Operating Characteristics of the Submerged Arc Process

Investigation resolves some of the speculation on how certain variables affect operating characteristics

BY B. G. RENWICK AND B. M. PATCHETT

ABSTRACT. The influence of flux decrease in heat transfer to the flux suspected (but not conclusively composition, wire diameter and cur­ burden for slag melting as current proved) for a considerable period. rent level on deposition rates, weld levels rise. The transition current is The primary process variables, in bead dimensions and flux consump­ similar to those found in C02 atmo­ order of importance, are (Ref. 1): tion in submerged arc welding has spheres for all fluxes, and the arc 1. Current: polarity and magnitude been investigated. Four flux types characteristics of non-carbonate 2. Voltage representing a wide range of com­ fluxes are likely controlled by nitro­ 3. Speed position and basicity were used: gen and oxygen from the atmosphere, 4. Electrode diameter these were an acid manganese sili­ and possibly oxygen from flux oxide 5. Stickout cate flux; a high alumina "neutral"; a decomposition. Endothermic carbon­ 6. Flux composition highly basic flux; and a basic flux con­ ate decomposition has no effect on 7. Width and depth of flux layer taining large quantities of carbon­ electrically dominated process The process effects of some of these ates. Direct current electrode posi­ characteristics such as electrode variables are clearly established, tive polarity was used with electrodes melting rates and penetration, but while others are still obscure, and the of 1.6, 3.2 and 6.4 mm diam, over a heat extraction from the arc cavity interaction of several at once can be total current range of 150-1000 A. adjacent to the slag wall is re­ extremely complicated. Current, volt­ Penetration and bead reinforce­ sponsible for the observed decrease age and welding speed are the most ment increased with current and de­ in bead width in comparison to the important variables. creased as wire diameter increased at other fluxes. Current type, polarity and magni­ constant current, and were not af­ Flux consumption generally fol­ tude have generally agreed effects on fected by flux composition. Deposi­ lowed bulk density with the exception electrode melting rates, weld bead tion rates, while increasing with cur­ of the highly basic flux, which had a dimensions and flux consumption. Di­ rent, decreased with wire diameter lower consumption than predicted by rect current electrode negative polar­ and were also unaffected by flux com­ bulk density considerations. This be­ ity produces the highest melting rates; position. Bead width and flux con­ havior was associated with a smaller dc positive polarity the lowest, with ac sumption initially increased with cur­ slag bead size. As a result, the ap­ coming between the other two (Refs. rent, reached a maximum, and then parently more expensive basic flux 1-4). Increases in current level for any tended to decrease. The maxima oc­ was in.fact the cheapest flux to use polarity increase electrode melting curred in both bead width and flux per length of weld deposited. rates, usually as a linear function of consumption at a characteristic cur­ current (Refs. 3,4), but occasionally rent for each wire diameter, which investigators plot nonlinear relation­ was similar for all flux compositions. Introduction ships (Refs. 2,3). The average bead width also de­ The majority of published work on There are many reports which com­ creased by an additional amount the submerged arc process has been ment on the effect of current on bead when the carbonate flux was used. concerned with process technology dimensions (Refs.3-7). Penetration The process behavior is explained and metallurgy rather than process and reinforcement increase with in­ in terms of the plasma jet phe­ fundamentals, due in part to the dif­ creasing current in all cases, but in nomenon occurring in an atmo­ ficulties in visually assessing process some work bead width continually in­ sphere, within the arc cavity, having features and in part to the complexity creases with current (Ref. 6), while dissociable gas characteristics. This of flux formulations. In fact, explicit other investigators have found that causes an increase in heat transfer data on flux chemistry have been bead width reaches a maximum and toward the plate and a consequent available only in very recent times. then remains constant or decreases Flux composition is known to in­ (Ref. 3). Flux consumption generally fluence the metallurgical properties of increases with current (Refs. 2,4) but B. G. RENWICK is Director, North East In­ deposited weld metals, and some ef­ can reach a maximum and then de­ dustrial Supplies Pty. Ltd., Victoria, Aus­ tralia. B. M. PATCHETT is Senior Re­ fect on process variables such as crease (Ref. 3). search Otticer, Cranfield Institute of Tech­ electrode melting rates, bead dimen­ The same group of investigators nology. Bedford MK43 OAL, England. sions and thermal efficiency has been found that voltage increases reduce

