Operating Characteristics of the Submerged Arc Process

Transcription

1 Operating Characteristics of the Submerged rc Process Investigation resolves some of the speculation on how certain variables affect operating characteristics BY B. G. RENWICK ND B. M. PTCHETT BSTRCT. The influence of flux composition, wire diameter and current level on deposition rates, weld bead dimensions and flux consumption in submerged arc welding has been investigated. Four flux types representing a wide range of composition and basicity were used: these were an acid manganese silicate flux; a high alumina neutral; a highly basic flux; and a basic flux containing large quantities of carbonates. Direct current electrode positive polarity was used with electrodes of, and mm diam, over a total current range of Penetration and bead reinforcement increased with current and decreased as wire diameter increased at constant current, and were not affected by flux composition. Deposition rates, while increasing with current, decreased with wire diameter and were also unaffected by flux composition. Bead width and flux consumption initially increased with current, reached a maximum, and then tended to decrease. The maxima occurred in both bead width and flux consumption at a characteristic current for each wire diameter, which was similar for all flux compositions. The average bead width also decreased by an additional amount when the carbonate flux was used. The process behavior is explained in terms of the plasma jet phenomenon occurring in an atmosphere, within the arc cavity, having dissociable gas characteristics. This causes an increase in heat transfer toward the plate and a consequent B. G. RENWICK is Director, North East Industrial Supplies Pty. Ltd., Victoria, ustralia. B. M. PTCHETT is Senior Research Otticer, Cranfield Institute of Technology. Bedford MK43 OL, England. decrease in heat transfer to the flux burden for slag melting as current levels rise. The transition current is similar to those found in C0 2 atmospheres for all fluxes, and the arc characteristics of non-carbonate fluxes are likely controlled by nitrogen and oxygen from the atmosphere, and possibly oxygen from flux oxide decomposition. Endothermic carbonate decomposition has no effect on electrically dominated process characteristics such as electrode melting rates and penetration, but heat extraction from the arc cavity adjacent to the slag wall is responsible for the observed decrease in bead width in comparison to the other fluxes. Flux consumption generally followed bulk density with the exception of the highly basic flux, which had a lower consumption than predicted by bulk density considerations. This behavior was associated with a smaller slag bead size. s a result, the apparently more expensive basic flux was in.fact the cheapest flux to use per length of weld deposited. Introduction The majority of published work on the submerged arc process has been concerned with process technology and metallurgy rather than process fundamentals, due in part to the difficulties in visually assessing process features and in part to the complexity of flux formulations. In fact, explicit data on flux chemistry have been available only in very recent times. Flux composition is known to influence the metallurgical properties of deposited weld metals, and some effect on process variables such as electrode melting rates, bead dimensions and thermal efficiency has been suspected (but not conclusively proved) for a considerable period. The primary process variables, in order of importance, are (Ref. 1): 1. Current: polarity and magnitude 2. Voltage 3. Speed 4. Electrode diameter. Stickout 6. Flux composition 7. Width and depth of flux layer The process effects of some of these variables are clearly established, while others are still obscure, and the interaction of several at once can be extremely complicated. Current, voltage and welding speed are the most important variables. Current type, polarity and magnitude have generally agreed effects on electrode melting rates, weld bead dimensions and flux consumption. Direct current electrode negative polarity produces the highest melting rates; dc positive polarity the lowest, with ac coming between the other two (Refs. 1-4). Increases in current level for any polarity increase electrode melting rates, usually as a linear function of current (Refs. 3,4), but occasionally investigators plot nonlinear relationships (Refs. 2,3). There are many reports which comment on the effect of current on bead dimensions (Refs.3-7). Penetration and reinforcement increase with increasing current in all cases, but in some work bead width continually increases with current (Ref. 6), while other investigators have found that bead width reaches a maximum and then remains constant or decreases (Ref. 3). Flux consumption generally increases with current (Refs. 2,4) but can reach a maximum and then decrease (Ref. 3). The same group of investigators found that voltage increases reduce WELDING RESERCH SUPPLEMENT! 69-S

