Ni based alloy flux cored wire

Abstract

A Ni based alloy flux cored wire including a Ni based alloy as a sheath is provided, wherein the sheath contains predetermined ranges of Ni, Cr, Mo, Ti, Al, and Mg relative to the total mass of the sheath, control is made to ensure predetermined C and Si, the composition of the whole wire, which is the sum total of the sheath components and flux components enveloped in the sheath, contains predetermined ranges of Ni, Cr, Mo, Mn, W, Fe, Ti, Al, and Mg relative to the total mass of the wire, and control is made to ensure predetermined C, Si, Nb, P, and S.

Claims

1. A Ni based alloy flux cored wire, comprising: a sheath and flux, wherein the sheath comprises, relative to a total mass of the sheath: Ni: 60 to 80 percent by mass, Cr: 1 to 15 percent by mass, Mo: 8 to 22 percent by mass, Ti: 0.002 to 0.40 percent by mass, Al: 0.03 to 0.40 percent by mass, Mg: 0.010 to 0.025 percent by mass, C: 0.020 percent by mass or less, and Si: 0.15 percent by mass or less, and wherein the wire comprises, relative to a total mass of the sheath and the flux: Ni: 53 to 75 percent by mass, Cr: 1 to 15 percent by mass, Mo: 10 to 20 percent by mass, Mn: 1.5 to 5.5 percent by mass, W: 1.5 to 5.0 percent by mass, Fe: 2.0 to 8.0 percent by mass, Ti: 0.002 to 0.50 percent by mass, Al: 0.02 to 0.50 percent by mass, Mg: 0.003 to 0.03 percent by mass, C: 0.050 percent by mass or less, Si: 0.20 percent by mass or less, Nb: 0.030 percent by mass or less, P: 0.015 percent by mass or less, and S: 0.010 percent by mass or less, and wherein the Ni based alloy flux cored wire reduces occurrence of blowholes in a weld zone, without impairing welding operability.

2. The Ni based alloy flux cored wire according to claim 1, wherein a ratio calculated by [C]/([Ti]+[Al]+[Mg]3) is 0.11 or less, where percent by mass of C, Ti, Al, and Mg contained in the sheath are represented by [C], [Ti], [Al], and [Mg], respectively.

3. The Ni based alloy flux cored wire according to claim 1, wherein the flux enveloped in the sheath comprises a sum total of at least two members selected from the group consisting of TiO.sub.2, SiO.sub.2, and ZrO.sub.2: 3 to 15 percent by mass, and a sum total of compounds of Na, K, and Li, in terms of Na, K, and Li simple substances: 0.1 to 1.0 percent by mass, relative to the total mass of the wire.

4. The Ni based alloy flux cored wire according to claim 1, wherein the sheath comprises, relative to the total mass of the sheath, 0.03 to 0.10 percent by mass of Ti.

5. The Ni based alloy flux cored wire according to claim 1, wherein the sheath comprises, relative to the total mass of the sheath, 0.06 to 0.10 percent by mass of Al.

6. The Ni based alloy flux cored wire according to claim 1, wherein the sheath comprises, relative to the total mass of the sheath, 0.010 to 0.020 percent by mass of Mg.

7. The Ni based alloy flux cored wire according to claim 1, wherein the sheath comprises, relative to the total mass of the sheath, 0.010 percent by mass of C or less.

8. The Ni based alloy flux cored wire according to claim 1, wherein the sheath comprises, relative to the total mass of the sheath, greater than 0.010 to 0.020 percent by mass of Mg.

9. The Ni based alloy flux cored wire according to claim 1, wherein the sheath comprises, relative to the total mass of the sheath, 0.013 to 0.020 percent by mass of Mg.

10. The Ni based alloy flux cored wire according to claim 2, wherein the flux enveloped in the sheath comprises a sum total of at least two members selected from the group consisting of TiO.sub.2, SiO.sub.2, and ZrO.sub.2: 3 to 15 percent by mass, and a sum total of compounds of Na, K, and Li, in terms of Na, K, and Li simple substances: 0.1 to 1.0 percent by mass, relative to the total mass of the wire.

11. The Ni based alloy flux cored wire according to claim 2, wherein the ratio is 0.05 or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph showing the relationship between the sheath components and the number of generation of blowholes; and

(2) FIG. 2 is a schematic diagram showing the groove shape and the stacking procedure of a butt weld joint in vertical butt welding in an example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(3) The embodiments according to the present invention will be described below in detail.

(4) A flux cored wire according to the present invention includes a Ni based alloy as a sheath. The composition of the sheath contains predetermined ranges of amounts of Ni, Cr, Mo, Ti, Al, and Mg relative to the total mass of the sheath, where C and S are controlled to predetermined amounts or less.

