WELDING RESEARCH

SUPPLEMENT TO THE W E L D I N G J O U R N A L , M A R C H 1978

Sponsored by the American Welding Society and the Welding Research Council l i II j

Slag/Metal Interaction, Oxygen and Toughness

in Submerged Arc Welding

Fused fluxes containing 45% CaF2/ 35% Al203 and 20% CaO yield less oxygen in the weld deposit than do agglomerated fluxes with the same constituents,

and Al additions to a 45% CaF2, 35% Al203/ 20% CaO flux lower the oxygen contents of weld deposits to below that of the electrode

while the addition of up to 1.2% Al to the flux improves weld notch toughness

BY T. H. NORTH, H. B. BELL, A. NOWICKI AND I. CRAIC

Part I—Flux Formulation and Oxygen Content During Submerged Arc Welding

ABSTRACT. The influence of flux formulation on the oxygen content of submerged arc deposits has been investigated. When using low oxygen potential flux formulations composed of mixtures of CaF.,, ALO., and CaO, deposit oxygen contents were marked­ly lower using fused fluxes than in using agglomerated fluxes. The main source of oxygen when welding w i th fluxes composed of CaF,,, ALO :, and CaO was that due to decomposit ion of flux constituents.

Oxygen pick-up during welding wi th CaO-ALOrCaF,, fluxes was main­ly determined by gas/metal reactions occurring at the electrode tip region. There was no correlation between the FeO content of slags and the oxygen content of deposits. Consequently slag/metal equi l ibr ium was not at­tained, and derivation of an effective reaction temperature during welding

was not feasible. Aluminum additions to (45 wt-%

CaF,, 35 wt-% ALO,, 20 wt-% CaO) flux lowered the oxygen content of depos­its to below that of the electrode. Such low oxygen levels were obtained at the expense of increased contents of aluminum in solution.

Introduction

The submerged arc welding process is superficially simple in operation.

Paper to be presented at the AWS 59th Annual Meeting in New Orleans, Louisiana, during April 3-7, 1978.

Dr. T. H. NORTH is a Lecturer in Metallurgy, H. B. BELL is Professor of Metallurgy, and A. NOWICKI and I. CRAIG are Graduate Students, University of Strathclyde, Glas­gow, Scotland.

Moreover, the final weld deposit composition is the end-point of a complex interplay of physical and chemical factors. Submerged arc fluxes for welding steels are composed of a complex mixture of oxides, halides, carbonates, silicates and ferro-alloys. Consequently, the formulation of fluxes has a major influence on the final deposit oxygen content, and on its notch toughness.

This paper examines the factors determining the transfer of oxygen to the weld metal during submerged arc welding. Considerable accent has been placed on the concept of basicity of submerged arc fluxes as a means of producing low oxygen content weld deposits. In terms of our knowledge of slags, such use of basicity ratios is incorrect, and it is important to differ­entiate between the basicity of the flux employed and the oxygen poten­tial during welding.

Basic oxides such as FeO and M n O have relatively high oxygen potentials, e.g.,

W E L D I N G RESEARCH SUPPLEMENT I 63-s

2Fe + O, ^ 2 F e O • log P„„ (at 1600 C, 2912 F) = -8 .2

while an acidic oxide such as A l 2 0 3 has a very low oxygen potential, i.e.,

4AI + 30, ss 2ALO;1 • log P„, (at 1600 C, 2912 F) = -19.9

The oxygen potential represents the driving force for oxygen transfer from the oxide to the metal and depends on the reaction:

Oj3S2 [ 0 ] , ; A C ° = -57,000 -1.38 T cal

When basicity is considered, the important factor is the oxygen ion activity in the slag. Whi le single ion activities cannot be determined, the fol lowing charge reactions may be considered:

0*-(. l ag) + ' /2S,U^S'- ' ( s ,a 8 ) + Vi

o8y n)

and, Vi p.,(B) + 5/4 0 2 y + vi

O'-(„„) ss P O J - U . ) (2)

In the case of reaction (1), a high oxygen ion concentration favors reac­tion to the right, whi le a high oxygen potential favors reaction to the left, i.e., basicity and oxygen potential counteract each other. In the case of the reaction involving phosphorous (i.e., reaction (2) ), oxygen potential and oxygen ion activity act together, and both should be high for dephos-phorization to occur.

The oxygen potential during steel making is generally considered as the partition of oxygen between metal and slag, and is related to the ferrous oxide content of the slag, i.e.,

F e + [0 ] % ss FeO(slag)

and the oxygen partit ion (L) is given as: L = activity of oxygen in the metal (a0)/activity of ferrous oxide in the slag (aP e 0)

During welding the activity of oxy­gen in the metal (a„) is given by the wt-% oxygen content. If equi l ibr ium is attained during the welding operation, the oxygen content wou ld be propor­tional to the ferrous oxide activity in the slag. The activity coefficient of ferrous oxide is higher in basic slags than in acid slags; this means that for a given ferrous oxide content in the slag the oxygen content of the metal would be higher wi th basic slags than wi th acid slags (if equi l ibr ium conditions are attained during welding).

It is readily apparent that flux formu­lations yielding the lowest weld metal oxygen contents must be derived from a consideration of the oxygen poten­tial of flux constituents and not from

basicity considerations. The oxygen potential of flux constituents can be assessed from the Ellingham diagram, e.g., oxides such as A l 2 0 3 are very stable whi le oxides such as FeO and CuzO are not so stable. Since calcium metal and magnesium metal boil at 1500 and 1100 C (2732 and 2012 F) respectively, CaO and MgO decom­pose to oxygen and calcium and magnesium vapors during the high temperature cycle of welding Simi­larly, Na ,0 and K,0 decompose, producing sodium and potassium va­pors and, at temperatures above 1100 C (2012 F) they have higher oxygen potentials than FeO. Oxides such as Si02 and T iO, have oxygen potentials intermediate between FeO and Al203 .

The quantity of oxygen transferred to the metal is markedly temperature dependent, since the solubility of oxygen in iron increases with tempera­ture increase, i.e., from 0.19% at 1550 C (2822 F) to 0.79% at 2000 C (3632 F). As a result, for a given oxygen potential the higher the temperature the more oxygen wi l l be transferred.

The foregoing discussion has as­sumed the attainment of thermody-namic equil ibrium during submerged arc welding. Elucidation of whether thermodynamic equil ibrium actually occurs is an important facet of this investigation. Certainly the time of contact of metal and slag is l imited; temperatures range from 2400 C (4532 F) (the droplet formation stage) to 1520 C (2768 F) (the fusion line region), and it is readily apparent that a simple slag-metal interaction at a constant temperature is not being considered.

Aims of Research Program

Since submerged arc welding is a complex process, simply-formulated, laboratory-prepared fluxes provide an essential tool for examination of such a system. The advantage of employing simple fluxes of known formulation is that the thermophysical properties and solution thermodynamics are avail­able. Consequently, meaningful de­ductions concerning slag/metal inter­action, oxidation and reduction, and alloy transfer during welding can be made.

Preliminary tests were carried out using fluxes based on the systems CaO-MgO-SiO, and CaO-MgO-TiO,. Table 1 shows the oxygen content of bead-on-plate deposits when using different formulations. The high oxy­gen contents found were due to the presence of Si02 in the CaO-MgO-Si02 formulations and to T i 0 2 in the CaO-MgO-Ti0 2 formulations. These results confirm data of other investiga­tors.1-4

On the basis of preliminary tests, it

was decided that a flux formulat ion composed of highly-stable oxides and/or halides should be employed. As a result, laboratory-prepared fluxes based on the CaO-CaF,-AI203 system are investigated. A number of lines of investigation were fo l lowed:

1. Evaluation of flux formulations in the system CaO-CaF2-AI203 depositing the lowest oxygen contents when a single electrode composit ion was em­ployed; factors such as loss of alloy elements to the slag during welding and the form of flux manufacture (agglomerated and fused) on weld metal composit ion were also investi­gated. Under ideal conditions, welding tests would have been carried out using pure iron wire, but this was not available and the research program employed commercial electrodes con­taining various manganese contents.

2. Examination of the means of oxidation and deoxidation during sub­merged arc welding wi th particular emphasis on the role of deoxidant additions in the flux in determining the electrode tip and final deposit oxygen contents.