WELDING RESEARCH SUPPLEMENT! 69-S must satisfy, e.g., arc stability, slag re­ Table 1 — Chemical Composition of Welding Consumables (wt. %) moval, bead surface finish, tolerance to rust and protection of the weld Metal C Mn Si S metal from the atmosphere. These BS4360 plate 0.22 1.04 — 0.032 0.014 criteria, and others such as melting 1.6 mm wire 0.11 1.64 0.77 0.012 0.026 temperature, place constraints on the 3.2 mm wire 0.09 1.20 0.09 0.007 0.021 amounts of chemical compounds 6.4 mm wire 0.06 0.42 0.03 0.026 0.025 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, Table 2 — Composition (wt %) and Properties of Four Types of Welding Flux MgO, Si02, Al203, Ti02 and CaF2 (Ref. 9). The only common concept used to distinguish among fluxes is that of Constituents Acid Alumina Carbonate Basic basicity, developed from the his­ CaO/MgO — 10 34 torical concept in the steel industry of ( a CaCO 3 ' — — 46 — "acid" and "basic" refractory furnace SiO; 40 5 5 8 linings. MnO 50 15 — — Al203 — 50 — 22 The formulas cannot predict any CaF2 5 15 10 30 physical changes in process be­ Ti02 — — 15 — havior due to flux composition, and 20 Zr02 — — — they are at best a crude representa­ Other(b) 5 5 5 6 tion of the chemical behavior of Basicity 0.75 1.15 2.7 3.0 fluxes. There are several formulas Bulk density 1.83 1.18 1.14 1.58 used to calculate basicity, all of which gm/cm3 tend to give similar rankings. The concept is generally applied to as­ sessing weld metal quality, particular­ (a) Carbonates include up to 5% each of Mg. Sr. Ba. K and LI carbonates (b) Mostly Binder Silicates. ly fracture toughness (within the gen­ eral proposition that more basicity means better toughness). However, no systematic investigations of the ef­ electrode melting rates, especially at Penetration decreases with an in­ fects of basicity on process behavior high currents, while flux consump­ crease in electrode diameter at con­ have been done, despite the fact that tion is increased. Both phenomena are stant current (Ref. 5). However, there basicity is the only generally ac­ accounted for by an increase in arc has been little work done on the ef­ 2 cepted flux classification method length, which reduces l R resistance fect of an increase in electrode diam­ available. preheating of the electrode stickout eter on overall process performance, and increases the arc cavity size. The especially in the presence of a variety A new type of flux using carbonates effect of voltage on bead dimensions of flux compositions. has been found to affect process be­ is not entirely agreed. One investiga­ Flux composition and the width and havior by reducing the total heat in­ tion (Ref. 6) found that voltage in­ depth of the flux layer are the two put in submerged arc welding. This is creases increase bead width while items considered to be of least impor­ due to the endothermic decomposi­ maintaining a constant reinforce­ tance, and are also the two variables tion of the carbonates to form oxides ment, while another (Ref. 3) found that with the least amount of published and C02 gas, which reduces heat in­ bead width increased while reinforce­ data available. No references could put by up to 20% (Ref. 10), and in­ ment decreased. No comprehensive be found which give reliable informa­ fluences Mn recovery and weld metal fundamental explanation of these tion regarding the effects of the depth cooling rates in mild steel (Ref. 11). phenomena has been put forward to and width of the flux layer, and most However, the location of the heat loss account for the changes in process of the information on flux composition has not been isolated, and the effect parameters, particularly bead dimen­ effects is based on speculation. on electrode melting rates and bead dimensions has not been in­ sion variations. Several authors (Refs. 2,3,7) pro­ vestigated. Welding speed has no detectable pose that flux composition can af­ effect on electrode melting rates (Ref. fect electrode melting rates and bead Flux consumption is not known to 7), and while the effect of speed on dimensions such as penetration, but be affected by chemical composition bead dimensions, especially penetra­ no systematic investigation could be or basicity, but can be influenced by tion, is fairly complex, it is accounted found which determined how com­ physical properties such as density for by the decrease in heat input as a mercial flux composition influences and particle size (bulk density) (Refs. function of voltage, current and process behavior, and any differ­ 12,13). speed. Later work (Ref. 6) has shown ences in melting rates observed are The literature shows that the empir­ that increases in speed reduce often marginal. The only definite alter­ ical relationships between the primary penetration, bead width and rein­ ation in melting rates and bead di­ process variables (current, voltage, forcement when current and voltage mensions attributed to flux composi­ welding speed) are fairly well estab­ are constant, and has confirmed that tion was found in an investigation lished although areas of doubt re­ electrode melting rates are un­ using very simple fluxes containing main. However, the fundamental affected. one or two chemical compounds nature of their effects on arc physics Data on the less important process (Ref. 8), which also gave wide vari­ is not clear, and this makes an overall variables are more scarce, and in ations in arc stability, and the effects assessment of process variables dif­ some cases are almost entirely ab­ are not therefore directly comparable ficult. The effects of the minor vari­ sent. Decreases in electrode size (in­ with those produced by the far more ables such as flux composition are creases in current density) and in­ complicated compositions of com­ particularly vague, and their effect on creases in electrode stickout at a con­ mercial fluxes. electrode melting rates and bead stant current increase the electrode The chemical complexity of com­ dimensions has not been clearly melting rate in both submerged arc mercial fluxes is simply a result of the established. and open arc processes (Refs. 2-5). large number of criteria which they The aim of this project is the