(5) The composition of the whole wire, which is the sum total of the sheath components and flux components enveloped in the sheath, contains predetermined ranges of amounts of Ni, Cr, Mo, Mn, W, Fe, Ti, Al, and Mg relative to the total mass of the wire, and C, Si, Nb, P, and S are controlled to predetermined amounts or less.

(6) In the flux cored wire, preferably, the ratio calculated by [C]/([Ti]+[Al]+[Mg]3) is specified to be 0.11 or less, where percent by mass of C, Ti, Al, and Mg contained in the sheath are represented by [C], [Ti], [Al], and [Mg], respectively.

(7) In the flux cored wire, preferably, the flux enveloped in the sheath contains the sum total of at least two types selected from the group consisting of TiO.sub.2, SiO.sub.2, and ZrO.sub.2: 3 to 15 percent by mass, the sum total of compounds of Na, K, and Li (the sum total in terms of Na, K, and Li simple substances): 0.1 to 1.0 percent by mass, and incidental impurities relative to the total mass of the wire.

(8) The reasons for the limitations of the components of the flux cored wire will be described below.

(9) The reasons for the limitations of the component numerical values of the sheath will be described below.

(10) Ni: 60 to 80 percent by mass in sheath

(11) The Ni based alloy is used as the sheath metal for the purpose of not impairing the homogeneity of the weld metal and suppressing addition of the alloy to the flux in order to avoid the flux from being excessively filled. If the Ni content in the Ni based alloy is less than 60 percent by mass, the contents of other elements increase inevitably, although elements, e.g., Cr and Mo, other than Ni in the sheath degrade the drawability of the sheath, and the productivity is degraded. On the other hand, if the Ni content is more than 80 percent by mass, most of the other alloy elements are added to the flux and, thereby, the flux filling ratio (the ratio of the mass of flux to the total mass of flux cored wire) becomes excessive. If the flux filling ratio becomes excessive, drawing of the wire becomes difficult in the production process and the productivity is degraded. Therefore, the Ni content in the sheath is specified to be 60 to 80 percent by mass.

(12) Cr: 1 to 15 percent by mass in sheath

(13) Chromium has an effect of improving the corrosion resistance and the strength of the weld metal. In order to obtain the above-described effect, the Cr content in the sheath is specified to be 1 percent by mass or more. On the other hand, if the Cr content in the sheath is more than 15 percent by mass, the hot workability of the metal sheath is degraded and forming of the sheath becomes difficult. Therefore, the Cr content in the sheath is specified to be 1 to 15 percent by mass.

(14) Mo: 8 to 22 percent by mass in sheath

(15) Molybdenum is an element indispensable for ensuring the strength of the weld metal. If the Mo content in the sheath is less than 8 percent by mass, it is necessary that Mo be added to the flux in order to obtain the strength of the weld metal, and the flux filling ratio becomes excessive. On the other hand, if the Mo content in the sheath is more than 22 percent by mass, the hot workability of the metal sheath is degraded and forming of the sheath becomes difficult. Therefore, the Mo content in the sheath is specified to be 8 to 22 percent by mass.

(16) Ti: 0.002 to 0.40 percent by mass in sheath

(17) Titanium in the sheath serves as a deoxidizing component and plays a role in reducing the amount of dissolved oxygen in the molten metal, suppressing the reaction C+O=CO (gas), and reducing the amount of generation of blowholes. If the Ti content in the sheath is less than 0.002 percent by mass, the effect is not obtained. On the other hand, if the Ti content in the sheath is more than 0.40 percent by mass, the hot workability of the metal sheath is degraded and forming of the sheath becomes difficult because of the influence of deposition of intermetallic compounds, e.g., Ni.sub.3Ti. Therefore, the Ti content in the sheath is specified to be 0.002 to 0.40 percent by mass. The Ti content in the sheath is preferably 0.03 percent by mass or more and preferably 0.10 percent by mass or less.

(18) Al: 0.03 to 0.40 percent by mass in sheath

(19) Aluminum in the sheath serves as a deoxidizing component and play a role in reducing the amount of dissolved oxygen in the molten metal and reducing the amount of generation of blowholes as with Ti. If the Al content in the sheath is less than 0.03 percent by mass, the effect is not obtained. On the other hand, if the Al content in the sheath is more than 0.40 percent by mass, the hot workability of the metal sheath is degraded and forming of the sheath becomes difficult because of the influence of deposition of intermetallic compounds, e.g., Ni.sub.3Al. Therefore, the Al content in the sheath is specified to be 0.03 to 0.40 percent by mass. The Al content in the sheath is preferably 0.06 percent by mass or more and preferably 0.10 percent by mass or less.

