Powder core welding wire and corresponding method for welding metals

Abstract

The present invention relates to a flux-cored wire comprising a sheath and a flux filling the sheath, wherein the flux comprises a titanate and a nanoparticulate oxide selected from the group consisting of TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3 and mixtures thereof.

Description

TECHNICAL FIELD

[0001] The present invention relates to welding of metal substrates with flux-cored wire. It also relates to a method for manufacturing flux-cored wire. It is particularly well suited for the construction, shipbuilding, transportation industry (rail and automotive), energy related structures, oil and gas industry and offshore industry. BACKGROUND

[0002] Welding of metal substrates with filler wire is known, particularly when gaps have to be filled. The filler wire can be fed from the side into the weld (as in gas shielded tungsten arc welding and laser welding), or it can also be a consumable electrode (as in submerged arc welding, gas shielded metal arc welding, gas shielded flux-cored wire arc welding and hybrid laser welding, where the arc head is a gas shielded metal arc). In some cases the filler wire is in the form of a flux-cored wire, i.e. a wire that is hollow and filled with a flux containing components that improve the properties. Slag formers are added to protect the weld pool and to shape and support the weld. Iron powder is used to increase the deposition rate. Powdered alloys are added to produce low alloy deposits or to improve mechanical properties. Deoxidizers and fluxes are used to refine the weld metal.

[0003] Patent application WO 00 / 16940 discloses the use of titanates such as Na2Ti307or K2TiO3to achieve deep penetration gas shielded tungsten arc welds. The titanate is applied to the weld zone as part of the filler wire to provide deep penetration welds in carbon steels, chromium-molybdenum steels, stainless steels and nickel-based alloys. The titanate compounds of WO 00 / 16940 are used in the form of high purity powders of about 325 mesh or finer, 325 mesh corresponding to 44 μm. To control arc drift, weld consistency and the slag and surface appearance of the weldment, various additional components can be optionally added to the titanate-based filler wire, including transition metal oxides such as TiO, TiO2, Cr2O3and Fe2O3, silica, manganese silicides, fluorides and chlorides. All of the compounds of the flux have a micron size.

[0004] Although the penetration is improved with the fluxes disclosed in WO 00 / 16940, the penetration is not optimal for steel substrates.

[0005] There is therefore a need to improve the weld penetration in steel substrates and thus the mechanical properties of the welded steel substrates. There is also a need to increase the deposition rate and productivity of the welding with flux-cored wire. SUMMARY

[0006] To this end, the present invention relates to a flux-cored wire comprising a sheath and a flux filling said sheath, wherein the flux comprises a titanate and a nanoparticulate oxide selected from the group consisting of TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3and mixtures thereof.

[0007] The powder cored welding wire according to the application can also have the optional features listed below, taken alone or in combination:

[0008] - the titanate is chosen from the group consisting of Na2Ti307, NaTi03, K2Ti03, K2Ti205, MgTi03, SrTi03,

[0009] BaTi03, CaTi03, FeTi03and ZnTi04or mixtures thereof,

[0010] - the percentage of nanoparticulate oxides in the flux is less than or equal to 80% by weight,

[0011] - the percentage of nanoparticulate oxides in the flux is greater than or equal to 10%,

[0012] - the size of the nanoparticles is between 5 nm and 60 nm,

[0013] - the percentage of titanate in the flux is greater than or equal to 45% by weight,

[0014] - the diameter of the titanate is between 1 pm and 40 pm,

[0015] - the sheath is made of steel,

[0016] - the powder cored welding wire also comprises microparticulate compounds chosen from microparticulate oxides and / or microparticulate fluorides,

[0017] - the powder cored welding wire also comprises microparticulate compounds chosen from Ce02, Na20, Na202, NaBi03, NaF, CaF2, cryolite (Na3AlF6) and mixtures thereof,

[0018] - the powder cored welding wire also comprises lime, silica, manganese oxide and calcium fluoride in the form of micrometric and / or millimetric size particles.

[0019] The application also relates to a process for manufacturing a powder cored welding wire, said process comprising the following sequential steps:

[0020] A. mixing at least a titanate and nanoparticulate oxides chosen from the group consisting of Ti02, Si02, Zr02, Y203, Al203, M0O3, Cr03, Ce02, La203and mixtures thereof,

[0021] B. introducing the mixture obtained into the sheath of the cored welding wire to form a powder cored welding wire.

