A Study of the Submerged Arc of Titanium

Submerged of titanium is technologically feasible; the major problem today is the operability of the

BY D. C. HILL AND C. L. CHOI

ABSTRACT. This report presents the lurgical compatibility and structural CaCI2 CsCI-CaCI, RbCI-CaCI, results of a study of halides as can­ integrity. didate materials for submerged arc The technical tasks associated with welding of titanium alloys. Criteria are this program involve identification of defined for optimum performance candidate flux systems, formulation of and tests are performed to screen fluxes, and welding tests. Identifica­ candidate fluxes. CaF2-base fused tion of candidate systems includes fluxes are found to offer preferred consideration of oxygen activity, welding characteristics. Four promis­ moisture resistance, and char­ ing compositions are identified: CaF2, acteristics. Formulation of these flux­ CaF2-(5%) BaCI2, CaF2-(5%) es requires the development of new SrF2«SrCI2 and CaF2-(5%) BaCI2- process technology. The successful (2%) LiF. completion of the program is demon­

Groove welds made with CaF2 flux strated by welding tests. and Ti-6AI-2Cb-1Ta-1 Mo Most of the literature dealing with 2 4 6 8 10 12 produce strength-toughness com­ the formulation of fluxes for the sub­ EXPOSURE TIME (hours) binations of 1082 MPa_^ 47 merged arc welding of titanium has 2 MN\m/m (157 ksi — 41 kskin.) with been published in the Soviet Union by Fig. 1 — Moisture absorption data for no auxiliary shielding and 999 MPa — S. M. Gurevich and co-workers at the selected fused chlorides and chloride 69 MNvm/m2 (145 ksi — 60 kskin.) Paton Welding Institute (Ref. 1). In ad­ compounds with auxiliary argon shielding. Heat dition, Gurevich has US Patent 3,551 ,- treating the welds at 535 C for 1 h 218 "Flux for Welding Titanium and its resulted in small decreases in Alloys" (Ref. 2). Gurevich has con­ welding applications. The preferred strength and corresponding small in­ centrated on developing a CaF2 base flux compositions are CaF2-(5- creases in toughness. flux to which small amounts of BaCI2, 21%)BaCI2-(1-5%)NaCI-(0.5-1.5%)NaF NaCI and NaF are added. The (Ref. 2). Introduction applicable quaternary phase di­ The only extensive study of fluxes agram has not been developed, but for the submerged arc welding of The high reactivity of titanium pre­ since the quantities of NaF involved in titanium conducted in the United vents the use of oxide-base sub­ the flux are small, the system may be States was done by H. F. Petsch of merged arc fluxes such as those represented by the CaF2-BaCI2-NaCI Electric Boat under contract to the developed for ferrous welding. In ternary diagram. This diagram has Naval Applied Science Laboratory order to develop fluxes suitable for been established (Ref. 3) and shows (Ref. 5). It is not known whether any titanium welding, investigators have that all of the fluxes covered by the patents were issued as a result of this built on a CaF2 base. While satis­ Gurevich patent are single phase work. Petsch also concentrated on factorily providing a medium for CaF2 solutions with melting points in developing a CaF2 base flux. The maintaining a stable arc, these fluxes excess of 1000 C. The Gurevich fluxes composition with the best operability have not been capable of fulfilling the are reported to produce high quality was CaF2-(5%)BaCI2-(2%)LiF. additional requirements of metal- welds with no porosity and good Minimum weldmetal oxygen was ob­ mechanical properties (Ref. 4). It is tained with C a F 2 - (5 %) L i F - not clear from the patent whether (3.5%)SrCI2«SrF2. Both of these fluxes these fluxes must be fused or whether can be expected to solidify as single D. C. HILL is Group Leader and C. L. CHOI simple mechanical mixtures of the is Senior Research Metallurgist, Linde Re­ phase CaF2 solutions at tem­ search Department. flux components will suffice for peratures in excess of 1000 C. These

