Method for manufacturing a welded joint by laser-arc hybrid welding

Abstract

The invention relates to a method for manufacturing a welded joint, the method comprising the following sequential steps: I. providing at least two metal substrates, wherein at least one metal substrate is a steel substrate having a thickness of at least 8 mm and being bounded by at least one bevel, wherein the bevel is at least partially coated with a pre-coating comprising a titanate and a nanoparticulate oxide selected from the group consisting of TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeCO2, La2O3 and mixtures thereof, and II. welding the at least two metal substrates along the at least partially coated bevel by laser-arc hybrid welding in a guided arc configuration.

Description

[0001] The present invention relates to welding of metal substrates by laser-arc hybrid welding, in particular in the case where at least one of the metal substrates is a steel substrate locally coated with a flux to improve the weld quality. The invention also relates to the corresponding steel substrates and to a method for manufacturing steel substrates. The invention is particularly well adapted to the construction, shipbuilding, transport industry (railway and automotive), energy-related structures, oil and gas and offshore industries.

[0002] It is known to weld steel substrates by laser-arc hybrid welding. This welding technique combines the principles of laser beam welding and arc welding. Depending on the device used, there are four main types of laser-arc hybrid welding processes: Tungsten Inert Gas (TIG) (also known as Gas Tungsten Arc (GTA)), Gas Metal Arc (GMA) (sometimes referred to by its subtypes as Metal Inert Gas (MIG) or Metal Active Gas (MAG)), Plasma Arc and Submerged Arc (SA).

[0003] The combination of laser and arc processes leads to an increase in both the welding penetration depth and the welding speed (compared to each process alone). However, despite these improvements, there is still room for limiting the occurrence of cracks in the weld and improving the process stability and thus the welding penetration.

[0004] There is therefore a need to improve the quality of the weld made by laser-arc hybrid welding and thus the mechanical properties of the welded steel substrates. There is also a need to improve the deposition rate and productivity of the laser-arc hybrid welding.

[0005] To this end, the present invention relates to a method for manufacturing a welded joint, said method comprising the following sequential steps:

[0006] I. providing at least two metal substrates, wherein at least one metal substrate is a steel substrate having a thickness of at least 8 mm and being delimited by at least one bevel, wherein said bevel is at least partially coated with a pre-coating comprising a titanate and a nanoparticulate oxide selected from the group consisting of Ti02, Si02, Zr02, Y203, Al203, M0O3, Cr03, Ce02, La203and mixtures thereof, and

[0007] II. welding the at least two metal substrates along the at least partially coated bevel by laser-arc hybrid welding in a guided arc configuration.

[0008] The method according to the present invention can also have the following listed optional features taken alone or in combination:

[0009] - the titanate is chosen from Na2Ti307, NaTi03, K2Ti03, K2Ti205, MgTi03, SrTi03, BaTi03, CaTi03, FeTi03and ZnTi04, and mixtures thereof,

[0010] - the thickness of the pre-coating is between 10 pm and 140 pm,

[0011] - the percentage of nanoparticulate oxides in the pre-coating is lower than or equal to 80% by weight,

[0012] - the percentage of nanoparticulate oxides in the pre-coating is higher than or equal to 10% by weight,

[0013] - the size of the nanoparticles is between 5 nm and 60 nm,

[0014] - the percentage of titanate in the pre-coating is higher than or equal to 45% by weight,

[0015] - the diameter of the titanate is between 1 pm and 40 pm,

[0016] - the pre-coating further comprises a binder,

[0017] - the percentage of binder in the pre-coating is between 1 % and 20% by weight,

[0018] - the electric arc of the laser-arc hybrid welding is chosen from a submerged arc, a gas shielded metal arc, a gas shielded tungsten arc and a plasma arc.

[0019] - the pre-coating further comprises microparticulate compounds chosen from microparticulate oxides and / or microparticulate fluorides,

[0020] - the pre-coating further comprises microparticulate compounds chosen from the list consisting of Ce02, Na20, Na202, NaBi03, NaF, CaF2, cryolite (Na3AlF6) and mixtures thereof.

