Welding flux composition and method for welding a corresponding metal

Abstract

The present invention relates to a method for producing a welded joint, comprising the following successive steps: I. providing at least two metal substrates, at least one of which is a steel substrate; and II. simultaneously welding the at least two metal substrates with a welding head, applying a welding flux comprising a titanate and a nanoparticulate oxide selected from the group consisting of TiO2, SiO2, ZrO2, YO3, Al2O3, MoO3, CrO3, CeO2, La2O3, and mixtures thereof onto the at least two metal substrates in front of the welding head.

Description

Technical Field

[0001] The present invention relates to welding of metal substrates using a welding flux. The present invention is particularly well-suited for construction, shipbuilding, transportation industries (railway and automotive), energy-related structures, oil and gas, and offshore industries.

Background Art

[0002] It is well-known to weld metal substrates using different welding techniques such as gas metal arc welding (GMAW), gas tungsten arc welding (GTAW) also known as tungsten inert gas welding (TIGW), submerged arc welding (SAW), laser beam welding (LBW), narrow gap welding also known as narrow groove welding, laser-arc hybrid welding, etc. Welding can be carried out with the help of a welding flux to increase the penetration in the substrate. This welding flux is different from the shielding flux which is mainly used to protect the welding zone from oxidation during welding.

[0003] International Patent Application Publication No. 00 / 16940 discloses that deep penetration gas tungsten arc welding is achieved using titanates such as Na2Ti3O7 or K2TiO3. To give deep penetration welding in carbon steel, chromium-molybdenum steel, stainless steel and nickel-based alloys, the titanate is applied to the welding zone either as part of the welding flux or as part of the filler wire. The titanate compounds of International Publication No. 00 / 16940 are used in the form of high-purity powders of about 325 mesh or finer, corresponding to 44 μm. Various additional components including transition metal oxides such as TiO, TiO2, Cr2O3 and Fe2O3, silicon dioxide, manganese silicides, fluorides and chlorides can be optionally added to the titanate-based filler wire to control arc instability, bead consistency and the slag and surface appearance of the weld. All compounds of the flux have micrometer dimensions.

[0004] Penetration is improved by the flux disclosed in WO 00 / 16940, but the penetration is not optimal for steel substrates.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Therefore, there is a need to improve the welding 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 welding.

Means for Solving the Problems

[0007] For this purpose, the present invention is a method for manufacturing a welded joint, comprising the following successive steps: I. providing at least two metal substrates, at least one of which is a steel substrate, and II. applying, simultaneously with the welding of the at least two metal substrates by a welding head, onto the at least two metal substrates, in front of the welding head, a welding flux comprising a titanate and a nanoparticulate oxide selected from the group consisting of TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3 and mixtures thereof. relates to a method comprising.

[0008] The method according to the invention may also have any of the following features considered individually or in combination.

[0009] · The titanate is selected from Na2Ti3O7, NaTiO3, K2TiO3, K2Ti2O5, MgTiO3, SrTiO3, BaTiO3, CaTiO3, FeTiO3, and ZnTiO4 or a mixture thereof. · The thickness of the welding flux is 10 to 140 μm. · The percentage of nano-sized oxide particles in the welding flux is 80 wt% or less. · The percentage of nano-sized oxide particles in the welding flux is 10 wt% or more. · The nano-particles have a size included in 5 to 60 nm. · The percentage of titanate in the welding flux is 45 wt% or more. · The diameter of the titanate is 1 to 40 μm. · The welding flux is applied using a flux hopper. · The shielding flux is further applied in front of the welding head on at least two metal substrates simultaneously with the welding so as to cover the welding flux. · The shielding flux is applied using a flux hopper. · The welding flux is also the shielding flux. · The welding flux further contains lime, silica, manganese oxide, and calcium fluoride in the form of particles of micrometer and / or millimeter size. · The welding is performed by submerged arc welding, narrow-gap welding based on submerged arc welding, or laser-arc hybrid welding based on submerged arc welding.

[0010] The present invention also relates to a welding apparatus including a welding head, a first flux hopper disposed in front of the welding head and suitable for applying a shielding flux, and a second flux hopper suitable for applying a welding flux and disposed further in front of the welding head than the first flux hopper.

[0011] The following terms are defined.

[0012] · Nanoparticles are particles with a size of 1 to 100 nanometers (nm). · Titanate refers to an inorganic compound containing titanium, oxygen, and at least one additional element such as an alkali metal element, alkaline earth metal element, transition metal element, or metal element. They can be in the form of their salts.

[0013] Without being bound by any theory, the welding flux according to the present invention is considered to mainly modify the physics of the molten pool. In the present invention, not only the properties of the compound but also the size of the oxide particles being 100 nm or less is considered to modify the physics of the molten pool.

