METHOD FOR WELDING USING POINTS OF MARTENSITIC STAINLESS STEEL SHEETS

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Method for welding two 0.10 to 6.0 mm thick steel sheets having the following composition : 0.005 % ≤ C ≤ 0.3 %; 0.2 % ≤ Mn ≤ 2.0 %; traces ≤ Si ≤ 1.0 %; traces ≤ S ≤ 0.01 %; traces ≤ P ≤ 0.04 %; 10.5 % ≤ Cr ≤ 17.0 %; traces ≤ Ni ≤ 4.0 %; traces ≤ Mo ≤ 2.0 %; Mo + 2 x W ≤ 2.0 %; traces ≤ Cu ≤ 3 %; traces ≤ Ti ≤ 0.5 %; traces ≤ Al ≤ 0.2 %; traces ≤ O ≤ 0.04 %; 0.05 % ≤ Nb ≤ 1.0 %; 0.05 % ≤ Nb + Ta ≤ 1.0 %; 0.25 % ≤ (Nb + Ta)/(C + N) ≤ 8; traces ≤ V ≤ 0.3 %; traces ≤ Co ≤ 0.5 %; traces ≤ Cu + Ni + Co ≤ 5.0 %; traces ≤ Sn ≤ 0.05 %; traces ≤ B ≤ 0.1 %; traces ≤ Zr ≤ 0.5 %; Ti + V + Zr ≤ 0.5 %; traces ≤ H ≤ 5 ppm; traces ≤ N ≤ 0.2 %; (Mn + Ni) ≥ (Cr -10.3 - 80 x [(C + N)2]); traces ≤ Ca ≤ 0.002 %; traces ≤ rare earths and/or Y ≤ 0.06 %; the remainder being iron and impurities resulting from the production process; the temperature (Ms) of the sheet being ≥ 200 °C; the temperature (Mf) of the sheet being ≥ -50 °C; the microstructure of the sheet containing at most 0.5 % of carbides and at most 20 % of residual ferrite, the remainder being martensite; characterised in that it comprises the following steps, with (e) being the thickness of each of said sheets or of the thinnest one of said sheets : a first welding step, with a duration (t) in ms : for thicknesses (e) of 0.10 to 0.50 mm, t = (40 x e + 36) ± 10 %; for thicknesses (e) of 0.51 to 1.50 mm : t = (124 x e - 13) ± 10 %; for thicknesses (e) of 1.51 to 6.0 mm : t = (12 x e + 47) ± 10 %; and with a clamping force (F) in daN : for thicknesses (e) of 0.10 to 1.50 mm : F = (250 x e + 90) ± 10 %; for thicknesses (e) of 1.51 mm to 6.0 mm : F = (180 x e + 150) ± 10 %, during which step a current is applied between the welding electrodes, the intensity of said current being between 80 and 100 % of the maximum authorised intensity corresponding to the expulsion of melted metal; a second step with the intensity being between zero and 1 kA; and a third step with the intensity being from 3.5 kA to 4.5 kA, over a duration of at least 755 ms.