(20) Mg: 0.004 to 0.025 percent by mass in sheath

(21) Magnesium in the sheath serves as a deoxidizing component and play a role in reducing the amount of dissolved oxygen in the molten metal and reducing the amount of generation of blowholes as with Ti. If the Mg content in the sheath is less than 0.004 percent by mass, the effect is not obtained. On the other hand, if the Mg content in the sheath is more than 0.025 percent by mass, the amount of spatter increases during welding and the welding operability is degraded. Therefore, the Mg content in the sheath is specified to be 0.004 to 0.025 percent by mass. The Mg content in the sheath is preferably 0.010 percent by mass or more and preferably 0.020 percent by mass or less.

(22) C: 0.020 percent by mass or less in sheath

(23) Carbon in the sheath is present as an incidental impurity. Carbon in the sheath is bonded to O easily during welding and is converted to a CO gas, so as to cause generation of blowholes. Therefore, the C content in the sheath is specified to be 0.020 percent by mass or less, and more preferably, the C content in the sheath is 0.010 percent by mass or less.

(24) Si: 0.15 percent by mass or less in sheath

(25) Silicon in the sheath is present as an incidental impurity. Silicon in the sheath combines with Ni present as an incidental impurity to generate a low-melting point compound, so that the hot cracking resistance is degraded. Therefore, the Si content in the sheath is specified to be 0.15 percent by mass or less.

(26) Remainder

(27) The remainder of the components of the sheath may contain 4.0 percent by mass or less of Mn, 7.0 percent by mass or less of Fe, and 4.0 percent by mass or less of W. However, if Mn in the sheath is more than 4.0 percent by mass or W is more than 4.0 percent by mass, the hot workability of the metal sheath is degraded and forming of the sheath becomes difficult. Meanwhile, if Fe in the sheath is more than 7.0 percent by mass, the hot cracking resistance is degraded. The others are incidental impurities. Examples of incidental impurities include P, S, Cu, Nb, V, and N besides C and Si described above.

(28) The reasons for the limitations of the component numerical values relative to the total mass of the wire will be described below.

(29) Ni: 53 to 75 percent by mass relative to total mass of wire

(30) Nickel is alloyed with various metals and imparts excellent mechanical performances and corrosion resistance to the weld metal. However, if the Ni content in the flux cored wire is less than 53 percent by mass relative to the total mass of the wire, stable austenite microstructure is not formed when the weld metal is diluted. On the other hand, if the Ni content in the flux cored wire is more than 75 percent by mass relative to the total mass of the wire, the amount of addition of the other alloy elements becomes insufficient, so that the mechanical performance is not ensured. Therefore, the Ni content is specified to be 53 to 75 percent by mass relative to the total mass of the wire. Examples of Ni sources of the flux cored wire according to the present invention include the Ni based alloy constituting the sheath and metal Ni and a NiMo alloy contained in the flux. In the present invention, the contents of them are converted to the content of Ni, and the resulting value is taken as the Ni content.

(31) Cr: 1 to 15 percent by mass relative to total mass of wire

(32) Chromium has an effect of improving the corrosion resistance and the strength of the weld metal. However, if the Cr content in the flux cored wire is less than 1 percent by mass relative to the total mass of the wire, the effect is not obtained. On the other hand, if the Cr content in the flux cored wire is more than 15 percent by mass relative to the total mass of the wire, the hot cracking resistance is degraded. Therefore, the Cr content is specified to be 1 to 15 percent by mass relative to the total mass of the wire. Examples of Cr sources of the flux cored wire according to the present invention include the Ni based alloy constituting the sheath and metal Cr, an FeCr alloy, and Cr.sub.2O.sub.3 contained in the flux. In the present invention, the contents of them are converted to the content of Cr, and the resulting value is taken as the Cr content.

(33) Mo: 10 to 20 percent by mass relative to total mass of wire

(34) Molybdenum has an effect of improving the corrosion resistance and the strength of the weld metal. However, if the Mo content in the flux cored wire is less than 10 percent by mass relative to the total mass of the wire, the corrosion resistance and the strength of the weld metal are not ensured. On the other hand, if the Mo content in the flux cored wire is more than 20 percent by mass relative to the total mass of the wire, the hot cracking resistance is degraded. Therefore, the Mo content is specified to be 10 to 20 percent by mass relative to the total mass of the wire. Examples of Mo sources of the flux cored wire according to the present invention include the Ni based alloy constituting the sheath and metal Mo and an FeMo alloy contained in the flux. In the present invention, the contents of them are converted to the content of Mo, and the resulting value is taken as the Mo content.