[0022] The present invention also relates to a method for manufacturing a welded joint, said method comprising arc welding or laser welding a steel material with a flux-cored wire comprising a sheath and a flux filling said sheath, wherein the flux comprises a titanate and a nanoparticulate oxide selected from the group consisting of Ti02, Si02, Zr02, Y203, Al203, M0O3, Cr03, Ce02, La203and mixtures thereof.

[0023] The following terms are defined:

[0024] - Nanoparticle is a particle having a size comprised between 1 nanometer (nm) and 100 nanometers (nm).

[0025] - Titanate means an inorganic compound comprising titanium, oxygen and at least one additional element such as an alkali element, an alkaline earth element, a transition metal element or a metal element. They can be in the form of their salts.

[0026] Without wishing to be bound by any theory, it is believed that the flux included in the flux-cored wire mainly modifies the molten pool physical properties. It seems in the present invention that not only the nature of the compound but also the size of the oxide particles equal to or less than 100 nm modifies the molten pool physical properties.

[0027] Indeed, the flux is melted and incorporated in the molten metal in the form of a dissolved substance and, if the welding technique involves an electric arc, in the form of an ionized substance. Due to the presence of the titanate and the oxide nanoparticles in the electric arc, the electric arc contracts.

[0028] Moreover, the flux dissolved in the molten metal modifies the Marangoni flow, which is a mass transfer at the liquid-gas interface due to a surface tension gradient. In particular, the composition of the flux modifies the surface tension gradient along the interface. This change in surface tension induces a reversal of the fluid flow towards the center of the weld pool. This reversal induces an increase in the weld penetration and in the welding efficiency, which in turn induces an increase in the deposition rate. Without wishing to be bound by any theory, it is believed that the nanoparticles dissolve at lower temperature than the microparticles and therefore more oxygen is dissolved in the molten pool, which activates the reversed Marangoni flow.

[0029] When the welding technique involves an electric arc, the effect of the reversed Marangoni flow is combined with a higher plasma temperature due to the electric arc contraction, which further increases the weld penetration and the material deposition rate. When the welding technique involves a laser beam, the reversed Marangoni flow helps to maintain a proper keyhole shape, which in turn prevents gas entrapment and therefore porosity in the weld.

[0030] Moreover, the dissolved oxygen acts as a surfactant, which in turn improves the wettability of the molten metal on the base metal and therefore avoids critical defects such as lack of fusion at the edges, which are prone to occur in the weldment.

[0031] Furthermore, since the component of the flux increases the surface tension with temperature, the wettability of the weld material increases along the edges, which are colder than the center of the molten pool, which prevents slag inclusion. DETAILED DESCRIPTION

[0032] The application will be better understood by reading the following description, provided only for explanatory purposes and in no way intended to be limiting.

[0033] The flux-cored wire comprises a sheath and a flux filling said sheath.

[0034] In the case of the present application, the material of the sheath is not particularly limited. It can be steel, for example copper-plated C-Mn steel.

[0035] The wire generally has a diameter of 0.8 mm to 4 mm. As for the sheath, its thickness varies according to the chosen filling percentage. The filling percentage is the ratio of the weight of the flux component or "filler" compared to the total weight of the wire.

[0036] The flux of the flux-cored wire comprises a titanate and a nanoparticulate oxide selected from the group consisting of Ti02, Si02, Zr02, Y203, AI2O3, M0O3, Cr03, Ce02, La203and mixtures thereof. In other words, the flux comprises a titanate and at least one nanoparticulate oxide, wherein the at least one nanoparticulate oxide is selected from the group consisting of Ti02, Si02, Zr02, Y203, AI2O3, M0O3, Cr03, Ce02, La203and mixtures thereof. This means that the flux does not comprise any other listed nanoparticulate oxide.