152-8 I JUNE 1 97 6 fluxes performed best when made as melt. Time-temperature data was chloride mixture or chloride com­ mechanical mixtures of the flux com­ taken using a Houston Instruments y-t pound was found with a melting point ponents. In general, the overall per­ recorder. For casting, the melt was above 1000 C. This disputes the find­ formance of these fluxes could be poured into a graphite mold and ings of E. P. Dergunov et al (Ref. 6) judged inferior to the claimed per­ allowed to solidify. The flux was who found a significant region of high formance of the Gurevich fluxes. crushed in a Bico Pulverizer. melting point chloride mixtures in the This program seeks to re-examine The fused fluxes were analyzed for RbCI-CsCI-CaCI2 system. The high- the application of submerged arc carbon content, as contamination welding to titanium by considering the from the crucible would be unaccep­ fundamental requirements for a flux table. Typical carbon analyses were: system and by experimentally measuring the physical char­ Melt Wt % Carbon acteristics of candidate fluxes. NaCI 0.02 RbCI 0.02 Flux Studies RbOCaClj 0.02 Fused Flux Preparation CaF2 0.01 Note that the carbon content did not Fused fluxes were prepared by exceed 0.03%. charging into a high purity graphite crucible and melting in a 30 kW Elec­ Melting Point Studies trotherm Induction Furnace. Flux lots were 250 grams and 2000 grams. The Melting point determinations on 0 2 4 6 8 10 flux was melted under air for 15 halide fluxes were made using a ther­ EXPOSURE TIME (hours) minutes. For thermal arrest studies, a mal arrest technique. Those systems Fig. 2 — Moisture absorption data for se­ Pt-Pt/Rh thermocouple shielded with studied included RbCI-CsCI-CaCI2 lected fused fluorides and fluoride com­ an alumina tube was immersed in the and RbCI-CsCI-BaCI2. No chloride, pounds

Table 1 — Welding Parameter Study for Fused CaF, Flux

Wire Volt­ Cur­ Exten­ Travel Wire Elec­ Flux Slag Bead size, age, rent, sion, speed, feed, trode burden, remo­ smooth­ Bead Bead mm V A mm mm/s mm/s angle mm val ness shape color

1.6 28 205 20 6.3 108 vert 20X13 — P P shiny 1.6 33 215 20 6.3 108 vert 20X13 — F F yellow 1.6 32.5 210 20 6.3 94 vert 20X18 — G G lustrous 1.6 31.5 210 20 6.3 94 vert 20X26 — G G dull 1.6 34.5 200 20 6.3 87 vert 20X26 — G G blue 1.6 34.5 200 20 6.3 87 vert 20X26 G G P shiny 3.2 35.5 420 20 6.7 36 vert 26X26 F G P yellow 3.2 36 400 20 6.7 33 vert 26X26 F — — — 1.6 34 240 20 6.3 108 vert 26X26 F G F — 1.6 34 245 20 6.3 108 vert 20X26 F G VG Yellow 1.6 34 260 20 6.3 138 vert 20X26 F G G dull 1.6 34 260 20 6.3 138 vert 20X26 F G G yellow 1.6 34.5 220 20 5.1 94 vert 20X26 G G G yellow 1.6 34 245 13 6.3 99 vert 20X26 G G G yellow 1.6 30 240 13 6.3 110 10°lead 20X26 G G G — 1.6 34 245 13 6.3 97 vert 20X26 G G G — 1.6 34 240 13 6.3 97 vert 20X26 G G G — 1.6 34 240 13 6.3 97 vert 20X26 G G G — 1.6 34 235 13 6.3 97 vert 20X26 G G G yellow 1.6 34 240 13 6.3 97 vert 20X26 G G G — 1.6 34 240 13 6.3 97 vert 20X26 G G G — 1.6 34 220 13 6.3 76 vert 20X26 G P P — 3.2 32 400 13 8.5 40 vert 26X26 G G G yellow 3.2 34.5 440 20 8.5 36 vert 26X26 G G G yellow 3.2 34.5 390 20 8.5 42 10° lead 26X26 G G G yellow 3.2 34.5 405 26 8.5 42 vert 26X39 G G G dull 3.2 34 435 26 8.5 47 vert 26X39 F F G yellow 3.2 35 415 26 8.5 42 vert 26X39 F G G dull 3.2 33.5 445 19 8.5 48 vert 20X26 F F F yellow 3.2 34 425 19 8.5 42 vert 33X39 F G G yellow 3.2 36 430 19 8.5 42 vert 33X39 F G G yellow 3.2 35 450 19 8.5 48 vert 26X26 F G F yellow 3.2 34 600 19 8.5 70 vert 26X26 P G G yellow 3.2 35 425 19 8.5 42 vert 26X26 G G G blue 3.2 35 430 19 8.5 42 10° lag 26X26 G G G yellow 3.2 35 430 19 8.5 42 10° lag 26X26 G F P yellow 3.2 34 390 26 8.5 38 vert 26X33 G G G yellow 3.2 36 425 26 8.5 44 vert 26X33 G G G yellow 3.2 34 390 26 8.5 38 vert 26X33 G G G dull 3.2 34 380 26 8.5 38 vert 26X39 G F P yellow 3.2 34.5 220 19 8.5 22 vert 26X39 VG VG VG yellow