2 Table 1 Chemical Composition of Welding Consumables (wt. %) Metal C Mn Si S BS4360 plate mm wire mm wire mm wire Table 2 Composition (wt %) and Properties of Four Types of Welding Flux Constituents CaO/MgO CaCO ( 3 a ' SiO; MnO l CaF 2 Ti0 2 Zr0 2 Other(b) Basicity Bulk density gm/cm 3 cid lumina (a) Carbonates include up to % each of Mg. Sr. Ba. K and LI carbonates (b) Mostly Binder Silicates. electrode melting rates, especially at high currents, while flux consumption is increased. Both phenomena are accounted for by an increase in arc length, which reduces l 2 R resistance preheating of the electrode stickout and increases the arc cavity size. The effect of voltage on bead dimensions is not entirely agreed. One investigation (Ref. 6) found that voltage increases increase bead width while maintaining a constant reinforcement, while another (Ref. 3) found that bead width increased while reinforcement decreased. No comprehensive fundamental explanation of these phenomena has been put forward to account for the changes in process parameters, particularly bead dimension variations. Welding speed has no detectable effect on electrode melting rates (Ref. 7), and while the effect of speed on bead dimensions, especially penetration, is fairly complex, it is accounted for by the decrease in heat input as a function of voltage, current and speed. Later work (Ref. 6) has shown that increases in speed reduce penetration, bead width and reinforcement when current and voltage are constant, and has confirmed that electrode melting rates are unaffected. Data on the less important process variables are more scarce, and in some cases are almost entirely absent. Decreases in electrode size (increases in current density) and increases in electrode stickout at a constant current increase the electrode melting rate in both submerged arc and open arc processes (Refs. 2-). Carbonate Basic Penetration decreases with an increase in electrode diameter at constant current (Ref. ). However, there has been little work done on the effect of an increase in electrode diameter on overall process performance, especially in the presence of a variety of flux compositions. Flux composition and the width and depth of the flux layer are the two items considered to be of least importance, and are also the two variables with the least amount of published data available. No references could be found which give reliable information regarding the effects of the depth and width of the flux layer, and most of the information on flux composition effects is based on speculation. Several authors (Refs. 2,3,7) propose that flux composition can affect electrode melting rates and bead dimensions such as penetration, but no systematic investigation could be found which determined how commercial flux composition influences process behavior, and any differences in melting rates observed are often marginal. The only definite alteration in melting rates and bead dimensions attributed to flux composition was found in an investigation using very simple fluxes containing one or two chemical compounds (Ref. 8), which also gave wide variations in arc stability, and the effects are not therefore directly comparable with those produced by the far more complicated compositions of commercial fluxes. The chemical complexity of commercial fluxes is simply a result of the large number of criteria which they must satisfy, e.g., arc stability, slag removal, bead surface finish, tolerance to rust and protection of the weld metal from the atmosphere. These criteria, and others such as melting temperature, place constraints on the amounts of chemical compounds which can be incorporated into a flux for welding any metal or alloy. Fluxes for welding steels are generally made from combinations of MnO, CaO, MgO, Si0 2, l 2 0 3, Ti0 