3. Estimation of the attainment of equil ibrium during welding wi th labo­ratory-prepared fluxes.

4. Examination of the effect of oxygen and aluminum on the notch toughness of submerged arc deposits; this work is presented in Part II of this paper.

Experimental Procedure

Materials

The chemical composit ion of the mild steel plate used in welding tests is given in Table 2. Proprietary electrode wires were employed throughout and encompass a range of manganese levels—Table 2.

The experimental fluxes employed in this program were based on the CaO-AI,03-CaF2 ternary system. Meth­ods of flux preparation were as fol lows:

Agglomerated Fluxes (Table 3). 1. Dry mixing of 4 kg of pure

components to give a desired flux formulation for 30 min.

2. Wet mixing after addit ion of alkali silicate binders (corresponding to 2.5 wt-% Na ,0 , Vi wt-% K..O and 1 wt-% SiO, in the flux).

3. After agglomeration the flux was baked on trays at 450 C (842 F) for 3 h.

Fused Fluxes (Table 3). 1. Dry mixing of 10 kg of flux in a

mixer; the CaO employed was ob­tained from calcination of CaCO;, at 1000 C (1832 F) for 2 h.

2. Melt ing of flux in a graphite crucible using a high-frequency melt­ing furnace.

64-s I M A R C H 1978

Table 1—Flux Formulations and Deposit Oxygen Contents During Bead-on-Plate Welding-S3 Electrode Used Throughout, %

SiO,

63 53 43 32

Designation

CMS 1 CMS 2 CMS 3 CMS 4 CMT 1 CMT 2 CMT 3

CaO

20 30 40 50 20 30 40

MgO

14 14 14 14

7.5 7.5 7.5

TiO

----70 60 50

lagO

2.5 2.5 2.5 2.5 2.5 2.5 2.5

KsO

0.5 0.5 0.5 0.5 0.5 0.5 0.5

Oxygen deposits (1650 C, 3002 F)

0.085 0.086 0.054 0.042 0.063 0.068 0.056

Table 3-Chemical Compositions of Laboratory-Prepared Fluxes ("A"—Agglomerated Fluxes; "B"—Fused Fluxes), Wt-%

C

0.065 0.15 0.08 0.10 0.12 0.11

Mn Si

0.84 0.15 0.45 0.23 0.47 0.18 0.98 0.17 1.59 0.29 2.10 0.23

S

0.01 0.009 0.012 0.008 0.012 0.03

P

0.016 0.011 0.02 0.02 0.012 0.03

(O) (1650 C, 3002 F)

0.0053 0.006 0.031 0.013 0.008 0.017

(O) (1800 C, 3272 F)

-----

0.016

Al (total)

-----

0.0045

Al acid sol­uble

— --- • -

0.0025

Al acid

insol­uble

— -- •

--

0.002

Table 2—Chemical Compositions of Electrodes and Plate Materials, %

Designation

Base metal B1 Base metal B2 Electrode S1 Electrode S2 Electrode S3 Electrode S4

3. Crushing of flux to the desired particle size.

In order to maintain consistency with agglomerated fluxes the initial fused fluxes contained 2.5 wt-% Na,0, 0.5 wt-% K,0 and 1 wt-% SiO,. In tests where deoxidant additions were made during welding, it was convenient to add aluminum via the flux since main­tenance of constant current and voltage conditions throughout pro­vided a reproducible means of achiev­ing any chosen aluminum level.5

When aluminum additions were re­quired, these were made by mixing 200 mesh aluminum powder with crushed fused flux for 8 h in a roller drum. In control tests where aluminum was added to the 45 wt-% CaF,, 35 wt-% Al ,0 3 , 20 wt-% CaO formulat ion, no Na,0 , K,0 or SiO, additions were present.

Welding Conditions

Reverse polarity was employed throughout. Ten-high pads were used to overcome problems caused by d i lu­tion during welding operations. Ten-high pads were deposited as fol lows: four weld beads, fol lowed by three, then by two and finally by the test weld. The welding conditions throughout were 600 A, 32 V, 0.25 m/ min (9.8 ipm).

Electrode Tip Collection during Welding

Electrode tip collection was carried out using a modif ied torch design—see Fig. 1. This allowed argon gas to pass through the welding head prior to arc

initiation and to keep f lowing during the welding operation.

Electrode tips were collected by retracting the electrode into the argon stream when stable welding condi­tions had been achieved during bead-on-plate welding. This means of elec­trode tip collection providing material from a range of possible situations, i.e., droplet transfer may have just oc­curred or droplets growing at the elec­trode tip having various dimensions may be collected.

In order to overcome this problem 10 electrode tips were collected and analyzed for oxygen content at any particular welding condit ion. In e'ffect, the oxygen content found was the

WATER COOLING

COPPER CONTACT TUBE

Designat ion" '

1B 2B 4A 5A 6A

7A and 7B 8A 9A

10A 11A 12A 13A 14A 15A 16A

17A and 17B 18A 19A 20A 21A 22A 23A 24A 25A 26A 27A

28A and 28B 29A

30A and 30B

CaF2

100 100

5 5

10 10 10 10 15 15 20 20 20 20 25 25 25 30 30 30 35 35 35 40 40 40 45 45 45

A l 2 0 3

— -

55.0 58.0 34.0 45.0 52.5 57.5 50.0 47.0 35.0 45.0 50.0 56.0 45.0 50.0 55.0 40.0 50.0 53.0 40.0 44.0 52.0 35.0 45.0 50.0 35.0 45.0 48.0

CaO

_ -

40.0 37.0 56.0 45.0 37.5 32.5 35.0 38.0 45.0 35.0 30.0 24.0 30.0 25.0 20.0 30.0 20.0 17.0 25.0 21.0 13.0 25.0 15.0 10.0 20.0 10.0

7.0

Fig. 7.—Modified torch for electrode tip collection tests

" ' A l l fluxes except 1B contain 2.5 w t - % Na-O, 0.5 w t -KzO and 1 w t - % SiO, respectively.

mean oxygen content of the electrode tip region at any welding condit ion. Since it can be difficult to assess where the collected droplet begins and the unfused electrode ends, only the last mill imeter length of collected elec­trode tip samples were analyzed for oxygen.

Vacuum fusion analysis was em­ployed throughout. Two test tempera-tures-1650 C (3002 F) and 1850 C (3272 F)—were examined since previous in-vestigators"? noted differences in the determined oxygen contents of alumi­num-kil led samples when tested at different temperatures. At any temper­ature the vacuum fusion analysis gave a reproducibility of ±0.002%.

Chemical Analysis

Aluminum analysis was carried out using the British Standard (B.S.19) photometric method of analysis." The eriochrome-cyanine method gave val­ues for the acid-soluble and acid-insoluble aluminum contents when the residues of the initial acid-solution treatments were separately analyzed.

Slag samples were analyzed by means of absorption spectrophotome-try. Prior to slag analysis, samples were crushed and iron particles were removed by means of two procedures, i.e., using a strong magnet, and by

W E L D I N G RESEARCH SUPPLEMENT I 65-s

means of a l iquid separation technique using methylene iodide. Both methods

of iron particle removal from slag samples had been found satisfactory

CaO

Fig. 2—Agglomerated flux formulations and deposit oxygen contents when welding with S3 electrode containing 0.008% oxygen

Table 4—Chemical Analyses of Weld Deposits Made Using Agglomerated Fluxes ("A" Series) and Fused Fluxes ("B" Series)—S3 Electrode Employed Throughout, wt-%

Designation

4A 5A 6A 7A 8A 9A

10A 11A 12A 13A 14A 15A 16A 17A 18A 19A 20A 21A 22A 23A 24A 25A 26A 27A 28A 29A 30A

1B 2B 7B

17B 28B 30B

C

0.090 0.087 0.090 0.075 0.085 0.104 0.088 0.089 0.073 0.086 0.080 0.100 0.064 0.075 0.097 0.075 0.075 0.080 0.081 0.069 0.075 0.074 0.074 0.065 0.075 0.064 0.100 0.105 0.11 0.095 0.105 0.100 0.09

s, 0.050 0.060 0.020 0.050 0.050 0.076 0.064 0.074 0.098 0.062 0.050 0.060 0.076 0.060 0.082 0.050 0.070 0.060 0.070 0.100 0.075 0.096 0.092 0.08 0.06 0.10 0.09 0.21 0.18 0.19 0.18 0.12 0.14

