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This investigation deals with the fatigue properties and material parameters for a silicon alloyednodular cast iron. The material follows the Swedish standard SS 140725. The objectives for thisinvestigation where to evaluate properties of the material in a fracture mechanic sense of view. Inthis first part, the attention was paid to the basic fracture mechanic properties, i.e. da/dN-curvesand Paris law parameters. It also include R-dependence behaviour evaluated for R-values fromR= 0 to R= 0,8. The main incitement for using the closure free approach is that it produces thefastest crack propagation rate that can be found at given conditions and load levels. This paper isthe first part of the investigation of the silicon alloyed nodular iron SS 140725 and will befollowed by subsequent parts. The investigation in total is a part of the nordic project “CastDesign 2005”.