AU2005222500B2 - Welding wire - Google Patents

Description

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S):: Daido Tokushuko Kabushiki Kaisha ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys Level 10, 10 Barrack Street, Sydney, New South Wales, Australia, 2000 INVENTION TITLE: Welding wire The following statement is a full description of this invention, including the best method of performing it known to me/us: 5102 WELDING WIRE FIELD OF THE INVENTION The present invention relates to a welding wire for use in the MIG welding of Ti-baseg ma ore particularly, the present invention relates to a welding wire- allowing the compatibility between. stable arc and stable droplet transfer, and as a result, enabling the formation of the excellent -bead-shape. Further, when a welding wire of the present invention is used in a Ti thermal spraying, the stability 9f.arp,an also be achieved and then an excellent coatng layer. of .the. thermal spray can be obtained. BACKGROUND :OF THE INVENTI ON As for the welding of a member made of Ti or a Ti alloy, MIG welding (Metal Inert Gas Welding) that is more excellent in welding efficiency has received attention in place of TIG welding (Tungsten Inert. Gas Welding). The MIG welding is allowed to proceed in accordance with the following embodiment. In a condition that a welaing wire made of Ti or a Ti alloy fed from a wire feeder and a base metal to be welded are surrounded by a shielding gas, an arc is generated between bo h. The droplets of the welding wire generated at this step are transferred and landed on the base metal to be welded, thereby to continuously form beads. The things that matter at this step are: stabilization of the generated arc; and stable transfer and landing of droplets from the welding wire on the weld zone. When-the-generated arc is not stable, or droplets-are not transferred to the weld zone with stability, for example, as shown in Fig. 7, constriction occurs in the formed bead, and the uniformly overlying 'state -is not!achieved.- It is difficult to say that the bead in such a shape ensures the reliability of the strength characteristics at the weld zone. Incidentally, Ti 1i activee metal. Therefore, when an oxygen-containing gas is used as a shielding gas, not only the bead surface is oxidized -but also.the. reduction of ductility of the weld-zone is -caused. Such being the case, in general, a high purity inert gas such as a pure Ar gas is used* s a siielding gas. However, the following fact is also known: when oxygen is contained in the shielding gas, the datho'de spot upon arc generation is fixed on the base metal to be welded under the welding wire; as a result, arc is stabilized (see, Reference 1) This means as follows: oxygen is supplied to the 2 field of the generated arc, so that the cathode spot is stabilized, and as a result, the generated arc is also stabilized. Based on such a fact, the following welding wires of Ti materials have been proposed (see, Reference 2). This welding wire is a welding.wire configured as..follows: on the surface layer portion of a welding wire made of'i or a Ti alloy, an oxygen enriched layer with a higher oxygen--concentration than that of the inward layer-portion of the welding wire is. formed -and the thickness of the oxygen enriched layer is larger than that-of the very thin natural oxide film present on the, surfgpe of the welding wire. This welding wire is manufactured in the following manner. For example, -a Ti material of a preferable composition is once rolled, and then, heat treated in an oxygen-containing atmosphere to form a Ti oxide layer (oxygen enriched layer) thicker than the natural oxide film on the surface layer portion. Then, the resulting welding wire is cold rolled to a prescribed wire diameter. Then, this welding wire is used as a welding wire for MIG welding. In consequence, oxygen is fed to the field of the generated arc from the oxygen enriched layer even' when an oxygen containing gas is not used as a shielding gas. Therefore, the cathode spot is stabilized. As a result, a bead in a favorable shape is formed. 3 [Reference 1] PrQceedings of National Meeting of Japan Welding Society 65 (1999), 276 [Reference 2] JP 2003-326389 A However, according to the subsequent study on the welding wire of Reference....2.,.it has been proved that, when MIG -welding is carried out with this welding wire, the:u: %i following phenomenon occurs First, the cathode spot of the generated arc is situated at the position of the base metal to be welded under the welding wire as deduced, and stabilized without fluctuating. However, at the tip of the welding wire, there are generated two types of arcs: the concentrated arc in such a shape as shown in Fig.'8' (which is hereinafter referred to as a concentrated arc); and the diffused arc in such a shape as shown in Fig. 9 (which is hereinafter referred to as a diffused arc). The former arc has been stabilized, and the latter arc has been unstable. Then, when the former concentrated arc is generated, the tip of the welding wire is invariably released in the form of droplets, which transfer to the weld zone. Thus, the shape / outward appearance of the formed bead become favorable. However, when the latter diffused arc is generated, droplets may not be released from the welding 4 C WRPonb1DCC\K \29759_l DOC-i11/201D wire tip. Even when droplets are released, the length of time required for the release is long. Therefore, the transfer time of the droplets to the weld zone is also long. As a result, the droplets cannot transfer to the weld zone during one pulsed 5 current flow period, so that the next one pulsed current flow is carried out prior to the completion of transfer of the droplet. For this reason, the overlying state of the formed bead becomes ununiform, and constriction or the like may occur partially along the direction of welding. Further, a large 10 amount of spatters are generated, resulting in the poor outward appearance of the bead. Such a phenomenon is conceivably generated due to the fact that the tip of the welding wire, i.e., the anode spot has been unstabilized. The present invention seeks to provide a welding wire 15 which solves such a problem, and whereby both of the cathode spot and the anode spot upon arc discharge are stabilized, and hence the arc is stabilized, and the transfer of droplets is also stabilized. SUMMARY OF THE INVENTION 20 The present inventors have made eager investigation to examine the problem. As a result, it has been found that the foregoing disadvantages can be substantially overcome by the following -5welding wire. With this finding, the present- invention is accomplished. The present invention is ixinly 'irected'to the following items: (1) A welding wire comprising Ti or a Ti alloy, wherein the welding wire has: an oxygen enriched layer on a surface thereof; and a metal compound having at least one metal- selected from the group consisting of alkali metal-s and alkaline earth metals. (2) The welding wire according to item (1), wherein the content of the metal coqmpound is 0.002 to 0.050% by weight based on the. total weight of the welding wire. (3) The welding wire according to item (1), wherein the welding wire has cracks on the surface, and the metal compound is present in the cracks. (4) The welding. wire .according to item (1), wherein the boiling point of the metal is 2000*C or less. (5) The welding' wire accordincf to it m' (1),'wherein the metal compound is a metal compound containing Ca. (6) The welding wire according to item (1), wherein the value of Tw/Dw is 0.3 x 10-3 to 1 x 10-1, wherein Tw represents the thickness of the oxygen enriched layer, and Dw represents the wire diameter of the welding wire, and wherein the average oxygen concentration of -theoxygen enriched layer is not less than' 1%'by weight. 6 (7) The welding wire according to item (6), wherein the average oxygen concentration of the oxygen enriched layer is 1 to 40% by weight. (8) The welding wire according to item (1), wherein the surface roughness of the welding wire .is 10 pm or less in terms of the surface roughness expressed as Ry specified according to JIS B.0601. -(9) The welding wire according to item-(6) -wherein the value of Tw/Dw is 1 x 10-3 to 50 x 10-% wherein Tw represents the thickness of the oxygen enriched layer, and Dw represents the wire. digineter of the welding. wire, and wherein the average oxygen concentration of the oxygen enriched layer is 1 to 30% by weight. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a microphotograph of a surface of a welding wire of the present invention. Fig. 2 is a cross-sectional microphotograph of a of a surface layer portion.of.. awelding wire of the invention. Fig. 3 is a microphotograph of a surface layer portion before wire drawing during man.ufittiring of a welding wire of the invention. Fig. 4 is a correlation diagram between the ionization voltage and the boiling point of each metal. 7 Fig. 5 is an explanatory di~gr&nt'of the concentrated arc defined in the invention..

