Effect of in an GTAW Shielding Gas: Arc Characteristics and Bead Morphology

Hydrogen content in the shielding gas may have as strong an influence on joint penetration as current

BY M. ONSOIEN, R. PETERS, D.L. OLSON AND S. LIU

ABSTRACT. The influence of hydrogen idation, undercutting, porosity, in- rent-carrying capacity of the arc at a additions to an argon shielding gas on the clusions, fusion, and joint penetration given voltage, or arc length (Refs. 5, 6). heat input and weld bead morphology (Refs. 1-4). The actual voltage to main- An addition of hydrogen to argon or was investigated using the gas tungsten tain a stable high-pressure arc is para- gives an arc a wider temperature process. Variations in weld metrically determined by the arc length distribution, a larger heat input and a bead size and shape with hydrogen ad- and welding current level, and is influ- slightly reducing atmosphere (Reg. 2, 7). ditions were related to changes in the enced by the conductivity of the arc. The higher heat input can partially be re- ability of the arc to generate heat and not Charge carrier concentration and the lated to the dissociation of diatomic hy- to generate perturbations in the weld mean free path between electron-parti- drogen in the arc to form atomic hydro- pool caused by Marangoni fluid flow. cle interactions are the two major factors gen, which then recombines to the that determine arc conductivity. A gas molecular form in the cooler regions of the Introduction with low-ionization potential will easily arc and at the surface of the workpiece ionize to form a plasma. As a result, the (Ref. 7). Ionization of atomic hydrogen Shielding gases have as a primary role "large" number of electrical charge carri- contributes further to the increase in heat the protection of the weld and its sur- ers in the arc increases the electrical con- input. Similarly, the presence of hydrogen roundings from atmospheric and ductivity. The ionization potential of an also affects the current-carrying capacity . At an adequate flow rate, they is an indirect measure of the cur- of argon or helium. The reducing atmos- displace these two gases from the weld phere will lead to a cleaner weld bead sur- zone. The ability of a shielding gas to per- face and, in multiple pass welds, reduces form the protective role will depend on the tendency for oxide/slag buildup. In gas its chemical composition, which has a tungsten arc welding, hydrogen also significant influence on arc initiation, arc serves to prevent oxidation of the non- stability, plasma diameter, and plasma KEY WORDS consumable (Refs. 2-4). temperature (radial temperature distribu- Addition of hydrogen to the shielding tion and peak temperature). The physical Hydrogen Effect gas has also been reported to increase the and chemical nature of the shielding gas Argon Shielding Gas surface tension of liquid because of a decrease in surface oxygen also affects other arc and weld properties GTAW concentration (Ref. 8). Surface tension such as metal transfer, spatter, surface ox- Arc Characteristics and its gradients can significantly affect Bead Morphology weld bead size and morphology. A clean Heat Input M. ONSOIEN, D.L. OLSON and S. LIU are liquid metal surface promotes conditions Arc Resistance with the Center for Welding and Joining Re- where Marangoni fluid flow (surface ten- Joint Penetration search, Colorado School of Mines, Golden, sion driven flow) and the dominant Colo. R. PETERS is with Delft Technological Heat Gener. Process mechanism in the overall weld pool me- University, Delft, The Netherlands. Welding Potential chanics, which results in a broader and Paper presented at the AWS 75th Annual shallower weld bead (Refs. 9-11). If the Meeting, held April 10-14, 1994, in Philadel- reducing action of hydrogen is sufficient phia, Pa. to remove surface oxygen, then hydro-

10-s I JANUARY 1995 gen additions should promote

Marangoni fluid flow and form shallow 17 " I " I " I " I " I " I " I "

and wide weld beads. Since hydrogen IS

additions may affect many physical prop- 1S erties of the plasma, this investigation is performed to determine the hydrogen in- J teraction or interactions that control the ."" V reported variations in heat input and |,,

bead morphology. II

Experimental Procedure 11(10 ' 80, . 1~, . 120, . 140, . |Eo, . 180, . 200, . 220 EO 100 120 140 180 180 200 220 o 0 vol.pct. H 2 w@d]ng Cu~nt (~1 Tests were designed and performed to Weldlne Cummt (A) • 1 vol.pct. H 2 v 2 vol.pct. H 2 evaluate the influence of hydrogen addi- • 3 voi.pct. H2 tions to argon shielding gas on the arc a 4- vol.pct. H 2 characteristics and bead morphology in 17 • , • , . , . , - , . , . , . Arc LJreU~ - 8.5 mm A~-IIm . • . ; 18 of Type 304 18 stainless steel. The shielding gases used 15