70-S I MARCH 1976 assessment of fundamental relation­ ships 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 par­ ticularly on electrode and flux melt­ ing 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.

Fig. 1 — Metal deposition rate vs current Fig. 2 — Metal deposition rate vs current Experimental Procedure — 1.6 mm electrode — 3.2 mm electrode Materials

Mild steel, 38 mm thick, cor­ Welding voltage was determined responding to BS 4360 grade 43A was with an Avometer which effectively chosen for the base metal, along with damped out transients to give con­ three standard submerged arc elec­ stant readings. The current for each trode wires of 1.6, 3.2 and 6.4 mm run was recorded on an ultraviolet diam. The chemical compositions are galvanometer recorder, which also listed in Table 1. Bead-on-plate test had a timing device used to give weld­ specimens 38 X 300 X 325 mm were ing times to within 0.1 s. flame cut from the single large plate, and degreased and hand ground be­ Conditions fore welding. Four fluxes of widely varying basicity were used, one of The prime variables in this study which contained a large proportion of were electrode wire diameter, cur­ carbonates. The chemical composi­ rent and flux composition. Other tions are listed in Table 2. The fluxes welding variables were fixed as covered the range of available com­ follows: mercial types: 1. Welding current type — dc elec­ 1. A fused acid manganese-silicate trode positive flux of basicity 0.75 2. Welding voltage — 30 V ACID GRADE 50 OP 170 3. Nozzle-to-plate distance — 25 mm OP Al TT 2. An agglomerated bauxite-based CARS '503' flux of basicity 1.15 4. Welding speed — 0.41 m/min 3. An agglomerated carbonate- Weld runs of about 275 mm in length 900 10O0 based flux of basicity 2.7 were made for all four fluxes using 4. An agglomerated basic low-silica each wire diameter in the following Fig. 3 — Metal deposition rate vs current — 6.4 mm electrode flux of basicity 3.0 current ranges: Basicity was calculated using the 1.6 mm diam, 150-400 A following formula: 3.2 mm diam, 300-600 A 6.4 mm diam, 400-1000 A important only with the smallest wire Basicity = Before and after welding, the elec­ CaO f MgO + CaF + K Q + 1/2MnO for a stickout of 25 mm. 2 2 trode wire, fused and unfused flux The bead dimension results (Figs. Si02 + 1/2(AI203+ Ti02 + Zr02) were weighed on a 1 kg capacity 4-9) show that bead widths initially in­ For the carbonate flux, the total car­ balance to accurately assess elec­ creased with current, then dropped or bonate content was substituted for trode melting rates and flux consump­ remained constant after reaching a the CaO and MgO. tion to within ± 2%. Slices 50 mm maximum; on the other hand, rein­ wide were cut from each sample forcement increased slightly up to the Equipment plate, polished, and etched on both level of maximum bead width, and ends to assess depth of penetration, then increased at a greater rate with The weld runs were made with two bead width and reinforcement. power sources: a Hagglunds 1200 A the 1.6 mm wire (Fig. 5). drooping characteristic transformer Results This effect was more pronounced rectifier, which used an arc voltage on penetration, which increased very control (variable wire feed speed) unit Metal deposition rates, penetra­ rapidly at currents above the bead to regulate arc characteristics, and a tion, bead width and reinforcement width maximum (Fig. 4). The rate of Union Carbide 500 A constant poten­ and flux consumption are shown in increase was less noticeable with the tial transformer rectifier unit, which Figs. 1-12 as functions of welding cur­ larger wires (Figs. 6,8). Penetration had a self-correcting arc control (con­ rent for each wire diameter and for all dropped with increases in wire diam­ stant wire feed speed). No differ­ flux compositions. The metal deposi­ eter at a given current level; for ex­ ences in process characteristics were tion versus current results (Figs. 1-3) ample, at 400 A the values for the 1.6, noted between the two sources when show that flux composition had no 3.2 and 6.4 mm wires were 7.0, 4.5 used under identical conditions. The discernible effect on melting rates. and 3.0 mm respectively (Figs. 4, 6, 8). only special piece of equipment was For a given current, melting rates Maximum bead widths and reinforce­ an asbestos board box 300 X 50 X 38 were equivalent for the 6.4 and 3.2 ment values increased as electrode mm deep used to retain a constant mm wires, but higher for the 1.6 mm diameter increased (Figs. 5,7,9). volume of flux around the weld run. wires; this indicates that l2R heating is The only measurable influence of