S

0.016 0.015 0.016 0.016 0.017 0.016 0.015 0.015 0.015 0.015 0.017 0.020 0.018 0.017 0.016 0.017 0.019 0.019 0.018 0.017 0.018 0.017 0.017 0.017 0.018 0.017 0.019 0.005 0.01

o.ot 0.0". P.014 0.014

P

0.013 0.014 0.013 0.014 0.015 0.015 0.015 0.014 0.013 0.015 0.015 0.013 0.014 0.014 0.015 0.014 0.015 0.015 0.015 0.014 0.015 0.015 0.015 0.013 0.015 0.014 0.016 0.010 0.019 0.017 0.015 0.016 0.017

M n

0.77 0.63 0.68 0.77 0.81 0.71 0.77 0.73 0.68 0.73 0.81 0.81 0.79 0.82 0.76 0.80 0.88 0.81 0.79 0.82 0.93 0.87 0.83 0.93 0.77 0.97 0.94 1.35 1.35 1.07 1.04 1.12 1.07

Mo

0.02 0.02 0.02 0.03 0.02 0.02 0.02 0.02 0.02 0.02 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.02 0.02 0.02 0.03 0.03 0.03 0.03 0.03 0.03 0.02 0.05 0.02 0.02 0.03 0.01 0.02

Cu

0.11 0.12 0.11 0.12 0.12 0.11 0.12 0.11 0.11 0.11 0.12 0.13 0.11 0.12 0.13 0.11 0.11 0.10 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.14 0.05 0.19 0.14 0.15 0.15 0.15

Oxygen (1650 C 3002 F)

0.0725 0.1270 0.0750 0.0941 0.0640 0.0930 0.0761 0.0860 0.0852 0.0962 0.0671 0.0780 0.0666 0.0640 0.0746 0.0743 0.0740 0.0645 0.0731 0.0680 0.0460 0.0700 0.0486 0.0470 0.0471 0.0473 0.0345 0.007 0.064 0.0264 0.0215 0.026 0.0175

by previous investigators.5-910

Nitrogen analysis of weld samples was carried out using the Kjeldahl method and had an accuracy of ±0.002%.

Results and Discussion

The initial tests were carried out wi th agglomerated fluxes made from CaC03 , and CaF2. CaC03 was used to avoid problems of moisture absorp­tion. Figure 2 shows the range of flux formulations examined—from 5 to 45 wt-% CaF2, 34 to 58 wt-% A l , 0 3 and 7 to 56 wt-% CaO. All flux formulations were chosen to have melting points below 1500 C (2732 F), and Table 4 gives the final deposit analyses (of the tenth run of ten-high pads) when employing an electrode having 0.12%C, 0.29%Si, 0.012%S, 0.012%P, 1.59%Mn, 0.008% [O].

The welds deposited using agglom­erated fluxes had relatively high oxy­gen contents, and there was a correla­tion between the CaC03 content of fluxes and the oxygen content of weld deposits. Increasing calcium carbonate content in fluxes increased the oxygen content of weld deposits (Fig. 3) and contradicted the results of a previous study." The relationship between the oxygen content of weld deposits and the calcium carbonate content in the flux formulations (given as the equiva­lent CaO content) was as fol lows: % [OJaeposit = 0.001 (%CaO) + 0.042

The loss of manganese from the electrode during welding also in­creased as the calcium carbonate content of the flux increased—Fig. 4. The relationship between the loss of manganese during welding and the calcium carbonate content of flux formulations (given as the equivalent CaO content) was:

(% Mn loss) = 0.362 (% CaO) + 39.81 MnH p o t r o d e

where % / KA \ .—„, Mn loss = ( ~ M n - ' " ) 1 0 0 %

M l p l i a r *

While deposits made using agglom­erated fluxes had relatively high oxy­gen contents, they did supply useful information:

1 The main source of oxygen dur­ing welding was C 0 2 evolved from calcination of the CaCO,, in agglomer­ated fluxes.

2. The slag composit ion formed during welding was similar to that in later tests using carbonate-free fluxes; this was of particular value when con­sidering the possible formation of some pseudo-equil ibrium reaction temperature during welding.

3. The FeO contents of slag samples were similar to those of carbonate-free fluxes—Table 5.

In order to remove the effects of

66-s I M A R C H 1978

CaC03 in flux formulations, a series of fused fluxes were made based on the CaO-AI203-CaF, system. In order to maintain consistency wi th agglomer­ated flux formulations, fused fluxes contained 2.5 wt-% Na20, 0.5 wt-% K,0 and 1 wt-% Si02 . The oxygen content of deposits made wi th fused fluxes were lower than those made wi th agglomerated fluxes—Fig. 3 and Ta­ble 4.

Employment of fused CaF, as a flux for submerged arc welding produced weld deposits wi th oxygen contents equal to that of the electrode—Table 4. Apart from slight voltage fluctuations ( ± 2 V), about any chosen value CaF, flux performed satisfactorily during deposition of ten-high pads. However, in industrial welding situations the low viscosity of this flux would lead to inadequate bead profiles.

The addit ion of 2.5 wt-% Na ,0 and 0.5 wt-% K,0 to fused CaF2 flux produced a marked increase in the deposit oxygen content, i.e., from 0.007% oxygen (that of the electrode employed) to 0.064% oxygen. In effect, the deposition of low oxygen content weld metal is promoted by the employment of fluxes containing the minimum content of alkali oxides consistent w i th adequate arc stability during welding.

Commentary

The important factors apparent from a consideration of the tests using agglomerated and fused fluxes are as follows:

1. Almost identical slag composi­tions produce deposits wi th markedly different oxygen contents when ag­glomerated and fused fluxes are com-

0-12

0-10 %I0]

DEPOSIT 0 . 0 8

0-05

004

002

%[CaO]

Fig. 3—Relation between the deposit oxygen content and the calcium carbonate content (given as the equivalent CaO content) of agglomerated fluxes. • are agglomerated fluxes and A are fused fluxes)

pared . 2. The (FeO) content of slags do not

differ markedly even when the differ­ence in deposit oxygen content are large.

3. Small additions of Na ,0 and K,0 raise the oxygen content of weld deposits and oxygen-free CaF flux produces weld metal having the same oxygen content as the electrode wire used.

All the above effects can be explained by assuming that oxygen pick-up occurs at the electrode tip region during welding, i.e., the impor­tance of C 0 2 evolution in agglomer­ated fluxes, of Na20 and K20 addi­tions, and the lack of correlation between FeO content in slags and oxygen content in weld deposits. It is

further suggested that oxygen pick-up at the electrode tip is determined by a gas/metal reaction. The main source of oxygen is due to carbonate and oxide decomposition during welding, i.e., CaCO, decomposit ion (in agglom­erated fluxes), CaO, Na20 and K,0 decomposition (in fused fluxes), and Na ,0 and K20 decomposit ion in the case of fused CaF2 flux. The reactions occurring are:

CaCO, ̂ C a O + C02(,,) CaOssCa(g) + 72 02(s) N a 2 0 ^ 2 Na(s) + Vt 0 2 Q

FeO is produced during welding and comes from oxidation of the metal. Some of the iron oxide could be due to desorption of oxygen from the weld metal during cooling and solidifica-

Table 5—Flux Formulations Where Fe,0:l and MnO Additions Are Made to CaF2 • Al203 • CaO Fl uxes

Electrode Flux designation

S1 S1 S1 S1 S1 S1 SI S2 S2 S2 S2 S2 S2 S2 S2 S3 S3 S3 S3 S3

1B 1B 7B 7B 7B

28B 28B

7B 7B

28B 28B 28B 28B 28B 28B 30A 7A 7B 7B 7B

Al additn. to flux, %

0.20

0.20 0.80

0.40

0.40

0.40

0.20 0.40

Fe203

additn. to flux, %

— -— ---— ----2.0 3.0

-------

M n O additn. to flux, %

_ ------------

1.0 2.0

-----

O weld metal, %

0.032 0.015 0.043 0.034 0.030 0.032 0.030 0.029 0.024 0.031 0.024 0.037 0.047 0.034 0.040 0.0345 0.084 0.025 0.016 0.012