were pure argon and argon with 1, 2, 3 14 and 4 vol-% hydrogen. A constant-cur- 13 rent power source was used with a direct 13 current electrode negative polarity to |,, 12 make bead-on-plate welds. The diameter 11

of the 2% thoriated tungsten electrode 10 10

was 3.2 mm (1/8 in.), and the electrode , . , . , . • , . i . i , , . , • , . J . 80 1~ 120 140 1110 180 200 22O 980 ' 80/ , IO0' • 120' • 140' ' 1(10 i80 2OO 220 tip had a vertex angle of 30 deg. The tip (A) Wmkllnql cummt (A) Wlldlng Cu~.t of the electrode was truncated with a flat top of 1.3-mm diameter (0.05-in.). The base material used was a Type Fig. 1 -- Arc characteristics for GTA welds with five different argon-hydrogen shielding gas mix- 304 stainless steel, and its chemical com- tures and arc lengths of: A -- 2.5 ram; B -- 5 mm; C -- 6.5 ram; D -- 8 mm. position is shown in Table 1. The test plates measured 12.7 x 76 x 152 mm (0.5 x 3 x 6 in.). The plate thickness satisfies Table 1--Chemical Composition of the 304 Stainless Steel Base Plate the usually accepted conditions of three- Alloying Elements (wt-%) dimensional heat transfer (-0.5 in.) Bead-on-plate welds were made C Si Mn Ni Cr P S Cu Co Mo V using systematic variations in welding 0.03 0.44 1.54 9.3 18.9 0.025 0.003 0.10 0.11 0.01 0.01 parameters. The current settings were 80, 100, 130, 160 and 200 A. The arc lengths were 2.5, 5.0, 6.5 and 8.0 mm (0.1, 0.2, 0.25 and 0.3 in.). The shielding gas flow rate was fixed at 11.8 L/min (5.6 ftg/h), and the welding travel speed for all the welds was 2.1 mm/s (5 in./min). The travel speed was maintained constant to welding voltage to 18 I I I I ensure similar effect of travel speed on maintain the welding bead shape in each specimen. arc. 2 vol.pct. H 2 The weld specimens were sectioned Hydrogen addi- 16 and prepared according to standard met- tions also increased [] a ,'",/: allographic techniques and macroetched the welding voltage, • . • ,~r /// using Villela's reagent to reveal the bead confirming the influ- 14 size and shape, that is, area, joint pene- ence of dissociation • • - . ~" - tration and width• ionization of the di- atomic gas. With in- 12 Results and Discussion creasing arc length, the welding potential "1o 10 The arc characteristic curves for vari- increases, and the in- ous arc lengths and hydrogen contents in fluence of the hydro- S • IOOA the shielding gas are shown in Fig.lA to gen content becomes / V 130A 1D. For a constant arc length, welding even more apparent. • 160A voltage was observed to increase with in- It is known that in- [] 200 A creasing welding current. This change is creasing the arc 6 I , I , t I 2 4 6 8 1o expected because of the arc temperature length increases the 0 increase with increasing welding cur- arc resistance, and it Arc Length (ram) rent. A higher arc temperature generally appears that further indicates a more chaotic charge carrier increases in arc resis- Fig. 2 -- Extrapolation of welding voltage to obtain zero arc length motion path, which requires higher tance occurs with in- potentials.

WELDING RESEARCH SUPPLEMENT I 11-s for both dissociation of

7 .... , .... J .... 4 .... [ .... ; .... , .,.. ,. H 2 and ionization of : ~. tooA // ¢~l I=mA o / ,L ~" I atomic hydrogen. The addition of hy- i ,~v"~1,,'~" /" / drogen to argon requires i higher applied potential I 3 to maintain a stable arc, and increasing hydro- gen content further in- creases the welding po- "~2;; .... f1 4 i • Io l 4 • | IO tential. If the welding arc is modeled as a series circuit, it is possible to isolate the portion of the potential drop that is un-

