Method for manufacturing welded joints by narrow gap welding

Abstract

The present invention relates to a method for the production of a welded joint, comprising the following successive steps: I. providing at least two metal substrates, at least one of which is a steel substrate having a thickness of at least 50 mm and separated by at least one sidewall, said sidewall being at least partially coated with a pre-coating 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; and II. welding of the at least two metal substrates along the at least partially coated sidewalls by narrow gap welding.

Description

[Technical Field]

[0001] The present invention relates to the welding of metal substrates by narrow gap welding, in particular where at least one of the metal substrates is a steel substrate locally coated with a welding flux to improve the quality of the weld. The present invention also relates to corresponding steel substrates and methods for the production of steel substrates. The present invention is particularly well suited to the construction, shipbuilding, oil and gas and offshore industries. [Background technology]

[0002] It is known to weld steel substrates thicker than about 50 mm by narrow gap welding, also known as narrow groove welding. This welding technique can be defined as a multi-pass welding process using filler metal between two substrates spaced by a gap narrow compared to the thickness of the substrates. The gap can be a single V-groove with a small root spacing and sidewalls sloped up to about 5°, or it can be a narrow gap of constant width. Narrow gap welding techniques are well established for submerged arc welding (SAW), gas metal arc welding (GMAW), and gas tungsten arc welding (GTAW).

[0003] During narrow gap welding, when the weld reduces the cross-sectional thickness of the base metal, various defects can occur, such as sidewall lack of fusion, slag entrapment, centerline cracks, or undercuts.

[0004] The occurrence of these defects can be reduced by strictly setting the welding parameters, especially through robotized welding. Nevertheless, this solution is not entirely satisfactory. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, there is a need to improve the quality of the welds produced by narrow gap welding, and therefore the mechanical properties of the welded steel substrates. There is also a need to improve the welding speed and productivity of narrow gap welding. [Means for solving the problem]

[0006] To this end, the invention relates to a method for the manufacture of a welded joint, comprising the following successive steps: I. Providing at least two metal substrates, at least one of which is a steel substrate having a thickness of at least 50 mm and separated by at least one sidewall, said sidewall being at least partially coated with a precoating 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; II. Welding the at least two metal substrates along the at least partially coated sidewalls by narrow gap welding; The present invention relates to a method, comprising:

[0007] The method according to the invention may also have any of the features listed below, considered individually or in combination.

[0008] the titanates are selected from Na2Ti3O7, NaTiO3, K2TiO3, K2Ti2O5, MgTiO3, SrTiO3, BaTiO3, CaTiO3, FeTiO3 and ZnTiO4 or mixtures thereof; The thickness of the pre-coating is between 10 and 140 μm. The percentage of nanoparticle oxide in the pre-coating is not more than 80% by weight; The percentage of nanoparticle oxide in the pre-coating is 10% by weight or more; The nanoparticles have a size comprised between 5 and 60 nm, The percentage of titanate in the precoating is 45% by weight or more; The diameter of the titanate is 1~40μm, The pre-coating further comprises a binder; The percentage of binder in the pre-coating is 1-20% by weight; Narrow gap welding is performed using one of the following welding techniques: submerged arc welding, gas metal arc welding, and gas tungsten arc welding. the pre-coating further comprises a particulate compound selected from particulate oxides and / or particulate fluorides, The pre-coating further comprises a particulate compound selected from the list consisting of CeO2, Na2O, Na2O2, NaBiO3, NaF, CaF2, cryolite (Na3AlF6) and mixtures thereof.

[0009] The present invention relates to a method for the manufacture of a pre-coated steel substrate, which method comprises the following successive steps: A. Providing a steel substrate having a thickness of at least 50 mm and bounded by at least one side wall; B. at least partially depositing on said sidewalls a pre-coating solution 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; The present invention also relates to a method, including:

[0010] The method for the production of a pre-coated steel substrate according to the invention may also have any of the features listed below, considered individually or in combination.