(35) Mn: 1.5 to 5.5 percent by mass relative to total mass of wire

(36) Manganese has an effect of making S harmless by bonding to S which forms a low-melting point compound with Ni to degrade the hot cracking resistance. However, if the Mn content in the flux cored wire is less than 1.5 percent by mass relative to the total mass of the wire, the effect of making S harmless is not obtained. On the other hand, if the Mn content in the flux cored wire is more than 5.5 percent by mass relative to the total mass of the wire, the slag peeling property is degraded. Therefore, the Mn content is specified to be 1.5 to 5.5 percent by mass relative to the total mass of the wire. Examples of Mn sources of the flux cored wire according to the present invention include the Ni based alloy constituting the sheath and metal Mn and an FeMn alloy contained in the flux. In the present invention, the contents of them are converted to the content of Mn, and the resulting value is taken as the Mn content.

(37) W: 1.5 to 5.0 percent by mass relative to total mass of wire

(38) Tungsten is a component to improve the strength of the weld metal. However, if the W content in the flux cored wire is less than 1.5 percent by mass relative to the total mass of the wire, the strength of the weld metal is not ensured. On the other hand, if the W content in the flux cored wire is more than 5.0 percent by mass relative to the total mass of the wire, the hot cracking resistance is degraded. Therefore, the W content is specified to be 1.5 to 5.0 percent by mass relative to the total mass of the wire. Examples of W sources of the flux cored wire according to the present invention include the Ni based alloy constituting the sheath and metal W and an FeW alloy contained in the flux. In the present invention, the contents of them are converted to the content of W, and the resulting value is taken as the W content.

(39) Fe: 2.0 to 8.0 percent by mass relative to total mass of wire

(40) Iron is added to ensure the ductility of the weld metal. If the Fe content in the flux cored wire is less than 2.0 percent by mass relative to the total mass of the wire, the ductility of the weld metal is not ensured. On the other hand, if the Fe content in the flux cored wire is more than 8.0 percent by mass relative to the total mass of the wire, the hot cracking resistance is degraded. Therefore, the Fe content is specified to be 2.0 to 8.0 percent by mass relative to the total mass of the wire. Examples of Fe sources of the flux cored wire according to the present invention include the Ni based alloy constituting the sheath and metal Fe, an FeMn alloy, an FeCr alloy, an FeMo alloy, and an FeTi alloy contained in the flux. In the present invention, the contents of them are converted to the content of Fe, and the resulting value is taken as the Fe content.

(41) Ti: 0.002 to 0.50 percent by mass relative to total mass of wire

(42) Titanium contained in the flux cored wire serves as a deoxidizing component and plays a role in reducing the amount of dissolved oxygen in the molten metal, suppressing the reaction C+O=CO (gas), and reducing the amount of generation of blowholes. If the Ti content in the flux cored wire is less than 0.002 percent by mass relative to the total mass of the wire, the effect is not obtained. On the other hand, if the Ti content in the flux cored wire is more than 0.50 percent by mass relative to the total mass of the wire, the hot cracking resistance of the weld metal is degraded. Therefore, the Ti content is specified to be 0.002 to 0.50 percent by mass relative to the total mass of the wire. Examples of Ti sources of the flux cored wire according to the present invention include the Ni based alloy constituting the sheath and metal Ti and an FeTi alloy contained in the flux. In the present invention, the contents of them are converted to the content of Ti, and the resulting value is taken as the Ti content. In this regard, this Ti content is specified to be the content of Ti derived from metal Ti and Ti alloys soluble in sulfuric acid, where Ti derived from oxides, e.g., TiO.sub.2, insoluble in sulfuric acid is not included.

(43) Al: 0.02 to 0.50 percent by mass relative to total mass of wire

(44) Aluminum contained in the flux cored wire serves as a deoxidizing component and plays a role in reducing the amount of dissolved oxygen in the molten metal and reducing the amount of generation of blowholes as with Ti. If the Al content in the flux cored wire is less than 0.02 percent by mass relative to the total mass of the wire, the effect is not obtained. On the other hand, if the Al content in the flux cored wire is more than 0.50 percent by mass relative to the total mass of the wire, the hot cracking resistance of the weld metal is degraded. Therefore, the Al content is specified to be 0.02 to 0.50 percent by mass relative to the total mass of the wire. Examples of Al sources of the flux cored wire according to the present invention include the Ni based alloy constituting the sheath and metal Al and an FeAl alloy contained in the flux. In the present invention, the contents of them are converted to the content of Al, and the resulting value is taken as the Al content. In this regard, this Al content is specified to be the content of Al derived from metal Al and Al alloys soluble in sulfuric acid, where Al derived from oxides, e.g., Al.sub.2O.sub.3, insoluble in sulfuric acid is not included.