C,j~ * 200 A related with the arc phe- ¶ cunw,t = Iio A / / nomenon by extrapolat- *~- // • o 0 vol.pct. H2 I1" ,J" • 1 vol.pct. H 2 ing the data of measured v 2 vol.pct. H 2 /~/ / voltage to zero arc 4 /. ~11 o • 3 volpct H 2 It / length -- Fig. 2. The o 4 vol.pct. H2 I ! nonarc portion includes I /,~¢ O1" the tungsten electrode, = ;s /.. ~" the work and other con- ductive paths of the , .... . | SO 1 * I welding circuit. By sub- A,c ~ (ram) tracting the nonarc po- tential from the welding Fig. 3 -- Effect of arc length on arc voltage for GTA welds made with five argon-hydrogen shielding gas mixtures potential (voltage) data, and welding current levels of: A -- 80 A; B -- 100 A; C -- 130 A; D --180 A; E -- 200 A. the arc voltage is ob- tained. The arc voltage creases in hydrogen content. This expla- ization energy less than that of the first plotted as a function of arc length for var- nation agrees with the experimental find- ionization energy for argon, 13.6 and ious currents and hydrogen contents in ings that increases in arc resistance will 15.8 eV, respectively, the formation en- the shielding gas is shown in Fig. 3A to E. require higher applied potentials to ergy of a hydrogen ion is greater than that The results show a strong influence of hy- achieve a stable welding arc. Even of an argon ion, considering the thermal drogen content on the potential needed though monatomic hydrogen has an ion- equilibrium and the law of mass action across the arc to achieve a suitable weld- ing plasma. At all welding currents, the welding arc voltage increased with the

. • , - , • , • , arc length. And at each welding current, 0.07 - ~ " ' " ' /vc Len~h -- 5 mm : /m= L*ngth. 2.5 rnm welding arcs with higher hydrogen con- o.oe tents required higher voltage to stabilize

0.05 the arc. 0.05 Examining Fig. 1A to D, it can be rec- ~'~ 0.04 0.04 ognized that the slope of these curves is

0.03 t o.03 a measure of the arc resistance. As the arc

0.02 .... /'~ ~ ._v~ v - resistance increases, the arc voltage must also be increased to sustain the arc. The .o electrical resistance of the arc is plotted 0.00 Iv i - 1 . i o.1111 ' - ' ' * ' i , i 1 2 3 4 as a function of the hydrogen content in I 2 3 4 o 80A Amount of Amount of H~imen (voLpct.) Hydro~ln (~l.pct.) Fig. 4A to D for the various arc lengths • 10OA and current levels studied in this investi- v 13OA gation. Higher hydrogen content in the • 160A o 200 A shielding gas resulted in higher arc resis- 0.07 " ' " ' " ' " ' " ' 0.07 Are L~'~,.h - S.5 ~ 'i~iAte Lenoth -- 0 mm •0 .-~ tance. This observation is particularly 0.06 o.o0 o~ true for lower current welds, for example,

0.00 0 05 between 80 to 160 A -- Fig. 4B to D. In- creasing welding current from 80 to 160 0.04 1" • v 0.04 V A changed the arc resistance-hydrogen Le V . - -V 0.03 0 03 content relationship. It appears that in- :x ~_.-"~ r:7"7 . P 0.02 - o ~ - -(~ o o 0,02 Q creases in the hydrogen content en- ~r- ~- • hances the expected increase in arc re- o.0T sistance with increased arc length. At 0 O0 I I I I I o.o0 i , • ' • ' higher welding currents, for example, 0 1 2 3 4 1 2 3 4 Amount of Hydrogen (vol.pct,) Amount of Hydrog*n (~l.pct.) 200 A, the arc resistance remained al- most constant with the amount of hydro- Fig. 4 -- Effect of amount of hydrogen in the argon-based shielding gas on arc resistance for GTA gen added in the shielding gas. Arc resis- welds made with arc lengths of: A -- 2.5 mm B -- 5 mm C -- 6.5 m; and D -- 8 mm. tance is, however, also a function of the

12-s I JANUARY 1995 number of charge carri-

. , - , . , . • , • , . , • , . ers. If the number of 0.07 0.07 CurraNt - B0 A .#V' Curront - 100 A --/ charge carriers is al- 0.05 ~" 0.06 O.OB /t" ready sufficient to sus- 0 ? 0.05 '~" 0.05 tain a stable arc because /" 8 o.o,~ of the higher applied .... .,t/ 0.04 ~' /17" D ~ y current, then small addi- 0.03 0.03 II.... tions of hydrogen will 0.02 0.02 have no or minimum ef- o.01 0.01 0.0l I fect on arc resistance. Z. , . o.o0 o.oo ~ - ' • ' " ' - ' ' 0.00 2 4 8 0 10 For 2.5-mm arc length, 2 4 0 0 lO 2 4 0 0 10 Arc LmmJth (ram) Arc LImoth (ram) the trends are less clear Arc Lmngth (ram) and the hydrogen addi- tions showed only a small influence on arc