WELDING RESEARCH SUPPLEMENT! 153-8 est melting point found in this system C. Three were determined to be in ex­ grade components in a Patterson- was 896 C for CsCI»CaCI2. The high­ cess of 1300 C. These are CaF2, 1364 Kelley Blender. Flux lots were 250 est melting point of any chloride ma­ C; SrF2, 1340 C; and, BaF2, 1302 C. grams and 2000 grams. terial was 963 C for BaCI2. The lowest was 611 C for LiCI. Blended Flux Preparation Moisture Resistance Studies Many fluorides, fluoride mixtures Moisture absorption data was col­ and fluoride compounds were found Blended fluxes were prepared by lected for fluxes of interest by ex­ with melting points in excess of 1000 mechanically mixing dried, reagent posing dried, sized flux to saturated air at 25 C. Representative moisture

7. 4 6 8 10 12 absorption data for fused chlorides ) and chloride compounds is given in 3 Fig. 1. Perhaps with the exception of 1 " - RbCI, all other materials are unsatis­ 2 factory. The hydration rates are ex­ " SrF, 1 tremely high. CaCI2 shows, not sur­ CJ K CaF?-15SrFj prisingly, the highest rate. p CaF,-5SrF, o Figure 2 presents data for fused CaF, fluorides and fluoride compounds. 0 -- BaCI, CaF2 and MgF2 show the lowest hy­ ^ dration rates. 3 - I Fused solid solutions of CaF2 with z other halides show faster hydration l 2 o than pure CaF2 as illustrated in Fig. 3. CJ CaF,15BaCI, The excess fluorination or chlorina- CaF,-5BaCI, 5 1 tion of CaF2 appears to increase 5 b hydration rates. Blended fluxes comprising CaF2 EXPOSURE TiME (hours) EXPOSURE TIME (hours) and other halides exhibit faster hydra­ Fig. 3 — (a) Moisture absorption ot fused Fig. 4 — (a) Moisture absorption ot blend­ tion than pure CaF2 as shown in Fig. 4. CaF2-SrF2 fluxes, (b) Moisture absorption ed CaF2-SrF2 fluxes, (b) Moisture absorp­ The hydration rate is somewhat of fused CaF2-BaCI2 fluxes tion ot blended CaF2-BaCI2 fluxes higher than for fused fluxes because

Table 2 — Bead-on-Plate Welds

Wire Volt­ Cur­ Exten­ Travel Wire Elec­ Flux Slag Bead size age. rent, sion, speed, feed, trode burden, remo­ smooth­ Bead Bead Flux mm V A mm mm/s mm/s angle mm val ness shape color