[0021] The application also relates to a method for manufacturing a pre-coated steel substrate, said method comprising the following sequential steps:

[0022] A. providing a steel substrate having a thickness of at least 8 mm and being delimited by at least one bevel having an oblique truncation of between 1 ° and 10°,

[0023] B. depositing at least partially on said bevel a pre-coating solution comprising a titanate and nanoparticulate oxides chosen from Ti02, Si02, Zr02, Y203, Al203, M0O3, Cr03, Ce02, La203and mixtures thereof.

[0024] The method for manufacturing a pre-coated steel substrate according to the application can also have, taken separately or in combination, the following listed optional features:

[0025] - the deposition of the pre-coating solution is performed by spin coating, spray coating, dip coating or brushing,

[0026] - in step B), the pre-coating solution further comprises a solvent,

[0027] - in step B), the pre-coating solution comprises from 1 g / L to 200 g / L of nanoparticulate oxide,

[0028] - in step B), the pre-coating solution comprises from 100 g / L to 500 g / L of titanate,

[0029] - in step B), the pre-coating solution further comprises a binder precursor,

[0030] - the method further comprises a drying step of the pre-coated steel substrate obtained in step B).

[0031] The present application also relates to a steel substrate having a thickness of at least 8 mm and being delimited by at least one oblique edge having an oblique truncation of 1 ° to 10°, wherein said oblique edge is at least partially coated with a pre-coating comprising a titanate and a nanoparticulate oxide selected from Ti02, Si02, Zr02, Y203, AI203, M0O3, Cr03, Ce02, La203and mixtures thereof.

[0032] The following terms are defined:

[0033] - a nanoparticle is a particle having a size comprised between 1 nanometer (nm) and 100 nanometers.

[0034] - a titanate refers to an inorganic compound containing 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.

[0035] - "coated" means that the steel substrate is at least partially covered with a pre-coating. The coverage can for example be limited to the area of the steel substrate that will be welded. "Coated" inclusively includes "directly on" (without an intermediate material, element or space in between) and "indirectly on" (with an intermediate material, element or space in between). For example, coating the steel substrate can include applying the pre-coating directly on the substrate, without intermediate material / element in between, and applying the pre-coating indirectly on the substrate, with one or more intermediate material / element (such as a corrosion protection coating) in between.

[0036] Without wishing to be bound by any theory, it is believed that the pre-coating mainly changes the physical properties of the molten pool during welding. It appears that in the present invention, not only the nature of the compounds, but also the size of the oxide particles, equal to or less than 100 nm, change the arc and molten pool physical properties.

[0037] Indeed, the first arc that is made melts the pre-coating 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. Due to the presence of titanate and nanoparticles in the arc, the arc is pinched and the temperature of the molten metal pool is increased. Thus, it is easier to form a keyhole, i.e. a literal hole in the steel substrate caused by its evaporation, by laser impinging the molten metal pool. This increases the process efficiency.

[0038] Moreover, the pre-coating dissolved in the molten metal changes the Marangoni flow, which is a mass transfer at the liquid-gas interface due to a surface tension gradient. In particular, the components of the pre-coating change the gradient of the surface tension along the interface. This change of surface tension causes a fluid flow to reverse towards the center of the weld pool. Without wishing to be bound by any theory, it is believed that nanoparticles dissolve at lower temperature than microparticles, thus there is more oxygen dissolved in the molten pool, which activates a reverse Marangoni flow. The latter helps to maintain a proper keyhole shape, which in turn prevents gas entrapment and thus pores in the weld.

[0039] Furthermore, the titanate mixed with the nanoparticles oxides changes the interaction of the plasma plume with the laser beam. In particular, the increase of oxygen due to the dissolution of the pre-coating reduces the scattering of the laser beam. Thus, the laser spot diameter is reduced while the keyhole effect is enhanced. This allows the energy beam to penetrate even deeper and to be delivered into the joint very efficiently. This increases the welding penetration and minimizes the heat affected zone, which in turn limits the parts deformation.

