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Graphite growth morphologies in cast iron
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
2014 (Engelska)Ingår i: Solidification and Gravity VI, Trans Tech Publications Inc., 2014, s. 458-463Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

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 microsegregation 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.

Ort, förlag, år, upplaga, sidor
Trans Tech Publications Inc., 2014. s. 458-463
Serie
Materials Science Forum, ISSN 0255-5476 ; 790-791
Nyckelord [en]
And thermodynamics, Cast iron, Clusters, Graphite morphology, Ion etching, Micro-segregation, Transition
Nationell ämneskategori
Metallurgi och metalliska material
Identifikatorer
URN: urn:nbn:se:kth:diva-146699DOI: 10.4028/www.scientific.net/MSF.790-791.458Scopus ID: 2-s2.0-84901434605ISBN: 978-303835093-4 (tryckt)OAI: oai:DiVA.org:kth-146699DiVA, id: diva2:725212
Konferens
6th International Conference on Solidification and Gravity; Miskolc, Lillafured; Hungary; 2 September 2013 through 5 September 2013
Anmärkning

QC 20140616

Tillgänglig från: 2014-06-16 Skapad: 2014-06-13 Senast uppdaterad: 2014-11-07Bibliografiskt granskad
Ingår i avhandling
1. On the Inoculation and Graphite Morphologies of Cast Iron
Öppna denna publikation i ny flik eller fönster >>On the Inoculation and Graphite Morphologies of Cast Iron
2014 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Research was conducted to understand the nucleation mechanism of graphite flakes and nodules and the effect of various elements on the growth morphology of graphite. Investigations were started on flake graphite cast iron. The effect of S on the graphite morphology and MnS was experimentally analysed. The influence of various type of oxides on the growth morphology of MnS and their relation with the graphite growth morphology was studied carefully through series of experiments, and results were related to the thermodynamic calculations, performed to predict the nucleation of oxides and sulfides at any temperature. The calculations were supported by EDX analysis on particles in the samples, showing sequential nucleation of flake graphite. The austenite volume fraction and the dendrite growth orientations were affected by the addition of Al to the melt. The effect of aluminium oxide and sulfur was studied on the austenite growth morphology with the help of colour etching technique. Thermal analyses were performed to study the effect of sulfur content on austenite volume fraction and growth morphology using DSC. The latent heat of solidification and the rate of austenite formation was studied and related to the sulfur content in the alloy.

To study the effect of O and S on the graphite morphology, pure Fe-C alloy was prepared and strong de-oxidizers and de-sulfurizer (Mg, Ca and Sr) were tested. With the help of ion etching and polishing, we were able to reveal the graphite growth morphology. The morphological changes in the graphite were explained by relating it to the composition of the melt in regard of dissolved S and O in the melt. The effect of other trace elements such as S, F, O, N, P, B and Se, was also investigated by testing them on an ultra-pure Fe-C alloy. The possibility of substituting a foreign atom in the basal plane of graphite was analysed based on the bonding energy between C and the foreign atoms. The resulting change in the structure of the basal plane was studied using Avogadro software and the resulting model were compared with the experimental results. The basal plane of nodular, flake and undercooled graphite was studied with the help of HRTEM, which showed differences in the lattice spacing between different graphite morphologies. The latent heat measurement showed that flake graphite have higher energy than the undercooled or vermicular graphite. This research made us enabled to tell about the growth along c-plane in graphite and the reason behind the transition of graphite morphology.

The effect of inoculation temperature and inoculation sequence on the nodularity was studied. EDX analysis were performed and the results were compared to the thermodynamic calculations.  It was found that, the melt composition is controlling the graphite growth morphologies. Strong de-oxidizers and de-sulfurizer are necessary to reduce O and S to a level where it does not influence the graphite growth morphology. The effect of various elements on the activity of oxygen in the melt is calculated. High Al cast iron was also studied. The major problem associated with this type of alloy was that, the Mg was not effective in producing nodular graphite. Experiments showed that de-oxidizers stronger than Mg are required to increase the nodularity. Thermodynamic calculations showed that the activity of oxygen in the melt was changing strongly by increasing the Al content in the alloy. This was increasing the required oxygen level to nucleate MgO.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2014. s. 76
Nationell ämneskategori
Metallurgi och metalliska material
Forskningsämne
Teknisk materialvetenskap
Identifikatorer
urn:nbn:se:kth:diva-155545 (URN)978-91-7595-349-6 (ISBN)
Disputation
2014-11-28, B2, Brinelvagen 23, KTH, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning

QC 20141107

Tillgänglig från: 2014-11-07 Skapad: 2014-11-07 Senast uppdaterad: 2014-11-07Bibliografiskt granskad

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Muhmond, Haji MuhammadFredriksson, Hasse
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