Fig. 6 is a photograph showing a bead formed by the use of a welding wire of Experimental Example 6. Fig. 7 is a photograph showing a bead in a defective shape. Fig. 8 is a photograph showing an example of the concentrated arc. Fig. 9 is a photograph showing an example of a diffused arc. DETAILED DESCRIPTION OF THE INVENTION The foregoing effects are achieved by a welding wire comprising Ti or a Ti alloy, wherein the welding wire has: an oxygen enriched layer on a s-urface thereof- and- a metal compound having at least one metal selected from the group consisting of alkali metals and alkaline earth metals. In the present invention, the term "welding wire" has a meaning including a 'wire' Zod for thermal spraying (thermal spraying wire) as well as a wire rod for welding. First, the surface microphotograph and -the cross sectional microphotograph of the surface layer portion of the welding wire of the invention are shown as Figs. 1 and 2, respectively. As apparntA from Fig. 1, this welding

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wire is formed such that the surface is covered with an oxygen enriched layer, and fine surface cracks generated in a wire drawing step described. later are distributed over the surface of the entire welding wire. The foregoing surface cracks are, as shown in Fig. 2; formed as cracks with a depth from the oxygen enriched layer on the welding wire surface toward the inward layer portion of the base material. Then, in the cracks, the compound'described-. later, including an aJkali metal or an alkaline earth metal is packed. In the invention, the oxygen enriched layer, and the average oxygen concentration thereof are defined as follows. Namely, the cross section. of.the welding wire is mirror polished, and is subjected to area analysis by EPMA (Electron Probe Micro Analysis) as to the oxygen concentration distribution. The oxygen concentration at the central part of the welding wire obtained by the analysis is taken as l., and.-the region having an oxygen concentration of 1.2 or more (i.e., having an oxygen concentration of not le s t1(axn. '1 times as 'large as that of the central part) is taken as an oxygen enriched layer. Further, the average value (5 measuring points) of the oxygen concentration in a region with the oxygen concentration of 1.2 or more is taken as the average oxygen concentration of the oxygen enriched layer. Incidentally, 9 when the oxygen concentration varies along the circumferential direction- of the welding wire cross section, concentration measuring' circles are set at various position along the radius of the cross section, and the oxygen concentrations are averaged along the respective concentration measuring circles, thereby to determine the oxygen concentration distribution along the radius of the cross'section, averaged along the circumferenti-a-direction. Then, the region having an oxygen concentration of not less than 1.2 times as large as that of the central part in the oxygen concentration distribution along the radius of the cross section is taken as the oxygen enriched layer. The thickness of the -oxygen- enriched- layer of the invention is preferably larger than that of the natural oxide film generated on the welding wire surface. The thickness of the natural oxide film is generally 40 to 100 Further, the oxygen enriched layer of the invention preferably satisfies the following .relationship. Namely, it is preferable -that. the value of Tw/Dw is 0.3 x 10' to 1 x 10-1, where Tw denotes the thickness of the oxygen enriched layer,' arid Dw denotes the wire diameter of the welding wire, and that the average oxygen concentration of the oxygen enriched layer is not less than 1% by weight. By forming the oxygen enriched layer having 10 such a thickness and average oxygen concentration, it is possible to largely improve the feedability of the welding wire via a conduit tube of a wire' keed. Further,' the stability of the arc for carrying out arc'welding or arc thermal spraying also becomes favorable. When the Tw/Dw is less than 0.3 x 10-- (Tw is 0.03% of Dw), or the average oxygen concentration of the oxygen enriched layer is less than 1% by weight, the-feedability improving effect becomes insufficient. Further, the arc becomes more likely to be unstabilized, resulting in a disadvantage for forming a uniform welding bead or spray deposit. When the Tw/Dw is 1x 10' (Tw is 10% of Dw) or more, a very long time is required for the formation treatment of the oxygen enriched layer, and the effects are poor for the difficulty of the formation. When it is used for welding or the like, det imental effects such as the reduction of the welded joint strength of the welding structure may be rather caused. The upper limit value of the average oxygen concentration of the oxygen enriched layer is described below. The average oxygen concentration of the oxygen enriched layer becomes'miiniiiW*hen the .entire oxygen enriched layer is formed of titanium oxide. The value becomes conceivably equal to the -oxygen..content -ratio calculated from the molecular formula -of the oxide formed. 11 For example, when the oxidetto be formed is Tio 2 , the upper limit value of the average oxygen concentration calculated from the stoichiometric oxygen content is 40.06% by weight (calculated assuming that the atomic weight of Ti is 47.88 and the atomic weight of oxygen is 16.0). . Alternatively, a Ti oxide having a still higher oxygen stoichiometric ratio of oxygen than that of TiO 2 may be formed. For example, when-Ti 2 0 is formed, the upper limit value of- the--average oxygen concentration is 45.52% by weight. Therefore, it is .4 generally unconceivable that the maximum value of the average oxygen concentration of the oxygen enriched layer exceeds 45.52% by weight. As a result, in the invention, it can be said that the maximum value of the average oxygen concentration of the oxygen enriched layer is 45.52% by weight. However, when.the value of the average oxygen concentration of the oxygen enriched layer is set to 45.52% by weight, adverse effects such as the deterioration of ductility of a welded .joint may. occur. Therefore, the average oxygen concentration of the oxygen enriched layer is preferably not more-tha.n-40% by weight. In order to make the arc stabilizing effect more remarkable, the ratio Tw/Dw pf the thickness of the oxygen enriched layer Tw to the wire diameter Dw is preferably adjusted in the range of 1 x 10- to 1 x 10-. Particularly, when the oxygen diffused layer is formed in addition to the 