[0040] Moreover, since the components of the pre-coating increase the surface tension with temperature, the wettability of the welding material increases along the slope that is cooler than the center of the molten pool, which prevents slag entrapment.

[0041] Additionally, it is observed that the nanoparticles improve the homogeneity of the applied pre-coating by filling the gaps between the microparticles and covering the surface of the microparticles. This helps to stabilize the welding arc, thus improving the welding penetration and quality.

[0042] Reference will now be made to the drawings in which Figure 1 The present application will be better understood by reading the following description, which is only provided for purposes of illustration and is in no way intended to be limiting.

[0043] The pre-coating 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 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 Ti02, Si02, Zr02, Y203, AI2O3, M0O3, Cr03, Ce02, La203and mixtures thereof. This means that the pre-coating does not comprise any other nanoparticulate oxide than the ones listed.

[0044] The titanate is selected from the group 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 believed 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 invention. The skilled person will know which one has to be chosen depending on the specific situation. To this end, the ease of melting and dissolving of the titanate, the extent to which it increases the dissolved oxygen content, how the additional elements of the titanate affect the physical properties of the weld pool and the microstructure of the final weld will be taken into account. For example, NaTi07is advantageous due to the presence of Na, which improves the formation and shedding of the slag.

[0045] Preferably, the diameter of the titanate is between 1 pm and 40 pm, more preferably between 1 pm and 20 pm, and advantageously between 1 pm and 10 pm. This titanate diameter is believed to further improve the arc constriction and the reverse Marangoni effect. Moreover, having small micron-sized titanate particles increases the specific surface area available for mixing with the nanoparticulate oxide and further adhering the nanoparticulate oxide to the titanate particles. It also makes the particles easier to spray.

[0046] Preferably, the weight percentage of the titanate in the dry weight of the pre-coating is higher than or equal to 45%, more preferably between 45% and 90%, and even more preferably between 45% and 75%.

[0047] The nanoparticulate oxides are chosen from Ti02, Si02, Zr02, Y203, Al203, M0O3, Cr03, Ce02, La203and mixtures thereof. These nanoparticles are easily dissolved in the bath, provide oxygen to the bath, thus increasing the depth of penetration and stabilizing the keyhole preventing defects. Contrary 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 would prevent the heat from properly melting the steel, and their metallic ions do not tend to recombine with the oxygen in the bath.

[0048] Preferably, the nanoparticles are Si02and / or Ti02, and 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.

[0049] Other examples of mixtures of nanoparticulate oxides are:

[0050] - yttria-stabilized zirconia (YSZ), which is a ceramic in which the cubic crystal structure of zirconium dioxide (Zr02) is stabilized at room temperature by the addition of yttrium oxide (Y203),

[0051] - a 1 : 1 : 1 combination of La203, Zr02and Y203, which helps to adjust the refractory effect and to promote the formation of inclusions.

[0052] Preferably, the size of the nanoparticles is between 5 nm and 60 nm. This nanoparticulate diameter is believed to further improve the uniform distribution of the coating.

[0053] Preferably, the weight percentage of nanoparticulate oxides in the dry weight of the pre-coating is lower than or equal to 80%, preferably higher than or equal to 10%, more preferably between 10% and 60%, even more preferably between 20% and 55%. In some cases, it can be necessary to limit the percentage of nanoparticles to avoid too high a refractory effect. The person skilled in the art, knowing the refractory effect of each nanoparticle, will adjust the percentage according to the specific case.

[0054] According to one variant of the application, after the pre-coating is applied on the steel substrate and dried, the pre-coating consists of titanate and nanoparticulate oxides.