FeO (slag), %

1.44 1.36 2.04 1.49 1.43 0.79 0.69 1.73 1.58 0.69 0.63 1.49 2.48 1.22 1.07 1.29 1.87 1.40 1.35 1.68

M n O (slag), %

0.32 0.22 0.65 0.19 0.71 0.19 0.13 0.19 0.13 0.26 0.19 0.38 0.64 0.77 1.22 0.29 0.33 0.25 0.31 0.33

W E L D I N G RESEARCH SUPPLEMENT I 67-s

1.2

11

to

•9

• 8

-7

- 6

• 5

. 4

c

' %Mn WELD METAL

•

^ S . •

• •

• •

10 20

•

• ^

•

30 40

•

•

50

•

6 0 7 0

%[0] ELECTRODE TIP

%CaO in FLUX

Fig. 4—Relation between the manganese content of deposits and the calcium carbonate content (given as the equivalent CaO content) of agglomerated fluxes. S3 electrode employed through­out

%[0)

WELD METAL

°/o AI in FLUX

Fig. 6—Effect of aluminum additions in the flux on deposit oxygen contents. S4 electrode and (45 wt-% CaF,, 35 wt-% Al.,0„ 20 wt-% CaO) flux

t i o n . H o w e v e r , t h e a m o u n t o f FeO present in slags is t o o great t o have c o m e w h o l l y f r o m th is source. O t h e r possib le sources c o u l d be f r o m the d i sso lu t i on (by t h e slag) of an o x i d e f i lm f o r m e d o n d rop le t s or f r o m the o x i d a t i o n or i ron vapo r in t he gas f i l m

DATUM LEVEL

%AI in FLUX

Fig. 5—Relation between the aluminum content in the flux and oxygen content of electrode tips (the datum level is that when electrode tips are collected using fused CaF., flux). S4 electrode and (45 wt-% CaFz, 35 wt-% Al,0„ 20 wt-% CaO) flux

CONDUCTIVITY (mhos)

ohm cm

Fig. 7—Specific electrical conductivity vs. temperature data lor laboratory-prepared and proprietary fluxes, where A is Lincoln No. 7 flux; B is BX7 electroslag flux; C is BOC-MUREX Muraflux A; D is Oerlikon OP41TT flux; E is BOC-MUREX 1009 flux; F is (45 wt-% CaFi, 35 wt-% AI..O* 20-wt% CaO) flux

s u r r o u n d i n g d rop le ts . Cer ta in l y the re is no re la t ion b e t w e e n the FeO c o n t e n t o f t he slag a n d the oxygen

c o n t e n t o f w e l d depos i t s . A d d i t i o n a l expe r imen ts w e r e car r ied

o u t t o c o n f i r m that oxygen p i c k - u p

68-s I MARCH 1978

during welding was dependent on gas/metal reactions at the electrode tip region:

1. Addition of Fe,03 and MnO to Fluxes. Two series of welds were de­posited using (45 wt-% CaF2/ 35 wt-% Al203 , 20 wt-% CaO) flux containing 2% and 3% Fe,0.„ and 1% and 2% MnO. The results of these tests are given in Table 5.

Although there was a slight increase in oxygen content of welds due to dissociation of Fe,03, it was notable that the fractional increase in oxygen content of deposits was very much less than the increase in the FeO content of the slags. These results again confirmed that there was no correla­tion between the FeO content of the slag and the weld deposit oxygen content.

2. Examination of Electrode Tip Ox­ygen Contents. Electrode tips were collected when welding wi th 45 wt-% CaF,, 35 wt-% A l 2 0 3 , 20 wt-% CaO f lux-Fig 5. It is readily apparent that the mean oxygen content of the electrode tip region was slightly higher than that of the weld deposit when using the same welding condi­t ions-Fig. 6. This confirmed that oxy­gen transfer took place at the elec­trode tip and little change occurred in the weld pool.

The droplet formation stage is char­acterized by approximately 2400 C (4352 F) high temperatures,12 vigorous motion of droplet material and emana­tion of the arc from localized anode spots (during reverse polarity weld­ing). At such temperatures, all avail­able oxygen wi l l be dissolved in l iquid iron. The only other source of oxygen in solid weld deposits is trapped flux. Since the solubility of oxygen in solid iron is extremely low (0.003% ±0.003% at 1295 to 1380 C (2363 to 2516 F)) , " oxygen is precipitated as iron, manga­nese and silicon oxides (or combina­tions of these) during weld metal solidification. Since the rate of solidifi­cation is high, it is unlikely that these oxides wi l l have an equil ibr ium com­position.

Employment of Deoxidants During Welding

Deoxidation by means of silicon and aluminum additions is an inherent feature of steelmaking practice. Con­sequently, aluminum additions were made to the fused flux formulation (45 wt-% CaF2, 35 wt-% Al 20 3 , 20 wt-% CaO) in order to lower the final weld deposit oxygen content. This particular flux formulation provided excellent running characteristics and good slag removal properties, and had known thermo-physical properties—viscosity of 0.10 poise at 1500 C (2732 F), and

Table 6-Weld Deposit Analyses When Using 45 wt-% CaF2, 35 wt-% ALO „ 20 wt-% CaO Flux Containing Aluminum Additions, Wt-%

C Mn Si S P O at 1650 C O at 1800 C Al (flux) Al (total) Al (acid soluble) Al (acid insolubl Nitrogen (%AI)2 X (%0) '

W1 ( A W ) " '

W2 (SR)

0.11 1.49 0.11 0.013 0.020 0.031"" 0.034""

-0.006 0.0015

;)0.0045 0.011 1.4 X 1 0 "

W3 ( A W ) " ' W 4 (SR)

0.13 1.52 0.14 0.008 0.020 0.0265"" 0.026"" 0.40 0.0095 0.003 0.0065 0.009 1.2 x 10 •

W5 (AW) " " W6 (SR)

0.11 1.52 0.16 0.010 0.019 0.0205"" 0.0204"" 0.80 0.0125 0.0055 0.007 0.008 1.3 x 10" '

W7 (AW)" " W8 (SR)

0.13 1.56 0.18 0.010 0.019 0.0145"" 0.0157"" 1.20 0.0195 0.0125 0.007 0.010 1.5 X 10-"

W9 (AW)" "

W10 (SR)

0.13 1.60 0.20 0.009 0.019 0.0105"" 0.0145"" 1.60 0.031 0.022 0.009 0.013 2.9 x 1 0 "

W11 (AW)" "

W12 (SR)

0.12 1.59 0.21 0.009 0.019 0.0095"" 0.011"" 2.00 0.045 0.034 0.011 0.012 2.7 X 10-"

" "AW—as-welded; SR—stress-relieved. " "Four tests carried out.

0.30 poise at 1600 C (2912 F), surface tension of 300 erg/cm- in the 1500-1700 C (2732-3092 F) temperature range, and a liquidus temperature of 1370 C (2948 F)." This particular flux formulation also had a specific elec­trical conductivity similar to that of other proprietary flux brands17—Fig. 7.

Increasing aluminum contents in the flux during deposition of ten-high pads produced a continuous decrease in the oxygen content of the final runs—Fig. 6. As the aluminum content of the flux increased, there was a continuous increase in the aluminum content of weld deposits. Figure 8 shows the relationship of aluminum content in the flux, total aluminum content of the weld metal, and the acid-soluble and acid-insoluble alumi­num contributions to the total deposit aluminum content. It is readily appar­ent that the acid-insoluble aluminum level was uninfluenced by increasing aluminum contents in the flux—Table

Widgery1"' indicated that the vac­uum fusion analysis method gave much lower oxygen values than the neutron activation analysis technique on similar samples, and that inclusion content evaluations based on metallo­graphic counting could not be related to the oxygen values found by the vacuum fusion method. Also when deoxidizing steel melts wi th aluminum additions, Franklin" found that the vacuum fusion method at a test temperature of 1650 C (3002 F) gave values 60 ppm lower than when testing was carried out at 1800 C (3272 F). In the case of sil icon-killed steel melts Franklin found similar oxygen values at both 1650 and 1800 C (3002 and 3272 F) testing temperatures. In Table 2 it is apparent that some weld deposits gave higher oxygen contents when tested at the higher tempera­ture, i.e., by as much as 40 ppm.

