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

Abstract

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...

Solidification of Thin Wall Ductile Iron Castings with Hypereutectic Composition

“…It usually applies to nodules count and to a smaller extent to the matrix. From work 1) results that risers or multiply inlets can significantly reduce structure inhomogeneity.…”

“…1,2) As a result there are continuous changes of structural features of cast iron with changes of its properties accordingly.…”

“…It has been proved 3,4) that it is possible to produce thin wall ductile iron (TWDI) with wall thickness even below 3 mm (without chills, cold laps and misruns). TWDI can be lighter than their substitute made of aluminum alloys [5][6][7] and characterized similar or better mechanical properties, definitely better dumping capacity.…”

“…Numerous studies have been published on thin wall ductile iron, particularly on the solidification morphologies, 8) microstructure characterization, 3,9,10) mechanical properties, 11,12) carbide formation factors, 1,13,14) production, 15,16) mould filling 17,18) and thermal analysis. 19) Moreover, various experimental relationships have been developed between the chemical composition, 10,14,16) pouring temperature, 14) spheroidization and inoculation practice, 14,15) casting geometry, 20) plate thickness, 2,10,14) and mould materials.…”

Effect of chill formation on the mechanical properties and microstructure of grey and nodular cast irons used in automotive industry

“…Sonuç olarak silisyum ilavesi mutlak çil eğilimi azalır. Minimum et kalınlıkta çil döküm için veya kama şeklinde dökümlerde çil derinliği, çil oluşum eğilimi ile ilgili olup, Si içeriği arttıkça çil derinliği azalmaktadır [11]. Döküm sırasında soğutma hızı büyük ölçüde tasarım ve doğal sıcaklık tarafından yönetilir.…”