 to 80 deg at the time of producing the clad steel pipe by subjecting the clad steel to double Vee grooving and subjecting the double Vee groove thereof to seam welding

Plasma arc welding method and apparatus in which a swirling flow is imparted to a plasma gas to stabilize a plasma arc

Abstract: There is provided a plasma arc welding method, characterized in that a portion of a front side workpiece material is heated and melted by a plasma arc to form a molten pool thereat, that the molten pool is held not to fall or drop under a surface tension acting thereto and is brought into contact with a portion of a rear side workpiece material under a pressure which is exerted by the plasma arc and/or a shielding gas, further that the portion of the said rear workpiece material is brought into a molten state by a thermal conduction thereto so that the two workpiece materials may be welded together, and that a swirling flow is imparted to a plasma gas of the plasma arc. There is also provided a plasma welding apparatus for using the above mentioned plasma arc welding method, characterized in that the apparatus comprises: a plasma torch which has a plasma flushing outlet for swirling and flushing a plasma gas of the plasma arc around an electrode therefor.

Prevention of contact tube melting in arc welding

Abstract: A method and apparatus for preventing catastrophic melting of the contact be in continuously-fed consumable electrode arc welding due to wire feed interruptions by monitoring the movement of the wire electrode with a high frequency sensor such as all optical encoder having a resolution on the order of <0.1 second and switching off the power to the welding apparatus if the wire electrode speed falls below a predetermined threshold.

High-bandwidth continuous-flow arc furnace

Abstract: A high-bandwidth continuous-flow arc furnace for stream welding applications includes a metal mass contained in a crucible having an orifice. A power source charges an electrode for generating an arc between the electrode and the mass. The arc heats the metal mass to a molten state. A pressurized gas source propels the molten metal mass through the crucible orifice in a continuous stream. As the metal is ejected, a metal feeder replenishes the molten metal bath. A control system regulates the electrode current, shielding gas pressure, and metal source to provide a continuous flow of molten metal at the crucible orifice. Independent control over the electrode current and shield gas pressure decouples the metal flow temperature and the molten metal flow rate, improving control over resultant weld characteristics.

Submerged arc welding method for high-cr ferritic heat resisting steel

Abstract: PURPOSE:To provide the submerged arc welding method which prevents the crack of a weld metal and easily and efficiently yields the defectless weld metal having enhanced creep rupture strength and improved toughness at the time of welding the thick plates of high-strength heat resisting steels. CONSTITUTION:The crack of the weld metal to be generated at the time of welding the thick plates with the large heat input is prevented and the creep rupture strength and toughness are exceedingly enhanced by combining a wire formed by specifying C, Si, Mn, Cr, Nb, V and N and further lowering the content of B as low as possible and a flux formed by specifying CaO or MgO, Al2O3 and SiO2 and lowering the content of the B as low as possible in such a manner that the Mo, W, Ni and B satisfy specific ratios by specific formula. Then, the reliability of the crack resistance, creep rupture characteristic and toughness of a welded joint part is greatly improved by executing welding for the high-strength heat resisting steels.

Manufacture of welded steel tube

Abstract: PURPOSE:To improve the applying capacity of the existing welding line by improving welding speed by using gaseous CO2 shielded arc welding in combination with submerged arc welding CONSTITUTION:A steel strip is formed in a spiral state and submerged arc welding S1 is executed to the butting parts from an inner side When the welded part holds >=150 degC, gaseous CO2 shielded arc welding G1 is executed from an outside, further, submerged arc welding S2 is executed Consequently, load on the submerged arc weldings S1, G1 is reduced by gaseous CO2 arc shielded arc welding G1, high speed welding can be made, welding defects given when CO2 gas shielded arc welding G1 is applied at a high speed, can be prevented by the holding heat of the preceeding submerged arc welding part and the manufacturing speed of a welded steel tube can be improved

Submerged arc welding bonded flux

Abstract: PURPOSE: To submerged arc welding bonded flux which is capable of imparting weld metal of higher toughness, good welding workability and m.ore particularly an improvement in the affinity of beads at bevel surfaces and the consequent improvement in fatigue strength and is suitable for steels for low-temp. service. CONSTITUTION: This submerged arc welding bonded flux contains 20 to 45 MgO, 10 to 30% Al 2 O 3 , 5 to 15% CaF 2 , 5 to 20% SiO 2 , 2 to 10% metal carbonate (in terms of CO 2 ) and 2 to 20% total of one or two kinds of CaO and BaO and contains 0.5 to 5% total of one or two kinds of metal Si, metal Al and metal Ti, 1 to 7% total (total Ti) of and Ti oxide (in terms of Ti), 0.1 to 0.5% total of one or two kinds of metal B and B oxide (in terms of B) and 0.005 to 0.15% S. More particularly, this submerged arc welding bonded flux is suitable for the steels for low temp. service to be used mainly for ocean structures, LPG tanks, etc., with which particularly the high toughness and fatigue strength are required for the weld zones. COPYRIGHT: (C)1995,JPO