2 and CaF 2 (Ref. 9). The only common concept used to distinguish among fluxes is that of basicity, developed from the historical concept in the steel industry of acid and basic refractory furnace linings. The formulas cannot predict any physical changes in process behavior due to flux composition, and they are at best a crude representation of the chemical behavior of fluxes. There are several formulas used to calculate basicity, all of which tend to give similar rankings. The concept is generally applied to assessing weld metal quality, particularly fracture toughness (within the general proposition that more basicity means better toughness). However, no systematic investigations of the effects of basicity on process behavior have been done, despite the fact that basicity is the only generally accepted flux classification method available. new type of flux using carbonates has been found to affect process behavior by reducing the total heat input in submerged arc welding. This is due to the endothermic decomposition of the carbonates to form oxides and C0 2 gas, which reduces heat input by up to 20% (Ref. 10), and influences Mn recovery and weld metal cooling rates in mild steel (Ref. 11). However, the location of the heat loss has not been isolated, and the effect on electrode melting rates and bead dimensions has not been investigated. Flux consumption is not known to be affected by chemical composition or basicity, but can be influenced by physical properties such as density and particle size (bulk density) (Refs. 12,13). The literature shows that the empirical relationships between the primary process variables (current, voltage, welding speed) are fairly well established although areas of doubt remain. However, the fundamental nature of their effects on arc physics is not clear, and this makes an overall assessment of process variables difficult. The effects of the minor variables such as flux composition are particularly vague, and their effect on electrode melting rates and bead dimensions has not been clearly established. The aim of this project is the 70-S I MRCH 1976

3 assessment of fundamental relationships in submerged arc welding from a consideration of flux composition, electrode size and current levels. The basic variable to be studied is flux composition, and its effect particularly on electrode and flux melting rates, and bead dimensions. The process has been simplified as much as possible by fixing variables of predictable effect such as welding speed, voltage and stickout, and using the least complicated electrical condition of industrial relevance, i.e., direct current, electrode positive polarity. Experimental Procedure Materials Mild steel, 38 mm thick, corresponding to BS 4360 grade 43 was chosen for the base metal, along with three standard submerged arc electrode wires of, and mm diam. The chemical compositions are listed in Table 1. Bead-on-plate test specimens 38 X X mm were flame cut from the single large plate, and degreased and hand ground before welding. Four fluxes of widely varying basicity were used, one of which contained a large proportion of carbonates. The chemical compositions are listed in Table 2. The fluxes covered the range of available commercial types: 1. fused acid manganese-silicate flux of basicity n agglomerated bauxite-based flux of basicity n agglomerated carbonatebased flux of basicity n agglomerated basic low-silica flux of basicity 3.0 Basicity was calculated using the following formula: Basicity = CaO f MgO + CaF 2 + K 2 Q + 1/2MnO Si /2(I Ti0 2 + Zr0 2 ) For the carbonate flux, the total carbonate content was substituted for the CaO and MgO. Equipment The weld runs were made with two power sources: a Hagglunds 1200 drooping characteristic transformer rectifier, which used an arc voltage control (variable wire feed speed) unit to regulate arc characteristics, and a Union Carbide 00 constant potential transformer rectifier unit, which had a self-correcting arc control (constant wire feed speed). No differences in process characteristics were noted between the two sources when used under identical conditions. The only special piece of equipment was an asbestos board box X 0 X 38 mm deep used to retain a constant volume of flux around the weld run. Fig. 1 Metal deposition rate vs current mm electrode Welding voltage was determined with an vometer which effectively damped out transients to give constant readings. The