CaF2-5SrF2 (fused) 1.6 33.5 230 19 6.3 108 Vert 25X25 G — lustrous CaF2-15SrF2 (fused) 1.6 33.5 225 19 6.3 108 Vert 25X25 G — — lustrous MgF2-25 at % NaF (fused) 1.6 29 280 19 6.3 159 Vert — — — — — 3.2 34 390 25 8.5 42 Vert F F CaF2 (fused) — — — CaF2-10BaF2 (fused) 1.6 34 250 19 6.3 — Vert — G F P black CaF2-5BaCI2 (blended) 1.6 34.5 205 19 6.3 105 Vert 22X25 — P P dull CaF2 (fused) 1.6 20 195 19 6.3 117 Vert 22X13 — P P yellow CaF2-5BaCI2 (fused) 1.6 34 240 19 6.3 108 Vert 22X25 G P P dull CaF2-5SrF2 (fused) 1.6 33.75 240 19 6.3 108 Vert 22X25 G F F shiny CaF2-15SrF2 (fused) 1.6 34 235 19 6.3 108 Vert 22X25 G F F shiny CaF2-5(SrCI2«SrF2) (fused) 1.6 34 240 19 6.3 108 Vert 22X25 F F F shiny CaF2-3(SrCI2»SrF2)-10BaCI2 (fused) 1.6 33.5 245 19 6.3 105 Vert 22X25 P P P dull shine CaF2-2LiF-5BaCI2 (fused) 1.6 34 240 19 6.3 105 Vert 22X25 P F F It. yellow MgF2-5 at % NaF (fused) 1.6 30 235 19 6.3 123 Vert — — — — — MgF2-25 at % NaF (fused) 1.6 30 260 19 6.3 147 Vert — — — — — P P MgF2-5 at % KF (fused) 1.6 34 260 19 6.3 123 Vert — — — 22X25 P P P CaF2-5SrF2 (fused) 1.6 33 270 19 6.3 108 Vert — CaF2-10BaF2 (fused) 1.6 33.5 220 19 6.3 — Vert — G F P black 4.7 CaF2-40CaCO3-15AI2O3 (fused) 1.6 34.5 230 19 — Vert — — — — — P CaF2-15CaC03-15AI203 (fused) 1.6 34.75 250 19 6.3 108 Vert — — P dull dark F G CaF2-5BaCI2 (blended) 1.6 34 255 19 6.3 105 Vert 22X25 — — F G bluish-yellow CaF2-5SrF2 (blended) 1.6 34 255 19 6.3 105 Vert 22X25 — bluish-yellow CaF2-15SrF2 (blended) 1.6 34 240 19 6.3 123 Vert 22X25 — F F CaF2-3AI (blended) 1.6 34.5 220 19 5.1 94 Vert 22X25 F P P yellow G P P dark gray CaF2-5BaF2 (blended) 1.6 34 245 13 6.3 91 Vert — F CaF2-30BaF2 (blended) 1.6 34 245 13 6.3 91 Vert — — G — P P CaF2-50BaF2 (blended) 1.6 37 280 13 6.3 85 Vert — — — G F F yellow CaF2-2LiF-5BaCI2-2KF (fused) 1.6 34 240 19 6.3 108 Vert — VP CaF2-2LiF-5BaCI2-2NaF (fused) 1.6 34.5 230 19 6.3 108 Vert — — VP — CaF2-1.2BaCI2-0.7NaF-0.3SrF2 (fused) 1.6 33.5 225 19 6.3 108 Vert 25X25 F — — dull CaF2-3AI (blended) 1.6 34 245 19 6.3 100 Vert 25X25 F F F dull CaF2-20CaO-3AI (blended) 1.6 34 245 19 6.3 100 Vert 25X25 VP VP VP cracks CaF2-15AI203 (blended) 1.6 34 245 19 6.3 100 Vert 25X25 VP VP VP cracks CaF2-15AI203-3AI (blended) 1.6 34 245 19 6.3 100 Vert 25X25 VP VP VP cracks

154-s I JUNE 197 6 Table 3 — Welding Parameter Evaluation for Candidate Fused Fluxes'")

Wire Volt­ Cur­ Exten­ Travel Wire Flux Slag Bead size, age, rent, sion, speed. feed, burden, remo­ smooth­ Bead Bead Fused fluxes mm V A mm mm/s mm/s mm val ness shape color

CaF2-5(SrCI2«SrF2) 1.6 34 260 19 6.3 123 22X25 — P P dull shine CaF2-5(SrCI2'SrF2) 1.6 34.75 200 19 6.3 94 " — — — — CaF2-5(SrCI2«SrF2) 1.6 37 200 19 6.3 72 — — — — — CaF2-5(SrCI2«SrF2) 1.6 34 190 19 6.3 57 — — — — — CaF2-5(SrCI2»SrF2) 1.6 33.5 235 19 6.3 108 25x25 — — — — P CaF2-2LiF-5BaCI2 1.6 33-35 360-220 19 6.3 123-65 22X25 — P dull shine CaF2-2LiF-5BaCI2 1.6 34 200 19 6.3 67 — — — — — CaF2-2LiF-5BaCI2 1.6 33.5 220 19 6.3 108 25X25 F G G shiny CaF2-2LiF-5BaCI2 1.6 33.5 280 19 5.5 — — P — — — CaF2-2LiF-5BaCI2 1.6 33.5 230 19 4.2 — — — — — — CaF2-2LiF-5BaCI2 1.6 34 225 19 6.3 108 — — — — — CaF2-2LiF-5BaCI2 1.6 34 220 19 6.3 108 25X25 — G G — dull CaF2-2LiF-5BaCI2 3.2 37.5 420 25 8.5 42 25X38 — V.P. V.P. CaF2-2LiF-5BaCI2 3.2 34 420 25 8.5 42 25X38 — V.P. V.P. dull 38 F CaF2-2LiF-5BaCI2 3.2 34 400 25 8.5 — F dull shine CaF2-2LiF-5BaCI2 3.2 34 380 25 8.5 42 — — — — — CaF2-2LiF-5BaCI2 3.2 34-38 390 25 8.5 42 — — — — — P CaF2-2LiF-5BaCI2 3.2 35 400 25 8.5 42 25X19 — P dull gray CaF2-2LiF-5BaCI2 3.2 35 420 19 8.5 42 25X19 — F F dull gray P CaF2-2LiF-5BaCI2 3.2 31 460 13 8.5 41 25X19 — P dull gray P CaF2-2LiF-5BaCI2 3.2 34 400 25 6.3 41 25X19 — P dull gray CaF2-2LiF-5BaCI2 3.2 35 350 25 6.3 33 — — — — — CaF2-5BaCI2 1.6 34 260 13 4.7 59 — — — — — CaF2-5BaCI2 1.6 34 260 13 4.7 59 — — — — — P P CaF2-5BaCI2 1.6 36 210 19 4.7 85 25X25 — dull shine P CaF2-5BaCI2 1.6 36 240 19 4.7 108 25X25 — P dull shine P P CaF2-5BaCI2 1.6 34.5 250 19 4.7 131 25X25 — dull shine P CaF2-5BaCI2 1.6 34.5 300 19 4.2 108 25X25 — P dull shine CaF2-5BaCI2 1.6 36.5 255 19 6.3 104 25X25 — P P dull shine P CaF2-5BaCI2 1.6 34 190 19 4.2 78 25X25 — P dull shine CaF -5BaCI 1.6 34.25 240 19 6.3 108 P P 2 2 _