WELDING RESEARCH SUPPLEMENT! 71-s flux composition on the weld bead crease of penetration and reinforce­ tained large numbers of bubbles, as dimensions was a decrease of 15- ment was the same for a given wire shown in Fig. 14. The associated weld 20% in bead width for the 3.2 mm and diameter, ie., 350 A for 1.6 mm, 550 A metals produced with the 3.2 and 6.4 6.4 mm electrode wires using the car­ for 3.2 mm, and 750 A for 6.4 mm; this mm electrodes, especially at high cur­ bonate flux. Bead shapes produced suggests that a change in arc rent levels, contained gross porosity. for the range of variables investigated characteristics was responsible for all are summarized in Fig. 13. of the observed effects. Discussion Flux consumption initially in­ Bead shape and surface appear­ creased with current, reached a max­ ance can only be assessed qualita­ In this project, previous work has imum at a characteristic current and tively, but there are practical implica­ been duplicated to some extent to then decreased for each of the three tions of surface roughness and bead confirm established trends, and addi­ electrode diameters. Increasing the irregularities. The most distorted tional process features have been in­ wire diameter at a given current in­ bead shapes and poorest surface vestigated for a limited number of ex­ creased flux consumption (Figs. 10- quality were associated with the car­ perimental variables chosen to isolate 12). The acid flux exhibited the high­ bonate flux, followed by the basic, fundamental influences. est consumption rate in most cases, alumina and acid flux welds, in that The increase in deposition rates followed by the alumina flux, and car­ order. The worst beads for all fluxes with current confirms the findings of bonate flux. These results were con­ were associated with the largest wire several other workers, although Dray- sistent with the relative bulk density (6.4 mm) at high current levels. The ton (Ref. 3) commented that the rela­ values listed in Table 2. However, the carbonate flux produced clean, bright tionship was nonlinear dc for elec­ basic flux had the lowest consump­ weld metal surfaces, while some dis­ trode positive operation. However, the tion rate in nearly all cases, which is coloration (oxidation) was observed results obtained in this work and in not consistent with its bulk density; with the other fluxes. Drayton's are virtually identical, and this indicates that another factor is The carbonate slag was the most the linear relationship was confirmed more important in its particular case. difficult to detach, especially for high to a confidence level of 95% by The result is that the basic flux, de­ current and/or large diameter elec­ regression analysis. spite its higher initial cost per unit trodes, followed by the basic flux. The The most important fact to emerge weight, is the cheapest flux to use on alumina and acid slags were "self lift­ from the present work is that flux a cost per meter basis, as shown in ing," except at high current levels composition has no effect on melting Table 3. The current level at the point using the 6.4 mm diam wire. The rates over a wide range of chemistry of maximum flux consumption and two "difficult-to-remove" slags, par­ and basicity and a wide range of elec­ bead width and change in rates of in­ ticularly the carbonate slag, con­ trode diameters and current levels.