[0055] According to another variant of the application, the pre-coating further comprises at least one binder which embeds the titanate and the nanoparticulate oxide and improves the adhesion of the pre-coating on the steel substrate. This improved adhesion further prevents the particles of the pre-coating from being blown away by the flow of the shielding gas when used. Preferably, the binder is purely inorganic, in particular to avoid the fumes that can be generated by organic binders during welding. Examples of inorganic binders are sol-gel of organo-functional silanes or siloxanes. Examples of organo-functional silanes are silanes functionalized with groups of the family of amines, diamines, alkyls, amino-alkyls, aryls, epoxies, methacryl, fluoroalkyls, alkoxy, vinyl, mercapto and aryl in particular. Amino-alkyl silanes are particularly preferred because they greatly improve the adhesion and have a long shelf life. Preferably, the binder is added in an amount of 1 to 20% by weight of the dry pre-coating.

[0056] According to another variant of the application, the pre-coating further comprises a microparticulate compound, such as a microparticulate oxide and / or a microparticulate fluoride, such as Ce02, Na20, Na202, NaBi03, NaF, CaF2, cryolite (Na3AlF6). The shift from nanoparticles to microparticles for some of the nanoparticles listed above mitigates the health and safety issues associated with the use of some of these oxides. Na20, Na202, NaBi03, NaF, CaF2, cryolite can be added to improve the slag formation, such that further prevention of the inclusion of slag is achieved. It also helps to form a slag that can be easily separated. The pre-coating can comprise 0.1 to 5% by weight of Na20, Na202, NaBi03, NaF, CaF2, cryolite or a mixture thereof in the dry weight of the pre-coating.

[0057] Preferably, the thickness of the pre-coating is 10 to 140 pm, more preferably 30 to 100 pm.

[0058] The pre-coating at least partially covers one bevel of the steel substrate. The bevel can have any shape compatible with laser-arc hybrid welding. For the purposes of the present application, it is only defined by a thickness of at least 8 mm, such that it is compatible with laser-arc hybrid welding and is welded to another metal substrate at least partially through the bevel. Depending on the thickness of the sample, the bevel can have a single Y or a double Y shape. The bevel angle is preferably 1 to 10°. Lower angles can promote lack of edge fusion, while higher angles will require more passes to fill the material. When the bevel has a double Y shape, the bevel angle refers to the angle of each Y.

[0059] Preferably, the bevel is milled such that the roughness Rz is higher than 4 pm, more preferably 4 to 16 pm. Such a roughness improves the adhesion of the pre-coating on the bevel.

[0060] Preferably, the steel substrate is a carbon steel.

[0061] The steel substrate can optionally be coated with an anticorrosion coating on at least a portion of one of its sides. Preferably, the anticorrosion coating comprises a metal selected from the group consisting of zinc, aluminum, copper, silicon, iron, magnesium, titanium, nickel, chromium, manganese and alloys thereof.

[0062] In a preferred embodiment, the anticorrosion coating is an aluminum-based coating comprising less than 15 wt.% of Si, less than 5.0 wt.% of Fe, optionally 0.1 wt.% to 8.0 wt.% of Mg and optionally 0.1 wt.% to 30.0 wt.% of Zn, the remainder being Al and unavoidable impurities resulting from the manufacturing process. In another preferred embodiment, the anticorrosion coating is a zinc-based coating comprising 0.01 wt.% to 8.0 wt.% of Al, optionally 0.2 wt.% to 8.0 wt.% of Mg, the remainder being Zn and unavoidable impurities resulting from the manufacturing process.

[0063] The anticorrosion coating is preferably applied on both sides of the steel substrate.

[0064] In terms of process, after the steel substrate is provided, a pre-coating solution is at least partially applied on the substrate bevel to form a pre-coating.

[0065] The pre-coating solution comprises a titanate and a nanoparticulate oxide as described above for the pre-coating. In particular, it comprises 100 g / L to 500 g / L of titanate, more preferably 175 g.L -1 to 250 g.L -1 . In particular, it comprises 1 g.L -1 to 200 g.L -1 of nanoparticulate oxide, more preferably 5 g.L -1 to 80 g.L -1 . Thanks to these concentrations of titanate and nanoparticulate oxide, the quality of the weld obtained with the help of the corresponding pre-coating is further improved.