(a) angle vertical in all cases

of the smaller particle sizes and the Bead-on-Plate Welds rate appears to be directly propor­ tional to the relative quantity of each Screening of fluxes was ac­ component. complished by making bead-on-plate welds. Welding conditions used were Welding Studies approximately those identified in the parameter study, but occasionally Welding Parameter Study modifications were necessary for specific fluxes. Both the 1.6 mm and The identification of proper welding the 3.2 mm electrodes were used on conditions is necessary for evalua­ Ti-6AI-4V baseplate. A complete tion of candidate fluxes. A com­ summary of the compositions tested prehensive series of tests was per­ and the results obtained is given in formed to select the optimum range Table 2. The best performance was of welding conditions for each of two obtained with fused CaF -(5%) BaCI , electrodes: 1.6 mm Ti-6AI-4V and 3.2 2 2 fused CaF -(5%)SrF «SrCI and fused mm Ti-6AI-2Cb-1Ta-1Mo. Param­ 2 2 2 CaF -(5%)BaCI -(2%) LiF. Further eters investigated included current, 2 2 characterization of these fluxes was voltage, extension, angle, travel made. The results are listed in Table 3. speed, flux burden, slag removal, and bead shape and appearance. Fused Oxygen analyses of welds made with the best operating fluxes were CaF2 was used as the flux for these experiments. The baseplate was Ti- made. The welding conditions and ox­ 6AI-4V. The results are listed in Table ygen contents are given in Table 4. 1. The conditions developed in this Note that the blended fluxes pro­ study were: duced welds with considerably higher oxygen contents than did the fused Electrode Size fluxes. This is probably due to the Parameter 1.6 mm 3.2 mm "floating" behavior of the blended fig, 5 — (a) Radiograph of groove weld made with fused CaFi and no auxiliary Current, A 240 400 fluxes causing poor shielding. shielding, (b) Radiograph of groove weld Voltage, V 34 35 Halide-Oxide-Metal Fluxes made with fused CaF2-5BaCI2-2LiF and no Travel, mm /s 6.3 8.5 auxiliary shielding, (c) Radiograph ot Extension, mm 20 25 Attempts to produce satisfactory groove weld made with fused CaF2 and Angle Vert. Vert. oxide-halide fluxes with metallic corn- auxiliary argon shielding

WELDING RESEARCH SUPPLEMENT! 155-s Table 4 — Oxygen Analyses

Flux Current Voltage, Travel, Wirefeed, Extension, Oxygen A V mm/s mm/s mm ppm

CaF2 (fused) 400* 36V 6.8 33 19 2100 CaF2-5BaCI2 (fused) 240 34 6.3 108 19 1900 CaF2-5SrF2 (fused) 240 34 6.3 108 19 1800 CaF2-15SrF2 (fused) 235 34 6.3 108 19 1650 CaF2-5SrF2-SrCI2 (fused) 240 34 6.3 108 19 1800 CaF2-3SrF2«SrCI2-10BaCI2 (fused) 245 34 6.3 105 19 1700 CaF2-2LiF-5BaCI2 (fused) 240 34 6.3 105 19 1700 CaF2-5SrF2 (blended) 255 34 6.3 105 19 4000 CaF2 (blended) 220 35 5.1 94 19 3100 CaF2-3AI (blended) 220 35 5.1 94 19 3000

*3.2 mm wire used for this test only.