Table 3 — Comparison of Flux Costs

Wire Nominal Wt. of flux Cost of Cost of Flux diam current, fused/250 mm, flux/gm, flux/meter, type mm A 9 pence pence Acid 1.6 150 50.6 0.025 5.08 250 67.7 » 6.76 400 49.0 rr 4.88 3.2 300 65.5 .. 6.52 450 92.0 .. 9.20 600 83.0 „ 8.20 6.4 400 1027 „ 10.28 ACID GRADE 50 700 134.9 „ 13.48 OP 170 OPA1TT 1000 120.5 II 12.40 CARB '50J' Alumina 1.6 150 39.3 0.044 5.16 CURRENT AMPS 250 53.0 a 9.16 400 57.6 a 10.16 1.6 mm Fig. 4 — Penetration vs current • 3.2 300 55.1 ,, 9.72 electrode 450 68.1 „ 12.00 600 62.7 „ 11.04 6.4 400 63.9 „ 11.24 700 92.1 „ 16.20 1000 68.0 » 12.00 Basic 1.6 150 33.4 0.035 4.68 250 45.3 It 6.36 400 48.6 II 6.80 3.2 300 45.4 n 7.32 BEAD WIDTH 450 55.3 ,i 7.72 600 56.7 ,, 7.92 6.4 400 62.5 „ 9.16 • • ACID GRADE SO 700 88.3 ti 12.36 O O OP 170 fi A OPA1TT 1000 81.2 11.36 A * CARB '503' • Car­ 1.6 150 36.9 0.066 9.76 bonate 250 52.1 " 13.76 400 42.2 " 11.12 3.2 300 46.1 " 12.20 REINFORCEMENT 450 61.4 " 16.20 600 60.8 " 16.00 6.4 400 80.6 " 21.28 700 90.1 a 24.00 1000 85.1 a 22.44 Fig. 5 — Bead width and reinforcement vs current — 1.6 mm electrode

72-s I MARCH 1976 This implies that electrode melting 150 rates, excluding the influence of l2R # 150 /y% heating, are primarily a function of total current and electrode charac­ ,/ ,^ teristics, which are apparently unaf­ fected by flux chemistry. In particular, 10 0 endothermic carbonate decomposi­ £ &/ tion, which has been shown to cause a '71 tjt/ decrease in total heat input of up to 20%, has no effect on electrode melt­ 5-0 ys°> v ing rates. The dependence on total current and anode characteristics 5 0 f/ •^ alone is also consistent with the linear O O OP 170 A a OP41T1 *»&s0£yb KEV relationship between melting rate and *— * CARB '503' ' O— O 0P 170 A d 0P41TT current. 1 * A CARS '503 The only experimental evidence of HM- ± ± ± -*- ± -j- - an alteration in electrode melting Fig. 6 — Penetration vs current — 3.2 mm rates due to flux composition (Ref. 8) electrode Fig. 8 — Penetration vs current — 6.4 mm was connected with the use of over­ electrode simplified fluxes of dubious arc stabilizing capacity; and since all commercial fluxes are formulated to give adequate arc stability on elec­ trode positive polarity, it is therefore reasonable to expect that a given cur­ rent level will produce similar elec­ trode melting rates, once it is real­ ized that melting is a function of cur­ rent and electrode physical charac­ teristics. In this investigation, after the transi­ ACID GRADE 50 tion current was exceeded, penetra­ O O OP 170 L 6 OP41TT tion increased, bead width de­ * 4 CARB 503' creased and reinforcement in­ creased at a greater rate than was evi­ dent below the transition current; the REINFORCEMENT effects were most marked with the smallest diameter electrode, which provides a physical arc constriction. Fig. 7 — Bead width and reinforcement vs All fluxes, including the high carbon­ current — 3.2 mm electrode ate flux, produced the same changes REINFORCEMENT in bead configuration at the same cur­ rent level; thus the basic arc behavior the interaction of carbonate decom­ .Mh is similar in all cases. position and the dissociable gas arc. The behavior pattern established The present work shows that bead Fig. 9 — Bead width and reinforcement vs current — 6.4 mm electrode by the changes in bead dimensions width is the only process parameter to with current indicates the develop­ be measurably affected by carbonate ment of a plasma jet as the current in­ decomposition, primarily with the creases beyond a certain level for larger 3.2 and 6.4 mm electrodes. each wire diameter. The plasma jet The proposed explanation is that thermal losses (Ref. 10). The present concentrates the thermal energy in the heat extraction is concentrated in work shows where and how the heat is the arc discharge, and increases the the vicinity of the slag wall, which regained: the bright, unoxidized bead arc pressure. This forces liquid metal causes a thermal constriction on the surfaces of welds made with the car­ away from the central pool area, so outer surface of the arc discharge, bonate flux show that the surface ox­ producing a marked change in and a loss in melting capacity at the ides on the solidifying weld bead are penetration, and a narrowing of the periphery of the weld pool. The en­ removed via the reaction CO + MeO weld bead width. It also, for a reason­ dothermic reaction (where Me -* C02 + Me + heat. The bead width ably constant arc length and voltage, denotes metal) MeC03 + heat-> MeO reduction was not noticeable with the brings the electrode tip closer to the + C02 is the main source of the ther­ 1.6 mm electrode, for two reasons: plate surface, thus reducing the size mal constriction. However, it is possi­ the small electrode diameter pro­ of the arc cavity moving through the ble that the breakdown of C02 to form duced a physical restriction in arc flux; this in turn causes a drop in flux CO and O is a contributory factor. The anode size, which encouraged a consumption. The changes are dissociation core of the arc requires plasma jet effect and a stiffer arc less shown diagrammatically in Fig. 15. this breakdown; therefore it must oc­ susceptible to thermal constriction at The increase in reinforcement is cur as C02 passes through the outer relatively low currents; and flux con­ connected with the reduction in bead arc discharge toward the high sumption was lower for a given cur­ width. Since deposition rates con­ temperature core from the vicinity of rent, thus reducing the amount of heat stantly increase with current, rein­ the inner slag wall. The process en­ removed by carbonate decomposi­ visaged is shown schematically in forcement must rise sharply when the tion. The weld beads were also rela­ Fig. 16. bead width remains constant or de­ tively small, and would be more creases, in order to accommodate the Previous work on carbonate fluxes severely quenched by the mass of the extra mass of deposited metal. has proposed that this latter thermal plate, thus minimizing any thermal ef­ The additional decrease in bead loss is regained within the weld region fects of the flux on the solidification width in the carbonate flux is due to and does not contribute to overall characteristics.