O.O7 " ' " ' " ' " ' 0.07 resistance. Cu~t - 160 A Currmnt - 2O0 A o 0 vol.pct. H2 t Similarly, the arc re- 0.06 0.00 sistance is shown as a • 1 vol.pct. H2 0.00 v 2 vol.pct. H2 o o, f function of arc length for • 3 vol.pct. H 2 & 0.04 various currents and hy- / o 4 vol.pct. H 2 drogen contents in Fig. .!J o.O,o.o~o.o~ ~ t"" 5A to E. An increase in o.o2 -'..~~ the arc length results in 0.oi ~ ~ o.01 higher arc resistance. The data again show 0"000 2 4 8 0 I0 0"°°0 2 4 0 0 10 /v¢ ~,lth (ram) b..~h (~) that with arc lengths greater than 2.5 mm and Fig. 5 -- Effect of arc length on arc resistance for GTA welds made with five argon-hydrogen shielding gas mix- current levels below tures and welding current levels of: A -- 80 A; B --100 A; C -- 130 A; D -- 180A; E -- 200 A. 200 A, hydrogen addi- tions to a shielding gas have a significant influence on the arc re- Z is the stage of ionization, and for this will increase the transport parameter, L, sistance. It can also be observed that the case, Z is equal to one and n e is the elec- and decrease the conductivity of the data are consistent with the expected ex- tron concentration in the plasma. plasma. Consequently, the arc resistivity trapolation that the arc resistance will go For gas mixtures, the electron con- increases. This estimate agrees well with to zero at zero arc length. centration, ne, can be related to the indi- the experimental data in Figs. 4 and 5. The zero arc length potential, which vidual electron contributors by the law of The bead width was measured as a relates to the voltage drop mainly in the mixtures: function of hydrogen content in an argon tungsten electrode and thus the resistiv- shielding gas for various arc lengths (volt- ity of the cathode (electrode and cathode n e = XAneA + XHneH age) and current. Figs. 7A to D illustrates spot), was found to decrease with in- where XA and X H are the mole fractions the results and demonstrates a systematic creasing current as seen in Fig. 6. Know- of argon and hydrogen ions in the increase in width with increased current. ing that the increasing current increases plasma. XA is related to the temperature of the tungsten electrode XA by XA + X H = 1. neA and thus the resistivity of the hot tungsten and nell are the elec- electrode, it must be the increases in tron concentrations of 12 I I I I I I I thermionic emission of electrons at the argon and hydrogen cathode spot that gives the apparent re- calculated using the duction in resistance with increasing cur- Saha equation (Ref. • ••P "•0 rent. This explanation seems to suggest 13). The derivation of >~ 11 that the impedance associated with the this equation assumed -6 thermionic emission predominates over local thermal equilib- "" the impedance associated with the tung- 10 rium. Q.o sten electrode. With increasing hy- ,~.'" / Spitzer (Ref. 12) derived an expres- drogen content and • .".'.2~. sion for the conductivity of a plasma in- considering the situa- e, 9 / •Q,~ /0 volving single ionization, o, as: tion where the effec- <:P G tive ionization/disso- p ~O / / 0 0 vol.pct. H2 2 0 ~' • I vol.pct. H2 ciation" potential for N B / V 2 vol.pct. H 2 O. = 1.53 X 10-2 T3 hydrogen is much LnL • 3 vol.pct. H 2 larger than for argon, it n 4 vol.pct, H 2 where T is the arc temperature and L is can be realized that n e the transport parameter. L can be written i l I I l I I i I , decreases with in- 76O 80 100 120 14-0 160 180 200 220 as: creasing hydrogen Welding Current (A) 1.25 x 107T 3/2 content. Consider L= Equations 1 and 2, it is Z 1/2 Fig. 6 -- Influence of welding current on zero arc length potential Re apparent that increas- for GTA welds made with five argon-hydrogen shielding gas mix- ing hydrogen content tures.