YIELD STRESS (MPa) specimens were made. Both CaF2 welds had satisfactory integrity, but 600 700 800 900 1000 1100 1200 rV the CaF2-(5%)BaCI2-(2%)LiF weld did not. Radiographs are shown in NO AUX SHIELDING 4000 Figure 5. ARGON AUX SHIELDING MIG PROCESS (8) 3000 Mechanical Properties, Microstructure, and Composition of Groove Welds 2000 140 120 Mechanical Properties 120 £ 1000 L 100 n Specimens were cut from the two Hioo jl CaF welds for microscopic examina­ 80 > 2 00 80 ^ tion, tensile testing, Charpy V-notch 60 £ 60 1- testing and K!C evaluation. Specimen o testing details are given in the Ap­ 40 sT 40 * pendix. 20 Three Charpy V-notch specimens, 20 the tensile specimen and one K|C 90 100 110 120 130 140 150 160 170 180 specimen were tested at room tem­ YIELD STRESS (KSI) perature in the as-welded condition. Two Charpy V-notch specimens and Strength-toughness relations for the two groove welds tested Fig. 6 one Kic specimen were heat treated at 535 C for 1 h and tested at room temperature. ponents either by bonding or blend­ %. 'J- \ \%:&4fr ing failed. The presence of even A summary of the mechanical minor quantities (2% or more) of ox­ properties is given in Table 6. Note ide species causes extreme oxida­ that weld made with auxiliary argon tion of the weld deposit and trans­ shielding showed lower strength and verse cracking of the weld bead. Slag higher fracture toughness than the removal becomes impossible and weld made with no shielding. weld appearance is severely degrad­ AplotofK|C against yield stress for ed. This work was done with the sys­ the two welds is presented in Fig. 6. The upper and lower limit lines (Ref. tems CaF2-CaO-AI and CaF2-AI203-AI. 7) including K!C values of the GMAW Groove Welds process weld metal for Ti-6AI-4V (Ref. - •*£** 8) are also presented in this plot. It is Welds for mechanical properties important to note from this analysis were made in 13 mm thick Ti-6AI-4V that the performance of the sub­ «sr* merged arc weld in strength- K using fused CaF2 and fused CaF2- (5%)BaCI2-(2%)LiF. The filler wire was toughness combination behavior is Ti-6AI-2Cb-1Ta-1Mo. For CaF2, two comparable with that of the GMAW >,-,.. welds were made: one with auxiliary process weld. Furthermore these % argon shielding and another with no welds performed significantly better shielding. Details of the groove welds than the lower performance limit. This are listed in Table 5. implies that contamination from the Difficulties were encountered with atmosphere and from the flux is not sidewall wetting when welding with overwhelming, even in the case of no CaF2-(5%)BaCI2-(2%)LiF. The CaF2 auxiliary shielding. It is clear that, when welding with submerged arc Fig. 7 — Microstructure of groove weld welds were relatively easy to make. made with auxiliary argon shielding. X500, The completed welds were radio­ flux, an undermatched reduced 43% graphed before mechanical test composition should be ctiosen since

