Cyclic material behavior of repair welded thick-walled nodular cast iron for wind energy application

Large cast components made of nodular cast iron for wind energy turbines and heavy industry are usually not completely free of local material defects. Nevertheless, only the position, size and type characterize the defects and the reduction in cyclic material behavior and lifetime to be expected. Especially local defects at the components surface or near the surface lead to negative effects on lifetime, when high surface stresses and sharp notches or stress gradients are present in the component. But in any case, foundries strive for reducing their component rejects especially when it comes to wind energy components with masses up to several tens tons. Thus, even components with small surface or near-surface defects need to be brought into usage. One measure is to determine the defect characteristics and remove the defect by a defined manufacturing and a subsequent welding process. This procedure is common for steel castings and part of the production process but usually not accepted by certification bodies for wind energy components made of nodular cast iron. Within a research project called “nodularWELD” the possibilities of welding of EN-GJS-400-18LT were investigated. After a welding process with different welding electrodes on large cast blocks with pre-manufactured defects the quasi-static and cyclic material behavior of the base material and the welding filler material was determined. Additionally integral samples containing base material, the heat transfer zone and the welding filler material were investigated. The results are used to determine the cyclic material behavior of the cast component and to obtain a lifetime assessment concept for practical application.