Role of Residual Aluminium in Ductile Iron Solidification

Transcription

1 Paper 7-8(5).pdf, Page 1 of 11 Role of Residual Aluminium in Ductile Iron Solidification Copyright 27 American Foundry Society I. Riposan, M. Chisamera, S. Stan Politehnica University of Bucharest, Bucharest, Romania D. White Elkem Metals Inc., Pittsburg, Pennsylvania ABSTRACT The main objective of the present paper was the investigation of the role of a large range of final residual aluminium (.2-.5%) when added through pre-conditioner (FeSi, 5%Al), (.2-3%Al)- nodularisers and (.1-5.%Al) -Ca-FeSi inoculants. The most important parameters of thermal analysis were beneficially influenced by residual aluminium, and consequently resulted in higher eutectic temperatures and a lower degree of undercooling, higher temperature at the end of solidification and a greater negative peak of the depth of the first derivative at this temperature. In lower carbon equivalent conditions ( %), aluminium appears to have beneficial effects, such as: decreasing free carbides occurrence, increasing nodule count, and improving castings compactness, without affecting graphite morphology. Adding Al with the inoculant is by far the best solution to control residual aluminium level. Second best is to include it in the base iron such as with an Al bearing preconditioner. Including Al in the is the weakest choice..5.2wt.% Al residual is beneficial to improve ductile iron characteristics without the incidence of pinholes. INTRODUCTION A large range of residual aluminium content in the iron melt for ductile iron production could be recorded, depending on the charge materials, such as pig iron, steel scrap, ferrosilicon, aluminium products incidence etc. The nodularisers may also include a large level of aluminium, from less than.1%al and up to 2-3%Al. Aluminium content in FeSi-based inoculants covers a larger range, from.1%al up to 4-5%Al. Aluminium is recognized for contributing to pinhole formation in iron castings: lower contribution in ductile iron than in gray iron castings, especially due to the higher surface tension in Mgtreated irons..5-.2%al appears to be the critical range of residual aluminium in ductile irons, with regard to pinholing. New knowledge about the fundamental effects of aluminium in the gray iron nucleation process is now available. Comple (Mn,X)S compounds (where X=Fe, Al, O, Ca, Si, Sr, Ti, Zr etc.) usually less than 5. m in size, with an average.4-2. m well defined nucleus were found as the major nucleation sites for graphite in both un-inoculated and inoculated gray irons. Aluminium contributes to the formation of Al 2 O 3 -based sites which act as nucleation sites for (Mn,X)S compounds, even at a very low Al level (<.3%) in iron melt. Increasing the residual aluminium content in iron melt helps the initiation of graphite nucleation with lower undercooling. A.5-.1%Al content in melt appears to be beneficial, without the detrimental effect on pinhole occurrence in gray irons 1-4. Aluminium appears to play also an important role in nodular graphite nucleation in ductile irons. Generally, aluminium was found, in specific conditions in nodular graphite, as comple nitride 5-7, oy-nitrides in very low sulfur treated irons 6, or as comple silicates, as result of nodularisation and/or inoculation 8,9. A possible difference in micro inclusions system for induction furnace irons and cupola irons was identified many years ago 8. (Mg,Ca)S inclusions have been established as heterogeneous nuclei for graphite nodules in induction furnace iron. The inclusions identified in the cupola irons were found to consist of a miture of sulfides and silicates, which contained Mg, Ca and Al as primary constituents. The role of Al was also indirectly recognized in the model of graphite nodule formation, mainly as inoculant contribution 9 : MgS/CaS/CeS compounds are formed as the primary micro inclusions in the Mg-treated iron melt; the Mg-treatment process also introduces into the melt comple Mg-silicates, such as estatite (MgO SiO 2 ) and forsterite (2MgO SiO 2 ). However these phases present a large planer disregistry with graphite and will not act as nucleation sites. During subsequent inoculation with FeSi containing Al and X (Ca, Ba, Sr) alters many of these inclusions by forming heagonal silicate phases of XO-SiO 2 or the XO-Al 2 O 3-2SiO 2 on the surface of the oide inclusions. The (1) basal planes of these compounds can be favorable sites of graphite nucleation forming coherent/semicoherent low energy interfaces between the nucleant and graphite. The particles which act as nuclei for graphite spheroids in a ductile iron containing small amount of Mg and traces of Al were also identified as Al-Mg-Si nitrides (Al,Mg 2.5 Si 2.5 N), having a trigonal super lattice crystal structure derived from a heagonal AlN type fundamental cell 5.

