Method for spot welding of martensitic stainless steel sheets

Abstract

Method for welding two steel plates having a thickness of 0.10 to 6.0 mm and having the following composition: 0.005% ≤ C ≤ 0.3%; 0.2% ≤ Mn ≤ 2.0%; trace ≤ Si ≤ 1.0%; trace ≤ S≤0.01%; Trace ≤P≤0.04%; 10.5%≤Cr≤17.0%; Trace ≤Ni≤4.0%; Trace ≤Mo≤2.0%; Mo+2×W≤2.0%; Trace ≤Cu ≤3%; Trace ≤Ti≤0.5%; Trace ≤Al≤0.2%; Trace ≤O≤0.04%; 0.05%≤Nb≤1.0%; 0.05%≤Nb+Ta≤1.0%; 0.25%≤( Nb+Ta) / (C+N)≤8; Trace ≤V≤0.3%; Trace ≤Co≤0.5%; Trace ≤Cu+Ni+Co≤5.0%; Trace ≤Sn≤0.05%; Trace amount≤B≤0.1%; trace amount≤Zr≤0.5%; Ti+V+Zr≤0.5%; trace amount≤H≤5ppm; trace amount≤N≤0.2%; (Mn+Ni)≥(Cr‑10.3– 80×[(C+N) 2 ]); trace ≤ Ca ≤ 0.002%; trace ≤ rare earth elements and / or Y ≤ 0.06%; the rest is iron and impurities produced in the production process; the temperature of the steel plate (Ms) ≥ 200 ° C; the temperature of the steel plate (Mf )≥‑50°C; the microstructure of the steel plate contains not more than 0.5% of carbides and not more than 20% of residual ferrite, the rest being martensite; characterized in that it comprises the following steps: a first welding step, continuing Time is (t) in ms and has clamping force (F) in daN: for thickness (e) from 0.10 to 0.50mm: t=(40×e+36)±10%; for 0.51 to Thickness (e) of 1.50mm: t=(124×e–13)±10%; for thickness (e) of 1.51 to 6.0mm: t=(12×e+47)±10%; for 0.10 to 1.50mm For the thickness (e) of 1.51mm to 6.0mm: F=(180×e+150)±10%, where (e) is the the thickness of each of the above-mentioned steel plates or the thickness of the thinnest steel plate among them; in this step, an electric current is applied between the welding electrodes, the strength of which is 80% to 100% of the maximum permissible strength corresponding to the discharge of molten metal; A second step with an intensity of 0 to 1 kA; and a third step with an intensity of 3.5 kA to 4.5 kA for a period of at least 755 ms.

Description

technical field [0001] The present invention relates to the iron and steel industry, and more particularly to methods for spot welding steel plates. Background technique [0002] Hot-worked martensitic stainless steel sheets with adjustments in composition, initial microstructure, and heat treatment parameters that allow obtaining high mechanical properties and a strong capability for complex forming are known. Such steel sheets are described in the Applicant's document PCT / IB2017 / 051636 and are mainly used in the automotive industry. [0003] In terms of weight percent, their composition is as follows: [0004] 0.005%≤C≤0.3%; [0005] 0.2%≤Mn≤2.0%; [0006] Trace ≤Si≤1.0%; [0007] Trace ≤ S ≤ 0.01%; [0008] Trace ≤ P ≤ 0.04%; [0009] 10.5%≤Cr≤17.0%; preferably, 10.5%≤Cr≤14.0%; [0010] Trace amount≤Ni≤4.0%; [0011] Trace amount≤Mo≤2.0%; [0012] Mo+2×W≤2.0%; [0013] Trace ≤ Cu ≤ 3%; preferably, trace ≤ Cu ≤ 0.5%; [0014] Trace ≤Ti≤0.5%; [0015] Trace ≤ Al...

AI Technical Summary

Problems solved by technology

[0044] It is possible to improve the results by varying the welding parameters, i.e. by adding an afterheating pulse to the standard welding cycle (usually used for martensitic steels), but so far the optimizations performed have not resulted in welds with a duration of less than 5 s cycle for satisfactory weld quality

This is too long for vehicle manufacturers who must be able to weld these plates, and they must be mindful of the productivity constraints they face when used in the series production of vehicles

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