[0066] Advantageously, the pre-coating solution further comprises a solvent. The solvent allows a well-dispersed pre-coating. Preferably, the solvent is volatile at ambient temperature. For example, the solvent is selected from the group consisting of: water; volatile organic solvents such as acetone, methanol, isopropanol, ethanol, ethyl acetate, diethyl ether; and non-volatile organic solvents such as ethylene glycol.

[0067] According to one variant of the application, the pre-coating solution further comprises a binder precursor to embed the titanate and the 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 of the family of amines, diamines, alkyls, amino-alkyls, aryls, epoxys, methacryl, fluoroalkyls, alkoxy, vinyl, mercapto and aryl in particular. Preferably, the binder precursor is added in an amount of 40 g.L -1 to 400 g.L -1 of the pre-coating solution.

[0068] The pre-coating solution can be obtained by first mixing the titanate and the nanoparticulate oxide. The mixing can be performed under wet conditions with a solvent such as acetone, or under dry conditions, for example in a 3D powder shaker. The mixing favors the aggregation of the nanoparticles on the titanate particles, which prevents the unintentional release of the nanoparticles in the air, which would be a health and safety issue.

[0069] The deposition of the pre-coating solution can be performed in particular by spin coating, spray coating, dip coating or brush coating.

[0070] Preferably, the pre-coating solution is deposited only locally. In particular, the pre-coating solution is applied in the bevel region where the steel substrate is to be welded.

[0071] After the application of the pre-coating solution to the steel substrate, it can be optionally dried. The drying can be performed by blowing air or inert gas at ambient or hot temperature. When the pre-coating comprises a binder, the drying step is also a curing step during which the binder is cured. The curing can be performed by infrared (IR), near infrared (NIR), conventional oven.

[0072] Preferably, when the organic solvent is volatile at ambient temperature, no drying step is performed. In this case, the organic solvent evaporates, thereby forming a dry pre-coating on the metal substrate.

[0073] After the formation of the pre-coating on a part of the bevel of the steel substrate, this part can be welded to another metal substrate by laser-arc hybrid welding.

[0074] The arc of the laser-arc hybrid welding can be chosen among submerged arc, gas metal arc, gas tungsten arc and plasma arc. All these arcs can benefit from the application.

[0075] The average current is preferably between 40 A and 1000 A. The voltage is preferably between 1 V and 40 V.

[0076] The laser of the laser-arc hybrid welding can be selected from solid state lasers, such as Nd:YAG, Nd:glass, ruby, Nd:YLF, Yb:YAG, Yb:fiber, Ti:sapphire. Preferably, it is the most common Nd:YAG laser with an emission wavelength of 1064 nm or a Yb:YAG laser (1030 nm).

[0077] Any combination of arc and laser can benefit from the present application, as the pre-coating has a similar effect on different arcs and different lasers.

[0078] The welding is operated in a guided arc configuration. This means that the arc is in front of the laser beam. The arc hits the steel substrate first and melts it to form a molten pool. Then the laser hits the molten pool.

[0079] The other metal substrate can be a steel substrate of the same composition or a different composition than the pre-coated steel substrate. It 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 application. The other metal substrate is positioned along the pre-coated bevel edge of the steel substrate. Both substrates are then welded by laser-arc hybrid welding.

[0080] Depending on the welding technology, there can be a consumable electrode in the form of a welding wire (SAW, GMAW), or, if the electrode is not consumable, the material for the filler joint can be fed from the side in the form of a welding wire (GTAW, plasma). In both cases, the welding wire is made of, for example, Fe, Si, C, Mn, Mo and / or Ni.

[0081] Depending on the welding technology, the bevel edge can be at least partially covered with a protective flux. The protective flux protects the welding zone from oxidation during welding.

[0082] With the method according to the present application, a welded joint of at least a first metal substrate in the form of a steel substrate and a second metal substrate can be obtained, the first metal substrate and the second metal substrate being at least partially welded together by laser-arc hybrid welding, wherein the welding zone comprises a dissolved and / or precipitated pre-coating comprising titanate and nanoparticulate oxide.