[0014] In fact, the flux is melted and incorporated into the molten metal in the form of dissolved species and, when the welding technique involves an arc, into the arc in the form of ionized species. The presence of titanate and oxide nanoparticles in the arc causes the arc to converge.

[0015] Furthermore, the flux dissolved in the molten metal modifies the Marangoni flow, which is the mass transfer at the liquid-gas interface due to the surface tension gradient. In particular, the components of the flux modify the gradient of the surface tension along the interface. This change in surface tension results in a reversal of the fluid flow towards the center of the welding pool. This reversal leads to an improvement in weld penetration and welding efficiency, resulting in an increase in the deposition rate and thus productivity. Without being bound by any theory, it is considered that nanoparticles dissolve at a lower temperature than microparticles, and thus more oxygen dissolves into the molten pool, activating the reverse Marangoni flow.

[0016] When the welding technique involves an arc, the effect of the reverse Marangoni flow is combined with the higher plasma temperature due to arc convergence, further improving weld penetration and the material deposition rate. When the welding technique involves a laser beam, the reverse Marangoni flow contributes to the retention of an appropriate keyhole shape, which then prevents gas entrapment and thus pores in the weld.

[0017] Furthermore, dissolved oxygen acts as a surfactant to improve the wetting of the molten metal on the base metal, thus avoiding serious defects that tend to appear in welding such as lack of fusion at the edges.

[0018] Furthermore, as the flux components increase the surface tension with temperature, the wettability of the welding material increases along the edges that are colder than the center of the molten pool, which prevents slag entrapment.

[0019] The present invention will be better understood by reading the following description, which is provided purely for purposes of explanation and is in no way intended to be limiting.

Mode for Carrying Out the Invention

[0020] The present invention relates to the welding of steel substrates. Preferably, the steel substrate is carbon steel.

[0021] The steel substrate can optionally be coated on at least a part of one of its surfaces with a corrosion protection coating. Preferably, the corrosion protection coating contains a metal selected from the group consisting of zinc, aluminum, copper, silicon, iron, magnesium, titanium, nickel, chromium, manganese, and alloys thereof.

[0022] In a preferred embodiment, the corrosion protection coating is an aluminum-based coating containing less than 15% by weight of Si, less than 5.0% by weight of Fe, optionally 0.1 - 8.0% by weight of Mg, and optionally 0.1 - 30.0% by weight of Zn, with the balance being Al and unavoidable impurities resulting from the manufacturing process. In another preferred embodiment, the corrosion protection coating is a zinc-based coating containing 0.01 - 8.0% by weight of Al, optionally 0.2 - 8.0% by weight of Mg, with the balance being Zn and unavoidable impurities resulting from the manufacturing process.

[0023] The corrosion protection coating is preferably applied to both sides of the steel substrate.

[0024] The steel material can be welded to steel substrates of the same composition or different compositions. The steel material can also be welded separately, for example, to aluminum and the like.

[0025] The welding flux contains titanate and nanoparticle oxides selected from the group consisting of TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3, and mixtures thereof. In other words, the welding flux contains titanate and at least one nanoparticle oxide, and at least one nanoparticle oxide is selected from the group consisting of TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3, and mixtures thereof. This means that the welding flux does not contain other nanoparticle oxides other than those listed.

[0026] The titanate is selected from the group of titanates consisting of alkali metal titanates, alkaline earth metal titanates, transition metal titanates, metal titanates, and mixtures thereof. The titanate is more preferably selected from Na2Ti3O7, NaTiO3, K2TiO3, K2Ti2O5, MgTiO3, SrTiO3, BaTiO3, CaTiO3, FeTiO3, ZnTiO4, and mixtures thereof. These titanates are considered to further increase the penetration depth based on the effect of reverse Marangoni flow. It is the understanding of the inventors that all titanates behave similarly to some extent and increase the penetration depth. Therefore, all titanates are part of the present invention. Those skilled in the art will know which titanate to select according to specific cases. To do so, those skilled in the art will consider how easily the titanate melts and dissolves, how much the titanate increases the dissolved oxygen content, and how the additional elements of the titanate affect the physical properties of the molten pool and the final microstructure of the weld. For example, NaTiO7 is preferred due to the presence of Na that improves slag formation and detachment.

[0027] Preferably, the titanate has a diameter of 1 to 40 μm, more preferably 1 to 20 μm, and advantageously 1 to 10 μm. This diameter of the titanate is considered to further improve arc convergence and the inverse Marangoni effect. Furthermore, having small micrometer-sized titanate particles increases the specific surface area available for mixing with the nanoparticle oxides and further adheres the nanoparticle oxides to the titanate particles.