12 titanium oxide layer of the outermost--surface layer portion (with a thickness equal to the thickness of about 40 to 100 nm of the natural oxi-de film," or larger), the thickness of the oxygen enriched layer increases by that of the oxygen diffused layer. Therefore, the possibility becomes higher that the Tw/Dw falls within the foregoing preferable range. The preferable upper limits of the Tw/DW value and the -average oxygen concentration of the oxygen -enriched layer vary between the case that the-welding wire of the present invention is used as a wire rod for welding and the case that the welding wire is used as a wire rod for thermal spraying. When the welding wire of the present invention is used as a wire rod for thermal spraying, the requirement in terms of strength may not be so stringent for the spray deposit as for, the welded joint.portion *in many cases (of course there are some exceptions). For example, air may be used as a spraying medium for molten metal. In such a case, the oxygen concentration in the layer also inevitably increas-es -because the molten Ti metal is deposited as a spray deposit while reacting with oxygen in the air. This is, however, sufficieni;t for pj.actigal use, when high strength is not p.articularly.requDired. Furthermore, when the welding wire of the present invention is used as a wire rod -for thermal spraying, in view of the fact that oxidation eventually proceeds in molten state, 13 even an increase in the value of Tw/Dw and the average oxygen concentration of the oxygen enriched layer to the upper limit values does not particularly cause any hindrance. On the other hand, when used as a wire rod for welding, an excessively large thickness of the oxygen enriched layer or excessively high average oxygen concentration thereof may sometimes unfavorably cause,,,. degradation of the strength of a welded joint of the resulting welding structure or the strength of the spray deposit. Therefore, when used as a wire rod for welding, it is further preferable to rg,strict the Tw/Dw from 1.0 x 10-3 to 50 x 10- (Tw is 1 to 5% of Dw), and the average oxygen concentration of the oxygen enriched layer from 1 to 30% by weight. When used as a wire rod for thermal spraying, further when a high strength spray deposit is desired to be formed by u.ing. an inert gas such as argon as a spraying medium, and minimizing the oxidation, the Tw/Dw and the average oxygen concentration maybe preferably restricted within the same ranges. The welding wire of the present invention contains Ti as a main component. In the invention, the wording "containing Ti as a main coinp6nent" means that the component having the highest content in the welding wire is Ti. Ti is preferably contained in an amount- of ;not .less 14 than 50% by weight. When a Ti alloy is adopted, aiming at the improvements of the strength or the ductility of the resulting weld zone or the spray deposit, and the like, various additive elements may be contained as sub components. Examples of the adoptable additive elements and the preferable ranges of amounts of' these to be added are described below. (1)' AI: not more than 9% by weight Al has functions of stabilizing the a phase which is a low temperature phase of Ti, and being solid solved in the a phase and strengthening it. However, when the content thereof exceeds 9% by weight, an intermediate phase (intermetallic compound) of Ti 3 Al or the like is formed in a large amount, which leads to the inhibition of the toughness and the ductility. On the other hand, in order to make the foregoing ef.fect.jemarkable, Al is preferably added in an amount of not less than 1% by weight, and more preferably added within a range of from 2 to 8% by weight. (2) At least either of N and O:.not more than 0.5% by weight in total N and 0 also function. es the same a phase stabilizing and strengthening elements as with Al. Particularly, the effect of addition of ' is0 remarkable. However, a total content of these exceeding 0.5% by weight leads to the inhibition of the toughness or the ductility. 15- On the other hand, in order to make the. foregoing effect remarkable, these are'preferably-added-in a total amount of not less than 0.03% by weight, and more preferably added within a range of froni"0.d8-to 0.2% by weight. Incidentally, the oxygen content herein denotes the oxygen content of the inward lAyer 9; ortion other than the oxygen enriched layer in any case. (3),--One,--or two or more of V, Mo, Nb, and Ta:--not more -than 45% by weight in total All of these elements are stabilizing elements of the @ phase which is a Ti high temperature phase, and effective in achieving the improvement of the hot workability and the higher strength through the improvement of the heat treatability. However, all of these elements are high in specific gravity and high in melting point. Thus, excessive addition thereof not only, leads to. the impairment of the effects of the light weight and the high specific strength, specific to Ti alloys, but also causes a difficulty in manufacturing by melting due to the increase in the alloy melting point:.~ For- this reason, the upper limit of the total amount of these to be added is set at 45% by weight. On the other hand,. j.n Pq;ger tom~ke .the effect remarkable, these are preferably added in. a total amount of not less than 1% by weight. Mo or Ta may be added in a small amount- for improving the corrosion 16 resistance of the alloy. (4) One, or two or more of Cr, Fe, Ni, Mn, and Cu: not more than 15% by weight in total These elements also lave an effect of stabilizing the 3 phase, and are effective in achieving the improvement of the hot workability and the higher' strength through the improvement of the heat treatabilit y. However, any of these-tends to form an intermediate phase (e.gr., TiCr 2 , TiFe, Ti 2 Ni, TiMn, or Ti 2 CU) between it and Ti, and excessive addition thereof leads to degraded ductility and toughness. Therefore, the upper limit of the total amount of these to be added is set at 15% by weight. On the other hand, in order to make the effect remarkable, these are preferably added in a total amount of not less than 0.5% by weight. Ni may be added in a small amount- for improving the corrosion resistance of the alloy. (5) At least either of Sn and Zr: not more than 20% by weight in total These elements are known as neutral type additive elements for strengthening both of the a phase and the p phase. However, excessive- addition thereof -results in saturation of the effect, so that the upper limit of the total amount of these to be added is set at 20% by weight. On the other hand, in order to make the effect .remarkable, these are preferably added initotal amount of not less 1'7 than 0.5% by weight. (6) Si: not more than 0.7% by weight Si has effects of enhancing the creep resistance (creep rupture strength) of the alloy, and improving the heat resistance. However, an excessive addition thereof conversely causes the reduction of the creep rupture strength or the ductility due to the formation of an intermeta-llic compound' uc1As i 5 i5. Therefore the upper limit of the amount of Si to be added is set at 0.7% by weight. On the other hand, in order to.make .the-- effect remarkable, Si is preferably added-in-an amount of not less than 0.03% by weight, and more preferably added in an amount in the range of-.