Our research into the micro-energy produced during solidification of Compacted Graphite shows the beginning of nodular graphite formation shortly after the liquidus strong point and during dendrite thickening in a 20-25% nodular CGI. This energy signature ends shortly before the eutectic strong point. Total Mg was 0.011%. The amount of Mg required for nucleation is tiny, but residual Mg seems to also be required. One author hinted that Mg segregates into the Austenite but did not present research or attribution to this concept. This could possibly explain the transition from spheroidal to vermicular graphite. Does anyone know of such research or documentation?

Strong Point - Liquidus and Eutectic are zones of specific phase growth. The strong point is the point of highest energy generation of that zone and commonly called simply the Liquidus or Eutectic point. It is a minima of the first derivative if there is no recalesence and no supercooling.