[0011] In step B), the deposition of the pre-coating solution is carried out by spin coating, spray coating, dip coating or brush coating; In step B), the pre-coating solution further comprises a solvent; In step B), the pre-coating solution contains 1 to 200 g / L of nanoparticle oxide; In step B), the pre-coating solution contains 100-500 g / L of titanate; In step B), the pre-coating solution further comprises a binder precursor; The method further comprises a step of drying the pre-coated steel substrate obtained in step B).

[0012] The present invention also relates to a steel substrate having a thickness of at least 50 mm and bounded by at least one sidewall, said sidewall being at least partially coated with a pre-coating 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.

[0013] The following terms are defined:

[0014] Nanoparticles are particles between 1 and 100 nanometers (nm) in size.

[0015] Titanates refer to inorganic compounds containing titanium, oxygen, and at least one additional element, such as an alkali metal element, an alkaline earth element, a transition metal element, or a metallic element, which may be in the form of a salt thereof.

[0016] "Coated" means that the steel substrate is at least locally covered with a pre-coating. The coating can be limited, for example, to the area where the steel substrate will be welded. "Coated" encompasses "directly on" (without an intermediate material, element, or space between them) and "indirectly on" (with an intermediate material, element, or space between them). For example, coating a steel substrate can include applying a pre-coating directly on the substrate without an intermediate material / element, and applying a pre-coating indirectly on the substrate with one or more intermediate materials / elements (such as an anti-corrosion coating) between them.

[0017] Without being bound by any theory, it is believed that the pre-coating primarily modifies the arc and weld pool physics, and in the present invention, it is believed that the nature of the compound as well as the oxide particle size of 100 nm or less modifies the arc and weld pool physics.

[0018] In fact, the arc melts and incorporates the pre-coating into the molten metal in the form of dissolved species and into the arc in the form of ionized species, which are converged due to the presence of titanate and oxide nanoparticles in the arc.

[0019] Furthermore, pre-coatings dissolved in molten metal modify Marangoni flow, a mass transfer phenomenon at the liquid-gas interface due to surface tension gradients. Specifically, the components of the pre-coating modify the surface tension gradient along the interface. This modification of surface tension results in a reversal of fluid flow toward the center of the weld pool. Coupled with higher plasma temperatures resulting from arc convergence, this reversal results in improved weld penetration and welding efficiency, leading to higher deposition rates and ultimately increased productivity. Without being bound by any theory, it is believed that nanoparticles dissolve at a lower temperature than fine particles, thus dissolving more oxygen into the weld pool and activating reverse Marangoni flow.

[0020] Additionally, the dissolved oxygen acts as a surfactant, improving the wetting of the molten metal on the base metal, thus avoiding fatal defects that tend to appear during narrow gap welding processes, such as sidewall lack of fusion and undercutting.

[0021] Additionally, as the components of the pre-coating increase their surface tension with temperature, the wetting of the weld material increases along the cooler sidewalls of the molten pool compared to the center, which prevents slag entrapment.

[0022] Additionally, nanoparticles have been observed to improve the uniformity of the applied pre-coating by filling the gaps between the particles and covering the surfaces of the particles, which helps to stabilize the welding arc, thus improving weld penetration and quality.

[0023] The invention will be better understood from reading the following description, which is given purely for illustrative purposes and is not intended to be limiting in any way. DETAILED DESCRIPTION OF THE INVENTION

[0024] The pre-coating comprises a titanate and a nanoparticulate oxide selected from the group consisting of TiO2, SiO2, ZrO2, YO3, Al2O3, MoO3, CrO3, CeO2, La2O3, and mixtures thereof. In other words, the pre-coating comprises a titanate and at least one nanoparticulate oxide, wherein the at least one nanoparticulate oxide is selected from the group consisting of TiO2, SiO2, ZrO2, YO3, Al2O3, MoO3, CrO3, CeO2, La2O3, and mixtures thereof. This means that the pre-coating does not contain any other nanoparticulate oxides than those listed.

[0025] 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. More preferably, the titanate is selected from Na2Ti3O7, NaTiO3, K2TiO3, K2Ti2O5, MgTiO3, SrTiO3, BaTiO3, CaTiO3, FeTiO3, and ZnTiO4, and mixtures thereof. It is believed that these titanates further increase penetration depth based on the reverse Marangoni flow effect. It is the inventors' understanding that all titanates behave somewhat similarly and increase penetration depth. Therefore, all titanates are part of the present invention. Those skilled in the art will know which titanate to select depending on the specific case. To do so, they will take into account 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 physics of the weld pool and the microstructure of the final weld. For example, NaTiO7 is preferred due to the presence of Na which improves slag formation and desorption.