The relationship between the alumi-

70

60

50

40

30

20

10

%AL10 3

in DEPOSIT

•—————-i — —

, — . — • '

T ^ ^ " ^ -

y S /

total > ^ / -

^ * ^ ^ ' acid soluble

' " T - " ~~ " * acid insoluble

0 04 16 20 OS 1 2 %Al in FLUX

Fig. 8-Relation between aluminum content in the flux and total, acid-soluble and acid-insoluble aluminum content in submerged arc deposits

W E L D I N G RESEARCH SUPPLEMENT I 69-s

num content in the flux and the oxygen content at the electrode tip during welding is shown in Fig. 5. Since the oxygen content of ten-high pads deposited using pure calcium fluoride flux gave oxygen levels equal to that of the electrode wire (see Table 4), the datum level for tests where electrode tips were collected was that when using this particular flux, i.e., 0.016% oxygen (the mean of ten tests).

It is readily apparent from Fig. 5 that the presence of aluminum in the flux modified the oxygen content of metal at the electrode tip. In effect the presence of 1.2 wt-% aluminum in the flux successfully counteracted the ox­idizing tendency of the 45 wt-% CaF2, 35 wt-% Al 20 3 , 20 wt-% CaO flux formulation. In this connection the addition of 1.2 wt-% aluminum to the flux decreased the oxygen content of the final run of ten-high pads to that of the electrode employed—Fig. 6. In­creasing the aluminum content of the flux beyond 1.2 wt-% permitted depo­sition of ten-high pad weld deposits with oxygen contents less than that of the electrode employed. However, production of such low oxygen values was counteracted by a marked in­crease in the content of aluminum in solution in deposits—Fig. 8.

At the inception of this program it was thought that aluminum would act mainly in the weld pool, i.e., by deox­idizing the molten weld metal. How­ever, the effect of aluminum additions on the oxygen content of electrode tips suggested that it had an influence on the oxygen content of the elec­trode tip region, i.e., that it "mopped up" oxygen in the arc cavity and reduced the oxygen potential sur­rounding growing droplets.

Using aluminum additions it was possible to reduce the oxygen content of weld deposits below that obtain­able wi th aluminum-free fluxes; in­deed, with aluminum additions in fused CaF2 flux it was possible to lower the deposit oxygen content to below that of the electrode—Table 5. Table 5 also indicates that the low oxygen contents of welds made using alumi­num additions were not reflected in significantly lower FeO contents in slags and confirmed the previous data on aluminum-free fluxes.

Chemical Equilibrium and Effective Reaction Temperature During Welding

Many investigators have deduced effective reaction temperatures for slag/metal interaction during welding and values range from 1520 to 2500 C (2768 to 4532 F), depending on the element considered and the process employed.

Derivation of an effective reaction temperature during submerged arc welding assumes that equi l ibr ium ex­ists during welding and that mean­ingful extrapolations can be made from equil ibrium data applying to lower temperatures and to much simpler melts. If slag/metal equi l ib­rium exists during submerged arc welding using laboratory prepared fluxes, there should be a distinct rela­tionship between the FeO content of the slag and the oxygen content of deposits.

The activity coefficient y°FeO is high in CaF,-rich slags. However, measurements of the activity of FeO in CaF2-AI,03 and CaF2-CaO slags sug­gests that Y°FeO in the slags used during submerged arc welding is close to a value of one. This is particularly true if temperatures in the range of 2000 C (3632 F) are considered. It has been shown that there is no distinct correlation between the FeO content of slags and the oxygen content of weld deposits when welding w i th a number of electrodes of varying man­ganese content, and wi th various flux formulations. It fol lows that slag/ metal equil ibrium is not attained during submerged arc welding. Since the derivation of effective reaction temperature depends on this as­sumption, the concept of an effective reaction temperature during welding is untenable.

Weld deposits were analyzed for oxygen and for the total, soluble and insoluble aluminum contents when deoxidant additions were made during welding. The aluminum content of liquid weld metal comprises dissolved aluminum and precipitated Al,0.,. On solidification, the dissolved oxygen content in l iquid weld metal precip­itates as further A l ,0 3 . Consequently, the insoluble aluminum content which was analyzed in deposits came from two distinct sources. In addit ion rapid cooling during weld solidifica­tion could allow oxygen precipitation as FeO or hercynite (FeALO,).

Bearing this in mind, examination of aluminum deoxidation during sub­merged arc welding is best ac­complished using the total analyzed aluminum content values—Table 6. Deoxidation using aluminum de­pends on the reaction:

2 [Al] + 3 [ 0 ] ^ A L 0 3

and, the equil ibrium quotient (K) is given as:

K "AI..O,

[a„]2[a„]3

The equil ibrium quotient (K) has a value of 1014 at 1600 C (2912 F).";

Although the activity of alumina is less than one for the slags employed in this

program it is likely that the reaction is determined by precipitation of A l , 0 3

from the weld metal during cool ing, i.e., the solubility product of alumina [%AI]2 [%OJ3 should be considered.

Solubility product values in sub­merged arc deposits range from 1.29,10-' to 2.9.10"' and are typical of values occurring during conventional steelmaking practice.1" In effect, the conditions attained when aluminum additions are made during submerged arc welding are similar to those occur­ring when aluminum additions are made to molten steel containing oxy­gen in the ladle or mold during steel manufacture. It also follows that employment of a solubility product value of 1 0 " during submerged arc welding wil l permit calculation of the total aluminum content when the deposit oxygen content is evaluated using vacuum fusion analysis.

Conclusions

1. The final oxygen content of submerged arc weld deposits depends on the oxygen content of the elec­trode and on the chemical composi­tion of the flux employed. When using an oxide-free flux such as fused CaF, the weld metal oxygen content equaled that of the electrode. When using low oxygen potential flux formu­lations composed of mixtures of CaF2, A l ,0 3 and CaO, deposit oxygen con­tents were markedly lower in fused fluxes than in agglomerated fluxes.

2. The main source of oxygen when welding with fluxes composed of CaF2, A l ,0 3 and CaO was that due to decomposition of flux constituents during welding, i.e., CaC03 decompo­sition in agglomerated fluxes, CaO decomposition in fused fluxes, and Na20 and K20 decomposit ion when alkali oxide additions were made to fluxes.

3. Oxygen pick-up during welding wi th CaF,-AI,03-CaF2 fluxes was deter­mined by gas/metal reactions occur­ring at the electrode tip region. No correlation existed between the FeO content of slags and the oxygen content of weld deposits. Conse­quently, slag/metal equil ibrium was not attained, and derivation of an effective reaction temperature during welding was not feasible.

4. When welding wi th (45 wt-% CaF2, 35 wt-% A l ,0 3 , 20 wt-% CaO) flux, aluminum additions lowered the final weld metal oxygen content to below that of the electrode. Such low oxygen levels were obtained at the expense of increased contents of aluminum in solution. Aluminum ad-ditons in the flux modif ied the oxygen content of the electrode t ip region, and emphasized the importance of

70-s I M A R C H 1978

electrode t ip reactions in determining the final deposit composit ion during submerged arc welding.

References

1. Lewis, W. )., Faulkner, C. E., and Riep-pel, P. )., "Flux and Filler Wire Devel­opments for Submerged Arc Welding of HY80 Steel," Welding lournal, 40 (8), Aug. 1961, Research Suppl., pp 337-s to 345-s.

2. Palm, J. H., "How Fluxes Determine the Metallurgical Properties of Submerged Arc Welds," Welding journal 51 (8), Aug. 1972, Research Suppl., 358-s to 360-s.

3. Potapov, N. N., and Lyubavskii, K. V., "Oxygen Content of Weld Metal Deposited by Automatic Submerged Arc Welding," Welding Production, 1971, No. 1, pp. 16-20 (Welding Institute translation from Rus­sian).

4. Potapov, N. N., and Lyubavskii, K. V., "Interaction between the Metal and Slag in the Reaction Zone During Submerged Arc Welding," Welding Production, 1971, No. 7, pp. 14-18 (Welding Institute translation).