(45) Mg: 0.003 to 0.03 percent by mass relative to total mass of wire

(46) Magnesium contained in the flux cored wire serves as a deoxidizing component and plays a role in reducing the amount of dissolved oxygen in the molten metal and reducing the amount of generation of blowholes as with Ti. If the Mg content in the flux cored wire is less than 0.003 percent by mass relative to the total mass of the wire, the effect is not obtained. On the other hand, if the Mg content in the flux cored wire is more than 0.03 percent by mass relative to the total mass of the wire, the amount of spatter increases during welding and the welding operability is degraded. Therefore, the Mg content is specified to be 0.003 to 0.03 percent by mass relative to the total mass of the wire. Examples of Mg sources of the flux cored wire according to the present invention include the Ni based alloy constituting the sheath and metal Mg and a NiMg alloy contained in the flux. In the present invention, the contents of them are converted to the content of Mg, and the resulting value is taken as the Mg content. In this regard, this Mg content is specified to be the content of Mg derived from metal Mg and Mg alloys soluble in sulfuric acid, where Mg derived from oxides, e.g., MgO, insoluble in sulfuric acid is not included.

(47) C: 0.050 percent by mass or less relative to total mass of wire

(48) Carbon in the flux cored wire is an incidental impurity. If the C content in the flux cored wire is more than 0.050 percent by mass relative to the total mass of the wire, the amount of generation of blowholes mainly derived from a CO gas increases. Therefore, the C content is specified to be 0.050 percent by mass or less relative to the total mass of the wire. Examples of C sources of the flux cored wire according to the present invention include the Ni based alloy constituting the sheath and C as an incidental impurity contained in alloy components and a slag-forming agent in the flux.

(49) Si: 0.20 percent by mass or less relative to total mass of wire

(50) Silicon is an incidental impurity present in the flux cored wire. If the Si content in the flux cored wire is more than 0.20 percent by mass relative to the total mass of the wire, a low-melting point compound is generated by combination with Ni, so that the hot cracking resistance is degraded. Therefore, the Si content is specified to be 0.20 percent by mass or less relative to the total mass of the wire. In this regard, the Si content according to the present invention is specified to be the content of Si derived from metal Si and Si alloys soluble in hydrochloric acid and nitric acid, where Si derived from oxides, e.g., SiO.sub.2, insoluble in acids is not included.

(51) Nb: 0.030 percent by mass or less relative to total mass of wire

(52) Niobium is an incidental impurity present in the flux cored wire. If the Nb content in the flux cored wire is more than 0.030 percent by mass relative to the total mass of the wire, a low-melting point compound is generated by combination with Ni, so that the hot cracking resistance is degraded. Therefore, the Nb content is specified to be 0.030 percent by mass or less relative to the total mass of the wire.

(53) P: 0.015 percent by mass or less relative to total mass of wire, S: 0.010 percent by mass or less relative to total mass of wire

(54) Phosphorus and sulfur are incidental impurities present in the flux cored wire. If the P content in the flux cored wire is more than 0.015 percent by mass relative to the total mass of the wire or the S content is more than 0.010 percent by mass relative to the total mass of the wire, low-melting point compounds of these elements and Ni are generated, so that the hot cracking resistance is degraded. Therefore, the P content is specified to be 0.015 percent by mass or less relative to the total mass of the wire and the S content is specified to be 0.010 percent by mass or less relative to the total mass of the wire.

(55) Remainder: Incidental Impurities

(56) The remainder of the components in the whole flux cored wire are incidental impurities. Examples of incidental impurities include Cu, V, and N besides C, Si, Nb, P, and S described above.

(57) Also, besides the above-described wire components, small amounts of Ca, Li, and the like, which are wire components serving as fine conditioning agents of deoxidation and the like, may be contained in the flux.

(58) The reasons for the limitations of the other numerical values will be described below.

(59) Ratio calculated by [C]/([Ti]+[Al]+[Mg]3) of 0.11 or less, where percent by mass of C, Ti, Al, and Mg in sheath are represented by [C], [Ti], [Al], and [Mg], respectively

(60) Carbon in the sheath is an element serving as a generation source of CO gas blowholes. On the other hand, Ti, Al, and Mg are components serving as deoxidizing agents effective in suppressing generation of blowholes. The present inventors found that in the Ni based alloy flux cored wire, the ratio calculated by [C]/([Ti]+[Al]+[Mg]3), where percent by mass of C, Ti, Al, and Mg contained in the sheath are represented by [C], [Ti], [Al], and [Mg], respectively, was closely pertinent to the amount of generation of blowholes (refer to FIG. 1). That is, if this ratio exceeds 0.11, blowholes increase sharply. Therefore, it is preferable that the C, Ti, Al, and Mg contents in the above-described sheath and the C content in the whole wire be specified and, in addition, the ratio calculated by [C]/([Ti]+[Al]+[Mg]3) is specified to be 0.11 or less. More preferably, the ratio calculated by [C]/([Ti]+[Al]+[Mg]3) is 0.05 or less. In this regard, the above-described formula was derived on the basis of experiments.