[0026] Preferably, the titanate has a diameter of 1 to 40 μm, more preferably 1 to 20 μm, and advantageously 1 to 10 μm. This titanate diameter is believed to further improve arc convergence and the inverse Marangoni effect. Furthermore, having small micrometer titanate particles increases the specific surface area available for mixing with the nanoparticle oxide, further adhering the nanoparticle oxide to the titanate particles. Also, having small micrometer titanate particles makes the particles easier to atomize.

[0027] Preferably, the weight percentage of titanate in the dry weight of the pre-coating is 45% or more, more preferably 45% to 90%, even more preferably 45% to 75%.

[0028] The nanoparticle oxides are selected from TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3, and mixtures thereof. These nanoparticles dissolve easily in the molten pool, supplying oxygen to the molten pool and thereby improving wettability and enabling deeper weld penetration. In contrast to other oxides such as CaO, MgO, BO3, Co3O4, or Cr2O3, they do not tend to form brittle phases, do not have a high refractory effect that prevents heat from properly melting the steel, and their metal ions do not tend to recombine with oxygen in the molten pool.

[0029] Preferably, the nanoparticles are SiO2 and / or TiO2, more preferably a mixture of SiO2 and TiO2. It is believed that SiO2 primarily increases penetration depth and facilitates slag removal, while TiO2 primarily increases penetration depth and forms Ti-based inclusions that improve mechanical properties.

[0030] Other examples of nanoparticulate oxide mixtures include: Yttria-stabilized zirconia (YSZ), a ceramic in which the cubic structure of zirconium dioxide (ZrO2) is stabilized at room temperature by adding yttrium oxide (Y2O3), A 1:1:1 combination of La2O3, ZrO2 and Y2O3, which helps to adjust the refractory effect and promotes the formation of inclusions.

[0031] Preferably, the nanoparticles have a size comprised between 5 and 60 nm, which nanoparticle diameter is believed to further improve the uniform distribution of the coating.

[0032] Preferably, the weight percentage of nanoparticulate oxide in the dry weight of the precoating is 80% or less, preferably 10% or more, more preferably 10-60%, and even more preferably 20-55%. In some cases, the percentage of nanoparticles may have to be limited to avoid too high a fire-resistant effect. A person skilled in the art, knowing the fire-resistant effect of each type of nanoparticle, will adapt the percentage to each case.

[0033] According to one variant of the invention, a pre-coating is applied onto the steel substrate and, once dried, the pre-coating consists of titanate and nanoparticulate oxide.

[0034] According to another variant of the present invention, the precoating further comprises at least one binder that embeds the titanate and nanoparticulate oxide and improves the adhesion of the precoating to the steel substrate. This improved adhesion further prevents the precoating particles from being blown away by the shielding gas flow when a shielding gas is used. Preferably, the binder is purely inorganic to avoid toxic fumes that organic binders may generate, especially during welding. Examples of inorganic binders are organofunctional silanes or siloxane sol-gels. Examples of organofunctional silanes are silanes functionalized with groups from the amine, diamine, alkyl, amino-alkyl, aryl, epoxy, methacryl, fluoroalkyl, alkoxy, vinyl, mercapto, and aryl families, among others. Aminoalkylsilanes are particularly preferred because they significantly promote adhesion and have a long shelf life. Preferably, the binder is added in an amount of 1 to 20% by weight of the dried precoating.

[0035] According to another variation of the present invention, the precoating further comprises a particulate compound, such as a particulate oxide and / or particulate fluoride, such as CeO2, Na2O, Na2O2, NaBiO3, NaF, CaF2, or cryolite (Na3AlF6). For some of the nanoparticulate oxides listed above, the transition from nanoparticles to fine particles alleviates health and safety concerns associated with the use of some of these oxides. Na2O, Na2O2, NaBiO3, NaF, CaF2, or cryolite can be added to improve slag formation so that slag entrapment is further prevented. They also help form easily separable slag. The precoating may comprise 0.1 to 5 wt. % of Na2O, Na2O2, NaBiO3, NaF, CaF2, cryolite, or mixtures thereof, based on the dry weight of the precoating.