[0083] 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, NaTiO3, K2TiO3, K2Ti2O5, MgTiO3, SrTiO3, BaTiO3, CaTiO3, FeTiO3 and ZnTiO4 and mixtures thereof.

[0084] The nanoparticulate oxides are chosen from Ti02, Si02, Zr02, Y203, Al203, M0O3, Cr03, Ce02, La203, and mixtures thereof.

[0085] By "dissolution and / or precipitation of the pre-coating" is meant that components of the pre-coating can be drawn towards the center of the liquid-gas interface of the molten bath and even to the inside of the molten metal due to the reverse Marangoni flow. Some components dissolve in the molten bath, which leads to the enrichment of the corresponding elements in the weld. Other components precipitate and are part of the complex oxides forming precipitates in the weld.

[0086] In particular, when the amount of Al of the steel substrate is higher than 50 ppm, depending on the nature of the added nanoparticles, the weld zone contains inclusions containing in particular Al-Ti oxides or Si-Al-Ti oxides or other oxides. These precipitates of mixed elements are smaller than 5 pm. Thus, they do not impair the toughness of the weld zone. The inclusions can be observed by Electron Probe Micro-Analysis (EPMA). Without wishing to be bound by any theory, it is believed that the nanoparticulate oxides promote the formation of size-limited inclusions so that the toughness of the weld zone is not impaired.

[0087] Finally, the present application relates to the use of the welded joint according to the present application for the manufacture of parts for the oil and gas and offshore industries, shipbuilding, construction and transportation (railway and automotive). Example

[0088] A steel substrate having the chemical composition in weight percent disclosed in Table 1 was chosen:

[0089] C Mn Si P S N Al Fe 0.16-0.18 1.1-1.2 0.15-0.3 0.015 0.003 0.007 0.02-0.06 Balance

[0090] The steel substrate was 25 mm thick. The steel substrate had a tensile strength of 485 MPa to 620 MPa and a yield strength of 260 MPa.

[0091] Example 1

[0092] As Figure 1 shown in Figure 1, a sample 1 of 100 x 150 mm having bevels in the shape of double Y was prepared, each bevel being inclined at an angle a of 4° and the upper and lower bevels being separated by a gap 2 of 5 mm. The bevels were milled so that the roughness Rz of the bevels was 5 pm to 8 pm and the roughness Rz of the 5 mm gap was 6 pm to 15 pm. The bevels to be welded were cleaned from oil and dirt with acetone.

[0093] The sample 1 was not coated with a pre-coating.

[0094] For sample 2, an acetone solution containing MgTi03(diameter: 2 μm), Si02(diameter: 10 nm) and Ti02(diameter: 50 nm) was prepared by mixing acetone with the elements. In the acetone solution, the concentration of MgTi03was 175 g.L -1 . The concentration of Si02was 25 g.L -1 . The concentration of Ti02was 50 g.L -1 Then, the cleaned side walls of sample 2 were coated by spraying with the acetone solution. The acetone was evaporated. The percentage of MgTi03in the dried pre-coating was 70 wt%, the percentage of Si02was 10 wt% and the percentage of Ti02was 20 wt%. The pre-coating was 50 μm thick.

[0095] Samples 1 and 2 were each positioned side by side with a bare sample of the selected steel substrate spaced apart by a gap of 0.3 mm and were welded by laser-arc hybrid welding in a guided-arc configuration without preheating by making welding passes until the bevel was filled up and the joint was completed. The laser was a 16 kW Yb:YAG laser with a 0.3 mm spot. The arc equipment was a gas metal arc welding gun with argon / CO280 / 20 shielding gas. The feed wire contained a maximum of 0.06 wt% C, 0.8 wt% Si and 1.5 wt% Mn. The welding parameters are in Table 2 below:

[0096]

[0097] *: according to the invention

[0098] As is apparent from Table 2, sample 1 required two welding passes to be completely welded, while sample 2 required only one welding pass, with the same welding parameters. This first result has shown that the pre-coating according to the invention increases the depth of penetration and the productivity of the laser-arc hybrid welding in a guided-arc configuration.