current for each run was recorded on an ultraviolet galvanometer recorder, which also had a timing device used to give welding times to within 0.1 s. Conditions The prime variables in this study were electrode wire diameter, current and flux composition. Other welding variables were fixed as follows: 1. Welding current type dc electrode positive 2. Welding voltage 30 V 3. Nozzle-to-plate distance 2 mm 4. Welding speed 0.41 m/min Weld runs of about 27 mm in length were made for all four fluxes using each wire diameter in the following current ranges: mm diam, - mm diam, - mm diam, Before and after welding, the electrode wire, fused and unfused flux were weighed on a 1 kg capacity balance to accurately assess electrode melting rates and flux consumption to within ± 2%. Slices 0 mm wide were cut from each sample plate, polished, and etched on both ends to assess depth of penetration, bead width and reinforcement. Results Metal deposition rates, penetration, bead width and reinforcement and flux consumption are shown in Figs as functions of welding current for each wire diameter and for all flux compositions. The metal deposition versus current results (Figs. 1-3) show that flux composition had no discernible effect on melting rates. For a given current, melting rates were equivalent for the and mm wires, but higher for the mm wires; this indicates that l 2 R heating is Fig. 2 Metal deposition rate vs current mm electrode CID GRDE 0 OP 170 OP l TT CRS '03' O0 Fig. 3 Metal deposition rate vs current mm electrode important only with the smallest wire for a stickout of 2 mm. The bead dimension results (Figs. 4-9) show that bead widths initially increased with current, then dropped or remained constant after reaching a maximum; on the other hand, reinforcement increased slightly up to the level of maximum bead width, and then increased at a greater rate with the mm wire (Fig. ). This effect was more pronounced on penetration, which increased very rapidly at currents above the bead width maximum (Fig. 4). The rate of increase was less noticeable with the larger wires (Figs. 6,8). Penetration dropped with increases in wire diameter at a given current level; for example, at the values for the, and mm wires were 7.0, 4. and 3.0 mm respectively (Figs. 4, 6, 8). Maximum bead widths and reinforcement values increased as electrode diameter increased (Figs.,7,9). The only measurable influence of WELDING RESERCH SUPPLEMENT! 71-s

4 flux composition on the weld bead dimensions was a decrease of 1-20% in bead width for the mm and mm electrode wires using the carbonate flux. Bead shapes produced for the range of variables investigated are summarized in Fig. 13. Flux consumption initially increased with current, reached a maximum at a characteristic current and then decreased for each of the three electrode diameters. Increasing the wire diameter at a given current increased flux consumption (Figs ). The acid flux exhibited the highest consumption rate in most cases, followed by the alumina flux, and carbonate flux. These results were consistent with the relative bulk density values listed in Table 2. However, the basic flux had the lowest consumption rate in nearly all cases, which is not consistent with its bulk density; this indicates that another factor is more important in its particular case. The result is that the basic flux, despite its higher initial cost per unit weight, is the cheapest flux to use on a cost per meter basis, as shown in Table 3. The current level at the point of maximum flux consumption and bead width and change in rates of increase of penetration and reinforcement was the same for a given wire diameter, ie., 30 for mm, 0 for mm, and 70 for mm; this suggests that a change in arc characteristics was responsible for all of the observed effects. Bead shape and surface appearance can only be assessed qualitatively, but there are practical implications of surface roughness and bead irregularities. The most distorted bead shapes and poorest surface quality were associated with the carbonate flux, followed by the basic, alumina and acid flux welds, in that order. The worst beads for all fluxes were associated with the largest wire ( mm) at high current levels. The carbonate flux produced clean, bright weld metal surfaces, while some discoloration (oxidation) was observed with the other fluxes. The carbonate slag was the most difficult to detach, especially for