2 Paper 7-8(5).pdf, Page 2 of 11 Aluminium was also found in comple nitrides such as (Mg, Si, Al)N or oy-nitrides (Mg, Si, Al)ON mainly at very low sulfur level in the base iron (<.1%S). MgS/MgO compounds appear to be the major nucleation sites fore more than.1%s in treated irons 6. A spherical sulfide (Mg, Ca)S of about 1. m diameter was found near the center of graphite spheroids and thought to be a nucleus for graphite. A spherical MgO of about.2 m diameter was found in the sulfide and considered to be nucleus for the sulfide. The main constituent of the core of graphite is (Mg,Ca)S, enveloping MgO inside and accompanying (Mg,Si,Al)N outside 7. The main objective of the present paper was the investigation of the role of a large range of residual aluminium (.2-.5%) when added through pre-conditioner, nodularisers and inoculants in ductile iron production, at low level of carbon ( %) and carbon equivalent ( %), respectively. Is there an optimum level of Al? If so, what is the best way in the ductile iron process to introduce it? EXPERIMENTAL PROCEDURE High purity and careful selected charge materials were used for the eperimental program, at very low level of aluminium, sulfur and auiliary antinodulizing and carbide forming elements (Table 1). Table 1. Chemical Composition of Charge Materials (wt.%) Material C Si Mn P S Al Steel Scrap* Graphitic Recarburizer FeMn High Purity (HP)-FeSi Foundry Grade (FG)-FeSi *.35%Cr, <.11%Mo,.25%Ni,.3%Cu, <.1%Pb, <.2%Sb, <.2%Ti The base primary synthetic iron (1kg) was prepared in a coreless induction furnace (acid lining, 1kg, 1Hz) using selected steel scrap, high purity recarburizer, low Al-FeSi and FeMn as charge materials. The eperimental heats were obtained by re-melting of the base iron (3.78%C, 1.23%Si,.45%Mn,.18%P,.13%S,.4%Al) with 1% premium quality steel scrap addition, in a smaller induction furnace (acid lining, 1Kg, 24Hz). Each heat has contained 3 Kg charge. The iron melt overheated up to o C/ o F and maintained 1 minutes at this level. Before tapping the iron melt was superheated a short time (3 minutes) up to o C / o F and than tapped into the nodulizing ladle ( o C/ o F). Three aluminium sources were used for aluminium variation in final ductile iron composition: a) Al-FeSi alloy as preconditioner; b) Mg-FeSi alloys as nodularisers; c) Ca-FeSi alloys as inoculants (Table 2). In the ductile iron production, the base reference condition and the three variants as aluminium source were considered in the following schedule. Table 2. Chemical Composition of the Eperimental Alloys (wt.%) Role Material Al Si Ca Mg Fe Alloy Al Level Type Preconditioner Al-FeSi High bal Nodulariser Low bal Medium bal High bal Inoculant Ca-FeSi Low bal Ca-FeSi Medium bal Ca-FeSi High bal a) Reference/base variant: low Al-base iron was treated with low Al, alloy and inoculated (or not) with low Al, Ca-FeSi alloy; b) Preconditioning variant: Al-preconditioning of base iron (.4% Al-FeSi alloy; in stream addition, before Mgtreatment), followed by low Al, treatment and (or not) inoculation with low Al, Ca-FeSi alloy; c) Nodulariser variant: low Al-base iron was treated with medium and high Al, alloys, followed by inoculation (or not) with low Al, Ca-FeSi alloy; d) Inoculant variant: low Al-base iron was treated with low Al, alloy and inoculated (or not) with medium and high Al, Ca-FeSi alloys (Fig. 1).

3 Paper 7-8(5).pdf, Page 3 of 11 Fig. 1. General schedule of eperiments and final Al range level Figure 1. General schedule of eperiments and final Al range level Induction Furnace 3 kg iron melt Uninoculated iron 1 kg L 1 Nodulizing treatment MgFeS 1 kg L 2 In-stream addition Ca-FeSi Fig. 2. Schedule of eperimental program