[0099] After welding, the welds of both welded assemblies were inspected visually and by X-ray imaging and cross sections were microscopically analyzed.

[0100] Table 3 below details the microscopic analysis of each weld:

[0101]

[0102] *: according to the invention

[0103] The pre-coating increased the arc penetration by 10% and the laser penetration by 50%.

[0104] The X-ray imaging analysis revealed a crack along the weld of sample 1 and the cross section analysis revealed a crack in sample 1. These results have shown that the pre-coating improves the wettability.

[0105] Tensile test, Charpy-V test and hardness characterization also determined that the precoating on the bevel of the steel substrate improved the laser-arc hybrid welding in the guided arc configuration without degrading the mechanical properties of the joint.

[0106] Example 2

[0107] Sample 3 (with precoating) was prepared according to sample 2.

[0108] Then, the samples were welded with an increased travel speed (25 mm / s, i.e. an increase of 56%) and a reduced gap (0.2 mm) before welding, with and without preheating at 320°C, all other conditions being the same as in example 1.

[0109] The obtained results determined that the travel speed, and thus the productivity of the laser-arc hybrid welding, could be increased thanks to the precoating. Moreover, this productivity increase was not accompanied by a degradation of the mechanical properties of the joint and even by an improvement of some mechanical properties of the joint, as shown in table 4, where the results obtained with the preheated sample 3 are compared to the results obtained with the preheated sample 1 (detailed in example 1):

[0110]

[0111] *: according to the invention

[0112] The Charpy V-test was performed according to ISO 9016:2012 at T = -20°C.

[0113] “OK” in the column “breakage of the base material” means that the breakage of the sample at the end of the tensile test was on the base material, which is sought for the welded samples.

[0114] “OK” in the column “hardness” means that the hardness of the tested sample complies with the ISO 15614-1 :2017 standard.

[0115] Example 3

[0116] The influence of different precoatings on the welding of steel substrates was evaluated by finite element method (FEM) simulation. In the simulation, the precoating comprised nanoparticles oxides with a diameter of 10 nm to 50 nm and optionally MgTi03(diameter: 2 pm). The thickness of the coating was 40 pm. The arc welding was simulated with each precoating and the results are in table 5 below:

[0117]

[0118] *: according to the invention

[0119] The results show that, compared with the comparative example, the pre-coating according to the present invention improves the weld penetration and quality.

[0120] Example 4

[0121] For sample 17, an aqueous solution containing the following components was prepared: 363 g / L -1 MgTiO3 (diameter: 2μm), 77.8gL -1 SiO2 (diameter range: 12nm to 23nm), 77.8gL -1 TiO2 (diameter range: 36nm to 55nm) and 238g.L -1 3-Aminopropyltriethoxysilane (from Manufactured The solution was applied to the bevel of a steel substrate and dried by 1) IR and 2) NIR. The dried pre-coating was 40 μm thick and contained 62 wt% MgTiO3, 13 wt% SiO2, 13 wt% TiO2 and 12 wt% binder obtained from 3-aminopropyltriethoxysilane.

[0122] For sample 18, an aqueous solution containing the following components was prepared: 330 g / L -1 MgTiO3 (diameter: 2μm), 70.8gL -1 SiO2 (diameter range: 12nm to 23nm), 70.8gL -1 TiO2 (diameter range: 36nm to 55nm), 216g.L -1 3-Aminopropyltriethoxysilane (from Manufactured AMEO) and 104.5gL -1 A composition of organofunctional silanes and functionalized nanoscale SiO2 particles (manufactured by Evonik) The solution was applied to the bevel of a steel substrate and dried by 1) IR and 2) NIR. The dried pre-coating was 40 μm thick and contained 59.5 wt% MgTiO3, 13.46 wt% SiO2, 12.8 wt% TiO2, and 14.24 wt% binder obtained from 3-aminopropyltriethoxysilane and organofunctional silanes.