WELDING RESEARCH SUPPLEMENT I 13-s role of hydrogen becomes more apparent • , . , • , • , ..J • , • r " ' " ' and can be seen as strong a parameter as tO F 0 o o current to control penetration. For a con- 0 .° .... °• _--V--o stant-current welding situation increas- 8): .... • ...... _V____y_, i I ing the hydrogen content will cause a [ --~--~-_ ~ definite increase in the heat generation i eF - -- -e-- --~ -- -9- _ --II-- e~.~ 0 by the welding arc, which again will in- i ~ ~o - crease the penetration. For example, at ! 200 A and an arc length of 6.5 mm, an increase in hydrogen content from 0 to 4 A'~ IJn~h - ~ mm vol-% increased the penetration by over 0 I I I I I O~ 1 2 3 4 IKit 0 I 2 3 4 o 80A 50%. Amo.~! of ~yd~eln [v~l p~.) • 100 A The overall influence of hydrogen on m ! v 130A • 160A bead morphology can be seen in Fig. 9A a 200 A to D, which plots width-to-depth ratio as I . , - , - , • , | a function of hydrogen content. Increas- - Q .... rz 0 I( o O o [] " • • __~__--~-" ing hydrogen content significantly re- • _,rl - - - v ____ ..... -- I~ | duces the width-to-depth ratio, espe- cially for the lower current levels. This behavior is in agreement with observa- Z I tions reported in the literature (Ref. 14). II Comparing Figs. 7A to D, 8A to D, and 9A to D, it can be concluded that hydro- I gen influences weld depth more than An~ Length -- 8 mm koe41th -- 6.5 mm ,In I I I I I width, which is opposite to that expected i I I I 1 2 3 4 if the controlling mechanism for the in- I fluence of hydrogen was the surface ~im=w i

Fig. 7 -- Effect of amount of hydrogen in the argon-based shielding gas on weld bead width for cleaning of the weld pool surface and its GTA welds made with arc lengths of: A -- 2.5 ram; B -- 5 mm; C -- 6.5 ram; D -- 8 mm. I influence to promote Marangoni fluid flow (radially outward flow). ,~d[I With an arc length greater than 2.5 mm, The weld depth was found to be sig- Hydrogen in argon shielding gas was found to affect the welding arc in several I the bead width increased by a factor of four nificantly influenced by increases in hy- I with increasing current from 80 to 200 A. drogen content in the shielding gas. Fig- aspects, mainly the electrical conductiv- Bead width also showed a tendency to in- ure 8A to D illustrates the variation of ity of the arc. The presence of diatomic crease with increasing hydrogen content. depth as a function of hydrogen content hydrogen requires extra energy for disso- However, these variations were small for various conditions of arc length and ciation and ionization. For a particular compared to the influence of current. current. With increasing arc length, the set of welding parameters, the number of charge carriers in an argon shielding gas with hydrogen additions is decreased, and the welding voltage increased. As a

D , result, the amount of heat transferred to 0 UJI • O Q o 121 the weld and the size of the weld bead is o v _.~ also affected. Figure 10A to D illustrates the signifi- ] 1 cant increases in weld area (fusion zone) ~ I with increasing hydrogen content. The influence of hydrogen to increase the ef- fective heat input is more dominant for ~r" Arc Length - 5 ran1 Arc Longth - 2.5 mm the larger arc lengths and higher current I I I i 1 2 3 4 1 2 3 4 o 80A welds. It is apparent by considering both Amo.nt of I-~drogefl (~l pcl.} Ar~t of Hydr~n (~.pct.) • 100A the changes in weld area and width-to- v 130A

• 160A depth ratio with increasing hydrogen o 200 A content, that hydrogen increases the heat input by altering the heat generating m process in the arc and not by altering the 4 I [] O o 0 • weld pool fluid flow behavior as sug- • O !- " [] gested by a Marangoni fluid flow model.

Conclusions 11: Based on the experimental results, the

~klu~ h - 8 mm following main conclusions can be Arc Lo~gth -- 8S mm 0 Lf'"~'J~,, , l Arc,L~gr" ,ss mtm drawn: I 2 3 4 ! 2 3 4 Amount of H~dro~len (~t.p=t.) 1) Hydrogen additions to the shielding kr, ount of H~ro~n (~l.pct.) gas changed the arc characteristics and

Fig. 8 -- Effect of amount of hydrogen in the argon-based shielding gas on weld bead depth for increased the arc resistance in gas tung- GTA welds made with arc lengths of: A -- 2.5 mm; B -- 5 ram; C -- 6.5 ram; D -- 8 mm. sten arc welding, thus increasing the heat

14-s I JANUARY 1995 input and decreasing the depth-to-width 3) Hydrogen was found to have Acknowledgment ratio of the weld. changed the weld bead size and shape by 2) Hydrogen additions to the argon influencing the heat generating processes The authors appreciate and acknowl- shielding gas during gas tungsten arc in the arc and not by perturbing the weld edge the research support of the United welding can achieve increases in pene- pool fluid flow through Marangoni flow States Army Research Office. tration of over 50%. behavior. References