[0037] The titanate is selected from the group of titanates consisting of alkali titanates, alkaline earth titanates, transition metal titanates, metal titanates and mixtures thereof. The titanate is more preferably selected from the group consisting of Na2Ti307, NaTi03, K2Ti03, K2Ti205, MgTi03, SrTi03, BaTi03, CaTi03, FeTi03and ZnTi04and mixtures thereof. These titanates are thought to further increase the depth of penetration based on the effect of reverse Marangoni flow. The inventors understand that all titanates behave similarly to some extent and increase the depth of penetration. Therefore all titanates are part of the present application. The skilled person will know which one has to be chosen depending on the specific case. To this end, the ease of melting and dissolution of the titanate, how much it increases the dissolved oxygen content, how the additional elements of the titanate affect the physical properties of the molten pool and the microstructure of the final weld will be considered. For example, NaTi07is advantageous because the presence of Na improves the slag formation and detachment.

[0038] Preferably, the titanate has a diameter of 1 pm to 40 pm, more preferably of 1 pm to 20 pm and advantageously of 1 pm to 10 pm. This titanate diameter is believed to further improve the arc constriction and the inverse Marangoni effect. Moreover, having small micronic titanate particles increases the specific surface area available for mixing with the nanoparticulate oxides and enables further adhesion of the nanoparticulate oxides to the titanate particles.

[0039] Preferably, the titanate has a weight percentage in the dry weight of the flux greater than or equal to 45%, more preferably of 45% to 90%, even more preferably of 65% to 90%.

[0040] The nanoparticulate oxides are chosen from Ti02, Si02, Zr02, Y203, AI2O3, M0O3, Cr03, Ce02, La203and mixtures thereof. These nanoparticles dissolve easily in the bath, provide oxygen to the bath, thus improving the wettability and material deposition and enabling a deeper weld penetration. In contrast to other oxides such as CaO, MgO, B203, Co304or Cr203, they do not tend to form brittle phases, they do not have a high refractory effect that prevents the heat from properly melting the steel and their metal ions do not tend to recombine with the oxygen in the bath.

[0041] Preferably, the nanoparticles are Si02and Ti02, more preferably a mixture of Si02and Ti02. Si02is believed to mainly increase the depth of penetration and to make the slag removal easy, while Ti02mainly increases the depth of penetration and forms Ti-based inclusions that improve the mechanical properties.

[0042] Other examples of mixtures of nanoparticulate oxides are:

[0043] - yttria-stabilized zirconia (YSZ), which is a ceramic that stabilizes the cubic crystal structure of zirconium dioxide (Zr02) at room temperature by the addition of yttria (Y203),

[0044] - a 1 : 1 : 1 combination of La203, Zr02and Y203, which helps to adjust the refractory effect and to promote the formation of inclusions.

[0045] Preferably, the nanoparticles have a size of 5 nm to 60 nm. This nanoparticulate diameter is believed to further improve the uniform distribution of the flux.

[0046] Preferably, the nanoparticulate oxides have a weight percentage in the dry weight of the flux less than or equal to 80%, preferably greater than or equal to 10%, more preferably of 10% to 60%, even more preferably of 25% to 55%.

[0047] According to one variant of the application, the flux consists of titanate and nanoparticulate oxides selected from the group consisting of Ti02, Si02, Zr02, Y203, Al203, M0O3, Cr03, Ce02, La203and mixtures thereof.

[0048] According to another variant of the application, the flux can also contain iron powder as the remainder. The remainder can possibly represent up to 55% by weight of the flux.

[0049] According to another variant of the application, the flux also contains microparticulate compounds, such as microparticulate oxides and / or microparticulate fluorides, such as Na20, Na202, Ce02, NaBi03, NaF, CaF2, cryolite (Na3AlF6). The shift from nanoparticulate to microparticulate for some of the nanoparticulate oxides listed above mitigates the health and safety issues associated with the use of some of these oxides during the manufacture of the welding wire. Na20, Na202, NaBi03, NaF, CaF2, cryolite can be added to improve the formation of the slag, so that further prevention of slag inclusion is achieved. They also contribute to the formation of a slag that is easy to separate. The flux can contain from 0.1 to 5% by weight of Na20, Na202, NaBi03, NaF, CaF2, cryolite or mixtures thereof, by dry weight of the flux.

[0050] Compared to the application of the flux as a coating on the base material to be welded, the containment of the same composition in the sheath of the flux-cored wire is particularly advantageous. First of all, the additional step of coating the base material before welding is eliminated. Furthermore, there is no need to remove the excess coating along the weld after welding. In this regard, since all the particles provided by the flux-cored wire are dissolved in the molten pool, the particles are also more effectively utilized. Finally, the solvents and sprays during the coating step are avoided, which is beneficial for the health and safety of the operators.