[0123] In all cases, the adhesion of the pre-coated layer on the bevel was greatly improved.

[0124] The benefits of the present invention have been illustrated in the case of laser-arc hybrid welding with a MAG arc and a Yb:YAG laser in a guided arc configuration. However, it is extendable to other arcs and lasers, as all these technologies use a bevel that can be coated with a pre-coat, which changes the arc and the molten pool physical properties.

Claims

1. A method for manufacturing a welded joint, comprising the following sequential steps: I. Provide at least two metal substrates, wherein at least one metal substrate is a steel substrate, the steel substrate having a thickness of at least 8 mm and defined by at least one beveled boundary, wherein the beveled boundary is at least partially coated with a pre-coating comprising titanate and nanoparticle oxide, the nanoparticle oxide being selected from TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3, and mixtures thereof, and II. The at least two metal substrates are welded along at least partially coated bevels by laser-arc hybrid welding in a guided arc configuration.

2. The method according to claim 1, wherein the titanate is selected from: Na2Ti3O7, NaTiO3, K2TiO3, K2Ti2O5, MgTiO3, SrTiO3, BaTiO3, CaTiO3, FeTiO3 and ZnTiO4 and mixtures thereof.

3. The method according to claim 1 or 2, wherein the thickness of the pre-coating is from 10 μm to 140 μm.

4. The method according to claim 1 or 2, wherein the percentage of the nanoparticle oxide in the pre-coating is less than or equal to 80% by weight.

5. The method according to claim 1 or 2, wherein the percentage of the nanoparticle oxide in the pre-coating is greater than or equal to 10% by weight.

6. The method according to claim 1 or 2, wherein the size of the nanoparticles is from 5 nm to 60 nm.

7. The method according to claim 1 or 2, wherein the percentage of titanate in the pre-coating is greater than or equal to 45% by weight.

8. The method according to claim 1 or 2, wherein the diameter of the titanate is from 1 μm to 40 μm.

9. The method of claim 1 or 2, wherein the pre-coating further comprises an adhesive.

10. The method of claim 9, wherein the percentage of the adhesive in the pre-coating is from 1% to 20% by weight.

11. The method according to claim 1 or 2, wherein the arc of the laser-arc hybrid welding is selected from submerged arc, gas-shielded metal electrode arc, gas-shielded tungsten electrode arc, and plasma arc.

12. A method for manufacturing a pre-coated steel substrate, comprising the following sequential steps: A. A steel substrate is provided, the steel substrate having a thickness of at least 8 mm and being defined by at least one oblique boundary with a chamfer angle of 1° to 10°. B. Deposit at least partially on the inclined edge a pre-coating solution comprising titanate and nanoparticle oxide, wherein the nanoparticle oxide is selected from TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3 and mixtures thereof.

13. The method of claim 12, wherein in step B), the deposition of the pre-coated solution is performed by spin coating, spraying, dipping or brushing.

14. The method according to claim 12 or 13, wherein in step B), the pre-coating solution further comprises a solvent.

15. The method according to claim 12 or 13, wherein in step B), the pre-coating solution comprises 1 g / L to 200 g / L of nanoparticle oxide.

16. The method according to claim 12 or 13, wherein in step B), the pre-coating solution comprises 100 g / L to 500 g / L of titanate.

17. The method of claim 12 or 13, wherein in step B), the pre-coating solution further comprises an adhesive precursor.

18. The method according to claim 12 or 13, further comprising a drying step of the pre-coated steel substrate obtained in step B).

19. A steel substrate having a thickness of at least 8 mm and defined by at least one oblique boundary with a chamfer angle of 1° to 10°, wherein the oblique boundary is at least partially coated with a pre-coating comprising titanate and nanoparticle oxide, the nanoparticle oxide being selected from TiO2, SiO2, ZrO2, Y2O3, Al2O3, MoO3, CrO3, CeO2, La2O3, and mixtures thereof.

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