1. Bilmes, P., Gonzalez, A., LIorente, C,. 0 • , • , . , . , Llr.gth - 2.5 mm Am L~r~t~ - 5 mm and Solari, M. 1992. The effect of shielding 7 gas oxidation potential on GMA stainless steel weld microstructure and toughness. Lemit Ar- gentine, llW Doc. 11-1187-92, Amer. Delega- £ 0 tion, AWS, Miami, Fla. 2. Brosilow, R. 1978. Gases for shielded I |IS 4 metal arc welding. Welding Design and Fab- rication 46(10): 63-72. 3. Lucas, W. 1992. Shielding gases for arc |, welding -- part 1. Welding and Metal Fabri- cation 60(6): 218-225...... I i I I I t ~ 3 4 I 2 ..3 4 4. Hilton, D. 1990. Shielding gases for gas o 80A Amour~ ~f Hydrogen (v~.pd.) k~.,o,~t of l.~droe*n (vol,pct,) • IOOA metal arc welding. Welding and Metal Fabri- v 130A cation 58(7): 332-334. v 160A 5. Sadek, A. A., Ushio, M., and Matsuda, o 200 A F. 1987. GTA cathode and related phenom- , • , - r ' , • , Arc I.w~lh. O mm ena. Transactions ofJRWl 16(1 ): 195-210. 6. Welding Handbook, 7th Edition, Vol. 2, Welding processes --arc and gas welding and cutting, brazing and soldering, AWS, Miami, Fla. ,~ ~ -.'~ 7. Key, J. F., Chart, J. W., Mcllwain, M. W. 1983. Process variable influence on arc tem- perature distribution. Welding Journal 63(7):179-s to 184-s. 8. Wen, J., and Lundin, C. D. 1986. Tech- nical note: surface tension of 304 stainless "I, i? 1 2 3 4 steel under welding conditions. Welding Jour-

Amount =f Hydrog~m (~14~='~) Amount of Hydr~len (voI,pct.) nal 66(5):138-s. 9. Heiple, C. R., and Roper, J. R. 1982. Fig. 9 -- Effect of amount of hydrogen in the argon-based shielding gas on weld bead width-to- Mechanism for minor element effect on GTA depth ratio for GTA welds made with arc lengths of: A -- 2.5 ram; B -- 5 mm; C -- 6.5 ram; D fusion zone geometry. Welding Journal 61(4): -- 8ram. 97-s to 102-s. 10. Choo, R.T.C., and Szekely, J. 1991. The

, - , - , - , • , I v l • 1 " I • effect of gas shear stress on the marangoni 30 " At© Len91h. 5 mm flows in arc welding. Welding Journal 70(9): O O O a u 223-s to 230-s. 25 25 11. Lancaster, J. F. 1984. The Physics of "~ ,0 O "EE 2O Welding, Chapter 2, The physical properties of • _---° fluids at elevated temperatures, pp. 9-42, | ,s 'F- Pergamon Press, N.Y., N.Y. s __-V ~ | V 12. Spitzer, L. 1962. Physics of Fully Ion- | ,0 ized Gases. John Wiley, N.Y., N.Y. 13. Saha, M. N. 1920. Ionization in the solar chromosphere. Phil. Mag., 40, p. 472.

I , I , I , I , I 14. Bennett, B. 1990. Gasses for TIG and ! 2 3 4 I 2 3 4 0 80A . Welding and Metal Fab- ~t of H~roc., (~l.pct.) ~o~n~ of Hydrogen (~Lpc~.) • IOOA rication 58(7). v 130 A • 160A a 200 A

3O Arc Length - S mm .... L;~I~i~iii~ ()L~!i~! !,~:,:#~ ~~: ~ ~ { ~ ,~

[3 D 2~, T- 2~ I,,,R " ,, "~ 'Ii ~ = ~I O ~ r

[] ° * I,,F- .--"" t ,5 I

S

o 0.~- I 2 l 4

Amount of H)'d~gen (~l.pct.) Amount o1 Hydrogen (~l.pct.)

Fig. 10 -- Effect of amount of hydrogen in the argon-based shielding gas on weld bead area for GTA welds made with arc lengths of: A -- 2.5 mm; B -- 5 mm; C -- 6.5 ram; D -- 8 ram.

WELDING RESEARCH SUPPLEMENT I 15-s