high current and/or large diameter electrodes, followed by the basic flux. The alumina and acid slags were self lifting, except at high current levels using the mm diam wire. The two difficult-to-remove slags, particularly the carbonate slag, contained large numbers of bubbles, as shown in Fig. 14. The associated weld metals produced with the and mm electrodes, especially at high current levels, contained gross porosity. Discussion In this project, previous work has been duplicated to some extent to confirm established trends, and additional process features have been investigated for a limited number of experimental variables chosen to isolate fundamental influences. The increase in deposition rates with current confirms the findings of several other workers, although Drayton (Ref. 3) commented that the relationship was nonlinear dc for electrode positive operation. However, the results obtained in this work and in Drayton's are virtually identical, and the linear relationship was confirmed to a confidence level of 9% by regression analysis. The most important fact to emerge from the present work is that flux composition has no effect on melting rates over a wide range of chemistry and basicity and a wide range of electrode diameters and current levels. Table 3 Comparison of Flux Costs CURRENT MPS Fig. 4 Penetration vs current electrode CID GRDE 0 OP 170 OP1TT CRB '0J' mm Flux type cid lumina Wire diam mm Nominal current, Wt. of flux fused/ mm, Cost of flux/gm, pence 0.02» rr.... II a a,,» Cost of flux/meter, pence BED WIDTH CID GRDE SO O O OP 170 fi OP1TT * CRB '03' REINFORCEMENT Fig. Bead width and reinforcement vs current mm electrode Basic Carbonate It II n,i,, ti a a s I MRCH 1976

5 This implies that electrode melting rates, excluding the influence of l 2 R heating, are primarily a function of total current and electrode characteristics, which are apparently unaffected by flux chemistry. In particular, endothermic carbonate decomposition, which has been shown to cause a decrease in total heat input of up to 20%, has no effect on electrode melting rates. The dependence on total current and anode characteristics alone is also consistent with the linear relationship between melting rate and current. The only experimental evidence of an alteration in electrode melting rates due to flux composition (Ref. 8) was connected with the use of oversimplified fluxes of dubious arc stabilizing capacity; and since all commercial fluxes are formulated to give adequate arc stability on electrode positive polarity, it is therefore reasonable to expect that a given current level will produce similar electrode melting rates, once it is realized that melting is a function of current and electrode physical characteristics. In this investigation, after the transition current was exceeded, penetration increased, bead width decreased and reinforcement increased at a greater rate than was evident below the transition current; the effects were most marked with the smallest diameter electrode, which provides a physical arc constriction. ll fluxes, including the high carbonate flux, produced the same changes in bead configuration at the same current level; thus the basic arc behavior is similar in all cases. The behavior pattern established by the changes in bead dimensions with current indicates the development of a plasma jet as the current increases beyond a certain level for each wire diameter. The plasma jet concentrates the thermal energy in the arc discharge, and increases the arc pressure. This forces liquid metal away from the central pool area, so producing a marked change in penetration, and a narrowing of the weld bead width. It also, for a reasonably constant arc length and voltage, brings the electrode tip closer to the plate surface, thus reducing the size of the arc cavity moving through the flux; this in turn causes a drop in flux consumption. The changes are shown diagrammatically in Fig. 1. The increase in reinforcement is connected with the reduction in bead width. Since deposition rates constantly increase with current, reinforcement must rise sharply when the bead width remains constant or decreases, in order to accommodate the extra mass of deposited metal. The additional decrease in bead width in the carbonate flux is due to ,/ '71 O O OP 170 a OP41T1 * * CRB '03' Fig. 6 Penetration vs current mm electrode REINFORCEMENT Fig. 7 Bead width and reinforcement vs current