Executing Organisation: Bavarian Research Foundation
Heat resistant materials often have to be combined with cast materials, which leads to weld defects due to the high carbon content of the cast and the different thermal material properties. As there are no results of laser beam welding of heat resistant steel with cast steel without filler material and of the influence of the component layout, the aim of this project was set to analyze these two issues. Without usage of filler material there is a risk of cold cracks in the seam that are caused by hardness increase due to high carbon content as well as hot cracks caused by the high nickel content of some materials. Hence, the melt’s intermixture and heating and cooling rates must be studied.
One approach is to develop processing measures which enable an active change of the weld metal composition and metallurgical structure in weld metal and heat affected zone to avoid cold and hot cracking. Besides the development of process measures to systematically influence the intermixture of joining partners, laser based strategies of pre and post heating as well as inductive heating is planned to investigate regarding the temperature distribution in weld metal and heat affected zone.
By additional heat treatment during welding, the cooling rate, consequently the martensite content and the risk of cold cracking can be lowered. With regard to the global inductive pre- and post heating, it has been shown that not all material combinations could be welded without defects and, that the housing loses its dimensional stability during inductive heating, depending on the material. Overall, the inductive pre and post heating has not proven due to the lack of extra profit and the partly low dimensional stability. Compared with the laser based heat treatment, the heat in this strategy could only be introduced with low penetration and globally. In the case of local laser based pre and post heating, the defocused heat treatment with regard to the seam surface, crack and pore minimization proved to be the best of three investigated strategies, see figure. Since the weld quality was always the highest for all material combinations for the defocused heat treatment, the findings can very probably also be applied to other materials.