WELDING RESEARCH SUPPLEMENT! 73-s The increase in flux consumption ness of the plasma jet formation at is not clear, but the net effect is similar with wire diameter for a given current higher currents. This reasoning also to, if more limited in extent than, the is explained by arc cavity size, es­ indicates that the submerged arc pro­ C02 evolution from the carbonate pecially in the vicinity of the electrode cess is more efficient with relatively flux. Gas bubbles in the solidifying tip. A larger electrical anode area will small diameter electrode wires used slag interfere with the surface forma­ increase the size of the arc cavity at relatively high currents, since flux tion of the solidifying weld metal, which passes through the flux burden, consumption is minimized as metal producing a bead surface which thus melting more flux. The same deposition rates and weld penetra­ hampers slag removal, as shown in phenomenon accounts for the more tion are increased. Fig. 17. The problem is more acute at gradual changes in flux consump­ Flux consumption is the only higher currents, due to the larger tion, penetration and bead width with process variable which apparently quantities of slag melted and also current as electrode diameter in­ demonstrated any dependence on possibly to arc instabilities during creases — the larger anode size flux chemistry, and that was seen in metal transfer causing sudden move­ causes less physical constriction on the anomalous behavior of the basic ments of the weld pool. The problem the arc. thus lessening the abrupt- flux, which over a wide current range with larger electrode diameters is had a lower consumption rate than its probably aggravated by the pro­ bulk density would dictate. The basic gressively smaller quantities of deoxi­ Table 4 — Transition Currents for Mild slag beads were always smaller than dants used, particularly Mn and Si, Steel Electrodes the beads produced by the other which would increase the quantities of fluxes, but the reason or reasons for CO evolved during solidification, as Transition this can only be the subject of spe­ the observed weld bead porosity con­ Electrode Shielding current. firmed. diam. mm medium A culation at this stage. The thermal conductivity of the slag cavity wall is The importance of basic arc 1.6 Ar-1%02 270 one property which may be impor­ physics in the process behavior of 350 1.6 C02 tant submerged arc welding is shown 1.6 Sub. arc 350 The evolution of gases during flux clearly in the results. The carbonate 3.2 Ar-1%02 450 3.2 Sub. arc 550 melting and slag solidification affects flux must produce an arc atmo­ 6.4 Sub. arc 750 bead surface appearance and conse­ sphere dominated by C02, and a quently slag detachment to a signif­ comparison of transition currents for icant degree. Slag removal via "self- mild steel electrodes in inert and dis­ lifting" properties is generally asso­ sociable gases using electrode posi­ ciated with a phase change during tive polarity with those obtained in this cooling which gives a substantially work shows that the submerged arc different thermal contraction charac­ transition currents are consistent with teristic in comparison with the weld those found in C02 arc welding. Tran­ metal, and to a lesser extent with a sition currents in dissociable gases lack of chemical reaction between the are always higher than those found in slag and metal surfaces which may argon, because of the greater energy 5 io form a physical bond, especially with required to dissociate and ionize high alloy levels. Problems in slag molecular gases. detachment in this investigation were The dissociable gases most likely associated with the carbonate flux, to be involved in the arc cavity of non- and to a lesser extent with the basic carbonate fluxes are nitrogen (from flux, especially at high currents, and the atmosphere) and oxygen (from with the larger wire diameters. Both the atmosphere and possibly from fluxes formed slag containing quan­ dissociated oxides boiled away from tities of gas bubbles, and associated the flux). Submerged arcs can there­ uneven bead surfaces. fore be treated as dissociable arcs The source of gas in the basic flux similar to C02 arcs for purposes of Fig. 10 Flux consumption vs current comparison with arc processes not in­ 1.6 mm electrode volving fluxes, where fundamental be­ havior is more easily observed. Flux chemistry and basicity, at least for four widely varying compositions, • have no apparent effect on electrical­ / • ly dominated parameters such as penetration and electrode melting • / • rates. Chemistry does have an effect A on parameters relatively free from / electrical domination, such as bead width and flux consumption, especial­ ly with fluxes containing compounds which have an effect on heat transfer. l! / Welding conditions pushing the ex­ / treme limits of voltage, current and 4 welding speed have to be investi­ gated to assess the combined effect