[0036] Preferably, the thickness of the pre-coating is between 10 and 140 μm, more preferably between 30 and 100 μm.

[0037] The precoating at least partially covers one sidewall of the steel substrate. The steel substrate can have any shape compatible with narrow-gap welding. For purposes of this invention, a steel substrate is simply defined by a thickness of at least 50 mm to accommodate narrow-gap welding and a sidewall to be at least partially welded to another metal substrate. The sidewall is optionally beveled to further improve narrow-gap welding. The bevel angle is typically in the range of 2 to 20°, more preferably 2 to 5°. It is worth noting here that the improved wetting provided by the precoating makes it tolerable to have imperfections on the bevel. This avoids the usual expensive and precise machining of the bevel to obtain an extremely smooth, defect-free surface. Preferably, the bevel is knurled to have a roughness Rz greater than 4 μm, more preferably between 4 and 16 μm. Such roughness improves the adhesion of the precoating to the bevel.

[0038] Preferably, the steel substrate is carbon steel.

[0039] The steel substrate may optionally be coated on at least a portion of one of its faces with an anticorrosion coating, preferably comprising a metal selected from the group consisting of zinc, aluminum, copper, silicon, iron, magnesium, titanium, nickel, chromium, manganese and alloys thereof.

[0040] In a preferred embodiment, the corrosion-resistant coating is an aluminum-based coating containing less than 15 wt.% Si, less than 5.0 wt.% Fe, optionally 0.1-8.0 wt.% Mg, and optionally 0.1-30.0 wt.% Zn, with the remainder being Al and unavoidable impurities arising from the manufacturing process. In another preferred embodiment, the corrosion-resistant coating is a zinc-based coating containing 0.01-8.0 wt.% Al, optionally 0.2-8.0 wt.% Mg, with the remainder being Zn and unavoidable impurities arising from the manufacturing process.

[0041] The anticorrosion coating is preferably applied to both sides of the steel substrate.

[0042] For the process, once a steel substrate is provided, a pre-coating solution is applied at least partially onto the substrate sidewall to form a pre-coating.

[0043] The pre-coating solution contains titanate and nanoparticulate oxide as described above for the pre-coating. In particular, the pre-coating solution has a concentration of 100 to 500 g / L, more preferably 175 to 250 g / L. -1 Titanate. In particular, the pre-coating solution contains 1-200g.L -1 , more preferably 5 to 80 g.L -1 Thanks to their concentrations in the titanates and nanoparticulate oxides, the quality of the welds obtained with the help of the corresponding pre-coating is further improved.

[0044] Advantageously, the pre-coating solution further comprises a solvent, which allows for a well-dispersed pre-coating. Preferably, the solvent is volatile at ambient temperature. For example, the solvent is selected from volatile organic solvents such as water, acetone, methanol, isopropanol, ethanol, ethyl acetate, diethyl ether, and non-volatile organic solvents such as ethylene glycol.

[0045] According to one variant of the invention, the pre-coating solution further comprises a binder precursor to embed the titanate and nanoparticulate oxide and to improve the adhesion of the pre-coating on the steel substrate. Preferably, the binder precursor is a sol of at least one organofunctional silane. Examples of organofunctional silanes are silanes functionalized with groups from the amine, diamine, alkyl, amino-alkyl, aryl, epoxy, methacryl, fluoroalkyl, alkoxy, vinyl, mercapto and aryl families, among others. Preferably, the binder precursor is present in an amount of 40 to 400 g.L of the pre-coating solution. -1 is added in an amount of

[0046] The pre-coating solution can be obtained by first mixing the titanate with the nanoparticles of the oxide. This can be done either wet with a solvent such as acetone or dry, for example in a 3D powder shaker mixer. Mixing promotes strong agglomeration of the nanoparticles on the titanate particles, which prevents their unintended release into the air, which is a health and safety issue.

