CD-Laboratory for Materials Modelling and Simulation, Module 7: Process advance of heavy steel component casting by reduction of hot-tear-defect-volume

Creep resistant cast steels are used for high temperature components of power stations and other plants, in order to combine improved static and dynamic strength and economic manufacturing. The current loading of components in modern power plants is characterised by increased cyclic service conditions. Consequently, the optimisation of component geometry in combination with the improvement of the casting technique, the improvement of the inspection technique, including the realistic evaluation of non destructive findings, as well as knowledge of material dependent damage mechanics is required. In the steel foundry Linz products are casted up to a weight of 200 tons, with very complex geometry. Due to physical and chemical processes during the solidification, typical casting defects can arise, such as oxide film, grain boundary cracks, moulding material inclusions and volume defects, i.e. micro-pores, shrink holes and hot tears. The defect areas are removed separately from the casting and repaired by welding. As the repair procedure is rather costly and time-consuming, the defect-ratio is an important quality index. These natural defects, in particular hot tears or healed hot tears with segregation zones, occur despite of the improvement of the manufacturing quality. If of critical size and in critical places of higher stressed areas they can lead to failure due to crack growth. Therefore, in addition to the improvement of non destructive testing methods with regard to the reliable determination of size, position and distribution of defects in components, it is necessary to create methods to evaluate the acceptance of potential manufacturing flaws in the castings with specific consideration of the actual loading situation.