(5"fa 0.5% by weight. (7) At least either of Fd and Ru: not more than 0.5% by weight in total These elements have an effect of improving the corrosion resistance of the alloy. However, the upper limit of the amount of these to be added is set at 0.5% by weight in view of the saturation of the effect, and the like, because all are noble metals and thus expensive. On the other hand, in order to make the effect remarkable, these are preferably added in an amount of not less than 0.02% by weight. Specific examples of the alloy composition may include the following ones. (incidentally,....the..composition 18 is expressed as being headed by Ti, which is the main component, followed by sub-components as being connected with hyphens together with the composition numerals while omitting the unit of % by weight (for example, Ti-6% by weight Al-4% by weight V alloy is simply expressed as Ti 6Al-4V)). [1 a type alloys: Ti-5Al-2.5Sn, Ti-5 .5Al-3..5Sn-3Zr-lNb-.043Mo-0.3Si,-" and Ti-2.5Cu (2] Near a type alloys: Ti-6Al-2Sn-4Zr-2Mo-O.1Si, Ti-8Al-lMo-1V, Ti-2.25Al 2Sn-4Zr-2Mo, Ti- 6Al-2Sn-2Zr-2Mb-0. 25Si, Ti-6Al-2Nb-lTa O.8Mo, Ti-6Al-2Sn-l.5Zr-lMo-0.35Bi-O.lSi, Ti-6A1-5Zr-0.5Mo 0.2Si, and Ti-5al-6Sn-23r-lMo-0.25Si.. [3] a + #- type alloys: Ti-8Mn, Ti-3Al-2.5V, Ti-6Al-4V, Ti-6Al-6V-2Sn, Ti 7Al-4Mo, Ti-6Al-2Sn-4Zr -6Mo;"Ti-6Al-2Sn-2Zr-2Mo-2Cr-0.25Si, Ti-1OV-2Fe-3Al, Ti-4Al-2Sn-4Mo-0.2Si, Ti-4Al-4Sn-4Mo-0.2Si, Ti-2.25Al-11Sn-4Mo-0.2Si, -Ti-5Al-2Zr-4Mo-4Cr, Ti-4.5Al-SMo 1.5Cr, Ti-6Al-5Zr-4Mo-1Cu-0.2Sil and Ti-5Al-2Cr-lFe [4] 0 type alloys: Ti-13V-lCr-3Al, Ti-8Mo-8V-2Fe-3Al, Ti-3Al-8V-6Cr 4Mo-4Zr, Ti-li.5Mo-6Zr-4.5Sn, Ti-11V-13lr-2Al-2Sn, Ti-15Mo 5Zr, Ti-15Mo-5Zr-3Al, Ti-15V-3Cr-3Al-3Sn, Ti-22V-4A1, and Ti-15V-6Cr-4Al 19 [5] Near $ type alloy: Ti-10V-2Fe-3Al [6] Corrosion resistant alloys (while available for welding, they are particularly useful when a corrosion resistant coating layer is desired to be formed by thermal spraying): Ti-0.15Pd, Ti-0.3Mo-O.8Ni, and Ti-5Ta The welding wire of the invention can be obtained by once--roll-ing Ti or the Ti alloy ingot into a -coi-l,- thensubjecting the rolled coil to an oxidation treatment, and thereby forming an oxygen egniched layer on the surface. Specifically, in the welding wire of the invention, the oxygen enriched layer- can be formed-by -subjecting a metal welding wire to a thermal oxidation treatment in an oxygen-containing atmosphere. The usable oxygen-containing atmosphere is a gas atmosphere containing an oxygen compound such as an oxygen-'dn'taining nitrogen atmosphere (including an air atmosphere), or an-oxygen-containing inert gas atmosphere, or in addition, -water vapor. ... For forming the oxygen enriched layer- having a necessary and sufficient thickness, it is preferable to use an oxygen containing atmosphere-havih4"a partial pressure of oxygen of 5 x 10 to 15 x 10' Pa. Further, the treatment temperature is preferably set' at, for example, 500 to 800*C. On the other hand, other than the thermal oxidation treatment, there is an adoptable method in which titanium 20 oxide grains are embedded in the'w'eld'int wire sirfade, or" a titanium oxide layer is formed by a vapor phase 'deposition process such as vapor deposition or sputtering, resulting in an oxygen enriched layer. Alternatively, the titanium oxide layer may be formed by a known sol-gel process. Then, when the titanium oxide layer is formed according to any of these methods, it is further preferable that the oxygen diffused-layer is formed by a diffusion heat-treatment-. Fig. 3 shows the cross sectional microphotograph of the a coil welding wire in the foregoing state. As apparent from Fig. 3, no crack is generated in the surface made of the oxygen enriched layer at this stage. Subsequently, the coil welding wire is subjected to a cold wire drawing processy1g, resulting in a welding wire with a preferable wire diameter. At this step, depending upon the magnitude of the surface -reduction -ratio,- in the surface of the welding wire, cracks are formed from the surface toward the inside of the welding wire as shown in Fig. 1, which are generated in the form of a large number of surface cracks in the' su'fface layer portion of the welding wire. Incidentally, in the invention, the surface reduction ratio is defined as the -following equation: Surface Reduction Ratio (%) = (Cross sectional area of ielding Wre before wire drawing - Cross sectional area 21 of welding wire after wire drawing) / (Cross sectional area of welding wire before wire drawing) x 100 Then, finally, in the surface cracks, a metal compound having at least orie-detal selected from alkali metals and alkaline earth metals is packed, thereby to form the welding wire of the invention, shown. in Fig....2. In this manner, the -weld-ing-wire of-.the invention having an- oxygen enriched layer and a metal compound ismanufactured. As these metal compounds, metal compounds such as carbonates are preferred. In' particular, sodium carbonate, potassium carbonate, and calcium carbonate are preferred. The method for packing a metal compound in the cracks is described below. As the packing method, for example, mention may be made of the following method: any of these metal compounds is mixed in a lubricant, and wire drawing is carried out by the use of the lubricant for the cold wire drawing; as a result, surface cracks are generated, and at the same time, the lubricant is packed therein; resultingly, a metal compound is packed in the surface cracks. The amount of the metal compound to be packed may be adjusted by, for example, changing the mixing ratio of the metal compound with the lubricant, changing the thickness of the oxygen enriched.lay.er,.::or changing the surface 22 * ' . ..