mm electrode the interaction of carbonate decomposition and the dissociable gas arc. The present work shows that bead width is the only process parameter to be measurably affected by carbonate decomposition, primarily with the larger and mm electrodes. The proposed explanation is that the heat extraction is concentrated in the vicinity of the slag wall, which causes a thermal constriction on the outer surface of the arc discharge, and a loss in melting capacity at the periphery of the weld pool. The endothermic reaction (where Me denotes metal) MeC0 3 + heat-> MeO + C0 2 is the main source of the thermal constriction. However, it is possible that the breakdown of C0 2 to form CO and O is a contributory factor. The dissociation core of the arc requires this breakdown; therefore it must occur as C0 2 passes through the outer arc discharge toward the high temperature core from the vicinity of the inner slag wall. The process envisaged is shown schematically in Fig. 16. Previous work on carbonate fluxes has proposed that this latter thermal loss is regained within the weld region and does not contribute to overall 0 ^ *»&s 0 yb tjt/ ys >v f/ KEV &/ # /y%, ^ ' O O 0P 170 d 0P41TT * CRS '03 1 HM- ± ± ± -*- ± -j- - Fig. 8 Penetration vs current mm electrode.mh CID GRDE 0 O O OP 170 L 6 OP41TT * 4 CRB 03' REINFORCEMENT Fig. 9 Bead width and reinforcement vs current mm electrode thermal losses (Ref. 10). The present work shows where and how the heat is regained: the bright, unoxidized bead surfaces of welds made with the carbonate flux show that the surface oxides on the solidifying weld bead are removed via the reaction CO + MeO -* C0 2 + Me + heat. The bead width reduction was not noticeable with the mm electrode, for two reasons: the small electrode diameter produced a physical restriction in arc anode size, which encouraged a plasma jet effect and a stiffer arc less susceptible to thermal constriction at relatively low currents; and flux consumption was lower for a given current, thus reducing the amount of heat removed by carbonate decomposition. The weld beads were also relatively small, and would be more severely quenched by the mass of the plate, thus minimizing any thermal effects of the flux on the solidification characteristics. WELDING RESERCH SUPPLEMENT! 73-s

6 The increase in flux consumption with wire diameter for a given current is explained by arc cavity size, especially in the vicinity of the electrode tip. larger electrical anode area will increase the size of the arc cavity which passes through the flux burden, thus melting more flux. The same phenomenon accounts for the more gradual changes in flux consumption, penetration and bead width with current as electrode diameter increases the larger anode size causes less physical constriction on the arc. thus lessening the abrupt- Table 4 Transition Currents for Mild Steel Electrodes Electrode diam. mm io Shielding medium r-1%0 2 C0 2 Sub. arc r-1%0 2 Sub. arc Sub. arc Transition current Fig. 10 Flux consumption vs current mm electrode / / l! / / 4 / KEV o O OP 170 QP41TT CRB '03' Fig Flux consumption vs current mm electrode ness of the plasma jet formation at higher currents. This reasoning also indicates that the submerged arc process is more efficient with relatively small diameter electrode wires used at relatively high currents, since flux consumption is minimized as metal deposition rates and weld penetration are increased. Flux consumption is the only process variable which apparently demonstrated any dependence on flux chemistry, and that was seen in the anomalous behavior of the basic flux, which over a wide current range had a lower consumption rate than its bulk density would dictate. The basic slag beads were always smaller than the beads produced by the other fluxes, but the reason or reasons for this can only be the subject of speculation at this stage. The thermal conductivity of the slag cavity wall is one property which may be important The evolution of gases during flux melting and slag solidification affects bead surface appearance and consequently slag detachment to a significant degree. Slag removal via selflifting properties is generally associated with a phase change during cooling which gives a substantially different thermal contraction characteristic in comparison with the weld metal, and to a lesser extent with a lack of chemical reaction between the slag and metal surfaces which