[0028] Preferably, the weight percentage of titanate in the dry weight of the welding flux is 45% or more, more preferably 45% to 90%, and even more preferably 65% to 90%.

[0029] The nanoparticle oxides are selected from TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3, and mixtures thereof. These nanoparticles easily dissolve in the molten pool and supply oxygen to the molten pool, as a result, improving wettability and material deposition and enabling deeper weld penetration. In contrast to other oxides such as CaO, MgO, B2O3, Co3O4, or Cr2O3, they do not tend to form brittle phases, do not have a high refractory effect that hinders the accurate melting of steel by heat, and their metal ions do not tend to recombine with oxygen in the molten pool.

[0030] Preferably, the nanoparticles are SiO2 and TiO2, more preferably a mixture of SiO2 and TiO2. SiO2 mainly increases the penetration depth and facilitates slag removal, while TiO2 mainly increases the penetration depth and is considered to form Ti-based inclusions that improve mechanical properties.

[0031] Another example of a mixture of nanoparticle oxides is · Yttria-stabilized zirconia (YSZ), a ceramic in which the addition of yttrium oxide (Y2O3) stabilizes the cubic crystal structure of zirconium dioxide (ZrO2) at room temperature, · A 1:1:1 combination of La2O3, ZrO2, and Y2O3, which helps to adjust the refractory effect and promotes the formation of inclusions.

[0032] Preferably, the nanoparticles have a size included in the range of 5 to 60 nm. This nanoparticle diameter is considered to further improve the uniform distribution of the flux.

[0033] Preferably, the weight percentage of the nanoparticle oxide in the dry weight of the welding flux is 80% or less, preferably 10% or more, more preferably 10 to 60%, and even more preferably 25 to 55%.

[0034] According to a modification of the present invention, the flux consists of titanate and a nanoparticle oxide selected from the group consisting of TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3, and mixtures thereof.

[0035] According to another modification of the present invention, the welding flux further contains particulate oxides such as, for example, Na2O, Na2O2, CeO2, NaBiO3, NaF, CaF2, cryolite (Na3AlF6), and / or particulate compounds such as particulate fluorides. For some of the nanoparticle oxides listed above, the transition from nanoparticles to microparticles reduces health and safety concerns associated with the use of some of these oxides during wire manufacturing. Na2O, Na2O2, NaBiO3, NaF, CaF2, and cryolite can be added to improve slag formation so that slag entrapment is further prevented. They also help to form a slag that can be easily separated. The flux can contain 0.1 to 5 wt% of Na2O, Na2O2, NaBiO3, NaF, CaF2, cryolite, and mixtures thereof based on the dry weight of the welding flux.

[0036] Regarding the process, in the first step, the titanate and the nanoparticle oxide are preferably mixed. This can be done either under wet conditions using a solvent such as acetone or under dry conditions, for example, in a 3D powder shaker mixer. Mixing promotes strong aggregation of the nanoparticles on the titanate particles, which prevents the unintentional release of nanoparticles into the air, which is a health and safety concern.

[0037] Subsequently, the welding flux thus obtained is applied onto the metal substrate during welding, particularly directly onto the welding zone.

[0038] In particular, during welding of two metal substrates, the welding flux is applied at least partially simultaneously onto the two metal substrates. The welding flux is applied in front of the welding apparatus, particularly in front of the welding head. The welding head refers herein to an electrode or a laser head, either consumable or non-consumable, which generates an arc according to the welding technique. Thus, when the energy applied through the welding head impinges on a part of the substrate covered with the welding flux, the components of the welding flux are melted and dissolved into the molten pool. The dissolved titanate and nanoparticle oxides have the above-described effects.

[0039] The welding flux is preferably applied onto a part of the metal substrate immediately before this part impinges on the energy applied through the welding head.

[0040] Preferably, the welding flux is applied along the edge of the metal substrate to be welded with a width equal to at least the welding width so that the welding flux is efficiently dissolved into the molten pool.

[0041] Preferably, the thickness of the applied welding flux is 10 - 140 μm.

[0042] Preferably, the welding flux is stored in a flux hopper. This hopper is arranged in front of the welding apparatus, particularly in front of the welding head, and moves together with it. During welding, the hopper deposits the welding flux onto a small part of the metal substrate in front of the welding head. The flux hopper controls the rate of flux deposition.

[0043] In one variation of the present invention, the welding flux is applied onto two metal substrates before applying the shielding flux. In front of the welding head, there is first a flux hopper for storing the shielding flux, and then a flux hopper for storing the welding flux. In other words, the welding flux hopper is further in front of the welding head than the shielding flux hopper. As a result, the welding flux is applied at a first location on the metal substrate, and the shielding flux is applied at a second location so as to cover the welding flux. Thus, the welded zone is protected from oxidation during welding. From a process perspective, the application of both the welding flux and the shielding flux is simultaneous with welding.