156-s I JUNE 197 6 oxygen and nitrogen pickup will con­ measured by hardness and a small in­ stress relief and not to microstruc­ tribute to strength. crease in fracture toughness. These tural changes. effects are principally due to stress Microstructure relief rather than any microstructural Acknowledgment changes. The microstructure of the as- Financial support for this research was welded material was characterized by Conclusions provided through the Pro­ massive grains of acicular alpha sep­ gram, Office of Naval Research, Contract arated by alpha precipitated at prior The following conclusions have N00014-74-C-0406. Dr. Bruce A. Mac- beta grain boundaries, as shown in been drawn based on this work: Donald was the cognizant Scientific Of­ Fig. 7. Note that some of the acicular 1. Fluoride-base fluxes are re­ ficer. alpha may be alpha prime, the quired for the welding of titanium martensitic phase. alloys. References 2. No oxide component is toler­ 1. Memorandum 188: A Review of Chemical Composition able in these fluxes. Available Information on the Welding of 3. Bead-on-plate screening for flux Thick Titanium Plate in the USSR, De­ The compositions of base metal, operability is not satisfactory. fense Materials Information Center, filler metal and weldmetal are listed in 4. Fused fluxes offer superior Columbus, Ohio. March 6, 1964. Table 7. It is apparent that the major atmospheric protection to blended 2. Gurevich, S. M., "Flux for Welding Ti­ difference between the weld made fluxes. tanium and Its Alloys," US Patent 3,551,- with auxiliary argon shielding and the 218. December 29, 1970. 5. Fused CaF2 provides sufficient weld made without such shielding is protection and fluxing for the groove the nitrogen content of the weld- welding of titanium alloys even with metal. no auxiliary shielding. Table 5 — Groove Welds 6. Auxiliary argon shielding re­ Summary sults in somewhat reduced nitrogen Baseplate: Ti-6AI-4V, 13 mrr thick, Flux Studies contents, and yield stress, and there­ single V groove fore somewhat improved fracture Wire: Ti-6AI-2Cb-1Ta -1Mo, The low hydration rates of flourides toughness. 3.2 mm diameter makes them preferable as bases for 7. Submerged arc welding pro­ Flux: CaF2 (fused) and CaF2- 5BaCI2 titanium welding fluxes. The superior duces intermediate quality strength- -2LiF (fused) covering action of fused material in­ toughness properties. At 999 MPa dicates that the fluxes should be (145 ksij^Kic values of 69 MN\m/m2 Current: 400 A 35 V fused and not blended. No oxide (60 ksi\in.) are achievable. Voltage: components can be tolerated. Travel speed: 8.6 mm/s 8. Heat treating the welds at 535 C Wirefeed: 39 mm/s Four candidate fused fluxes were for 1 h in argon causes small de­ Extension: 25 mm identified using bead-on-plate welds. crease fn strength and correspond­ No. of passes: 4-5 These were: ing small increase in toughness. 1. CaF2 These effects are principally due to 2. CaF2-(5%)BaCI2 3. CaF2-(5%)SrF2«SrCI2 4. CaF2-(5%)BaCI2-(2%)LiF Fluxes 1 and 4 were used to make Table 6 — Weld Mechanical Properties With and Without Auxiliary Shielding groove welds in 13 mm Ti-6AI-4V. Only flux 1 made radiographically ac­ Property Noaux. shielding Argon aux. shielding ceptable welds. Yield stress: 1082 MPa (157 ksi) 999 MPa (145 ksi) Welds and Mechanical Properties Tensile strength: 1088 MPa (158 ksi) 1013 MPa (147 ksi) Elongation: 11% 10% 9% Fused CaF provides satisfactory Reduction of area: 14% 2 Hardness: 36.5 R 35.7 R shielding and fluxing action for mak­ c c Charpy (23 C) as-welded: 7J (5 ft-lb) 11 J (8 ft-lb) ing submerged arc welds with Ti-6AI- heat treated: 7 J (5 ft-lb) 11 J (8 fWb) 2 2Cb-1Ta-1Mo filler metal. Auxiliary K (23 C) as-welded: 47 MNsm/m (41 ksivinj 2 |C 2 69 MNvm/m (60 ksKjn.) argon shielding helps hold the nitro­ heat treated: 50 MNsm/m (44 kskin.) 71 MNsm/m2(62 ksKin.) gen content of the weld to 65 ppm as compared with 255 ppm with no shielding. Nitrogen apparently pro­ vides significant strengthening in this alloy; accordingly the weld made with argon shielding exhibits a lower yield Table 7 — Chemical Composition stress, 999 MPa (145 ksi), than the Base Filler Weld. aux. Weld, no weld made with no auxiliary shield­ metal metal argon shielding aux shielding ing, 1082 MPa (157 ksi). A strength- toughness analysis shows that these Al 6.34% 6.07% 6.35% 6.00% welds perform at an intermediate V 3.95 <.05 3.55 3.40 level and such an analysis conserva­ Cb <.02 2.14 .45 .45 tively implies that proper selection of Ta <.05 1.80 .66 .66 filler metal composition could result in Mo .01 .99 .25 .24 Kic values of 160 MNsm/m2 (140 ksi Fe .19 .04 .11 .12 sin.) at 758 MPa (110 ksi) yield stress. O 2200 ppm 2400 ppm 2130 ppm 1930 ppm N 48 28 65 255 Heat treating the welds at 535 C for C 290 170 230 280 1 h in an argon atmosphere caused a small reduction in strength as