High heat input one side submerged arc welding method

Abstract: PURPOSE:To execute one side/one pass welding without defect by using DC power source for a preceding electrode, using AC power source for an intermediate electrode/succeeding electrode and setting a distance between electrodes corresponding to plate thickness in one side/one pass submerged arc welding for a thick steel plate of the specific plate thickness. CONSTITUTION:In the one side/one pass welding of a thick steel plate of 50-80mm plate thickness, by using DC power source for a preceding electrode (L), by using AC power source for an intermediate electrode (M) and a succeeding electrode (T), high heat input submerged arc welding is executed with setting L-M distance between electrodes and M-T distance between electrodes corresponding to plate thickness such as 40mm/160mm L-M distance between electrodes 90mm/150mm M-T between electrode distance, etc., for 50mm plate thickness. Whereas the distance between electrodes is of the value measuring the distance between electrodes at groove bottom parts. By this method, one side/one pass welding of thick plate is performed without defect, the hand repair after welding is not required, improving efficiency of welding work.

Flux for one-side submerged arc welding and welding process using the same

Abstract: PURPOSE:To provide flux for a one-side submerged arc welding and one-side submerged arc welding method using the same to eliminate the problem of a one-side submerged arc welding performing at a high speed, and by which especially a sound surface bead and a rear bead can be attained. CONSTITUTION:The flux for a one-side submerged arc welding performing at a high speed, contains, by weight, 10 to 20% SiO2, to 15% CaO, 20 to 30% MgO, 8 to 18% TiO2, 2 to 8% F and 10 to 30% iron powder. A grain whose grain diameter exceeds 840mum, is =60%, a grain whose grain diameter is . Also, a welding is performed by using this bond flux and by using three electrodes or over at a speed of 1.0 to 2.0m/minute.

Wire and bonded flux for submerged arc welding of 780mpa or 960mpa steel

Abstract: PURPOSE:To lower preheating/inter passes temp. and to obtain the weld zone of high toughness in high weldability in the wire and flux for submerged arc welding of 780MPa steel or 960MPa high tensile strength steel. CONSTITUTION:The wire contains V, C, Si, Mn, Ni, Cr, Mo, N in an optimized quantity corresponding to 780MPa steel and 960MPa steel, further in the wire a carbon equiv. (Ceq) by the specific equation is of an optimized quantity corresponding to 780MPa steel and 960MPa steel. The bonded flux contains, in addition to V, SiO2, MgO, Al2O3, CaF2, CO2, Li, Si, one kind at least among Al, Mn, Mg, or one kind at least among MgF2, MnF2, or both in an optimized quantity.

Production of steel material for hydrogen induced cracking resistance

Abstract: PURPOSE:To obtain a steel material for hydrogen induced cracking resistance of a line pipe for sour and large heat input welding by restaining free oxygen content before deoxidation of the molten steel to a specific quantity and executing the stirring with inert gas and the standing in the specific times after adding Ca. CONSTITUTION:In the reducing method of the steel material for hydrogen induced cracking resistance by molten iron pretreatment, converter refining, ladle refining and continuous casting process, the carbon content at the end point in the molten steel in the converter is controlled so as to become =2 min by the inert gas and successivethe molten steel is stood for >=30 min in the ladle. By this method, even in the case of being a little desulfurized steel, A series inclusion (MnS) and B series inclusion (Ca-Al sulfated series inclusion cluster) causing to HAZ hydrogen cracking in the large heat input submerged arc welding is remarkably reduced, and the developing ratio of the HAZ cracking is remarkably reduced.

Welding method for making thick and large-diameter welded steel pipe

Abstract: PURPOSE:To suppress the degradation in bead shape in high-speed welding and degradation in rigidity so as to enable high-speed welding by combining a fused flux having a specific compsn. and multilayer multielectrode submerged arc welding and supplying DC current to the foremost electrode and AC current to the other succeeding electrodes. CONSTITUTION:The fused flux contg., by weight, 5 to 25% SiO2, 0.5 to 15% MnO, 5 to 25% CaO, 5 to 20% MnO, 2 to 20% Al2O3 2 to 10% TiO2, 1 to 5% BaO, 20 to 60% CaF2 and 0.3 to 1.5% B2O3 and satisfying (CaO+MgO)/SiO2=1.5 to 3.0 is used for welding of the first layer and the second layer of welding and the fused flux contg. 5 to 25% SiO2, 0.5 to 15% MnO, 5 to 25% CaO, 5 to 20% MnO, 2 to 20% Al2O3, 2 to 10% TiO2, 1 to 5% BaO, 20 to 60% CaF2 and 0 or <0.3% B2O3 and satisfying (CaO+MgO)/SiO2=1.5 to 3.0 is used for welding of the third and subsequent layers.