5. North, T. H., The Distribution of Manganese between Slag and Metal during Submerged Arc Welding," Welding Re­search Abroad, Jan. 1977, Vol. XXIII, pp. 2-40.

6. Franklin, A. O, Rule, O, and Widdow-son, R., "Effect of De-Oxidation Technique on the Oxygen Content of Inclusion Type in 0.2% Carbon Steel," journal of Iron & Steel Inst, 1969 Sept., pp. 1208-1218.

7. Bruch, )., "Determination of Cases in Steel and Application of the Results,"

lournal ol Iron & Steel Inst., 1972 March, pp. 153-162.

8. "British Standard Method for Alumi­nium Analysis in Iron & Steel," 8.5. Hand­book, No. 19, Photometric Method.

9. Christensen, N., and Chipman, )., "Slag-Metal Interaction in Arc Welding," WRC Bulletin No. 15, 1953.

10. Belton, C. R., Moore, J., and Tankins, S., "Slag-Metal Reactions in Arc Welding," Welding lournal, 42 (7), July 1963, Research Suppl., pp. 289-s to 297-s.

11. Tuliani, S. S., Boniszewski, T., and Eaton, N. F., "Carbonate Fluxes for Submerged Arc Welding of Mild Steel," Welding & Metal Fabrication, July 1972, pp. 247-259.

12. Erohin, A. A., "Heat Balance of Elec­trode Melting Process in Arc Welding," Physics of the Arc Symposium, 1962, London, pp. 164-170.

13. Sims, C. E., "The Nonmetallic Con­stituents of Steel," Trans. Met. Soc, A.I.M.E., |une 1959, V. 215, pp. 364-393.

14. Nafziger, R. H., "Oxide-Fluoride Flux Systems for Electroslag Melting," /. of Metals, V. 25, Nov. 1973, pp. 55-61.

15. Widgery, D., "De-Oxidation Practice for Mild Steel Weld Metal," Welding lour­nal, 55 (3), March 1976, Research Suppl., pp. 57-s to 68-s.

16. Fitterer, C. R., "Oxidation and Reoxi-dation in Modern Steel Refining," Chemical Metallurgy ol Iron & Steel, 1971, University of Sheffield, published by The Iron & Steel Institute, pp. 184-191.

17. Noor, M., North, T. H., and Bell, H. B. to be published.

Part II—Oxygen Content, Aluminum and Notch Toughness of Submerged Arc Deposits

ABSTRACT. The influence of alumi­num additions on the notch toughness of submerged arc welds has been investigated. Aluminum concentra­tions up to a critical level of 0.0195% in deposits (corresponding to 1.2 wt-% Al in the flux) improved notch toughness properties. At higher aluminum con­centrations, the toughness properties were worsened.

Aluminum additions had the dual advantage in that they lowered the final deposit oxygen content (raising the upper Charpy shelf values) and modified the weld metal microstruc­ture (so that the transition tempera­ture was lowered).

Introduction

High oxygen content in weld depos­its decreases the notch toughness of weld deposits.1819 It has been shown in Part I that aluminum additions during submerged arc welding produce very low oxygen contents in deposits.

Contradictory results have been indicated concerning the effect of aluminum additions on the notch

toughness properties of submerged arc welds, i.e., Lewis et al'-" noted that 0.027% aluminum in the deposit improved notch toughness properties, and greater contents of aluminum had a markedly detrimental effect on notch toughness when welding HY80 steel. Also, Kushnarev21 noted that aluminum additions up to 0.015% had a negligible effect on notch toughness and that an aluminum content of 0.020% was extremely detrimental to the notch toughness of submerged arc welds.

In this connection, contradictory results have also been obtained when aluminum additions were made during gas-metal-arc welding, i.e., Ul'yanov et a/22 noted that aluminum additions up to 0.60% during GMA-CO, welding were always detrimental to notch toughness properties. Widgery23 noted that 0.12% aluminum had no detect­able effect.

In this paper a systematic study of the effect of aluminum additions on the oxygen content, microstructure and mechanical properties of sub­merged arc deposits is carried out.

Experimental Procedure

The materials employed (plate, elec­trode and laboratory-prepared fluxes) were similar to those noted in Part I. The welding conditions were also identical.

Tests examining the effect of oxygen content on the notch toughness of submerged arc welds employed fluxes comprising varying contents of CaF2, A l jO j and CaO, and electrode wi th the fol lowing composit ion: 0.12% C, 0.29% Si, 0.012% S, 0.012% P, 1.59% M n , 0.008% (O).

The effect of aluminum on notch toughness was investigated using the control flux formulation of 45 wt-% CaF,, 35 wt-% Al 20 3 , 20 wt-% CaO and an electrode with 0.11% C, 0.24% Si, 0.03% S, 0.03% P, 2.10% Mn , 0.017% (O).

Charpy specimens were cut from the final run of ten-high pads and, there­fore, notch toughness results apply to single-run weld metal. Two forms of Charpy specimens were employed in this program—2.07 mm (0.08 in.) diam­eter specimens and 10 X 10 mm (0.39 X 0.39 in.) specimens. When 10 X 10 mm (0.39 X 0.39 in.) Charpy specimens were employed, great care was taken to cut samples only from the final run to ten-high pads. In all tests longitudinal Charpy specimens were employed, and notches were cut at right angles to the direction of weld­ing.

The content of pro-eutectoid ferrite present in weld deposits was evalu­ated using lineal analysis techniques. A Vicker's microscope wi th an automatic counting facility was employed throughout. The percentage of pro-eutectoid present at any given alumi­num level in the deposit was evalu­ated from an examination of sixty regions, i.e., ten traverses on each of 6 Charpy specimens.

Results and Discussion

Oxygen Content and Notch Toughness

Different flux formulations in the CaF2 • A l 2 0 3 • CaO system produced different oxygen potentials during welding (mainly due to differing CaCO., contents in agglomerated fluxes). For this reason, weld deposit analyses and weld metal microstruc­tures varied.

Changes in deposit microstructure were partly due to changes in weld metal composit ion and possibly due to different cooling rates during the welding operation, e.g., increasing car­bonate contents in submerged arc fluxes can modify weld cooling rates due to the endothermic decomposi­tion of limestone during welding.22

Weld samples were consequently

W E L D I N G RESEARCH SUPPLEMENT I 71-s

CHARPY

ENERGY .

joules

60

50

L0

30 002 0-04 005 008

%[0] DEPOSIT Fig. 9-Relationship between the 20 C Charpy values and the oxygen content of heat-treated deposits (lor sub-standard 2.07 mm diameter meter Charpy spec­imens)

Table 7 -

Al (flux)

% 0.4 0.8 1.2 1.6 2.0 0.4 0.8 1.2 1.6 2.00

Tensile Testing Results

Condit ion

As-welded As-welded As-welded As-welded As-welded Stress-relieved Stress-relieved Stress-relieved Stress-relieved Stress-relieved

0.2% proof stress,

M N / m 2

514.3 492.8 517.8 500.1 542.4 413.3 430.4 428.2 401.0 471.5

Ult imate tensile

strength, M N / m 2

646.9 597.4 666.1 647.1 637.9 545.5 562.6 566.7 539.3 536.2

Elongation,

25 29 28 27 30 31 31 29 31 29

Reduction of area,

% 56 57 55 57 55 63 60 61 60 62

given a high temperature furnace treatment-2 h at 925 C (1697 F), fol lowed by 2 h at 650 C (1202 F), and then air-cooled—in order to eradicate microstructural effects.

Weld composit ion variations were most apparent when considering the manganese content (see Table 4, Part I). Since Dorschu and Stout" have

noted that manganese changes from 0.6 to 1.6% caused no observable change in the notch toughness proper­ties of single-run submerged arc de­posits, it is possible to relate the impact values at 20 C (68 F) wi th the weld deposit oxygen content values. Figure 9 shows that high oxygen contents decrease notch toughness

and corroborates previous data.1819

Effect of Aluminum Content on Mechanical Properties

Tensile Tests. Table 7 shows the influence of aluminum on the tensile properties of submerged arc welds in the as-welded and stress-relieved con­ditions. The stress relief treatment was carried out at 600 C (1112 F) for one hour.