KEV of flux chemistry and physical prop­ ACID GRADE 50 o— O OP 170 O OP 170 erties, e.g.. bead formation at high A QP41TT A 0PA1TT —A CARB '503' A CARB '503' power, high speed conditions where maximum welding efficiency is CURRENT AMPS sought. It is hoped that concepts put Fig. 11 - Flux consumption vs current Fig. 12 — Flux consumption vs current forward in this paper will supply a 3.2 mm electrode 6.4 mm electrode basic framework which can be ex-

74-s ! MARCH 1976 FLUX ACID ALUMINA BASIC CARBONATE GRADE 50 GRADE OP 170 GRADE OP 41 TT GRADE 503

WIRE Dia.-mm. 1-6 1-6 1-6 1-6 1-6 1-6 16 1-6 1-6 1-6 16 1-6 BEAD SHAPE. —•<">— -o- -o- —o— —o- -o- -o>- -o- -- -o- -o-

CURRENT AMPS. 150 250 400 150 250 400 150 250 400 150 250 400

WIRE Dia.-mm. 32 32 32 32 32 32 32 32 32 32 32 32

BEAD SHAPE. —o— -- < ~v~ "\7- "^- ~X7~ -o- --

CURRENT AMPS. 300 450 600 300 450 600 300 450 600 300 450 600

WIRE Dia.-mm. 6-4 64 64 64 6-4 6-4 6-4 64 64 64 64 64

BEAD SHAPE -<=>- <=> -o- -o- -"v?- "0" " - -o--Q- -o-v-

F/'g. 13 — Effect of wire diameter and current levels on bead cross-sections

tended to assist in the fundamental analysis of such investigations. Gr50 Conclusions 1. On electrode positive polarity, OP 170 electrode melting rates increase linearly with current and are unaf­ Gr503 fected by flux composition over a wide range of basicity and carbonate content. Electrode melting is there­ fore a function of current and elec­ trode physics, not of flux composition. 0P41TT 2. Submerged arcs under both carbonate and non-carbonate fluxes have characteristics associated with C02 arcs, including similar transition currents. Above 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 penetra­ Fig. 14 — Slag bead profiles — 3.2 mm electrode, 450 A tion and reinforcement, and de­ creases in bead width and flux con­ sumption above the critical current. 3. The submerged arc process is most efficient when operated above the transition current, and it is there­ fore preferable to use relatively small diameter wires for a given stickout and current level. 4. Carbonate fluxes decrease bead width in comparison with non-car­ 1 ARC CAVITY HEAT EXTRACTION FROM SLAG WALL (CO; -f CO -I-0) ELECTRODE bonate fluxes, by the extraction of 2 SLAG WALL SLAG WALL. 3 FLUX DECOMPOSITION HEAT EXTRACTION FROM SLAG(CaCOj -»-Ca0 + C0:,) heat from the arc cavity near the slag ARC CAVITY 4 FLUX BURDEN BASE PLATE wall-base metal interface, due to en- 5 MOLTEN WELD POOL dothermic carbonate decomposition. 6 ELECTRODE WIRE Fig. 15 — Arc forces and bead formation 5. Flux consumption followed bulk as influenced by current level, (a) pre- Fig. 16 — End view schematic diagram of density for the fluxes used, except for transition arc discharge melting; (b) post heat extraction processes during carbon­ the basic flux. This may be due to its transition plasma jet operation ate flux decomposition

WELDING RESEARCH SUPPLEMENT! 75-s 1. FLUX BURDEN. 6. BASE PLATE. 2. SOLIDIFIED SLAG. 7. ELECTRODE WIRE.

