Interdendritic graphite (e.g. D graphite according to EN 20945, Figures 1
and 2) in hypereutectic cast iron (s. a. graphite classification chart) That becomes visible in metallographic specimen in the form of a cohesive net. Strictly speaking, this is not graphite degeneration yet; but at least unfavourable graphite distribution which will have a massive influence on the dynamic and mechanical properties of the material.
Additional references:
Graphite degeneration
Flake graphite cast iron
Nodular graphite cast iron
Compacted graphite cast iron
Eutectic graphite quantity