Literature search - Deteriorated Graphite Structures on Cast Iron Skins

The fatigue strength offerritic ductile iron, Grade EN-GJS-400-18U-LT. was determined for large section castings measuring 4 by 24 by 24 inches. Fatigue testing was conducted in bending fatigue in order to determine the influence of surface conditions on fatigue strength. Test specimens with various surface conditions were evaluated, including notched and un-notched specimens, as well as those containing surface defects typical of heavy section ductile iron castings. In addition, smaller, round axial fatigue test specimens were tested to produce the more typical laboratory fatigue test properties for comparison with other materialS tested for the Ductile Iron Society. Bending fatigue testing was conducted on two groups of specimens. A large number of specimens of intermediate size and obtained from the drag surface were tested to evaluate the effects of surface condition and notch sensitivity. Those specimens were nominally 1.6 in. thick by 2.0 in. wide by 12 inches long. Various notches were machined into the surface of the bars including U notches and V notches. The second group of bars consisted of large test specimens measuring 3.1 by 3.5 by 24 inches long and which were obtained from the cope surface. Some of these test bars were prepared with hand-ground notches that are blended with the cast surface to simulate the normal repair conditions obtained in commercial castings after removing dross and slag indications. Most of the testing was conducted at loads that produced failure so that the fatigue strength in the finite life region could be characterized. In this manner the sensitivity of the material to notches and surface defects could best be evaluated. Only a limited number of large fatigue bars could be tested, and fatigue testing in the finite life region was best for this reason.