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Table 5 contains predictions and Figure 22 shows a plot of the total strain versus predicted fatigue cycles for the two heat treated ferritic-pearlitic grades (60-40-18 and 100-70- 03), which had corresponding as-cast conditions. The cyclic properties of the heat treated grades generally obeyed expec- tations as follows:


1. In most conditions, the heat treatments produced greater low cycle fatigue lives for high ductility conditions


2. Although the high cycle fatigue resistance was af- fected less by heat treatment, slightly increased high cycle fatigue lives were obtained with higher strength conditions.


3. The normalized 25 mm samples of grade 100- 70-03 exhibited significantly greater monotonic strength as well as fatigue resistance in both the low and high cycle regime.


Table 5 contains predictions and Figures 23 and 24 respec- tively show predicted stress-life and plastic strain-life fatigue curves as a function of grade. Table 4 shows no observable trends in transition fatigue life.


Summary and Conclusions


1. This paper reviewed the contents and architecture of the AFS strain-life fatigue database for cast iron.


2. As expected, the monotonic a. Yield strengths of the ferritic, ferritic-pearlitic, and pearlitic irons decreased with increasing elongation,


b. Hardness, yield strength and tensile strength increased with decreasing ferrite content.


c. Ductility increased with increasing ferrite content. d. Elastic modulus and Poisson’s ratio were virtually identical for all the tested conditions.


3. The monotonic mechanical properties were altered with heat treatment for the 60-40-18 and 100-70-03 grades as follows: a. The yield and tensile strengths of as-cast grade 60-40-18 decreased slightly with subcritical annealing and decreased significantly with full annealing.


b. The ductility of as-cast grade 60-40-18 hardly changed with subcritical annealing; however, significant increases in ductility were obtained with full annealing.


Table 5. Predicted Fatigue Lives from ∆εT


/2 = (σ’f


/E) (2Nf)b + (ε’f


) (2Nf)c


for Selected Database Conditions


20


International Journal of Metalcasting/Spring 2012


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