[0047] The deposition of the pre-coating solution can be carried out notably by spin coating, spray coating, dip coating or brush coating.

[0048] Preferably, the pre-coating solution is deposited only locally, in particular the pre-coating solution is applied to the area of ​​the sidewall where the steel substrate will be welded.

[0049] Once the pre-coating solution has been applied onto the steel substrate, it can optionally be dried. Drying can be accomplished by blowing air or an inert gas at ambient or elevated temperatures. If the pre-coating includes a binder, the drying step is preferably also a curing step during which the binder is cured. Curing can be accomplished by infrared (IR), near infrared (NIR), or a conventional oven.

[0050] Preferably, no drying step is performed if the organic solvent is volatile at ambient temperature, in which case the organic solvent evaporates, leaving a dry pre-coating on the metal substrate.

[0051] Once the pre-coating is formed on a portion of the sidewall of the steel substrate, this portion can be welded to another metal substrate by narrow gap welding.

[0052] Narrow gap welding is well established for submerged arc welding (SAW), gas metal arc welding (GMAW), and gas tungsten arc welding (GTAW). All of these welding techniques can benefit from the present invention. Any other narrow gap welding technique can also benefit from the present invention.

[0053] The other metal substrate can be a steel substrate of the same or different composition as the pre-coated steel substrate. The other metal substrate can also be made of another metal, such as aluminum. More preferably, the other metal substrate is a pre-coated steel substrate according to the present invention. The other metal substrate is placed along the pre-coated sidewall of the steel substrate, separated by a gap that is narrow compared to the thickness of the steel. The gap is typically 8 to 25 mm wide, and the steel is typically 50 to 350 mm thick. The two substrates are then welded together by narrow gap welding.

[0054] The average current is preferably 100 to 1000 A. The voltage is preferably 8 to 30 V.

[0055] Depending on the welding technique, there can be a consumable electrode in the form of a wire (SAW, GMAW) or, if the electrode is not consumable, the material filling the joint can be supplied from the side in the form of a wire (GTAW). In both cases, the wire is made of, for example, Fe, Si, C, Mn, Mo and / or Ni.

[0056] Depending on the welding technique, the narrow gap may be at least locally covered by a shielding flux, which protects the welded zone from oxidation during welding.

[0057] Using the method according to the invention it is possible to obtain a welded joint of at least a first metal substrate in the form of a steel substrate and a second metal substrate, the first and second metal substrates being at least partially welded together by narrow gap welding, the welded zone comprising a dissolved and / or deposited pre-coating comprising a titanate and a nanoparticulate oxide.

[0058] 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, and more preferably selected from Na2Ti3O7, NaTiO3, K2TiO3, K2Ti2O5, MgTiO3, SrTiO3, BaTiO3, CaTiO3, FeTiO3, and ZnTiO4, and mixtures thereof.

[0059] The nanoparticulate oxides are preferably selected from TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3 and mixtures thereof.

[0060] "Dissolved and / or precipitated pre-coating" means that components of the pre-coating can be drawn toward the center of the liquid-gas interface of the weld pool due to reverse Marangoni flow, and even into the molten metal. Some components dissolve in the weld pool, resulting in a concentration of the corresponding element in the weld. Other components precipitate and are part of complex oxides that form precipitates in the weld.

[0061] In particular, when the Al content of the steel substrate exceeds 50 ppm, the welded zone contains inclusions, including, in particular, Al-Ti oxides or Si-Al-Ti oxides or other oxides, depending on the nature of the added nanoparticles. These precipitates of mixed elements are smaller than 5 μm. As a result, these precipitates of mixed elements do not impair the toughness of the welded zone. The inclusions can be observed by electron probe microanalysis (EPMA). Without being bound by any theory, it is believed that the nanoparticle-like oxides promote the formation of inclusions of a limited size so that the toughness of the welded zone is not impaired.