[0051] In terms of process, in a first step, the titanate and the nanoparticulate oxides are preferably mixed. The mixing can be carried out under wet conditions with a solvent, such as acetone, or under dry conditions, for example in a 3D powder vibration mixer. The mixing facilitates the agglomeration of the nanoparticles on the titanate particles, which prevents the unintentional release of the nanoparticles into the air, which would be a health and safety issue.

[0052] The flux thus obtained is then deposited on a thin narrow strip, which has been formed into a strip of U-shaped section by a forming roller in a previous step. The U-shaped strip filled with flux is then made to flow through special closing rollers, which shape it into a tube and tightly press the core material. The tube is then drawn through a draw die to reduce its diameter and further press the core material. The drawing tightly seals the sheath and, additionally, fixes the core material under pressure inside the tube, thus avoiding discontinuities of the flux.

[0053] After the powder cored welding wire according to the present application has been provided, a welded joint can be manufactured by arc welding or laser welding of a steel material with the powder cored welding wire.

[0054] Preferably, the steel substrate to be welded is a carbon steel.

[0055] The steel substrate can optionally be coated on at least a portion of one side thereof with a corrosion protection coating. Preferably, the corrosion protection coating comprises a metal selected from the group consisting of zinc, aluminum, copper, silicon, iron, magnesium, titanium, nickel, chromium, manganese and alloys thereof.

[0056] In a preferred embodiment, the corrosion protection coating is an aluminum-based coating comprising less than 15 wt.% Si, less than 5.0 wt.% Fe, optionally 0.1 wt.% to 8.0 wt.% Mg and optionally 0.1% to 30.0% Zn, the remainder being aluminum and unavoidable impurities resulting from the manufacturing process. In another preferred embodiment, the corrosion protection coating is a zinc-based coating comprising 0.01 wt.% to 8.0 wt.% Al, optionally 0.2 wt.% to 8.0 wt.% Mg, the remainder being Zn and unavoidable impurities resulting from the manufacturing process.

[0057] The corrosion protection coating is preferably applied on both sides of the steel substrate.

[0058] The steel material can be welded to a steel substrate of the same composition or a different composition. It can also be welded to another metal, such as aluminum.

[0059] The kind of welding technique is not limited, as long as it is compatible with the powder cored welding wire according to the present application and used as a side-fed welding wire (as in gas shielded tungsten arc welding and laser welding), or as a consumable electrode (as in submerged arc welding, gas shielded metal arc welding, gas shielded powder cored welding wire arc welding, narrow gap welding and hybrid laser welding, wherein the arc head is a gas shielded metal arc).

[0060] Depending on the welding technique, the welding zone can be covered by a protective flux. Such a flux protects the welding zone from oxidation during welding. Alternatively, the flux of the powder cored welding wire according to the present application further comprises additional components making the welding wire suitable for self-shielded welding. It preferably comprises lime, silica, manganese oxide and calcium fluoride in the form of micron and / or millimeter sized particles. These compounds provide a protective effect on the flux in addition to the effects provided by the titanate and the nanoparticulate oxides.

[0061] Finally, the present application relates to the use of the powder cored welding wire according to the present application for the manufacture of pressure vessels, offshore and oil and gas components, shipbuilding, automotive, nuclear components and generally heavy industry and manufacturing.

[0062] Embodiments

[0063] Example 1:

[0064] A flux comprising 70wt% MgTi03(diameter: 2pm), 10wt% Si02(diameter range: 12-23nm) and 20wt% Ti02(diameter range: 36-55nm) was prepared and introduced into a 0.5mm C-Mn steel sheath to form a 1.6mm diameter welding wire.

[0065] During a bead-on-plate Gas Tungsten Arc welding with a strength of 110A and a voltage of 10.8-12.8V on a structural steel (C-Mn S355) whose composition is detailed in Table 1 below, the cored wire of this designation Sample 1 was tested:

[0066] C Mn Si Al S P 0.102 0.903 0.012 0.04 0.0088 0.012

[0067] During these tests, Sample 1 was compared with the following commercial wires:

[0068] - MC710-H, which is a low carbon steel metal cored wire supplied by Lincoln Electrode. Its sheath is filled with iron powder (Sample 2),

[0069] OK Tubrodur 15CrMn O / G, which is a cored wire supplied by for low carbon steel, low alloy steel and C-Mn steel (Sample 3). The exact composition of its flux is unknown.