4 Paper 7-8(5).pdf, Page 4 of 11 The nodulizing treatment (2.5% Mg-FeSi alloys) was achieved in 3 Kg Tundish-Cover treatment ladle with a centered pocket (Fig. 2). Mg-FeSi alloy covered by a resin bonded sand plate. Every time the reaction started after complete filling of the ladle. After removing of the slag the Mg-treated liquid iron was divided in 1Kg batches, which were or not submitted to ladle inoculation treatment (.5% Ca-FeSi alloys). The inoculated or un-inoculated iron melt were poured by the 1Kg ladle after 15 sec waiting for melt homogenization. The two 1Kg batches were poured by two workers in the same time (6-7 sec) in furan resin molds ( o C/ o F). The order of pouring different samples was intentionally maintained the same, that is: Cross bar sample (shrinkage tendency) - Cylindrical samples (structure characteristics) - Quick-cups (thermal analysis) - Coin samples (spectral analysis). Shake out of the cast samples was performed at room temperature. RESULTS AND DISCUSSION FINAL CHEMISTRY OF DUCTILE IRONS Final chemical composition of Mg-FeSi treated irons, in un-inoculated and inoculated conditions and different sources of added aluminium is presented in Table 3. Al Source Table 3. Final Chemical Composition of Eperimental Ductile Irons Ca-FeSi Sample Chemical Composition* (wt.%) Treatment Inocu- Al C Si Mn S P Mg (Al level) lation (Al level) Equiv. Carbon CE, % Base Un-Inoc Condit. Ca-FeSi (No precond.) Precon- Un ditioner, AlFeSi Ca-FeSi Nodula- Un-Inoc riser (Med. Al) Ca-FeSi (No precond.) Un-Inoc (High Al) Ca-FeSi Inoculant Ca-FeSi (No (Med.Al) Precond.) Ca-FeSi (High Al) *Residual elements (wt.%):.3cu,.1ni,.3cr,.1v,.2ti,.2nb,.4co,.1w,.3sn,.1pb,.3sb,.1as. Low ranges of carbon content ( %C) and carbon equivalent level ( %CE) were selected, to increase the sensitivity of eperimental ductile irons to chill and shrinkage formation. The other representative elements in the base chemical composition are included in the normal range of ductile irons: %Mn, %S,.19-.2%P and.4 -.6%Mg res. Residual elements (ecepting Al) were achieved at low level. Final residual aluminium content in the un-inoculated and inoculated ductile irons was obtained in a large range, depending on the source variant (Tables 3, 4 and Fig. 3). Very low final aluminium content (<.5%Al) is typically for high purity base iron, subjected to treatment with low Al, and inoculated (or not) with low Al, Ca-FeSi alloy. Medium (usual) Al, Ca-FeSi inoculant increased Al-content up to.1%al. The general.1-.2%al range was obtained in different conditions: Al-FeSi preconditioning, medium Al, treatment or high Al, Ca-FeSi inoculation. The highest aluminium level, i.e. more than.4%al in the final iron is typically for high Al, treatment.

5 Paper 7-8(5).pdf, Page 5 of 11 Fig. 3. Final Al content in -treated, un-inoculated () and Ca-FeSi inoculated irons () Table 4. Al Level in Final Ductile Irons, Depending on Al Source Al Level Al-FeSi Treatment Ca-FeSi Inoculation In Final Irons (%) Preconditioning Low Al (<.1%) Med. Al (.8- High Al (2-3%) Low Al (<.1%) Med. Al (1.-1.5%) High Al (4-5%) 1.2%) ma [Al], % I - Al - PRECONDITIONING II - Al - NODULARISER III - Al - INOCULANT No Precond. Al-FeSi Low Al - Low Al - CaFeSi Low Al- Med. Al- High Al- No Al - Preconditioning Low Al - CaFeSi SOLIDIFICATION PATTERN The eperimental hypo-eutectic ( % carbon equivalent) ductile iron heats were subjected to thermal analysis, so cooling curves and their first derivatives were recorded (Fig. 4). Standard Quick-cups were used, with a cooling modulus of.75 cm, equal to a test bar 3 mm in diameter. The basic cooling curve gives some important information about the solidification (Fig. 4a): the lowest (TEU) and the highest (TER) eutectic temperatures, eutectic undercooling degree ( Tm = Tst - TEU) comparing to equilibrium stable eutectic temperature (Tst), eutectic recalescence degree ( Tr = TER - TEU) or the temperature at the end of solidification (TES). Additional information can be obtained from the first derivative of the cooling curve, which shows the cooling rate and its direction (dt/d, fig.4a): the maimum rate during recalescence (TEM) and the minimum value of the first derivative at the end of solidification (FDES). A low value for FDES is favorable, as is correlated to high amount of eutectic graphite at the end of solidification. Usually it is associated with a high nodule count and a low tendency for micro-shrinkage, especially if FDES < -3. o C/s 1. In the present eperiments, the theoretical temperatures in the stable system (Tst) and metastable conditions (Tmst) were calculated, depending on the final silicon content (Tst = %Si and Tmst = %Si). The Ts = Tst - Tmst difference was obtained in the o C range (48-55 o C for un-inoculated irons and o C for inoculated irons, respectively). According to low carbon equivalent, a higher level of eutectic undercooling degree ( Tm No Al - Preconditioning Low Al - Low Med. High Al Al - CaFeSi. Un-

6 Paper 7-8(5).pdf, Page 6 of 11 given Tst) was obtained: o C for un-inoculated irons and o C for inoculated irons. More accurate information could be obtained if Tmst is considered as reference for solidification pattern of cast irons (Fig. 5). seconds seconds Fig. 4. Cooling curve and first derivative parameters (a) and influence of Al-Ca-FeSi inoculant (b)

