ArcelorMittal

A process for manufacturing a press hardened laser welded steel part, includes providing at least one first steel sheet with a composition containing, by weight 0.062≤C≤0.095%, the at least one first steel sheet precoated with a metallic precoating of aluminum, or aluminum-based alloy, or aluminum alloy. providing at least one second steel sheet with a composition containing, by weight, from to 0.38% of carbon, the at least one second steel sheet precoated with a metallic precoating of aluminum, or aluminum-based alloy, or aluminum alloy; removing a portion of a thickness of the aluminum precoating at upper and lower sides along one side of a periphery of the at least one first steel sheet and the at least one second steel sheet; creating a welded blank by laser welding the at least one first steel sheet and the at least one second steel sheet, such that an aluminum content in a weld metal is lower than 0.3% by weight, the laser welding being performed along the periphery wherein the portion of the thickness of the aluminum precoating has been removed; heating the welded blank and holding the welded blank at a temperature Tm between 890 and 950° C., a holding duration Dm at the temperature being between 1 and 10 minutes, so as to obtain a heated welded blank; transferring the heated welded blank within a forming press, the transfer duration Dt being less than 10 s; hot forming the heated welded blank in the forming press so as to obtain a welded formed part; and cooling the welded formed part at a first cooling rate CR1 between 40 and 360° C./s in a temperature range between 750 and 450° C., and at a second cooling rate CR2 between 15 to 150° C./s in a temperature range between 450° C. and 250° C., wherein CR2<CR1.

Laser cutting process to produce n trimmed sub-blanks, n being an integer strictly greater than 1, from a mother blank made of metallic material, having the following steps: Op1/ positioning the mother blank on a cutting table having n laths arranged to be moveable relative to one another in a transverse direction, Op2/ clamping at least part of the mother blank to the cutting table, Op3/ cutting, using a laser source, n untrimmed sub-blanks from the mother blank in a longitudinal cutting direction, Op4/ separating the n laths of the cutting table from one another in a transverse direction, Op5/ releasing the clamping, Op6/ clamping the n untrimmed sub-blanks to the n laths, Op7/ laser trimming the n untrimmed sub-blanks in order to form n trimmed sub-blanks, Op8/ releasing the clamping, Op9/ discharging the n trimmed sub-blanks from the cutting table.

A welding flux including a titanate and a nanoparticulate Niobium compound chosen from among Niobium oxides, alkali niobates and mixtures thereof.

A method for the preparation of steel sheets for fabricating a welded steel blank is provided. The method includes a step of removing at least part of the first and second metal alloy layers in first and second peripheral zones of pre-coated steel first and second sheets, respectively, by simultaneously ablating the first and second precoatings in the first and second peripheral zones of the pre-coated steel first and second sheets to define first and second ablation zones, the first and second peripheral zones being zones of the first and second principal faces closest to the median plane and located on either side of the median plane.

A method for butt laser welding two metal sheets includes providing a first metal sheet and a second metal sheet and butt welding the metal sheets along a direction of welding. The butt welding step includes simultaneously generating a first front keyhole in the first metal sheet, generating a second front keyhole in the second metal sheet, and generating a back keyhole in the first and second metal sheets. The first and second front laser beams and the back laser beam are configured in such a manner that at each moment in time, a solid phase region and/or a liquid phase region of the metal sheets remains between the first front keyhole and the back keyhole and between the second front keyhole and the back keyhole.

A method for producing a zinc or zinc-alloy coated steel sheet with a tensile strength higher than 900 MPa, for the fabrication of resistance spot welds containing in average not more than two Liquid Metal Embrittlement cracks per weld having a depth of 100 μm or more, with steps of providing a cold-rolled steel sheet, heating cold-rolled steel sheet up to a temperature T1 between 550° C. and Ac1+50° C. in a furnace zone with an atmosphere (A1) containing from 2 to 15% hydrogen by volume, so that the iron is not oxidized, then adding in the furnace atmosphere, water steam or oxygen with an injection flow rate Q higher than (0.07%/h×α), α being equal to 1 if said element is water steam or equal to 0.52 if said element is oxygen, at a temperature T≥T1, so to obtain an atmosphere (A2) with a dew point DP2 between −15° C. and the temperature Te of the iron/iron oxide equilibrium dew point, then heating the sheet from temperature T 1 up to a temperature T 2 between 720° C. and 1000° C. in a furnace zone under an atmosphere (A2) of nitrogen containing from 2 to 15% hydrogen and more than 0.1% CO by volume, with an oxygen partial pressure higher than 10 −21 atm., wherein the duration t D of heating of the sheet from temperature T 1 up to the end of soaking at temperature T 2 is between 100 and 500 s., soaking the sheet at T 2 , then cooling the sheet at a rate between 10 and 400° C./s, then coating the sheet with zinc or zinc-alloy coating.

A pre-coated steel sheet wherein at least a region at the periphery ( 7 ) of at least one ( 6 a, 6 b ) of the opposite faces ( 6 a , 6 b ) of said pre-coated sheet ( 1,1′ ) is coated with an additional coating ( 8 ) selected for increasing the vapor pressure between the pre-coating ( 2 ) and said additional coating ( 8 ) during a laser welding method up to a critical pressure at which the pre-coating ( 2 ) is ejected away from the weld ( 14 ). Preferably, the vaporization temperature of the additional coating ( 8 ) is greater than the vaporization temperature of the pre-coating ( 2 ) and the additional coating includes gammagene elements like carbon and/or nickel. A steel part obtained by laser welding, preferably butt laser welding, of at least a first and second pre-coated steel sheet ( 1,1′ ) as above indicated is also provided.

Method for producing a precoated steel blank including the successive steps of: —providing a precoated steel strip including a steel substrate having, on at least one of its main faces, a precoating, the precoating including an intermetallic alloy layer and a metallic layer extending atop said intermetallic alloy layer, the metallic layer being a layer of aluminum, a layer of aluminum alloy or a layer of aluminum-based alloy, —laser cutting the precoated steel strip in order to obtain at least one precoated steel blank, the precoated steel blank including a laser cut edge surface resulting from the laser cutting operation, the laser cut edge surface including a substrate portion and a precoating portion, wherein the laser cutting is carried out in such a way that the substrate portion of the laser cut edge directly resulting from the cutting operation has an oxygen content greater than or equal to 15% in weight.

A pre-coated steel substrate coated with optionally, an anticorrosion coating and a pre-coating including at least one titanate and at least one nanoparticle, the steel substrate having a reflectance higher or equal to 60% at wavelengths between 6.0 and 15.0 μm.

A pre-coated steel substrate coated with: —optionally, an anticorrosion coating and —a flux including at least one titanate and at least one nanoparticle chosen from: TiO2, SiO2, Yttria-stabilized zirconia (YSZ), Al2O3, MoO3, CrO3, CeO2 or a mixture thereof, the thickness of the flux being between 30 and 95 μm.