Investigations on Laser Beam Welding Dissimilar Material Combinations of Austenitic High Manganese (FeMn) and Ferrite Steels

Abstract

For the past few years the customer's demand for more fuel efficient and at the same time safer vehicles has steadily increased. Consequently, light weight design has become one of the main interests in engineering. With regard to sheet metal components, a new class of high manganese steels, based on the TWIP (twinning induced plasticity) effect, provides the opportunity of shaping light weight designed thin and complex sheet metal geometries with advanced crash performance. In terms of weldability, due to their thermo-physical properties (high content of C, Mn, Al, Si), FeMn steels have to be handled differently in comparison to conventional steel grades. Particularly dissimilar material combinations of FeMn and ferrite steels are in the center of interest for industrial applications. This study reveals that metallurgical properties of dissimilar welding seams can be influenced considerably by laser beam welding, resulting in a change of the mechanical properties of the seam which is practicable without using filler material as described in (Flügge et al., 2011).

Method for evaluating the behavior of laser welded dissimilar material seams in single overlap configuration under impact loads by the example of twinning induced plasticity steels

“…As already described in Ref. 6, the reason for this behavior can be found in the favorable distribution of fingerlike martensitic structure in the outer regions of the seam.…”

“…That this may not always be the case for every testing condition has been shown in Ref. 6. In the cited study, the through welded TWIP/S420MC combination containing martensitic structure in the weld plane (3 m/min) shows a better performance than an austenitic joint (8 m/min) under quasi static loads, due to its favorable distribution.…”

“…This applies even more to those joints whose mechanical properties vary significantly by the changing the process parameters, as in the case of laser welded seams of TWIP and low carbon steels. 5,6 Conventionally, Charpy-V specimens are widely used for testing the impact strength of weld seams joined in a butt configuration. In order to evaluate the impact strength of a seam, a V-notch is very precisely machined into the weld metal, so that the crack will start, spread, and end within the seam.…”

“…For dissimilar material combinations, testing the right seam configuration is of major importance, because it is not only the mixing ratio of both joining partners that influences the mechanical properties of the seam but also the joint configuration combined with weld pool dynamics, influencing the distribution of weld metal structure and thus the seam properties. 6 Due to the described circumstances, Charpy specimens are of limited suitability for testing the impact strength of laser welded specimens especially for dissimilar material combinations joined in overlap configuration.…”

“…As prior studies 5,6 have shown that process parameters influence the mechanical properties of laser welded TWIP seams under quasistatic loads, it is the task of this study to examine the strength of the seams under dynamic loads. For this purpose, a Charpy impact test based method has been used for examination of mechanical properties of single overlap joints under dynamic loads.…”