the graphite morphology. This encourages investigation to estimate the crack resistance based on graphite mor- phology parameters.
crack initiation toughness parameter Ji/EP
Influence of Loading Rate, Microstructure and Temperature on Fracture Mechanical Toughness Properties of DCI
Quasi-Static Loading
As already outlined in the introduction, fracture mechanics testing of DCI under quasi-static loading can be performed using the appropriate standards for metallic materials. Ac-
is sensitive to
cordingly, Figure 11 shows crack resistance curves of ferrit- ic DCI materials with varying graphite morphology (mean curves of at least three specimens). 25
The figure addition-
ally includes a DCI material with chunky graphite degen- eration (GGG-40/C) and a malleable cast iron (GTS-35). It is demonstrated by the crack resistance curves as well as the deduced crack initiation toughness values (Figure 12) that the quasi-static crack resistance increases significantly by increasing roundness (shape factor) and increasing par- ticle size. As indicated by the values at -40°C, decreasing temperature did not dramatically influence the crack initia- tion toughness. Nevertheless, the result of GGG-40/4AZ underlines that a large ferrite grain size in the matrix may deteriorate the low temperature toughness behavior.
Figure 9. Mechanical properties and ferrite grain size in dependence on the graphite particle diameter. 25
Figure 10. Mechanical properties and quasi-static crack initiation toughness Ji/EP
(determined by DC potential
drop technique) in dependence on the product of graphite particle shape and distance.25
Figure 11.
Crack resistance curves of ferritic DCI
materials with varying graphite morphology, quasi-static loading, room temperature, SE(B)10 specimens, 20% sidegrooving.25
30
materials with varying graphite morphology, quasi-static loading, SE(B)10 specimens, 20% sidegrooving.25
Figure 12. Crack initiation toughness Ji/EP International Journal of Metalcasting/Volume 8, Issue 2, 2014 of ferritic DCI
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