Method for preparing metal sheets which are intended for producing a welded steel blank, comprising the successive steps according to which: - there are supplied at least one first and one second pre-coated steel sheets, formed from a substrate made of thermally treated steel (25, 26), which are able to undergo a martensitic or bainitic hardening after an austenitisation treatment, and from a pre-coating (15, 16) formed from a layer of intermetallic alloy (17, 18) in contact with said steel substrate, surmounted by a metallic layer of aluminium or aluminium alloy or based on aluminium (19, 20), said at least one first metal sheet comprising a main face, an opposite main face, and at least one secondary face, said at least one second metal sheet comprising a main face, an opposite main face, and at least one secondary face, characterised in that, after the supply: - there are positioned said at least one first and second metal sheets, leaving a clearance between 0.04 and 2 mm between said at least one secondary face and which are placed one opposite the other, the positioning of said at least one first and second metal sheets defining a median plane which is perpendicular to the main faces of said at least one first and second metal sheet, then - there are removed by melting and vaporisation, simultaneously on at least said main face and said main face, said layer of metallic alloy in a peripheral zone of said at least one metal sheet, and said layer of metallic alloy in a peripheral zone of said at least one metal sheet, said peripheral zones and being the zones of the main faces and which are nearest relative to said median plane situated on both sides relative to the latter. - there are supplied at least one first and one second pre-coated steel sheets, formed from a substrate made of thermally treated steel (25, 26), which are able to undergo a martensitic or bainitic hardening after an austenitisation treatment, and from a pre-coating (15, 16) formed from a layer of intermetallic alloy (17, 18) in contact with said steel substrate, surmounted by a metallic layer of aluminium or aluminium alloy or based on aluminium (19, 20), said at least one first metal sheet comprising a main face, an opposite main face, and at least one secondary face, said at least one second metal sheet comprising a main face, an opposite main face, and at least one secondary face, characterised in that, after the supply: - there are positioned said at least one first and second metal sheets, leaving a clearance between 0.04 and 2 mm between said at least one secondary face and which are placed one opposite the other, the positioning of said at least one first and second metal sheets defining a median plane which is perpendicular to the main faces of said at least one first and second metal sheet, then - there are removed by melting and vaporisation, simultaneously on at least said main face and said main face, said layer of metallic alloy in a peripheral zone of said at least one metal sheet, and said layer of metallic alloy in a peripheral zone of said at least one metal sheet, said peripheral zones and being the zones of the main faces and which are nearest relative to said median plane situated on both sides relative to the latter. - there are positioned said at least one first and second metal sheets, leaving a clearance between 0.04 and 2 mm between said at least one secondary face and which are placed one opposite the other, the positioning of said at least one first and second metal sheets defining a median plane which is perpendicular to the main faces of said at least one first and second metal sheet, then - there are removed by melting and vaporisation, simultaneously on at least said main face and said main face, said layer of metallic alloy in a peripheral zone of said at least one metal sheet, and said layer of metallic alloy in a peripheral zone of said at least one metal sheet, said peripheral zones and being the zones of the main faces and which are nearest relative to said median plane situated on both sides relative to the latter.