Wi th up to 1.6 wt-% aluminum in the flux (corresponding to a deposit aluminum content of 0.031%), no observable effect on tensile properties was noted. The only significant change occurred in the weld deposited using flux containing 2% aluminum, i.e., the 0.2% proof stress was raised. It is apparent from Table 3 in Part I that the nitrogen content of deposits made wi th different aluminum additions in fluxes did not vary markedly; also, the presence of aluminum nitride precipi­tation was not detected in the weld deposited using flux containing 2% aluminum.

The relationship between aluminum content and tensile properties in Table 7 applies to single-run weld metal and is similar to that existing when up to 1% aluminum is added to wrought plate material.24 In multipass welding situations aluminum additions are associated wi th increased tensile strength, e.g., in submerged arc weld­ing,2" in GMA (argon) and GMA (CO,) welding,2225 and in manual-metal-arc welding.26

Notch Toughness. Figures 10-13 show the marked effect of aluminum additions on the notch toughness of submerged arc welds, i.e., aluminum additions up to a critical level improve the notch toughness properties.

Figure 14 shows the relationship between the aluminum content of deposits and the Upper Charpy shelf values. Upper Charpy shelf values are raised when aluminum is added up to

TEMPERATURE'C.

Fig. 10— Effect of aluminum additions of the as-welded notch toughness properties of weld deposits (for 10 x 10 mm Charpy specimens). Flux formulation (45 wt-% CaF^ 35 wt-% A/2Oj, 20 wt-% CaO) with S4 electrode

TEMPERATURE C.

Fig. 11—Effect of aluminum additions on the as-welded notch toughness properties of weld deposits (for 10 x 10 mm Charpy specimens). Flux formulation (45 wt-% CaF,, 35 wt-% AlzO^ 20 wt-% CaO) with 54 electrode

72-s I M A R C H 1978

TEMPERATURE °C.

Fig. 12—Effect of aluminum additions on the stress-relieved notch toughness properties of weld deposits (for 10 X 10 mm Charpy specimens). Flux formulation (45 wt-% CaF.,, 35 wt-XA^O-,, 20 wt-% CaO) with S4 electrode

TEMPERATURE C

Fig. 13—Effect of aluminum additions on the stress-relieved notch toughness properties ol weld deposits (for 10 x 10 mm Charpy specimens). Flux formulation (45 wt-% CaF2 35 wt-% AltO„ 20 wt-% CaO) with S4 electrode

0.0195% ( in t h e d e p o s i t ) a n d are l o w e r e d w h e n fu r t he r a l u m i n u m is a d d e d .

The ef fect o f a l u m i n u m o n the uppe r shel f va lues is ana logous to that ex is t ing w h e n o t h e r d e o x i d a n t a d d i ­t i ons are m a d e d u r i n g w e l d i n g , e.g., s i l i con a d d i t i o n s in m a n u a l - m e t a l - a r c w e l d i n g . 2 6 The in i t ia l i m p r o v e m e n t in uppe r shelf va lues is associated w i t h decreased o x y g e n c o n t e n t o f depos i t s (see Fig. 6, Part I) a n d w i t h decreased i n c l u s i o n c o n t e n t .

Typ ica l i nc lus ions o c c u r r i n g in w e l d depos i t s m a d e w i t h f luxes c o n t a i n i n g a l u m i n u m a d d i t i o n s i n c l u d e a l u m i n a , a lum ino -s i l i ca tes , i nc lus ions r ich in c a l c i u m and a l u m i n u m , and manga ­nese su lph ide . Figure 15 s h o w s i n c l u ­s ions present in w e l d depos i t s , i.e., a 1.5 m i c r o a l u m i n o - s i l i c a t e i n c l u s i o n , a 2.5 m i c r o n i nc l us ion r ich in c a l c i u m a n d a l u m i n u m ( w h i c h is poss ib ly a slag par t i c le caugh t d u r i n g w e l d so l i d i f i ca ­t i o n ) , a n d a 3 m i c r o n a l u m i n a i n c l u ­s ion .

W h e n the a l u m i n u m c o n t e n t o f depos i t s exceeds 0.0195%, t h e c o n t e n t o f a l u m i n u m in s o l u t i o n rises m a r k e d l y (see Figure 8, Part I ) , and the fa l l in u p p e r shel f va lues is assoc ia ted w i t h increas ing c o n t e n t s o f a l u m i n u m in s o l u t i o n . Erasmus27 n o t e d a s imi la r e f fec t in w r o u g h t steels, i.e., a l u m i n u m a d d i t i o n s in excess o f that r e q u i r e d to r e m o v e n i t r o g e n f r o m s o l u t i o n d e ­creased n o t c h toughness s ince the so lub le a l u m i n u m c o n t e n t was i n ­creased.

Transition Temperature

It is appa ren t in Figs. 10 a n d 11 tha t t h e a s - w e l d e d p roper t i es o f depos i t s m a d e us ing f luxes c o n t a i n i n g a l u m i ­n u m p r o d u c e d h igher t oughness v a l ­

ues at any t e m p e r a t u r e t h a n t h e a l u m i ­n u m - f r e e f lux. Lewis et a/20 n o t e d that t h e a s - w e l d e d toughness p rope r t i es o f submerged arc w e l d s in HY80 steel w e r e h igher w h e n 0.027% a l u m i n u m was a d d e d a n d tha t f u r t he r increase in a l u m i n u m c o n t e n t had a marked l y d e t r i m e n t a l e f fec t on n o t c h t o u g h ­ness. These w o r k e r s also i n d i c a t e d that a l u m i n u m a d d i t i o n s m o d i f i e d r o o m -t e m p e r a t u r e and sub -ze ro n o t c h

UPPER SHELF ENERGY JOULES

stress-relieved

0 10 20 Fig. 14—Effect of aluminum content in the flux on the upper Charpy shelf values of weld deposits

t oughness p roper t i es in d i f f e r e n t ways , i.e., decreas ing a l u m i n u m c o n t e n t s i m p r o v e d r o o m t e m p e r a t u r e i m p a c t values and l o w e r e d sub -ze ro impac t values.

The a s - w e l d e d toughness results o f Kushnarev 2 1 s h o w e d no observab le i m p r o v e m e n t in n o t c h t oughness w h e n a l u m i n u m was a d d e d u p t o 0.015% ( in t he depos i t ) and s h o w e d a m a r k e d l y de le te r i ous e f fec t o f a l u m i ­n u m w h e n a d d e d up to 0.020%. It is i m p o r t a n t t o emphas i ze tha t t h e results in Figs. 10 and 11 app ly t o s ing le - run w e l d s and the results o f Lewis2" a n d Kushnarev 2 1 a p p l y t o mu l t ipass w e l d i n g s i tua t ions .

Figure 16 shows tha t a l u m i n u m levels u p to 0.0195% p r o d u c e d a marked i m p r o v e m e n t in t he t r ans i t i on t e m p e r a t u r e o f s t ress-re l ieved w e l d s . Further increases in a l u m i n u m c o n t e n t had a d e t r i m e n t a l e f fec t o n t h e t r a n ­s i t ion t e m p e r a t u r e o f s t ress-re l ieved we lds . The t rans i t i on t e m p e r a t u r e va l ­ue e m p l o y e d was the t e m p e r a t u r e c o r r e s p o n d i n g to an energy a b s o r p t i o n o f 70 jou les ; it was chosen s ince a d i rec t re la t ion b e t w e e n the 70 j o u l e t rans i t ion t e m p e r a t u r e a n d the 0.4 m m c.o.d. t rans i t i on t e m p e r a t u r e has been n o t e d p rev ious ly in s u b m e r g e d arc welds. 2 8

Tab le 6 in Part I s h o w s tha t increas ing a l u m i n u m c o n t e n t s in d e ­posi ts w e r e associated w i t h inc reas ing manganese a n d s i l i con c o n t e n t s in depos i ts . The manganese c o n t e n t i n ­creased f r o m 1.49 to 1.6% w h i l e t h e s i l i con c o n t e n t increased f r o m 0.11 to 0.21%. A 0 . 1 % manganese increase p roduces an i m p r o v e m e n t in t r a n ­s i t ion t e m p e r a t u r e o f a p p r o x i m a t e l y 4 C (7 F) in w r o u g h t C M n steels,29 a 5 C (9 F) i m p r o v e m e n t in mu l t i pass G M A

