Relationship Between the Trace Elements and Graphite Growth Morphologies in Cast Iron
- PDF / 6,109,694 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 16 Downloads / 198 Views
ODUCTION
THE transition of graphite morphologies in cast iron is not fully understood. Many attempts have been made to relate the morphology to the effect of inoculants. One often sees transitions from normal flake to fine undercooled graphite or from spheroidal to vermicular graphite. According to many authors, the graphite growth morphology is related to the impurities in the Fe base liquid,[1–4] while spherodizers are not necessary to form spheroidal graphite.[1,3] In an experiment with Ni-C alloy, spheroidal graphite was obtained when B was added to the melt.[5] Ahn et al.[6] reported the transformation in the graphite morphology from a rod to spheroidal shape with the application of pressure in a Ni-C alloy. The morphological change was caused by the ability of graphite to grow as a curved crystal under certain conditions, while under other conditions, this ability did not exist, and only flakes were formed.[4] It has been observed that with a higher cooling rate, the morphology of graphite transforms from flake to undercooled and to spheroidal graphite regardless of the presence of sulfur in the liquid of gray iron (sulfur is known to promote flake graphite). It is commonly accepted that flake graphite iron has a high concentration of oxygen and sulfur, while spheroi-
HAJI MUHAMMAD MUHMOND, Ph.D. Student, and HASSE FREDRIKSSON, Professor, are with the Materials Science and Engineering Department, Royal Institute of Technology, Brinellva¨gen 23, 10044 Stockholm, Sweden. Contact e-mail: [email protected] Manuscript submitted April 8, 2014. Article published online October 1, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
dal graphite iron has a much lower oxygen and sulfur content. Various authors have studied the effect of S and O and some metal atoms on the morphology of graphite.[1,3,7–9] The presence of S, O and metal atoms has been verified by Auger [1] and secondary ion mass spectroscopy analysis [9] at the interface and inside the graphite. Atoms can be added easily in the a-direction but with a lower probability of attaching in the cdirection normal to the monolayer,[3] depending on a different bonding in the different directions. The metal atom incorporation into the graphite lattice has been associated with the screw dislocations[9–11] and splitting and branching of the graphite, resulting in changes in the relative orientation of the basal plane during growth.[12,13] Wang and Kang.[14] observed that fringes of graphite consist of bends in the layer. Such faults have been observed by HRTEM analysis on a nanometer scale in spheroids.[15] In this investigation, the objective was to find any relation between trace elements (S, F, O, N, P, B, Se) and graphite morphology in pure binary (Fe-C) and ternary alloys (Fe-C-Si). The possibility of substituting a foreign atom in the basal plane of graphite was analyzed based on the bonding energy between C and the foreign atoms. The resulting change in the structure of the basal plane was compared with experimental results. The cross section of spheroidal graphite, fine undercoole
Data Loading...