WELDING RESEARCH SUPPLEMENT! 157-s 3. Materko. Z. A. and Bukhalova, G. A., tanium Alloy Weldments." November, were tested at room temperature in a Zh. Neorgan, Khim 8, 1963, p. 715. 1967. 325 J (240 ft-lb) capacity Baldwin. 4. Gurevich, S. M., Automat. Svarka 10, 1958. p. 3. Appendix Kic Testing — Three point bend­ 5. Petsch, H. F., Research Study to De­ ing at 25 mm/h (1 in./h) was used on velop a Submerged Arc Automatic Weld­ Mechanical Testing Methods 8.8 X 19 X 125 mm (0.35 X 0.75 X ing Process for Fabricating Butt Welds in 5.00 in.) specimens which were fa­ Thick Titanium Alloy Plate, US Navy Con­ Tensile Testing — Specimens, 6.4 tigue cracked. The fatigue cracking tract N00140-68-C-0148, Final Report. mm (.252 in.) round, were tested in a was carried out in three point bend­ 6. Dergunov, E. P. and Bergman, A. G., 44500 N (10,000 lb) capacity Instron at ing at R =_15 with a stress intensity of Dokl. Akad. Nank. SSR 75, 1950, p. 817. 0.009 mm/s (0.02 in./min) cross-head 22 MNxin/m2 (20 kskin.). This re­ 7. Pellini, W. S., "Criteria for Fracture speed. Elongation is total elongation sulted in a final fatigue growth rate of Control Plans," NRL Report 7406, Wash­ in 25 mm (1 in.). Reduction of area is approximately 1.3 mm/10,000 cycles ington, D.C, p. 64. May 11, 1972. measured at the final fracture (1.3 x 10 * mm/cycle). The testing 8. R. W. Huber, R. J. Goode and R. W. Judy Jr., NRL Report PB176490, "Frac­ diameter. conditions satisfied the requirements ture Toughness and Salt Water Stress Charpy V-Notch — Two-thirds size of ASTM Committee E-24 for valid Corrosion Cracking Resistance of Ti­ (6.7 X 10 mm) Charpy specimens K,r determinations.

WRC Bulletin 203 February 1975

"Niobium and Vanadium-Containing Steels for Pressure Vessel Service" by J. N. Cordea, Armco Steel Corp.

The effects of niobium (Nb) and vanadium (V) additions on the properties of plain carbon (C) steel have been well known for some years now. Recently, through refinements and processing technology, very effective use has been made of relatively small amounts of Nb or V (up to 0.2 wt-%) to significantly increase yield strength and improve notch tough­ ness. These improvements have resulted through optimization of Nb and V carbonitride pre­ cipitation hardening, ferrite grain size refinement, and a reduction in C content. The latter item also significantly improves . Nearly all of the industrialized countries of the world have taken advantage of the econ­ omy of producing higher strength steels with a minimum of extra alloying cost. This is espe­ cially true for structural applications where weight saving is so important. Many countries have also made effective use of these steels for pressure vessel applications. Although the United States is very active in high-pressure line-pipe development, very little activity has been directed toward using Nb and V steels for pressure vessels and other containers. The principal reason is that allowable-stress calculation as specified by the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code is usually governed by ten­ sile strength. While yield strength is increased significantly by Nb and V additions, there is a relatively small effect on tensile strength. Consequently, no direct advantage can be gained in pressure vessel design by an increase in yield strength. It is the purpose of this report to summarize the state of the art of Nb- and V-containing C-Mn steels for pressure vessel applications and to identify areas needing further research. Specifically, this report covers low-alloy steels with an upper yield-strength range of about 75 ksi (53 kg/mm2). A brief summary of the pressure vessel codes around the world is present­ ed in order to provide a basis for important material properties in the design of pressure vessels. Available steels, their mechanical properties and the technology for producing them are covered in detail. Although a few structural grades and pipeline steels from the United States are discussed, the main emphasis is directed toward foreign steels produced for pres­ sure vessel applications. Where appropriate, comparisons are made to similar composition structural grades produced in the United States. Weldability and other important properties necessary for satisfactory fabrication and service are evaluated. This work was initiated and sponsored by the Pressure Vessel Research Committee of the Welding Research Council, Fabrication Division, Subcommittee on Thermal and Mechanical Effects. The price of WRC Bulletin 203 is $6.50 per copy. Orders should be sent with payment to the Welding Research Council, United Engineering Center, 345 East 47th Street, New York, N.Y. 10017.

158-s i JUNE 197 6