Eutectic Cell and Nodule Count in Cast Iron: Part I. Theoretical Background

Fraś, E.; Górny, M.; López, H. F.

doi:10.2355/isijinternational.47.259

Cited by 12 publications

(14 citation statements)

References 20 publications

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“…(2), T c is the transition temperature for the solidification of cementite eutectic from graphite eutectic, or the chill formation temperature. 16) Also, from Fig. 3, it can be observed that as the wall thickness decreases (cooling rate increases), the minimal temperature at the onset of graphite eutectic solidification (T m ) decreases.…”

Section: Methodsmentioning

confidence: 86%

“…the heat flux extracted from the casting into the mold and the heat flux generated during solidification) the cooling rate can be expressed as. 16) . where: a -material mold ability to absorb heat, c -specific heat of the cast iron, s -wall thickness of the casting and Ti -initial temperature of the metal in the mold cavity just after pouring.…”

Section: Thermal Analysismentioning

confidence: 99%

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Effect of Cooling Rate and Titanium Additions on Microstructure of Thin-Walled Compacted Graphite Iron Castings

et al. 2014

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This article addresses the effect of cooling rate and of titanium additions on the exhibited microstructure of thin-walled compacted graphite iron (TWCI) castings as determined by changing molding media, section size and Ferro Titanium. The research work was carried out on TWCI castings and reference castings of 2-5 mm and 13 mm wall thickness, respectively. Various molding materials were employed (silica sand and insulating sand ''LDASC'') to achieve different cooling rates. Thermal analysis was implemented for determinations of the actual cooling rates at the onset of solidification. This study shows that the cooling rates exhibited in the TWCI castings varies widely (70-14°C/s) when the wall thickness is changed from 2 to 5 mm. In turn, this is accompanied by a significant variation in the compacted graphite fraction. The resultant cooling rates were effectively reduced by applying an insulating sand in order to obtain the desired graphite compactness. In addition, good agreement was found between the theoretical predictions of the solidification process and the experimental outcome. Ti additions in combination with LDASC sand molds were highly effective in promoting the development of over 80% compacted graphite in castings with wall thicknesses of 2 and 3 mm as evidenced by quantitative metallographic analyses.

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Section: Methodsmentioning

confidence: 86%

Section: Thermal Analysismentioning

confidence: 99%

Effect of Cooling Rate and Titanium Additions on Microstructure of Thin-Walled Compacted Graphite Iron Castings

et al. 2014

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“…2) can be calculated 16) In above expressions, DT m is the maximum degree of undercooling at the onset of graphite eutectic solildification (Fig. 2), Q is the cooling rate of cast iron at temperature, T s (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…4 results that for QϭQ cr , DT m ϭDT sc and the absolute chilling tendency of cast iron is given by 16) ......... (10) where N V ,cr is the critical cell count at TϷT c (close to chill, see Fig. 3, and Table 1).…”

Section: Absolute Chilling Tendency Ct Of Cast Ironmentioning

confidence: 99%

Mechanism of the Silicon Influence on Absolute Chilling Tendency and Chill of Cast Iron