W E L D I N G R E S E A R C H S U P P L E M E N T I 73-s

Fig. 15—Typical inclusions in weld deposits where aluminum additions were made to the flux; left to right A—1.5 micron alumino-silicate inclusion (X10.000); B—2.5 micron inclusion rich in calcium and in aluminum (X.10,000); C—3 micron alumina inclusion (X10.000). A, B, and C reduced 50% on reproduction

(argon) welds,"' a 7 C (13 F) improve­ment in single pass GMA (CO,) welds,22 and no observable effect on the toughness of single pass sub­merged arc welds when the manga­nese content was varied from 0.6 to 1.6%.31

An increase in silicon content pro­duces no observable effect on the notch toughness of single pass sub­merged arc deposits when added up to 0.5%," and promotes decreased tough­ness in GMA (argon) welds when added in the range 0.35 to 0.80%.30

Since the deposits examined in this program were single run deposits, the marked improvement in notch tough­ness of stress-relieved welds was not

readily explained by changes in silicon and manganese content of weld de­posits.

Change in the aluminum content of fluxes produced deposits wi th distinct microstructure variations. Figure 17 shows the relation between the alumi­num content of the flux and the content of pro-eutectoid ferrite in the deposit microstructure. Decreasing contents of pro-eutectoid ferrite (as the aluminum content increases) favor improved toughness in a manner similar to that occurring in GMA (CO,) welds.23

As the aluminum content was increased, the content of acicular ferrite increased and the presence of

this particular structure promoted im­proved notch toughness. The in­fluence of aluminum in promoting the formation of acicular ferrite is similar to that found when vanadium is added to welds in MnMoNb pipe steels32-33

and when titanium is added to CMn weld deposits." The deleterious effect of high aluminum contents in excess of 0.0195% in deposits was due to the rapid increase in the aluminum con­tent in solution (see Fig. 8, Part I).

Conclusions

1. The aluminum content in the flux which reduced the oxygen content of the deposit to that of the electrode

40

30

20

TRANSITION TEMPERATURE

°C

5C

40

30

20

10

% PRO-EUTECTOID FERRITE.

% Al in FLUX . Fig. 16—Effect of aluminum content in the flux on the transition temperature (corresponding to 70 joules) of stress relieved welds

20 0 -20 -40

TRANSITION TEMPERATURE °C

Fig. 17-Relation between the pro-eutectoid ferrite content and the transition temperature of stress relieved welds

74-s ( M A R C H 1978

employed gave best notch toughness, i.e., highest upper Charpy shelf values and lowest transition temperature. In the submerged arc tests examined, the critical aluminum level was 1.2 wt-% Al in the flux giving 0.0195% Al in the deposit.

2. Aluminum additions had a dual advantage in that they lowered the final deposit oxygen content (raising the upper Charpy shelf values) and modif ied the weld metal microstruc­ture (so that the transition tempera­ture was lowered).

References

18. Masubuchi, K., Monroe, R. E., and Martin, D. C, "Interpretive Report on Weld Metal Toughness," WRC Bulletin No. 19, pp. 1-38.

19. Kubli, R. A., and Sharav, W. W„ "Ad­vancement in Submerged Arc Welding of High Impact Steel," Welding lournal, 40 (11), Nov. 1961, Research Suppl., pp. 497-s to 502-s.

20. Lewis, W. )., Faulkner, C. E., and Rieppel, P. |., "Flux and Filler Wire Devel­opments for Submerged Arc Welding of HY80 Steel," Welding lournal, 40 (8), Aug.

1961, Research Suppl., pp 337-s to 345-s 21. Kushnarev, D. M., and Svetsinckii,

V. C , "Certain Special Features of the Struc­tures of Submerged Arc Welds Made with High-Basicity Fluxes," Automatic Welding, 1972, No. 12, pp. 17-21 (Welding Institute translation from Russian).

22. Ul'yanov, V. I., Parfessa, C. I., and Shevchuk, R. N., "Effects of the Aluminium in Electrode Wire on the Strength of C02

Weld Metal in St. 3 Steel," Automatic Weld­ing, 1974, No. 2, pp. 15-19 (Welding Insti­tute translation from Russian).

23. Widgery, D., "Deoxidation Practice for Mild Steel Weld Metal," Welding lour­nal, March 1976, 55 (3), Research Suppl., pp. 57-s to 68-s

24. Sage, A. M., and Copley, F. E. )., "The Notch Ductility and Tensile Properties of Some Synthetic Mild Steels," lournal of Iron & Steel Inst., August 1960, pp. 422-438.

25. Sibley, C. R., "The Effect of Alumi­num Additions to Mild Steel Weld Metal," Welding lournal, 35 (8), Aug. 1956, Research Suppl., pp. 361-s to 368-s.

26. Sakaki, H., "Effect of Alloying Ele­ments on the Notch Toughness of Basic Weld Metals," lournal Japan Welding Soc, Report I. Effect of Silicon, 1959, V. 28, pp. 858-863 (Translation by Welding Inst. from lapanese).

27. Erasmus, L. A., "Effect of Aluminium

Additions of Forgeability, Austenite Coars­ening Temperature, and Impact Properties of Steel," lournal of Iron & Steel Inst., (an. 1964, pp. 32-41.

28. Farrar, R. A., Juliani, S. S., and Norman, S. R., "Relationship between Frac­ture Toughness and Microstructure of Mild Steel Submerged Arc Weld Metal," Weld­ing and Metal Fabrication, Feb. 1974, pp. 68-73.

29. Van der Ween, "Development of Steels for Off-shore Structure," Rosenhain Conference, London 1976, pp. 223-232.

30. Moll, R. A., and Stout, R. D., "Compo­sition Effects in Iron-Base Weld Metal," Welding lournal, 46 (12), Dec. 1967, Research Suppl., pp. 551-s to 561-s.

31. Dorschu, K. E., and Stout, R. D., "Some Factors Affecting the Notch Tough­ness of Steel Weld Metal," Welding lournal, 40 (3), March 1961, Research Suppl., pp. 97-s to 105-s.

32. Sawhill, ). M., and Wada, T., "Proper­ties of Welds of Low Carbon Mn-Mo-Cb Line Pipe Steels," Welding lournal, 54 (1) Jan. 1975, Research Suppl., pp 1-s to 11-s.

33. Dolby, R. E., "Factors Controlling Weld Toughness—The Present Position," Part 2-Weld Metals, Welding Institute Report 14/1976/7 1976, pp. 1-29.

34. Ito, Y., and Nakanishi, M., Interna­tional Institute of Welding Document, I.I.W. Doc, XIIA-133-75.

WRC Bulletin 229 August 1977

(1) Dynamic Fracture-Resistance Testing and Methods for Structural Analysis

by E. A. Lange

The potential for the initiation of fast fracture can be predicted by the recently developed technology of linear elastic fracture mechanics (LEFM) which has produced the basis for an analytical approach to fracture resistance and structural integrity. To make fracture mechanics a viable engineering design tool, empirical correlations between practical dynamic test results and the basic parameters are needed. In this paper the attributes and limitations of the Charpy, Drop Weight-Nil Ductility Transition Temperature, Drop Weight Tear, and Dynamic Tear tests are discussed with respect to providing information useful in structural integrity analyses.

(2) Junction Stresses for a Conical Section Joining Cylinders of Different Diameter Subject to Internal Pressure

by W. J. Graff

The conical transition section of a cylindrical pressure vessel was instrumented inside and outside with electric resistance strain gages, and from the longitudinal and circumferential strains measured experimentally, the corresponding stresses were determined. The results were compared with calculated stresses from the theory of shells. The experimentally determined stresses exceeded code membrane stresses in the immediate vicinity of the junctions.

Publication of this paper was sponsored by the Welding Research Council. The price of WRC Bulletin 229 is $7.50 per copy. Orders should be sent with payment to the Welding

Research Council, United Engineering Center, 345 East 47th Street, New York, NY 10017.

W E L D I N G RESEARCH SUPPLEMENT I 75-s