Scanning Electron Microscopy of Graphite Growth in Iron and Nickel Alloys

“…Because of high carbon supersaturation of the eutectic austenite resulting from the decomposition of carbides, the crystal edges and corners grow faster than the faces producing the holes in the growing graphite aggregate (Figure 15). Alternatively, Mg atoms may block the step-growth of dislocations, as suggested by Minkoff and Nixon [146].…”

Section: Solid-state Growth Of Graphitementioning

confidence: 98%

Recent Developments in Understanding Nucleation and Crystallization of Spheroidal Graphite in Iron-Carbon-Silicon Alloys

Stefanescu

Alonso

Súarez

2020

Metals

View full text Add to dashboard Cite

The last decade has witnessed significant research efforts directed to the understanding of nucleation and crystallization of graphite and associated solidification phenomena, driven in part by the ever-growing interest in the use of spheroidal graphite cast iron in the manufacture of large castings, such as wind turbine parts. These applications raised new challenges to the production of sound castings, mostly because of the exceedingly long solidification times imposed by the size of the castings. These solidification conditions resulted in many instances in graphite degeneration with subsequent decrease in mechanical properties. Obviously, the subject of graphite nucleation and crystallization in cast iron is still in need of additional answers. Over the years, many reviews of the subject have been published. The goal of this paper is to provide an update on the advances achieved in comprehending the mechanisms that govern the nucleation and crystallization of spheroidal graphite and related imperfect morphologies from iron-carbon-silicon melts. In this analysis, we examine not only the crystallization of graphite in cast iron, but also that of metamorphic graphite (natural graphite formed through transformation by heat, pressure, or other natural actions), and of other materials with similar lattice structure and crystallization morphologies.

show abstract

“…In the absence of impurities, however, spherulitic graphite grows at a rather large undercooling; this has been attributed to a spiral growth mechanism (12). In the absence of impurities, however, spherulitic graphite grows at a rather large undercooling; this has been attributed to a spiral growth mechanism (12).…”

Section: Interface Mobilitymentioning

confidence: 99%

Graphite morphology control in cast iron

Subramanian¹,

Purdy²

1990

F. Weinberg International Symposium on Solidification Processing

View full text Add to dashboard Cite

Graphite morphology in cast iron is analysed in terms of nucleation and growth kinetics of graphite crystals in liquid iron. The high interfacial energy between the graphite/melt interface does not allow the homogeneous nucleation of graphite in the melt. The efficacy of the heterogeneous substrates influences the growth undercooling.At small driving forces, i.e., low supersaturation or small kinetic undercooling, graphite growth is characterised by faceted growth resulting in flake, compacted and spherulitic graphite morphologies. However, at large driving forces, there is a transition from faceted to non-faceted growth, resulting in a dendritic growth morphology.Flake morphology is rationalised in terms of impurity dependent crystal growth mechanisms, whereas a spherulitic morphology is attributed to a defect controlled spiral growth mechanism. Compacted graphite morphology is considered a transition between flake and spherulitic morphology.A thermodynamic approach is used to inter-relate the residual concentrations of impurities of technological interest, i.e., S and O as a function of the residual concentration of the reactive elements, Mg, Ca, and Ce in a typical cast iron melt at 1500C and atmospheric pressure. Such a diagram that quantitatively relates graphite morphology in thick cast iron sections to soluble concentrations of impurities is referred to as a graphite morphology control diagram.

show abstract

Scanning Electron Microscopy of Graphite Growth in Iron and Nickel Alloys

Cited by 33 publications

References 4 publications

Spherulites

Spherulites

Recent Developments in Understanding Nucleation and Crystallization of Spheroidal Graphite in Iron-Carbon-Silicon Alloys

Graphite morphology control in cast iron

Contact Info

Product

Resources

About