Fig. 3. Calculated and measured nodularity are compared for the step casting and crankcase. All values provided by the simulation are within the measurement tolerance of the measured samples.
Fig. 4. Shown is an example of measured S-N curves for ductile iron with two different pearlite contents.
lidified. During the following cooling process, the diffusion of alloying ele- ments within the austenite is consid- ered to predict the amount of graph- ite. Te additional consideration of segregation effects of alloying elements allows for the accurate prediction of ferrite and pearlite growth during the eutectoid phase transfer. Te calcula- tion of cooling conditions below the eutectoid phase transformation leads to the prediction of phase ratios of the matrix (ferrite/pearlite ratio, pearlite packaging). With this, it is possible to predict the static local mechanical properties over the entire casting.
Experimental Research to Locally Couple Microstructure and Expected Lifetime
Te framework of this research project included the evaluation of
major microstructure characteristics of a ductile iron (GJS-400) and a com- pacted graphite iron (GJV-450) and their impact on component lifetime. For GJS-400, the impact of its ferrite/ pearlite ratio was evaluated. For GJV- 450, its nodularity and pearlite content were evaluated. Both characteristics can be predicted locally with casting process simulation. Te consideration of inclusions and oxides was excluded on purpose in this research project. To realize a complete chain of
information, both materials un- derwent comprehensive cyclic load testing using tension–compression and cyclical bending tests for various microstructures. In order to develop a represen-
tative correlation between micro- structure and component lifetime, typical microstructures found in the
relevant castings were used in the test pieces. Due to the required sizes of the test pieces, only a limited amount of pieces could be derived from the castings (windmill bed- plate/frame, bearing support, and crankcase). Therefore, additional test castings were poured (Figure 2). Te different melts were dialed in
by the research partners in a manner to achieve typical variations in nodular- ity for compacted graphite iron (CGI) found in crankcases. Te different wall thicknesses in castings and test castings led to sufficient variation in ferrite/pearlite ratios for the gray iron. Te samples were machined and polished to exclusively evaluate the influ- ence of the microstructure on the lifetime performance. Te impact of the casting surface was not part of this research. Te fatigue test runs were per-
Fig. 5. Calculated durability values shown here as a function of the local microstructure prediction can be transferred into life- time analysis programs.
Fig. 6. The most stressed areas of the crankcase are in color.
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