reduction ratio in wire drawing. Incidentally, the one including a compound such as calcium hydroxide and calcium stearate is generally used as the lubricant. To such a.. lubricant,. for.,example, .a carbonate of a prescribed metal is mixed, so that the whole of the metal is packed in the surface cracks with being combined with calcium. Therefore, when. a compound of a metal -other -thancalcium is packed, -the following procedure may be adopted. The welding wire is once washed affr, wire drawing, thereby to remove the lubricant from the .. surfa.ce cracks. Then, by the use of a prescribed metal compound, the welding wire is passed through a wire drawing machine with a surface reduction ratio of 0%. When preferable alkali, metals or alkaline earth metals are contained in the lubricant itself, wire drawing may be carried out by the use of the lubricant. The welding wire of the invention is useful as a wire rod for welding used in MIG welding of a Ti material. Further, the welding wire of the invention also has the arc stability and the droplet transfer stabiity. thereforee, it can also be used as a wire rod for thermal spraying in an arc thermal spraying method. In the invention, examples of the, alkali metals include Li, Na, K, Rb, and Cs, and examples of the alkaline 23 earth metals include Ca, Sr, and Ba. Further, an appropriate metal is selected from alkali metals, and another appropriate metal is also selected from alkaline earth metals, and the compounds thereby may be tised together. Namely, the alkali metal and the alkaline earth metal may be contained together. The metal compound of the invention preferably has a metal-having a boiling point of 2000*C or less,.-more preferably 600 to 2000*C, among the alkali metals or the alkaline earth metals. Particularly, it preferably has one or more of K, Na, Ca. Further, a metal compound containing Ca is further preferably used. The content of the metal compound is preferably set at 0.002 to 0.050% by weight based on the total weight of the welding wire. This is for the following reason. When the content of the metal compound is less than 0.002% by weight, the effects of the metal compound are not sufficiently exerted. Accordingly, the rate of occurrence of-the concentrated arc becomes small. As a result, it becomes difficult to attain the object of generating one droplet during one pulsed current flow period. This causes a difficulty in forming a good bead. When the cdntenf6of 'the metal compound is larger than 0.050% by weight, the arc force becomes too strong. Thus, in the process of transfer- of. the-droplet to 24 the weld zone, the spattering phenomenon occurs centering on the droplet. As a result, outward roughness is generated certainly in the bead, but also in the sites other than the weld zone. Further, in view of the implementation of one droplet during one pul'sd- dUirent flow period, the content of the metal compound is preferably 0.007 to 0.015% by weight based on the total weight-of the.welding.wire. All of these metals -have- lower .boiling point and ionization potential than those of Ti which is the main component forming the- bas6 iaiterial. This is shown in Fig. 4. These metals are present in the cracks on the surface layer portion of the welding gwite of the present invention. Therefore, during MIG welding, prior to melting of the base material (Ti) by the arc heat, these metals are present in the field of the arc in the form of ionized metal vapors. For this reason, the generated arc becomes- a concentrated arc, and stabilized. Incidentally, the term "concentrated arc" referred to in the invention is defined as the following arc. This is described by reference to Fig. 5. A welding wire with a diameter D is arc discharged, and the boundary portion of the arc is visually observed. The.. arc so..,blurred that the boundary portion cannot be identified is naturally not recognized as the concentrated arc, but referred to as a diffused arc. Then, a truncated cone having a bottom face at a position lower than the lower end face of the welding wire by the diameter D of the welding wire is assumed. The arc in the case of 2 60 ", where 6 denotes the angle formed between the side face and the bottom face of the truncated cone, is referred to as the concentrated arc. When it is set that e 60 *, it is invariably possible to form a.