may form a physical bond, especially with high alloy levels. Problems in slag detachment in this investigation were associated with the carbonate flux, and to a lesser extent with the basic flux, especially at high currents, and with the larger wire diameters. Both fluxes formed slag containing quantities of gas bubbles, and associated uneven bead surfaces. Fig. The source of gas in the basic flux CURRENT MPS CID GRDE 0 O OP 170 0P1TT CRB '03' 12 Flux consumption vs current mm electrode is not clear, but the net effect is similar to, if more limited in extent than, the C0 2 evolution from the carbonate flux. Gas bubbles in the solidifying slag interfere with the surface formation of the solidifying weld metal, producing a bead surface which hampers slag removal, as shown in Fig. 17. The problem is more acute at higher currents, due to the larger quantities of slag melted and also possibly to arc instabilities during metal transfer causing sudden movements of the weld pool. The problem with larger electrode diameters is probably aggravated by the progressively smaller quantities of deoxidants used, particularly Mn and Si, which would increase the quantities of CO evolved during solidification, as the observed weld bead porosity confirmed. The importance of basic arc physics in the process behavior of submerged arc welding is shown clearly in the results. The carbonate flux must produce an arc atmosphere dominated by C0 2, and a comparison of transition currents for mild steel electrodes in inert and dissociable gases using electrode positive polarity with those obtained in this work shows that the submerged arc transition currents are consistent with those found in C0 2 arc welding. Transition currents in dissociable gases are always higher than those found in argon, because of the greater energy required to dissociate and ionize molecular gases. The dissociable gases most likely to be involved in the arc cavity of noncarbonate fluxes are nitrogen (from the atmosphere) and oxygen (from the atmosphere and possibly from dissociated oxides boiled away from the flux). Submerged arcs can therefore be treated as dissociable arcs similar to C0 2 arcs for purposes of comparison with arc processes not involving fluxes, where fundamental behavior is more easily observed. Flux chemistry and basicity, at least for four widely varying compositions, have no apparent effect on electrically dominated parameters such as penetration and electrode melting rates. Chemistry does have an effect on parameters relatively free from electrical domination, such as bead width and flux consumption, especially with fluxes containing compounds which have an effect on heat transfer. Welding conditions pushing the extreme limits of voltage, current and welding speed have to be investigated to assess the combined effect of flux chemistry and physical properties, e.g.. bead formation at high power, high speed conditions where maximum welding efficiency is sought. It is hoped that concepts put forward in this paper will supply a basic framework which can be ex- 74-s! MRCH 1976

7 FLUX CID LUMIN BSIC CRBONTE GRDE 0 GRDE OP 170 GRDE OP 41 TT GRDE 03 WIRE Dia.-mm. BED SHPE. <> o o- 16 -o>- -<G>- 16 <? CURRENT MPS. WIRE Dia.-mm. BED SHPE. o ~v~ \7- -<z>- ^- ~X7~ -<z?- ~ < 0-1>- CURRENT MPS. WIRE Dia.-mm. BED SHPE CURRENT MPS <=>- 64 -v? <=> Q v <?- 64 Q F/'g. 13 Effect of wire diameter and current levels on bead cross-sections tended to assist in the fundamental analysis of such investigations. Conclusions 1. On electrode positive polarity, electrode melting rates increase linearly with current and are unaffected by flux composition over a wide range of basicity and carbonate content. Electrode melting is therefore a function of current and electrode physics, not of flux composition. 2. Submerged arcs under both carbonate and non-carbonate fluxes have characteristics associated with C0 2 arcs, including similar transition currents. bove the characteristic transition currents for each wire diameter, a plasma jet is formed, which increases arc forces and the thermal pumping capacity of the arc. The results are increases in penetration and reinforcement, and decreases in bead width and flux consumption above the critical current. 3. The submerged arc process is most efficient when operated above the transition current, and it is therefore preferable to use relatively small diameter wires for a given stickout and current level. 