Analysis of the Fatigue Data of All Grades of Continuously Cast Ductile Iron Bars 2008-01-0701
Continuously cast ductile iron bars are practically free from shrinkage defects. The fatigue behavior of continuously cast ductile iron bars is, therefore, expected to be superior. Different grades of ductile iron (ASTM A536-84) are based on the mechanical properties. This paper analyzes the previously reported fatigue results with respect to the pearlite content in the matrix of the fatigue samples. Interesting findings from this analysis are as followed:
From bar size to bar size the fatigue limits varied a little within a grade of ductile iron. In the case of ASTM 65-45-12 (4512 DI) and 80-55-06 (5506 DI) grade ductile irons the variation of fatigue life was somewhat larger especially at stresses around or above the yield points of the metals. Fatigue ratios of 4512 DI were the highest and the ASTM 100-70-03 (7003 DI) grade ductile irons the lowest. The rate of increase of fatigue limits is lower than the rate of increase of tensile strengths among all continuously cast ductile iron grades when these irons are arranged in increasing order from lowest tensile strengths to highest tensile strengths. The correlation plots of pearlite with respect to fatigue lives and fatigue ratios show a high R squared value implying that there is a stronger effect of pearlite on these values. Increased pearlite content increased the number of fatigue failure cycles at a given stress level in both samples of edge region and in samples of mid-radius region.