droplet. Since the welding. wire. of. the invention has characteristics described above, it can be used for a wire feeder such as an apparatus for carrying out MIG welding. The surface roughness of the welding wire surface of the invention is preferably 10 pm or less in terms of the maximum height, which. is referred to as Ry, from the viewpoint of improving the feedability of the welding wire in the wire feeder. The, t e 6xygei enriched layer is formed with the foregoing thickness and average oxygen concentration. This advantageously acts for obtaining the welding wire surface which has been adjusted in surface roughness to such a numerical value. The surface roughness of the welding wire is preferably set at 0.5 pm or less in terms of the arithmetic average rouighriers Ra. 'FtIrther, the lower limit values of the niaximnm height Ry and the arithmetic average roughness Ra are not particularly 26.

restricted, and are appropriately set in view of the tradeoff with the cost. Incidentally, the present inventors confirmed that Ry can be reduced to about 1.0 pm, and that Ra to about 0*.l' 1n "incidentally, in this specification, the surface roughness denotes the one measured by the method specified irl JIS'.wB0601.994). In order to prevent the buckling of the welding wire in the wire feeder, the tensile strength of the- welding wire is preferably 400 to 1500 MPa. When the tensile strength is less than 400 MPa, it becomes difficult to sufficiently prevent the buckling. When the tensile strength exceeds 1500 MPa, the flexibility of the welding wire is impaired, leading to deficiencies such as breakage and a difficulty in winding. The tensile strength of the welding wire can be controlled by, for example, the adjustment of the surface reduction ratio of the cold working when the final stage of the wire drawing is carried out by cold working, or by the adjustment of the annealing temperature and the time when annealing is subsequently carried out for strain removal. The tensile strength of the welding wire is more preferably 400 to. 120-0 MPa. EXAMPLES 27 The present invention is now illustrated in greater detail with reference to Examples and Comparative Examples, but it should be understood that the present invention is not to be construed as being limited thereto. Experimental Examples 1 to 25 (1) Manufacture of weldine Wife Ti welding wire specified according to JIS H4670 (JIS Class 2, wire diameter 1.6 mm) was..used for- preparing Experimental Examples. Experimental. Examples 1 to 22 each having a thick oxygen enriched layer were prepared by being subjected to a heat treatdieanin an air at a temperature of 750 0 C for 6 minutes to form an oxygen enriched layer on the surface. Experimental Examples 23 to 25 each having a thin oxygen enriched layer were prepared in the same manner as in Experimental Examples 1 to 22 except that a temperature in a heat treatment was set at 450 0 C. On the other hand, powders of -carbonates of the alkali metals and the alkaline earth metals shown in Table 1 were prepared. As a lubricant, KOSHIN (a mixture of calcium hydroxide and calcium stearate, trade name, manufactured by KYOEISHA Chemical Co., Ltd.) was prepared. By the use of the lubricant, a wire drawing processing was carried out cold, resulting in a welding..wire..with.a wire 28 diameter (Dw) of 1.0 mm. The surface reduction ratio at this step was 37.5%. When a metal other than calcium is allowed to be present alone with the oxygen enr-iched-1ayer,-the welding. wire after wire drawing was once'-wa-shed with LIGHT CLEAN (detergent) to wash off KOSHIN. Then, the welding wire was passed through a wire draki'n4 machine by the use of a powder- of -a prescribed metal carbonate with a-surface reduction ratio of 0%, so that the powder was packed in the surface cracks. Experimental Example 25 that does not have a metal with the oxygen enriched layer was prepared by merely being washed in the same manner as the above after wire drawing. Each resulting welding wire was measured for the metal content (% by weight) of the metal compound, the thickness (Tw: pm) of the oxygen enriched layer, the tensile strength (MPa), the surface roughness, and the coefficient of dynamic friction according to the following specifications. Metal content: It is analyzed by the. inductively coupled plasma emission spectrometry. Oxygen enriched layer: As described above, the cross section of the welding wire was mirror polished. The polished surface was subject-ed- to area analysis on the oxygen concentration distribution by EPMA. The oxygen concentration at the cross section. centrall part.was. taken 29 as 1, and the region 'f the endingg wire having an oxygen concentration of 1.2 or more (i.e., having an oxygen concentration of not less than 1.2 times as large as that of the central part) was taken as the oxygen enriched layer. Average oxygen concentration: As described above, the average value (5 measuring points) of the oxygen concentration in the oxygen enriched- layer was determined, and it- was taken as the average oxygen concentration of -the oxygen enriched layer. Thickness of the oxygen enriched layer: It was taken as the average va-lue of the thickness of the oxygen enriched layer. Tensile strength: A 100-mm .Iona t;est.. piece was cut out from each welding wire, and pulled at a cross head speed of 1.0 mm/min by means of an Instron type tensile tester. Thus, a stress-strain curve was determined, and a maximum stress value was. read::as the tensile strength. Surface Roughness: A roughness curve was determined with a method specified by JIS B0601 (1994), i.n accordance with an embodiment in .which the. assessment .length was set along the longitudinal direction of the welding wire. The values of the maximum. height -Ry (pm) and the arithmetical average roughness Ra (pm) were respectively read therefrom. Coefficient of dyxamicfriction: This was measured by using a Bowden-Leben-type friction tester. Specifically, 30 a welding wire sample was set on a saniple table, a steel material for pressing was stacked thereon from above, and the sample table was moved at a constant velocity while pressing the steel material by a weight with a given weight. The frictional force at this step was detected by means of a strain gauge type load sensor. The foregoing results' ar-e~summarized and shown in Table-l 31 . 31.. . . . . . .

