Non homogenous microstructure of cast iron components - challenge for fatigue evaluation of non-destructively tested "defect free" components

The design of cyclically stressed cast iron components requires the knowledge about the non homogenous microstructure. Even 'defect free' non-destructively tested (NDT) components can show significant differences in cycle life. Typically structures are stressed by varying stress fields. Experimental and calculative fatigue evaluation methods have to take the interaction between varying stress fields and varying strength fields into account in order to deliver reliable fatigue life estimations in service. Only reliable fatigue evaluation methods can be the basis of optimized design, manufacturing and quality management of cast iron components. In the paper a method is presented which fulfils these requirements and paves the way for a localized fatigue evaluation of nodular and vermicular cast iron components. This method can be applied by means of cast simulation or image analyses of microsections. It was developed by microstructure analyses, fatigue tests on specimens w ith varying nodular and vermicular microstructure and proved out by measurements and tests on components. The dependencies were described by multivariate correlations.