2008

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Fig. 1. Castings according to ASTM standard for chill and chilling tendency estimation.ing to 1 400°C (2 552°F), the wedges (ASTM A367-55T standard) of the type (dimensions: B w ϭ2.5 cm and bϭ25°) were cast. From each melt, a sample was taken for chemical composition ( Table 1). A Pt-PtRh10 thermocouples was inserted in the center of the wedge cavity in the sand mold and an Agilent 34970A electronic module was employed for numerical temperature recording. Figure 2 shows typical cooling curve and their first derivative, where characteristic points are shown i.e. initial metal temperature T i just after filling of mold, minimal temperature T m at the onset of graphite eutectic solildification and cooling rate Q at the graphite eutectic equilibrium temperature T s . Cooling curves were used for determinations of the initial metal temperature, T i just after filling of mold (Table 1). After cooling, specimens for metallographic examination were taken from the wedges. Metallographic examinations were made on polished cross-sections of wedges (Fig. 3). After etching using nital, width of wedge, w was determined at which there are presented last precipitations of cementite (total chill) (Fig. 3). Next samples were polished again and etched using Stead reagent to reveal graphite eutectic cell boundaries (Fig. 3). The planar microstructure is characterized by the cell count, N F which gives the average number of graphite eutectic cells per unit area. The N F parameter can be determined by means of the, so-called variant II of the Jeffries method, and applying the Saltykov formula as an unbiased estimator for the rectangle S of observation. (1) where: N i is the number of eutectic cells inside rectangle S (Fig. 3a), N r is the number of eutectic cells that intersect the sides of the rectangle S but not their corners and F is the surface area of the rectangle S.The graphite eutectic cells has a granular microstructure, and it can be assumed that the spatial grain configurations follow the so-called Poisson-Voronoi model. two zones; (1) The portion closest to the apex was entirely free of any gray spots and it was designated as a clear chill, and (2) the portion starting at the end of the clear chill and continuing all the way down to the location were the last spot of cementite that is white iron is visible was designated as the mottled zone. The width, w of the total chill and the cell count, N F,cr were measured at the junction of the gray cast iron microstructure with the first appearance of chilled iron, see Fig. 3 (near the cementite eutectic formation temperature, T c ). The planar cell count, N F,cr in the vicinity of that junction was converted into the volumetric cell count, N V ,cr using Eq. (2). The results of these measurements are given in Table 1. AnalysisThe minimal temperature, T m at the onset of graphite eutectic solildification (see Fig. 2 In above expressions, DT m is the maximum degree of undercooling at the onset of graphite eutectic solildification (Fig. 2), Q is the cooling rate of cast iron at...

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“…The SGI and CGI castings can be tailored to fit an unusually broad diversity of needs, which remarkably, has opened new vistas for its application in the manufacture of automobile, construction, communication, transportation, agricultural, mining, heavy-machine, military and railroad components, which are traditionally produced by expensive forging and fabrication processes involving high grade alloy steels and other equivalent high performance materials [1][2][3][4][5][6][7][8][9][10][11][12][13].…”

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General Characteristic of the Ductile and Compacted Graphite Cast Iron

Górny

2015

Microstructure and Properties of Ductile Iron and Compacted Graphite Iron Castings

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This section provides basic information about the spheroidal graphite cast iron (SGI) and compacted graphite cast iron (CGI) which belong to the group of high-quality cast iron. The classification of SGI and CGI according to ISO standards, their characteristics and the use of modern types such as ADI or Si-Mo were provided. The solidification path was shown, pointing to the important role of surface active elements in shaping the form of graphite. Models presenting eutectic grain growth in SGI and CGI were also described. It was also shown that in this connection, the main surface active elements (O and S) cause changes in the growth direction, and additionally, the so-called anti-spheroidizers, such as Ti, Bi, Zr, P and N, characterized by strong normal segregation, lower the liquidus temperature of the melt, thus creating the liquid channels that characterize CGI, which then stimulate the formation of compacted graphite. The issues of the number of eutectic grains, the cooling rate and the occurrence of defects in castings were raised. Finally the spheroidizing/compacting treatments have been shown along with the general scheme of the SGI/CGI preparation process.Spheroidal graphite cast iron (SGI) and compacted graphite cast iron (CGI) belong to the group of high-quality cast iron, the production of which is continually increasing. The general classification of cast iron is shown in Fig. 6.1.Currently, SGI and CGI, belongs to a group of the most important engineering materials, in view of its:• high mechanical properties, • significant savings in cost and weight (compared to equivalent steel and aluminum alloys), • excellent combination of good castability and machinability, • less sensitive to the cooling rate compared to cast iron (FGI), • provides the starting material for the production of "high tech" austempered ductile iron (ADI) and austempered vermicular cast iron (AVCI),

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Eutectic Cell and Nodule Count in Cast Iron: Part I. Theoretical Background

Cited by 12 publications

References 20 publications

Effect of Cooling Rate and Titanium Additions on Microstructure of Thin-Walled Compacted Graphite Iron Castings

Effect of Cooling Rate and Titanium Additions on Microstructure of Thin-Walled Compacted Graphite Iron Castings

Mechanism of the Silicon Influence on Absolute Chilling Tendency and Chill of Cast Iron

General Characteristic of the Ductile and Compacted Graphite Cast Iron

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