[0062] Finally, the invention relates to the use of the welded joints according to the invention for the manufacture of pressure vessels, offshore and oil and gas components, shipbuilding, nuclear reactor components and heavy industry and manufacturing in general. [Example]

[0063] A steel substrate was selected having the chemical composition in weight percent disclosed in Table 1:

[0064] [Table 1]

[0065] [Table 2]

[0066] The steel substrate was 50 mm thick and had a tensile strength of 480 MPa and a yield strength of 395 MPa.

[0067] [Example 1] A 100 x 150 mm sample with a non-beveled sidewall was prepared. The sidewall to be welded was cleaned of oil and dirt with acetone.

[0068] Sample 1 was not coated with a precoat.

[0069] For sample 2, an acetone solution containing MgTiO3 (diameter: 2 μm), SiO2 (diameter: 10 nm), and TiO2 (diameter: 50 nm) was prepared by mixing acetone with the following elements: In the acetone solution, the concentration of MgTiO3 was 175 g / L. -1 The SiO2 concentration was 25 g.L -1 The concentration of TiO2 was 50 g.L -1 The cleaned sidewall of Sample 2 was then coated with an acetone solution by spraying. The acetone was allowed to evaporate. The percentage of MgTiO3 in the dried pre-coating was 70 wt%, the percentage of SiO2 was 10 wt%, and the percentage of TiO2 was 20 wt%. The pre-coating was 50 μm thick.

[0070] Samples 1 and 2 were each placed alongside a bare sample of the selected steel substrate separated by a 13 mm gap and welded using narrow gap gas metal arc welding by performing weld passes until the gap was filled and the joint was complete. The welding parameters are listed in Table 2 below.

[0071] [Table 3]

[0072] The composition of the consumable electrodes used in both cases is listed in Table 3 below.

[0073] [Table 4]

[0074] Sample 1 was welded with 12 passes, whereas Sample 2 was welded with 10 passes. This first result already shows that the pre-coating according to the invention improves the deposition rate and productivity of narrow gap welds.

[0075] Improved wetting of the weld metal on the bevel surface was also observed in Sample 2 compared to Sample 1.

[0076] After narrow gap welding, the welds of both welded assemblies were first inspected visually and then ultrasonically (both linear and volumetric). The welds were also analyzed visually and microscopically, especially by penetrant testing (LPI). Charpy impact tests were also performed on the weld metal at room temperature and at -40°C.

[0077] The results are summarized in Table 4 below.

[0078] [Table 5]

[0079] The results show that a pre-coating on the sidewall of the steel substrate improves narrow gap welds without reducing the mechanical properties of the joint. In particular, the results of Charpy tests at -40°C showed a positive effect of the pre-coating on the elasticity of the material.

[0080] [Example 2] The effect of different pre-coatings on welding of steel substrates was evaluated using finite element method (FEM) simulations. In the simulations, the pre-coatings included nanoparticle oxides with diameters of 10-50 nm and, optionally, MgTiO (diameter: 2 μm). The coating thickness was 40 μm. Arc welding was simulated using each pre-coating, and the results are shown in Table 5 below.

[0081] [Table 6]

[0082] The results show that the pre-coating according to the present invention improves the penetration and quality of the weld compared to the comparative example.

[0083] [Example 3] For Sample 16, an aqueous solution containing the following components was prepared: 363 g.L -1 of MgTiO3 (diameter: 2 μm), 77.8 g L -1 of SiO2 (diameter range: 12-23 nm), 77.8 g L -1 of TiO2 (diameter range: 36-55 nm) and 238 g.L -1 of 3-aminopropyltriethoxysilane (Dynasylan® AMEO manufactured by Evonik®). The solution was applied to the sidewall of a steel substrate and dried by 1) IR and 2) NIR. The dried precoating was 40 μm thick and contained 62 wt. % MgTiO3, 13 wt. % SiO2, 13 wt. % TiO2, and 12 wt. % binder derived from 3-aminopropyltriethoxysilane.