E N C4 C4 C N N N Nc 'D ~ 0 -a c s02 O. 0 C 0m0 0 0 0 0 0 0000 0' G o O . . .. .o ' Go o 40 C6 cd~ 0 0o co co c o co c o c 44 0 '~ 0 0o 0o 0 06 ad 0d 0d 0d 0 0 C: m m4 a) c 0 0 0 q o L o) m. 0i 0 0cc~ n r U) I0 D 0 V_ V_ T_ V_ VW CD 0 0 0: q * r E = E r E E E E 0 ~~~~~~ ~ ~ ~ -l ni -_ -x_.60- k Lx0 L x~~~~~~~ x X . U6 l6 LU~~ ~ ~ ~ I.u U: -L U L N ~ C N N N N 04 N N 0= C 0 a 0 0 0 .0 0 0. 00D 0) 0 0I 0> 0 0 o 6, o Do c0 0 0o 0 .*0 .0 .0 .0 .0 0 0 Go 0 0C OR 0 0 0 0 0 co Go o co 0 Go co G 00 Go00 0> la 0 0 C0 0D 0) 0n 0 CDP N* 04 C (N M C4 N C4 N 4 N A 4 N .1 co 0 0 0 0 0 0o 0 o6 6d 0 6 C6 66 ; c C CD C .. 0 o ~ ~ ~ ~ c 1 .)U00 Q 0D El 00 0 0 C0 *0 W W CCD0 0 CD0 0 W 0 >'D0 .4 0 a)0( 0 0 0 D 0 'a M S Ea E 'aS E S M. S S E M E U E M. E M EM .r ~a E E E m E '-E = E '-E '-E "r r r r r (2) MIG welding MIG weldings under the conditions shown in Table 2 were carried out using each welding wire shown in Table 1. In these MIG weldings, Digital Pulse CPDP-350 (manufactured by DAIHEN Corporation) was used as a welding electric power source. Table 2 Welding current. .40 A. Arc voltage 18V Pulse peak current 320 A Pulse peak time 1.2 ms Base current 30A Rise time 0.4 ms Fall time ..0.8 Ms. Welding speed.. -. - .600 mm/min Shielding gas amount Pure Ar, 15 Umin After shielding gas arnbunt"" Pure Ar, 40 Umin Back shielding gas amount Pure Ar, 10 Umin Conduit Tube made of metal, length 1500 mm The feedability of the welding wire during welding, the stability of the arc, and the amount of spatters generated were evaluated according to the following specifications. The shape of the bead formed, and the 34 tensile strength and-the elongation of the joint portion were evaluated according to the following specifications. Feedability of the welding wire: he case where no buckling of the wire had been generated during welding was rated as "AA", and the case where the buckling of the wire had been generated was rated as "B". Stability of arc: The state of the generated arc was photographed by means of a High Speed Camera "System Model 1000 (one image / 1 ms; manufactured bf'Nac Tric ), 'over 5 seconds after 2 seconds to 7 seconds from' the start of welding. Thus, the stability of the arc was rated from the image.The case where the rate of occurrence of the concentrated arc had been 80% or more was rated as "AA", the case of 65 to 80% was rated as "A", and the case of lower than 65% was rated as "B". Amount of spatters generated: Amount of sputters generated was rated by an amount of sputters having a diameter of 1 mm or more, which were deposited on the base metal, with reference to a welding length of 100 mm. After the completion of welding, the state in which spatters had been deposited on the base metal to be welded was visually observed. The case where no ppatter having a diameter of 1 mm or more had been deposited was rated as "AA", and the case where 1 to 10 spatters having the- diameter range had been deposited was rated as "A", and the case where 11 or 35 more spatters having the diameter range had been deposited was rated as "B". Bead shape: After welding, the bead was visually observed. The case where the width' had'been uni'form*and the outward appearance had been smooth was rated as "AA"., and the case where irregularities of the width of the bead had been small was rated as "A", and the case where irregularities of the width of the bead had been-large was rated as "B". Tensile strength of the joint portion: The case of a measured value of 340 MPa or more was rated as "AA", and the case of a measured value egual to, or smaller than this was rated as "B". The foregoing results are summarized and shown in Table 3. 36 0 0 a) ca a)Y cis c. C 4D4 )594. D4)00a0004 04 CL G . CLS'. 6E LE4 a9 a)a

E--

.5 0 (n r0 O) - -- E c F= -r-) E r cE E E CX eg ID D Co 1 0 oCU 4 (D cxM Co C ID 0- 6 X XUj x J )0 ul Ul6 Lt0',. w UlL 6Wx L Lb : w U w WCU As apparent from Tables 1 and 3, when a welding wire of Experimental Examplehaving an alkali metal or an alkaline earth metal is used, the arc is stabilized, and the bead shape becomes favorable in any case. Further, in Experimental Examples 1 to 20 in each of which the welding wire contains a metal compound in a proper amount, the effects are more excellent. However, when the welding 'wi're oi Experim'ental Example 25 which does not have a metal compound at all, and in which the thickness of the oxygen enriched layer is small, is used, the generation of the concentrated arc is reduced, and the amount of spatters also increases, resulting in a degraded bead shape. Incidentally, the photograph showing the shape of the bead formed by the use of the welding wire of Experimental Example 6 is .showi..in Fig. 6. As apparent from the drawing, use of this welding wire enables the formation of a bead with a uniform width and also in a uniformly overlying form, and good in both the outward appearance and the shape. Experimental Examples 26 to 41 welding wires were inaifactured in-'the 'same 'manner as in Experimental Examples 1 to 25, except that Ti alloy materials having constituents shown in Table 4 were used as 39 the base materials and that the alkali metals and the alkaline earth metals were used according to the type and contents shown in Table 4. -i40. * . 9 .. .. 4* g . . . . . . . . . . . .. . . . . . * -* 4.* .. *.. . . . . 4.. . - .... . . - . . *.. . * CD J C' C c' .. .'6 C=; (%J 6~ O C) C Co C 6 6 C) qcr 10, - - -r C2 C~ C= - - C> .o CD C), CD CC CD L co Go Co Co c t 4 co co 4= E C C 0b =0C Cm t 0)) :L c., c.lC:!aa l " ca :> 1q C ~ ~ 00 9 0 0 cz 0C% 6 146 cc 6 m 6 j 6 " T 6 . .c 9~ ~ F 6 6~6 60P cli ~ ~ CM I - 0 -- ( C ( 2=MF E E E = E uj LU k u .. y . a C1 C~ CJ C14 C14 o ~ c 6 ;. 6C 6 6D ~~C C. ~. . ~- q q- - M c= 0 0 0 r 6.................................... cn 0 6o 6D cc 6 0 t By the use of the welt'inq wires of Experimental Examples 26 to 41, MIG welding was carried out. The results are shown in Table 5. 43 a 0 CL 00 0 LL. cc 0 0. 0O '- L C4 r- c 4w a V)cM < ID D ~4 4) 4) 4) lU CD 0A I-.4)M E aEME' ME E &2 r=SSE ) EEF 0.0 C C x0 B~ LB2 na tLL .i ,L LOul u 6Lui wOxd cv,, a.. CL 0. 0.L .................... LU* .U .J .. . . . . . . . . . . .