3. PASSAGE OF COa GAS THROUGH MOLTEN SLAG. 8. ARC CAVITY. 4. GAS BUBBLES IN MOLTEN AND SOLIDIFIED SLAG. 9. MOLTEN WELD POOL. 5. WELD BEAD SHOWING SURFACE ROUGHNESS 10. MOLTEN SLAG. CAUSED BY GAS BUBBLES.

Fig. 17 — Side view schematic diagram of the effect ol gas evolution on bead shape

thermal transfer characteristics when Handbook, Chapter 24, Section II, Sixth Slag Composition on Heat Transfer and melted. The net result is that flux Edition, 1969. Arc Stability," Welding Journal, Vol. 53 (5), costs per meter of weld are lower with 2. Robinson. M. H., "Observations on May 1974, Res. Suppl., p 203-s. the basic flux, which is not the most Electrode Melting Rates During Sub­ 9. Palm, J. H.. "How Fluxes Determine merged Arc Welding," Welding Journal, the Properties of Submerged Arc Welds," inexpensive flux to purchase. Vol. 40 (11), Nov. 1961, Res. Suppl., Welding Journal, Vol. 51 (7), July 1972, 6. Weld bead appearance p 503-S. Res. Suppl., p 358-s. deteriorated at high current levels and 3. Drayton, P. A., "An Examination of 10. Patchett, B. M., Demos, G. A. and when C02 evolution was high due to the Influence of Process Parameters on Apps, R. L., "The Influence of Flux Com­ carbonate decomposition and/or gas Submerged Arc Welding," Welding Re­ position and Welding Parameters on Heat evolution in the metal caused by in­ search International, Vol. 2 (2), 1972, p 1. Distribution in Submerged Arc Welding," sufficient deoxidants in the electrode 4. Jackson, C. E., "The Science of Arc Welding Research International, Vol. 4 (2), wire. Gas bubbles caused surface Welding, Part II — Consumable Electrode 1974, p. 81. 11. Tuliani, S. S., Boniszewski, T. and roughness in solidifying weld metal, Welding Arc," Welding Journal, Vol. 39 (5), May 1960, Res. Suppl., p 177-s. Eaton, N. F., "Carbonate Fluxes for Sub­ which made slag removal difficult with 5. Jackson, C. E., "The Science of Arc merged Arc Welding of Mild Steel," Weld­ the carbonate flux, and to a lesser de­ Welding, Part III — What the Arc Does," ing & Metal Fabrication, Vol. 40 (7), 1972, gree with the basic flux. Welding Journal, Vol. 39 (6), June 1960, p. 247. Res. Suppl., p 225-s. 12. Butler, C. A. and Jackson, C. E„ Acknowledgments 6. Apps, R. L., Gourd, L. M. and Nel­ "Submerged Arc Welding Characteris­ son, K. A., "The Effect of Welding Vari­ tics of the CaO-Ti02-Si02 System," Weld­ The authors wish to thank Mr. K. A. Nel­ ables upon Bead Shape and Size in Sub­ ing Journal. Vol. 46 (10), Oct. 1967, Res. son for his assistance with the experimen­ merged Arc Welding," Welding & Metal Suppl.. p 448-s. tal work, and Dr. T. Boniszewski of Me- Fabrication, Vol. 31 (10), 1963, p 453. 13. Tagaki, O., Nishi, S. and Suzuki, K., trode Products for supplying the carbon­ 7. Jackson, C. E. and Shrubsall, A. E., "On Notch Toughness of Deposited Metal ate flux. "Control of Penetration and Melting Ratio in Automatic Arc Welding (Report 2)," with Welding Technique," Welding Jour­ Journal of the Japanese Welding Society, Vol. 31 (10) (27), 1962, p 821. References nal, Vol. 32 (4), April 1953, Res. Suppl., p 172-s. 14. Smith. A. A., C02 Welding of Steel, 1. American Welding Society Welding 8. Patchett, B. M., "Some Influences of The Welding Institute, Third Edition, 1970.

Discussion

The Welding Journal invites critical discussions by peers on technical matters appearing in the Welding Research Supplement. A 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 MARCH 1976