An investigation on the fatigue strength of repair welded nodular cast iron for heavy sections

Large cast components made of nodular cast iron for heavy industry and wind energy turbines are usually not completely free of local material defects. In the case those material defects occur locally and near the component's surface this will lead to negative effects on lifetime, when high surface stresses and sharp notches or stress gradients are present and interact. One measure to bring the components into usage for foundries is to determine the defect characteristics and remove the defect by a defined manufacturing and a subsequent welding process. Nevertheless, repair welding is not accepted by certification bodies due to a lack of knowledge of the cyclic material behavior of repair welded nodular cast iron. Within the research project “nodularWELD” the possibilities for welding thick-walled nodular cast iron are investigated on ferritic, ferritic silicon solid-solution strengthened and pearlitic cast iron grades. Afterwards the welded cast materials are subjected to cyclic stress based fatigue tests to determine the influence of the welding in comparison to the base material. Particularly, in the presented paper a comparison of the resulting fatigue strength of ferritic EN-GJS-400-18LT, ferritic silicon solid-solution strengthened EN-GJS-450-18 and EN-GJS-700-2 is conducted. The comparison is done for the base material and the welded condition by the help of axial and bending specimens. For the investigated material conditions, the results show reduction in the fatigue strength for axial loading for EN-GJS-400-18LT and EN-GJS-700-2 by about 30 % while the silicon solid-solution strengthened EN-GJS-450-18 dropped down to around 25 % of the fatigue strength of the base material.