(61) Sum total of at least two types selected from group consisting of TiO.sub.2, SiO.sub.2, and ZrO.sub.2: 3 to 15 percent by mass relative to total mass of wire

(62) Titanium oxide (TiO.sub.2) forms a homogeneous slag having good encapsulation property, has an effect of improving the arc stability and, therefore, is added as a primary component of a slag-forming agent. Examples of TiO.sub.2 sources include rutile, leucoxene, potassium titanate, sodium titanate, and calcium titanate. Silicon oxide (SiO.sub.2) is added as a slag-forming agent to increase the viscosity of the slag and obtain a good bead shape as with TiO.sub.2. Examples of raw materials for SiO.sub.2 include silica sand, potassium feldspar, wollastonite, sodium silicate, and potassium silicate. Zirconium oxide (ZrO.sub.2) has functions of improving the arc strength and improving the arc stability even in a low welding current region. Also, functions of accelerating solidification of the slag and improving the welding operability in vertical upward welding are performed. Therefore, ZrO.sub.2 is added as a slag-forming agent. Examples of ZrO.sub.2 sources include zircon sand and zirconia.

(63) If the sum total of at least two types selected from the group consisting of TiO.sub.2, SiO.sub.2, and ZrO.sub.2 in the enveloped flux is less than 3 percent by mass relative to the total mass of the wire, the characteristics of them serving as the slag-forming agents are not exerted sufficiently. On the other hand, if the sum total is more than 15 percent by mass, slag components in the wire become excessive, the amount of generation of slag during welding becomes excessive, the slag droops and drops from the weld zone easily, and slag inclusions occur easily in the weld zone. Therefore, in the present invention, the sum total of at least two types selected from the group consisting of TiO.sub.2, SiO.sub.2, and ZrO.sub.2 in the enveloped flux is specified to be 3 to 15 percent by mass relative to the total mass of the wire.

(64) Sum total of compounds of Na, K, and Li (sum total in terms of Na, K, and Li simple substances): 0.1 to 1.0 percent by mass relative to total mass of wire.

(65) In the flux, Na, K, and Li function as arc stabilizers and suppress generation of spatters. In the present invention, Na, K, and Li are added as Na compounds, K compounds, and Li compounds, respectively. Specifically, for example, LiF, NaF, KF, Na.sub.3AlF.sub.6, K.sub.2SiF.sub.6, K.sub.2TiF.sub.6, albite, potassium feldspar, and the like may be used. If the content of Na compounds, K compounds, and Li compounds in the flux is less than 0.1 percent by mass in terms of the sum total of Na, K, and Li, respectively, relative to the total mass of the wire, the function as the arc stabilizer is not obtained sufficiently, and the pit resistance is degraded. On the other hand, if the content of Na compounds, K compounds, and Li compounds in the flux is more than 1.0 percent by mass relative to the total mass of the wire, the amount of generation of spatters increases conversely. Therefore, in the present invention, the sum total of compounds, e.g., fluorides and oxides, of Na, K, and Li in the enveloped flux is specified to be 0.1 to 1.0 percent by mass in terms of Na, K, and Li simple substances relative to the total mass of the wire.

(66) In this regard, the remainder of the flux are Mn, W, Fe, and incidental impurities.

(67) The above-described flux cored wire according to the present invention may be favorably used in, for example, gas-shielded metal arc welding by using an Ar+CO.sub.2 mixed gas in welding of low temperature service steels, e.g., a 9% Ni steel and various high Ni alloys.

EXAMPLES

(68) The examples according to the present invention will be described below in comparison with the comparative examples out of the scope of the present invention.

(69) Cylindrical sheaths (Nos. A to L) were produced by bending bands which were made from Ni based alloys having the compositions shown in Table 1 below and which had a thickness of 0.4 mm and a width of 9.0 mm. Fluxes composed of metal raw materials and slag components (Nos. I to III) shown in Table 2 below were enveloped in these sheaths to produce flux cored wires (Nos. 1 to 15) having compositions shown in Table 3 below. The resulting wires were drawn in such a way that the diameter became 1.2 mm and, thereafter, the moisture content in the wire was reduced to 400 ppm or less through electric heating. The resulting wires were specified to be test wires.

