Tensile, Compression and Fracture Properties of Thick-Walled Ductile Cast Iron Components

Abstract

The article presents the outcome of a comprehensive program of tensile, compression and fracture toughness experiments, addressing thick-walled ductile cast iron inserts used for the production of three nuclear waste canisters. The resulting data are required as input to the assessment of the failure probability of the canisters. Moreover, these data are useful for the improvement of the casting technique as such. Although the same material specification is always used, material properties are found to show significant variation. Considerable attention is paid to linking the scatter in tensile properties to fractographic and microstructural observations. The main finding is that low ductility tensile test results can be primarily connected to the presence of specific casting defects, from which oxide films have the most detrimental effect. Another important observation is that compression experiments do not result in low ductility failure. During fracture testing, stable ductile crack propagation is observed. Basic fracture analysis of a tensile test is performed in order to better understand the effect of defect size, stress-strain behavior and fracture toughness on the ductility measured through tensile testing. Two opposing specimen size effects are observed.

Fatigue and Fracture Resistance of Heavy-Section Ferritic Ductile Cast Iron

“…It can be noted that the very long solidification time and the resulting microstructural alterations lead to low values of tensile strength and total elongation in comparison to conventional ferritic DCI; for instance, with respect to thick-walled (t > 60 mm) EN-GJS-400-15, the reduction in tensile strength and total elongation is about 20% and 75%, respectively. The yield-stress-to-tensile-strength ratio approaching the unity further denotes a very brittle material behavior, while, as expected, the yield stress is little affected [4], being the yield stress compliant with the minimum prescription of 240 MPa for EN-GJS-400-15. The results of the rotating bending fatigue tests are summarized in Table 4.…”

“…Casting large volume parts of weight on the order of tens of tons is particularly critical as the control of the final microstructure is rather difficult [3][4][5]. Consequently, solidification defects cannot be completely avoided, their presence must be somehow tolerated and different strategies are pursued to limit their detrimental effects.…”

Effects of Silicon on Mechanical Properties and Fracture Toughness of Heavy-Section Ductile Cast Iron

“…Karsay and E. Campomanes [4][5][6][7][8][9] studied the influence of silicon content on ductile iron, and found that lower silicon content can reduce the performance of chunky graphite iron, especially in its capacity to demonstrate good impact performance at low temperatures. The proper content of silicon can increase the nodularity and improve the mechanical properties of heavy section ductile iron, and inhibit graphite floatation and chunky graphite formation [10][11][12][13].…”

Microstructure influence on fatigue behaviour of nodular cast iron

“…The nodular cast iron grade EN-GJS-400-18-LT, in which graphite spheroids or nodules in a ferritic matrix provide large ductility and fatigue strength, is widely used. Specific shape of the graphite in the ferritic microstructure acts as the crack arrester and lowers the stress intensity in front of the crack, which makes it an appropriate material for such cyclically loaded structures [1][2][3][4][5]. Therefore, in order to prevent catastrophic failures and to prolong the service lifetime of wind turbine structures, it is important to consider the influence of the graphite nodule geometrical features (size, shape and distribution of nodules) on the fatigue crack initiation and propagation at the root of a geometrical discontinuity and local notches.…”