Development of high-strength cast steel for the design of optimised light weight hybrid constructions

The project had the aim to develop a new cast steel for offshore applications with an improved fatigue behaviour, when compared to other cast steels. This could be carried out successfully within a cooperation of Thyssen Guß AG (Mülheim, Germany), University of Vienna (Vienna, Austria), and the Fraunhofer-Institut für Betriebsfestigkeit (Darmstadt, Germany). Generally, the fatigue performance of an offshore construction can be enhanced significantly, if the welded connections in the critical regions are replaced by cast steel inserts with a smooth geometry, as this method enables a reduction of stress concentrations in critical zones. The newly developed high-strength cast steel GS - 12 MnMo 7 4 shows a further improvement in fatigue strength, when compared to other cast steels like the GS - 8 Mn 7, that was used for cast inserts so far (Christianus et al., 1991). This improvement can only be achieved, if internal defects like pores or shrinkages can be avoided. Otherwise, only a sligh t improvement is possible. The crack propagation rate of the steel GS - 12 MnMo 7 4 is lower than that for the CS - 8 Mn 7. Data obtained on specimens could he transferred successfully to estimate the fatigue behaviour of nodes in offshore structures.