Graphite Growth Morphologies in Cast Iron

Abstract

Graphite growth morphology was studied by using InLense detector on FEG-SEM after performing ion etching on the samples. Star like and circumferential growth mechanism of graphite was observed in the graphite nodules. Pure ternary alloy of hypo eutectic and hyper eutectic composition was treated with pure Mg, Ca and Sr, to study the effect of O and S concentration in the melt, on the transition of graphite morphology from nodular to vermicular/compacted and flake graphite. The change in the melt composition between the austenite dendrites due to micro-segregation of S, O and inoculants and their possible effects on the transition of graphite morphologies as well as the nucleation of new oxides/sulfides particles is discussed with the help of thermodynamics.

On the fatigue damage micromechanisms in Si‐solution–strengthened spheroidal graphite cast iron

“…25 The effect of these trace elements was divided into 3 parts: S and B as flake graphite stabilizer, O and F stabilizing compacted or vermicular graphite growth, and P and N mostly neutral. Muhmond et al 24 have shown that the graphite growth was along the circumference in SGI, and the tentative size of different growth region was reported by Di Cocco et al 7 These different growth regions created property variation within graphite nodules, which caused internal cracking of the graphite nodules at the interface of different growth regions. 26 Inoculant and nodulizer are added into the melt to stabilize these trace elements and achieve the desired graphite growth morphology.…”

“…24,25 Chunky, compacted, vermicular, and irregular graphite particles are commonly observed degenerated graphite elements due to poor treatment of the melt. Even if SGIs are treated to form spheroidal graphite nodules, other forms of graphite particles may grow due to the effect of other trace elements or insufficient addition of inoculant or nodulizer during the solidification process.…”

“…Other elements like S, F, O, P, N, and B can be found in trace quantity in cast irons. 24,28 The melt is treated with Mg-based nodulizer to control oxides and sulphides particles and favour spheroidal graphite growth. 25 The effect of these trace elements was divided into 3 parts: S and B as flake graphite stabilizer, O and F stabilizing compacted or vermicular graphite growth, and P and N mostly neutral.…”

“…Even if SGIs are treated to form spheroidal graphite nodules, other forms of graphite particles may grow due to the effect of other trace elements or insufficient addition of inoculant or nodulizer during the solidification process. 24,25 Chunky, compacted, vermicular, and irregular graphite particles are commonly observed degenerated graphite elements due to poor treatment of the melt. Other elements like S, F, O, P, N, and B can be found in trace quantity in cast irons.…”

“…It was also reported that MgO particles were found at the centre of graphite nodules. 24,28 The melt is treated with Mg-based nodulizer to control oxides and sulphides particles and favour spheroidal graphite growth. Mg forms MgO and MgS by dissolving O and S in the melt.…”