(70) TABLE-US-00001 TABLE 1 Sheath component (percent by mass) (remainder: incidental impurities) Sheath [C]/([Ti] + No. C Si Mn P S Ni Cr Mo Fe W Al Ti Mg [Al] + [Mg] 3) A 0.004 0.10 2.4 0.005 0.0002 64 8.1 16.6 5.8 2.3 0.074 0.002 0.0130 0.03 B 0.003 0.05 2.4 0.009 0.0002 66 8.0 16.0 4.6 2.3 0.043 0.006 0.0073 0.04 C 0.003 0.05 2.2 0.009 0.0002 67 7.8 15.4 4.5 2.2 0.041 0.002 0.0066 0.05 D 0.014 0.01 0.1 <0.002 0.0006 69 2.2 18.8 5.8 3.1 0.069 0.049 0.0069 0.10 E 0.017 0.05 0.1 <0.002 0.0009 69 2.2 19.2 5.8 3.1 0.065 0.046 0.0180 0.10 F 0.018 0.02 0.1 <0.002 0.0007 70 2.1 18.8 5.8 2.9 0.053 0.061 0.0068 0.13 G 0.011 0.01 0.1 <0.002 0.0010 70 2.0 19.0 5.8 2.9 0.017 0.045 0.0027 0.16 H 0.022 0.01 0.1 <0.002 0.0002 69 2.2 18.8 5.8 3.1 0.053 0.064 0.0073 0.16 I 0.025 0.05 0.1 <0.002 0.0002 69 2.2 19.2 5.7 3.0 0.038 0.056 0.0190 0.17 J 0.006 0.03 2.2 0.009 0.0006 66 8.2 15.7 4.9 2.3 0.017 0.002 0.0035 0.20 K 0.023 0.07 0.1 <0.002 0.0002 69 2.2 19.2 5.7 3.2 0.021 0.040 0.0099 0.25 L 0.017 0.14 2.4 0.005 0.0001 63 8.1 16.2 5.6 2.5 0.048 0.003 0.0034 0.28

(71) TABLE-US-00002 TABLE 2 Slag component relative to total mass of wire (percent by mass) Na, K, and Li Slag Sum total of values component converted from No. TiO.sub.2 SiO.sub.2 ZrO.sub.2 TiO.sub.2 + SiO.sub.2 + ZrO.sub.2 K.sub.2SiF.sub.6 NaF LiF compounds I 6.5 0.8 2.1 9.4 0.3 0.3 0.1 0.3 II 7.0 0.7 4.0 11.7 0.2 0.3 0.1 0.3 III 7.1 0.9 1.4 9.4 0.4 0.3 0.1 0.3

(72) TABLE-US-00003 TABLE 3 Metal component in wire (relative to total mass of wire, percent by mass) Wire Sheath Slag (remainder: incidental impurities) No. No. No. C Si Mn P S Ni Cr Mo Fe W Nb Al Ti Mg Example 1 A I 0.024 0.12 3.4 0.007 0.004 55.0 6.1 16.2 6.6 2.1 0 0.06 0.10 0.010 2 A II 0.024 0.13 3.4 0.007 0.004 53.1 6.1 16.1 6.3 2.0 0 0.06 0.10 0.010 3 A III 0.025 0.13 3.4 0.007 0.004 55.3 6.2 16.0 6.5 2.1 0 0.06 0.10 0.010 4 B I 0.024 0.09 3.5 0.010 0.004 56.8 6.2 15.5 5.6 2.2 0 0.03 0.10 0.006 5 C I 0.024 0.09 3.3 0.010 0.004 57.5 6.0 15.0 5.5 2.0 0 0.03 0.10 0.005 6 D I 0.033 0.06 3.5 0.005 0.004 57.2 5.7 15.1 5.4 2.4 0 0.05 0.04 0.005 7 E I 0.035 0.09 3.5 0.005 0.005 56.9 5.8 15.4 5.4 2.4 0 0.05 0.04 0.014 8 F I 0.036 0.06 3.5 0.005 0.004 57.5 5.7 15.0 5.4 2.3 0 0.04 0.05 0.005 Comparative 9 G I 0.030 0.06 3.5 0.005 0.005 57.4 5.6 15.2 5.3 2.3 0 0.01 0.03 0.002 example 10 H I 0.039 0.06 3.5 0.005 0.004 57.0 5.7 15.1 5.4 2.4 0 0.04 0.05 0.006 11 I I 0.041 0.09 3.5 0.005 0.004 57.0 5.8 15.4 5.3 2.3 0 0.03 0.04 0.015 12 J I 0.026 0.07 3.3 0.010 0.004 56.5 6.3 15.2 5.8 2.1 0 0.01 0.10 0.003 13 K I 0.040 0.10 3.5 0.005 0.004 56.8 5.8 15.4 5.3 2.4 0 0.02 0.03 0.008 14 L I 0.035 0.16 3.5 0.007 0.004 55.2 6.2 15.6 6.3 2.3 0 0.04 0.10 0.003 15 A I 0.051 0.12 3.5 0.007 0.004 55.6 5.9 16.2 5.6 2.1 0 0.06 0.10 0.010

(73) Vertical butt welding was performed by using the flux cored wire of Nos. 1 to 15 produced by the above-described method, and the arc stability during welding, the spatter suppression performance during welding, the bead appearance of weld zone, and the blowhole resistance were evaluated. The evaluation criteria were as described below.

