Investigation on joint characteristics of laser beam welded press hardenable ultra-high strength steels with ferritic-martensitic and martensitic microstructure

The introduction of stainless ultra-high strength steels with ferritic-martensitic and martensitic microstructure into sheet metal manufacturing depends on proper welding processes for these steel grades. The chromium and carbon content as well as the lack of appropriate process information for thermal joining of these steel grades in press hardened condition with UTS of up to 2.000 MPa at 15 % fracture strain classifies the weldability of these materials as limited. Efficient heat control and minimum heat input enable the welding of ferritic-martensitic and martensitic stainless steels by laser beam. This paper presents the results of strength evaluations of laser welded joints for the steel grades 1.4003, 1.4021, and 1.4034 in similar and dissimilar combinations with already established steels. By maintaining optimal welding conditions with pre- and postheating, and with respect to the testing angle and speed, press hardenable steels with ferritic-martensitic and martensitic microstructure overtop joining strength of already established 1.5528 by approx. 20 %. The paper gives an overview of the press hardening conditions, the welding parameterization, the welding seam hardness profiles for different steel-combination-arrangements, and the selected force-displacement-behavior. The paper finalize with a comparison of joint properties for considered material combinations for simple one-joint-specimen and complex structure specimen.