4. Carbonate fluxes decrease bead width in comparison with non-carbonate fluxes, by the extraction of heat from the arc cavity near the slag wall-base metal interface, due to endothermic carbonate decomposition.. Flux consumption followed bulk density for the fluxes used, except for the basic flux. This may be due to its Gr0 OP 170 Gr03 Fig. 14 Slag bead profiles mm electrode, ELECTRODE SLG WLL. RC BSE CVITY PLTE Fig. 1 rc forces and bead formation as influenced by current level, (a) pretransition arc discharge melting; (b) post transition plasma jet operation 0P41TT 1 RC CVITY HET EXTRCTION FROM SLG WLL (CO; -f CO -I-0) 2 SLG WLL 3 FLUX DECOMPOSITION HET EXTRCTION FROM SLG(CaCOj -»-Ca0 + C0:,) 4 FLUX BURDEN MOLTEN WELD POOL 6 ELECTRODE WIRE Fig. 16 End view schematic diagram of heat extraction processes during carbonate flux decomposition WELDING RESERCH SUPPLEMENT! 7-s

8 1. FLUX BURDEN. 2. SOLIDIFIED SLG. 3. PSSGE OF CO a GS THROUGH MOLTEN SLG. 4. GS BUBBLES IN MOLTEN ND SOLIDIFIED SLG.. WELD BED SHOWING SURFCE ROUGHNESS CUSED BY GS BUBBLES. 6. BSE PLTE. 7. ELECTRODE WIRE. 8. RC CVITY. 9. MOLTEN WELD POOL. 10. MOLTEN SLG. Fig. 17 Side view schematic diagram of the effect ol gas evolution on bead shape thermal transfer characteristics when melted. The net result is that flux costs per meter of weld are lower with the basic flux, which is not the most inexpensive flux to purchase. 6. Weld bead appearance deteriorated at high current levels and when C0 2 evolution was high due to carbonate decomposition and/or gas evolution in the metal caused by insufficient deoxidants in the electrode wire. Gas bubbles caused surface roughness in solidifying weld metal, which made slag removal difficult with the carbonate flux, and to a lesser degree with the basic flux. cknowledgments The authors wish to thank Mr. K.. Nelson for his assistance with the experimental work, and Dr. T. Boniszewski of Metrode Products for supplying the carbonate flux. References 1. merican Welding Society Welding Handbook, Chapter 24, Section II, Sixth Edition, Robinson. M. H., Observations on Electrode Melting Rates During Submerged rc Welding, Welding Journal, Vol. 40 (11), Nov. 1961, Res. Suppl., p 03-S. 3. Drayton, P.., n Examination of the Influence of Process Parameters on Submerged rc Welding, Welding Research International, Vol. 2 (2), 1972, p Jackson, C. E., The Science of rc Welding, Part II Consumable Electrode Welding rc, Welding Journal, Vol. 39 (), May 1960, Res. Suppl., p 177-s.. Jackson, C. E., The Science of rc Welding, Part III What the rc Does, Welding Journal, Vol. 39 (6), June 1960, Res. Suppl., p 22-s. 6. pps, R. L., Gourd, L. M. and Nelson, K.., The Effect of Welding Variables upon Bead Shape and Size in Submerged rc Welding, Welding & Metal Fabrication, Vol. 31 (10), 1963, p Jackson, C. E. and Shrubsall,. E., Control of Penetration and Melting Ratio with Welding Technique, Welding Journal, Vol. (4), pril 193, Res. Suppl., p 172-s. 8. Patchett, B. M., Some Influences of Slag Composition on Heat Transfer and rc Stability, Welding Journal, Vol. 3 (), May 1974, Res. Suppl., p 203-s. 9. Palm, J. H.. How Fluxes Determine the Properties of Submerged rc Welds, Welding Journal, Vol. 1 (7), July 1972, Res. Suppl., p 38-s. 10. Patchett, B. M., Demos, G.. and pps, R. L., The Influence of Flux Composition and Welding Parameters on Heat Distribution in Submerged rc Welding, Welding Research International, Vol. 4 (2), 1974, p Tuliani, S. S., Boniszewski, T. and Eaton, N. F., Carbonate Fluxes for Submerged rc Welding of Mild Steel, Welding & Metal Fabrication, Vol. 40 (7), 1972, p Butler, C.. and Jackson, C. E Submerged rc Welding Characteristics of the CaO-Ti0 2-Si0 2 System, Welding Journal. Vol. 46 (10), Oct. 1967, Res. Suppl.. p 448-s. 13. Tagaki, O., Nishi, S. and Suzuki, K., On Notch Toughness of Deposited Metal in utomatic rc Welding (Report 2), Journal of the Japanese Welding Society, Vol. 31 (10) (27), 1962, p Smith..., C0 2 Welding of Steel, The Welding Institute, Third Edition, Discussion The Welding Journal invites critical discussions by peers on technical matters appearing in the Welding Research Supplement. copy of the discussion will be mailed to the author for reply. Both discussions and reply will be printed together in these pages. Where conclusions and findings vary among different researchers, the reader will benefit from the information. 76-s I MRCH 1976