[0084] For Sample 17, an aqueous solution containing the following components was prepared: 330 g.L -1 of MgTiO3 (diameter: 2 μm), 70.8 g L -1 of SiO2 (diameter range: 12-23 nm), 70.8 g L -1 of TiO2 (diameter range: 36-55 nm), 216 g.L -1 of 3-aminopropyltriethoxysilane (Dynasylan® AMEO manufactured by Evonik®) and 104.5 g L -1 A composition of organofunctional silane and functionalized nanoscale SiO2 particles (Dynasylan® Sivo 110 manufactured by Evonik) was applied to the sidewall of a steel substrate and dried by 1) IR and 2) NIR. The dried precoating was 40 μm thick and contained 59.5 wt. % MgTiO3, 13.46 wt. % SiO2, 12.8 wt. % TiO2, and 14.24 wt. % binder derived from 3-aminopropyltriethoxysilane and the organofunctional silane.

[0085] In all cases, the adhesion of the precoating on the steel substrate was significantly improved.

[0086] Although the beneficial effects of the present invention have been demonstrated in the case of narrow gap gas metal arc welding, the following techniques are nonetheless extendable to other narrow gap welding techniques, particularly narrow gap gas tungsten arc welding and narrow gap submerged arc welding, since all of them use coatable sidewalls with pre-coatings, as the physics of the narrow gap weld pool is modified.

Claims

1. 1. A method for the manufacture of a welded joint, comprising the following successive steps: I. Providing at least two metal substrates, at least one of which is a steel substrate having a thickness of at least 50 mm and separated by at least one sidewall, said sidewall comprising a titanium dioxide film and a 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; and wherein the titanate is selected from the group consisting of 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 and mixtures thereof, The diameter of the titanate is 1 to 40 μm, the percentage of titanate in the precoating is greater than or equal to 45% by weight and less than or equal to 90% by weight; the percentage of the oxide nanoparticles in the pre-coating is 10% by weight or more and 80% by weight or less; II. Welding the at least two metal substrates together along at least partially coated sidewalls by narrow gap welding; Including, method.

2. The method according to claim 1, wherein said oxide nanoparticles have a size comprised between 5 and 60 nm.

3. The method of claim 1 or 2, wherein the pre-coating further comprises a binder, wherein the binder is an organofunctional silane or siloxane sol-gel.

4. The method of claim 3, wherein the percentage of binder in the pre-coating is 1 to 20% by weight.

5. 5. The method according to claim 1, wherein the narrow gap welding is performed using one welding technique selected from the group consisting of submerged arc welding, gas metal arc welding and gas tungsten arc welding.

6. 1. A method for the manufacture of a pre-coated steel substrate, comprising the following steps in succession: A. Providing a steel substrate having a thickness of at least 50 mm and bounded by at least one sidewall; B. 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 at least partially depositing on said sidewalls a pre-coating solution comprising oxide nanoparticles selected from the group consisting of: Including, The titanate is 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 and mixtures thereof, The diameter of the titanate is 1 to 40 μm, the percentage of titanate in the precoating is greater than or equal to 45% by weight and less than or equal to 90% by weight; the percentage of the oxide nanoparticles in the pre-coating is 10% by weight or more and 80% by weight or less; method.

7. The method according to claim 6, wherein in step B), the deposition of the pre-coating solution is carried out by spin coating, spray coating, dip coating or brush coating.

8. 8. The method according to claim 6, wherein in step B) the pre-coating solution further comprises a solvent.

9. The method according to any one of claims 6 to 8, wherein in step B) the pre-coating solution contains 1 to 200 g / L of oxide nanoparticles.

10. The method according to any one of claims 6 to 9, wherein in step B) the pre-coating solution comprises 100 to 500 g / L of titanate.

11. The method according to any one of claims 6 to 10, wherein in step B) the pre-coating solution further comprises a binder precursor, wherein the binder precursor is a sol of at least one organofunctional silane.

12. The method according to any one of claims 6 to 11, further comprising a step of drying the pre-coated steel substrate obtained in step B).

13. A steel substrate for welding having a thickness of at least 50 mm and bounded by at least one side wall, said side wall comprising a titanium dioxide powder and a titanium dioxide powder. 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; The titanate is 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 and mixtures thereof, The diameter of the titanate is 1 to 40 μm, the percentage of titanate in the precoating is greater than or equal to 45% by weight and less than or equal to 90% by weight; the percentage of the oxide nanoparticles in the pre-coating is 10% by weight or more and 80% by weight or less; steel substrate.

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