[0070] The results obtained with a 500mm wire are detailed in Table 2:

[0071]

[0072] *: according to the invention

[0073] The results show that the welding speed is significantly improved, while the material deposition is significantly improved.

[0074] In addition, the width of the deposited material was measured and compared. It appears that the welds obtained with Sample 1 are on average 16% larger than the welds obtained with Sample 2 and 21% larger than the welds obtained with Sample 3.

[0075] The components of the flux according to the invention show that the surface tension decreases with temperature, making the wettability of the weld material increase along the edges of the molten pool.

[0076] Example 2:

[0077] The effect of different fluxes on the welding of steel substrates was evaluated by Finite Element Method (FEM) simulation. In the simulation, the fluxes contained nano-particle oxides with a diameter of 10 nm to 50 nm and optionally MgTi03(diameter: 2 pm). The arc welding using various fluxes in the form of a flux-cored wire was simulated, the results of which are summarized in Table 3 below:

[0078]

[0079] *: according to the invention

[0080] The results show that the fluxes according to the invention improve the penetration and quality of the weld compared to the comparative fluxes.

Claims

1. A flux-cored wire comprising a sheath and a flux filling the sheath, wherein the flux comprises titanate and nanoparticulate oxides selected from the group consisting of Ti02, Si02, Zr02, Y203, Al203, M0O3, Cr03, Ce02, La203, and mixtures thereof, and wherein the percentage of titanate in the flux is greater than or equal to 45% by weight; wherein the diameter of the titanate is comprised between 1 pm and 40 pm, and wherein the percentage of nanoparticulate oxides in the flux is less than or equal to 55% by weight.

2. The flux-cored wire according to claim 1, wherein the titanate is selected from the group consisting of Na2Ti307, NaTi03, K2Ti03, K2Ti205, MgTi03, SrTi03, BaTi03, CaTi03, FeTi03, and ZnTi04, or mixtures thereof.

3. The flux-cored wire according to claim 1 or 2, wherein the percentage of nanoparticulate oxides in the flux is greater than or equal to 10% by weight.

4. The flux-cored wire according to claim 1 or 2, wherein the size of the nanoparticulate oxides is comprised between 5 nm and 60 nm.

5. The flux-cored wire according to claim 1 or 2, wherein the sheath is made of steel.

6. The flux-cored wire according to claim 1 or 2, further comprising microparticulate compounds selected from microparticulate oxides and / or microparticulate fluorides.

7. The flux-cored wire according to claim 6, further comprising microparticulate compounds selected from the group consisting of Ce02, Na20, Na202, NaBi03, NaF, CaF2, cryolite (Na3AlF6), and mixtures thereof.

8. The flux-cored wire according to claim 1 or 2, further comprising lime, silica, manganese oxide, and calcium fluoride in the form of micrometric and / or millimetric size particles.

9. A method for manufacturing a flux-cored wire, comprising the following sequential steps: A. mixing at least a titanate and nanoparticulate oxides selected from the group consisting of Ti02, Si02, Zr02, Y203, Al203, M0O3, Cr03, Ce02, La203, and mixtures thereof to form a flux, and wherein the percentage of titanate in the flux is greater than or equal to 45% by weight; wherein the diameter of the titanate is comprised between 1 pm and 40 pm, and wherein the percentage of nanoparticulate oxides in the flux is less than or equal to 55% by weight, B. introducing the obtained flux into a sheath of a core wire to form the flux-cored wire.

10. A method for manufacturing a welded joint, comprising arc welding or laser welding a steel material with a flux-cored wire comprising a sheath and a flux filling the sheath, wherein the flux comprises titanate and nanoparticulate oxides selected from the group consisting of Ti02, Si02, Zr02, Y203, Al203, M0O3, Cr03, Ce02, La203, and mixtures thereof, and wherein the percentage of titanate in the flux is greater than or equal to 45% by weight; wherein the diameter of the titanate is comprised between 1 pm and 40 pm, and ​ ​ ​ wherein the percentage of the nanoparticulate oxide in the flux is less than or equal to 55% by weight. wherein the percentage of the nanoparticulate oxide in the flux is less than or equal to 55% by weight.

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