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c. The yield and tensile strengths of the normalized 100-70-03 grade increased significantly with respect to the as-cast 100-70-03 grade in both the 25 mm and 76 mm section sizes.


d. The ductility of 25 mm as-cast samples of the 100-70-03 grade did not change when they were normalized.


e. The ductility of the normalized 76 mm samples was significantly lower than the 25 mm samples of the 100-70-03.


f. The quenched and tempered grade 120-90-02 had a significantly higher yield strength at the same ductility of the pearlitic 100-70-03 grade.


4. The cyclic properties of the grades obeyed expecta- tions as follows: a. As compared to the lower strength grades, the


higher strength grades had lower fatigue lives in the low cycle regime and higher fatigue lives in the high cycle regime.


b. As compared to the lower ductility grades, the higher ductility grades had higher fatigue lives in the low cycle regime and lower fatigue lives in the high cycle regime.


c. These predicted trends were observable, but only showed significance for the extremes, i.e., the differences in fatigue lives were only significantly greater than the range of the data for the two extreme conditions (the 60-40-18 and 120-90-02 grades).


5. No observable difference in transition (between the low and high cycle or plastic and elastic) fatigue life was observed.


Figure 22. Total strain-life fatigue curves are shown for the two heat treated ferritic-pearlitic grades with corresponding as-cast conditions. The points are actual data for three selected grades and the curves are the predicted lives from constants. The values in parentheses in the legend are the measured monotonic properties and ferrite contents. In most conditions, the heat treatments did not significantly affect the predicted fatigue life for the as-cast condition, although similar strength and ductility trends to those shown in Figure 21 were observed. It is noteworthy that the normalized 25 mm samples of grade 100-70-03 exhibited significantly greater monotonic strength and fatigue resistance in both the low and high cycle regime.


Figure 23. Predicted stress-life fatigue curves are shown as a function of grade and display the expected trends for all eight selected conditions. The higher strength grades exhibit greater lives at high cycles and decreased lives in the low cycle regime. The values in parentheses in the legend are the measured monotonic properties and ferrite contents.


International Journal of Metalcasting/Spring 2012


21


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