Overall description of main R&D challenges

• The mechanical properties of cast irons depend upon the microstructure and alloying and alloying additions. The material microstructure varies with the cooling rate, which is very inhomogeneous in thick walled wind turbine components. Thus, documenting the microstructure distribution and hence the distribution mechanical properties is a demanding R&D task. For practical and economical reasons it is impossible to do experimental casting and mechanical testing of real world wind turbine components, since their weight is very high, perhaps 25 tonnes. Machining of only one specimen would ruin a realistic research budget. A main R&D challenge for this type of goods is therefore to develop intelligent testing methods and mathematical models which can be applied to develop new knowledge and documentation of the relationship between alloying elements, trace elements and fatigue properties. In the optimal ductile iron the graphite will be present as spheroids with a well balanced size distribution in a ferritic matrix. In thick walled ductile iron components it is a challenge to control the microstructure that develops during solidification and subsequent cooling:
• Deformed graphite spheroids may be formed and significantly affect the component fatigue properties.
• Small concentrations of subversive elements such as Antimony, Lead and Titanium will contribute to the formation of deformed graphite.
• Balanced additions of rare earth metals (REM) may be used to counter act deformation of graphite and thus have a positive effect on the component fatigue properties.

Main goals

• To optimize nucleation conditions and microstructure in the used ductile iron based on additions of alloying and trace elements through innovative use of existing melt treatment.