Experimental Examples 42 to 53 Welding wires were manufactured in such a manner that the base material was made of JIS Class 2 as in the case of Example 1-24 and that the alkali metals and the alkaline earth metals were used according to the type and contents shown in Table 6..-.-.-. ± . ." .......... .

wu C1 04 C4 C' N N N 0to co 0 0 to co w O6 =0 0 D CD CO C O CD. CO. a.CO CO C) (0 co Co ) V6 6a c- 6 oc CO C CD (0 CD C CD CD (0 CD SN N N Nq N Nq N N N N N CC - ):, e 0c _M 0 3 N 30u (D 0) DC 0 0 0 N 0 0 ZD cc a CD 0 0 m L. fx 0 w0 Lb x00 al x >I (0(0 " i (0(0 E-CV Cuj CU U (U ( C Lt 000 wa 0 0L N The welding wires of. Experimentqal Examples 42 to 53 was mounted in a thermal spray unit of a wire feeder, and fed to a welding gun to be- thermally sprayed on the surface of an article to be processed. The feedability of the welding wire and the stability of the arc at this step were examined. The results are shown in Table 7. Table -7 Evaluation Feedability of welding Stability of arc wire Experimental Example 42 AA AA Experimental Example 43 AA AA Experimental Example 44 AA AA Experimental Example 46" AA AA Experimental Example 46 AA AA Experimental Example 47 AA.

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AA Experimental Example 48 AA AA Experimental Example 49 AA AA Experimental Example 50 AA AA Experimental Example 51 AA AA Experimental Example 52.-.- - .AA A Experimental Example 53 AA A The boiling point and the ionization potential of an alkali metal or an alkaline earth metal are lower than the melting point and the.ionizat-ion potential of Ti, respectively.,. Therefore, prior to melting of the base 48 material (Ti or Ti alloy) by the arc heat, the alkali metal or the alkaline earth metal is present in the form of an ionized metal vapor in the field of the generated arc. For this reason, the generated arc column becomes stable, resulting in a concentrated arc. 'urther, the" xygen in the oxygen enriched layer also stabilize the generated arc, and at the same time, reduces the surface tension of the welding wire surface, so that generated droplets become more likely to be released from the welding wire tip. These enable one droplet to transfer to the weld zone in one pulsed current flow period in MIG welding with reliability. As a result, the formation of the bead good in shape and outward appearance .becomes possible. With the welding wire of the present invention, the resulting arc becomes the concentrated arc, and one droplet transfer can be achieved during one pulsed current flow period with reliability. Therefore, the shape and the outward appearance of the b d at the weld zone become excellent. This welding wire is useful as a wire rod for welding in MIG welding of a ,Ti 'materiaij -or as a wire rod for thermal spraying at the time of Ti thermal spraying. While the present invention has been described in detail and with refereice to specific embodiments thereof, it will be apparent to one skilled in the art that various 49 changes and modifications can be made therein without departing from the spirit and scope thereof. The present application is based on Japanese Patent Application No. 2004-300497 filed on October 14, 2004, and the contents thereof are incorporated herein by reference. The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in Australia. Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. 50

Claims (9)

1. A welding wire including Ti or a Ti alloy, wherein the welding wire has: an oxygen enriched layer on a surface thereof; and a metal compound having at least one 5 metal selected from the group consisting of alkali metals and alkaline earth metals, and, wherein the welding wire has cracks on the surface, and the metal compound is present in the cracks. 10

2. The welding wire according to claim 1, wherein the content of the metal compound is 0.002 to 0.050% by weight based on the total weight of the welding wire.

3. The welding wire according to claim 1, 15 wherein the boiling point of the metal is 20000C or less.

4. The welding wire according to claim 1, wherein the metal compound is a metal compound containing Ca. 20

5. The welding wire according to claim 1, wherein the value of Tw/Dw is 0.3 x 10- to 1 x 10~1, wherein Tw represents the thickness of the oxygen enriched layer, and Dw represents the wire diameter of the welding wire, and 25 wherein the average oxygen concentration of the oxygen enriched layer is not less than 1% by weight. -51- C \NRPorbI\DCC\KMM2975x9_I DOC- I/11/2010

6. The welding wire according to claim 6, wherein the average oxygen concentration of the oxygen enriched layer is 1 to 40% by weight. 5

7. The welding wire according to claim 1, wherein the surface roughness of the welding wire is 10 pm or less in terms of the surface roughness expressed as Ry specified according to JIS B0601. 10

8. The welding wire according to claim 6, wherein the value of Tw/Dw is 1 x 10~3 to 50 x 10~3, wherein Tw represents the thickness of the oxygen enriched layer, and Dw represents the wire diameter of the welding wire, 15 and wherein the average oxygen concentration of the oxygen enriched layer is 1 to 30% by weight.

9. A welding wire, substantially as herein described with 20 reference to the accompanying drawings. -52-