[0044] In another variation of the present invention, the welding flux is also the shielding flux. The welding flux preferably further contains lime, silica, manganese oxide, and calcium fluoride in the form of particles of micrometer and / or millimeter size. These compounds provide a shielding effect to the flux in addition to the effects provided by titanates and nanoparticle oxides. Thus, the welded zone is protected from oxidation during welding.

[0045] In that case, the titanates and nanoparticle oxides are mixed at an earlier stage with additional components such as lime, silica, manganese oxide, and calcium fluoride in the form of particles of micrometer and / or millimeter size, and then the mixture is preferably applied onto two metal substrates using a flux hopper.

[0046] The type of welding technique to be used is not limited. The welding technique can be, for example, gas metal arc welding (GMAW), gas tungsten arc welding (GTAW) also known as tungsten inert gas welding (TIGW), submerged arc welding (SAW), laser beam welding (LBW), narrow gap welding also known as narrow groove welding, or laser-arc hybrid welding.

[0047] Even if that were the case, the modification in which the welding flux is also a shielding flux is particularly advantageous for welding techniques that use a shielding flux, such as submerged arc welding (SAW), narrow-gap welding based on SAW, and laser-arc hybrid welding based on SAW.

[0048] The present invention also relates to a welding apparatus designed such that two fluxes can be sequentially applied in front of the welding head.

[0049] This apparatus comprises a welding head, a first flux hopper arranged in front of the welding head and suitable for applying a shielding flux, and a second flux hopper suitable for applying a welding flux, the second flux hopper being arranged further in front of the welding head than the first flux hopper such that the welding flux is applied first and then covered by the shielding flux.

[0050] Preferably, the welding flux contains titanate and particulate oxides. More preferably, the welding flux contains titanate and nanoparticulate oxides selected from the group consisting of TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3, and mixtures thereof.

[0051] Finally, the present invention relates to the use of the flux according to the present invention for the manufacture of, for example, pressure vessels, offshore and oil and gas components, shipbuilding, automotive, nuclear reactor components, and general heavy industry and manufacturing.

Examples

[0052] [Example 1] The effects of different welding fluxes on the welding of a steel substrate were evaluated by finite element method (FEM) simulation. In the simulation, the fluxes contained nanoparticulate oxides with diameters of 10 - 50 nm and optionally MgTiO3 (diameter: 2 μm). Arc welding using each flux was simulated, and the results are shown in Table 1 below.

[0053]

Table 1

[0054] The results show that the flux according to the present invention improves the penetration and quality of the welded part as compared with the comparative flux.

Claims

1. A method for manufacturing a welded joint, comprising the following successive steps: I. Providing at least two metal substrates, wherein at least one of the metal substrates is a steel substrate, II. Applying a welding flux containing oxide nanoparticles selected from the group consisting of titanate and TiO ２ , SiO ２ , ZrO ２ , Y ２ O ３ , Al ２ O ３ , MoO ３ , CrO ３ , CeO ２ , La ２ O ３ and mixtures thereof while welding the at least two metal substrates by the welding head, including, wherein the titanate is selected from Na ２ Ti ３ O ７ , NaTiO ３ , K ２ TiO ３ , K ２ Ti ２ O ５ , MgTiO ３ , SrTiO ３ , BaTiO ３ , CaTiO ３ , FeTiO ３ and ZnTiO ４ or a mixture thereof, the diameter of the titanate is 1 to 40 μm, the percentage of the oxide nanoparticles in the welding flux is 10 wt% or more and 80 wt% or less, method.

2. The method according to claim 1, wherein the oxide nanoparticles have a size included in 5 to 60 nm.

3. The method according to claim 1 or 2, wherein the percentage of titanate in the welding flux is 45 wt% or more.

4. The method according to any one of claims 1 to 3, wherein the welding flux is applied using a flux hopper.

5. The method according to any one of claims 1 to 4, wherein a shielding flux is further applied in front of the welding head on the at least two metal substrates simultaneously with the welding so as to cover the welding flux.

6. The method according to claim 5, wherein the shielding flux is applied using a flux hopper.

7. The method according to any one of claims 1 to 6, wherein the welding flux is also a shielding flux.

8. The method according to claim 7, wherein the welding flux further comprises lime, silica, manganese oxide and calcium fluoride in the form of particles of micrometer and / or millimeter size.

9. The method according to any one of claims 1 to 8, wherein the welding is performed by submerged arc welding, narrow-gap welding based on submerged arc welding or laser-arc hybrid welding based on submerged arc welding.

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