(74) As for the welding, a 9% Ni steel sheet which is shown in Table 4 and which had a sheet thickness of 12 mm, a width of 250 mm, and a length of 300 mm was used. A base material having a groove angle of 60, a root gap of 5 mm, and a backing metal, as shown in FIG. 2, was subjected to partly mechanized welding, where three-layer three-pass vertical upward welding was performed. As for the welding condition at that time, the welding current was 160 A (direct current wire plus), the arc voltage was 26 V, 80% Ar-20% CO.sub.2 was used as the shield gas, the flow rate of shield gas was 25 L/min, and the welding speed was 11 to 15 cm/min.

(75) TABLE-US-00004 TABLE 4 C Si Mn P S Ni Fe 0.05 0.22 0.64 0.002 0.001 9.22 remainder *Others are incidental impurities

(76) The evaluation criteria were as described below.

(77) As for the evaluation result of each of the arc stability during welding, the spatter suppression performance during welding, and the bead appearance of weld zone, the case of very good was indicated by , the case of good was indicated by , the case of slightly poor was indicated by , and the case of poor was indicated by .

(78) The blowhole resistance was evaluated by the number of spherical defects of 0.4 mm or more (that is, the number of blowholes) detected on the basis of a radiographic testing after an excess weld metal and the backing metal was removed. At this time, start and end portions of the weld bead, that is, portions from start and end points to points at 30 mm from the start and end points, were specified to be out of the evaluation region. The case where the number of generation of blowholes every 240 mm of bead length was 5 or more was indicated by , the case of 6 to 10 was indicated by , the case of 11 to 15 was indicated by , and the case of 16 or more was indicated by .

(79) These results are shown in Table 5.

(80) TABLE-US-00005 TABLE 5 Spatter Wire Arc suppression Bead Blowhole No. stability performance appearance resistance Example 1 2 3 4 5 6 7 8 Comparative 9 example 10 11 12 X 13 X 14 X 15 X

(81) As shown in Table 5, Example Nos. 1 to 8 which satisfied the scope of the present invention exhibited good arc stability, spatter suppression performance, and bead appearance in the vertical upward welding, and the blowhole resistance of the weld zone was also good.

(82) Among Nos. 1 to 8 which were examples satisfying the scope of the present invention, Nos. 1 to 5 were examples in which the ratio calculated by [C]/([Ti]+[Al]+[Mg]3) on the basis of the chemical components of the sheath satisfied a more preferable specification, and excellent blowhole resistance was obtained as compared with that in Nos. 6 to 8.

(83) In Example No. 8, the amounts of C, Al, Ti, and Mg in the sheath satisfied the scope of the present invention, but the ratio calculated by [C]/([Ti]+[Al]+[Mg]3) was more than 0.11. Therefore, the blowhole resistance was excellent, although the number of generation of blowholes in No. 8 was 10, while the number of generation of blowholes in Nos. 6 and 7 were 6 to 7, so that the blowhole resistance was slightly poor as compared with that in Nos. 6 and 7.

(84) Comparative example Nos. 9 to 15 exhibited good vertical upward welding operability, but the blowhole resistance was insufficient. In No. 9, the Al and Mg contents in the sheath and relative to total mass of the wire were lower than the scope of the present invention, so that the blowhole resistance was degraded.

(85) In No. 10 and No. 11, the Al, Ti, and Mg contents in the sheath were within the scope of the present invention, but the C content in the sheath was higher than the scope of the present invention, so that the blowhole resistance was degraded. In No. 12, the Al contents in the sheath and relative to total mass of the wire were lower than the scope of the present invention, so that the blowhole resistance was degraded.

(86) In No. 13, the C content in the sheath was higher than the scope of the present invention and the Al content in the sheath was lower than the scope of the present invention, so that the blowhole resistance was degraded.

(87) In No. 14, the Mg content in the sheath was lower than the scope of the present invention, so that the blowhole resistance was degraded. In No. 15, the C, Al, and Ti contents in the sheath were within the scope of the present invention, but the C content relative to total mass of the wire was more than 0.050 percent by mass, so that the blowhole resistance was degraded.

(88) Up to this point, the present invention have been explained in detail with reference to the embodiments and examples. However, the gist of the present invention is not limited to the above-described contents and the scope of right is to be broadly interpreted on the basis of the claims. As a matter of course, various changes, modifications, and the like of the contents of the present invention can be made on the basis of the above description.