7 Paper 7-8(5).pdf, Page 7 of T1 = TEU Tmst, o C Inoculated Irons a) T2 = TER Tmst, o C Inoculated Irons b) 1 Al, % Un-inoculated Irons -3 1 Un-inoculated Irons Al, % T1 / Ts c).8 T2 / Ts d).6 Inoculated Irons.6 Inoculated Irons Al, % Al, % Fig. 5. Influence of residual Al on the undercooling parameters of un-inoculated () and inoculated ductile irons () T 1 = TEU - Tmst parameter illustrates the position of irons at the start of eutectic reaction, while T 2 = TER -Tmst at the end of this stage. In the eperimental conditions, un-inoculated irons mainly present a white iron solidification pattern ( T 1 <, T 2 < ), while inoculation moved the ductile irons to the positive value range of these parameters, in all of cases. But, also inoculated irons remain in a visible undercooling stage as T 1 / Ts ratio is mainly less than.6 level, while T 2 / Ts ratio is prevalent less than.7 reference. Cooling curves and their first derivatives show a visible difference at low and high residual aluminium level, such as Fig. 4b illustrates. 5.%Al-bearing Ca-FeSi alloy inoculation led to upper position of the cooling curve (higher TEU, TER) and the lower position of the depth of the first derivative at the end of solidification (lower FDES), as compared to ma..1%al bearing Ca-FeSi alloy use. Fig. 5 shows that the increasing of residual aluminium levels resulted in a positive trend of the representative parameters, higher level of T 1 and T 2, in both un-inoculated and inoculated irons and T 1 / Ts and T 2 / Ts ratios in inoculated irons, respectively. In inoculated ductile irons,.1-.2 wt.% Al appears to be an efficient range, while the Al-addition via inoculation is more efficient than Al-preconditioning or Al-bearing alloys. CARBIDES FORMATION SENSITIVITY For a first evaluation the A-wedge Test (W 3 and W 31/2 samples), ASTM A , was used. Two methods to evaluate chill sensitivity were applied. These were macrostructure (fracture) analysis and microscopic (metallographic) analysis (2% Nital etching) to differentiate clear and total chill areas. Metallographic analysis of chill test samples is a more realistic method to evaluate the chill sensitivity of ductile irons, due to difficulty to separate the white, mottled and free carbide areas in these irons by the visual difference in color technique. This is because the white color of carbides is very close to the silver color of the carbide free fracture, so it is difficult to identify very eactly the chilled area by visual rating. Iron melt condition, as un-inoculated and inoculated irons and cooling rate, as size of wedge test samples, was found as the most important clear influencing factors on the chill tendency. Lower carbon equivalent level led to a higher chill tendency of all of Mg-FeSi treated irons for both cooling rates (W 3 and W 31/2 samples), in un-inoculated state. Ca-FeSi inoculated irons are visibly less sensitive to chill formation, for both clear and total chill parameters and for both cooling rate conditions. Aluminium residual in the final iron melt does not appear to influence chill tendency in the eperimental conditions, as chill test evaluation. The round bar samples (25mm diameter, 1 mm length,.59 cm cooling modulus) were also used for microstructure analysis, as free carbides, metal matri and graphite characteristics (Table 5, Fig.6).

8 Paper 7-8(5).pdf, Page 8 of 11 Al Source Treatment (Al level) Ca-FeSi Inoculation (Al level) Table 5. Structure Characteristics Sample Al, (%) Graphite Nodularity, (%) Graphite Nodule Count (1/mm 2 ) Ferrite/ Pearlite Amount, (%) Base Un-Inoc Condition Ca-FeSi /6 25 (No /6 precond.) /7 2 Precon- Un ditioner, AlFeSi Ca-FeSi / /6 2 Nodula- Un-Inoc riser (Med. Al) Ca-FeSi /7 2 (No precond.) Un-Inoc (High Al) Ca-FeSi /8 25 Inoculant Ca-FeSi /7 5 (No (Med.Al) /7 5 precond.) Ca-FeSi (High Al) /6 3 Obs. Un-inoculated irons: White/Mottled Structure Free Carbides Amount, (%) Carbides, % Un-inoculated irons Al Al-Ca-FeSi 5 a) Graphite Nodularity, % b) Nodule Count, Nod./mm c) Fig. 6. Influence of residual aluminium on the free carbides amount (a), the graphite nodularity (b) and nodule count (c)

9 Paper 7-8(5).pdf, Page 9 of 11 Free carbides are normally present in un-inoculated irons, when white iron was primarily obtained (35-4% carbides), without residual aluminium visible influence. Less than 25% free carbides amount is typically for inoculated irons, with two representative ranges (Fig. 6a): 2 25% free carbides, for as Al-source; less than 5% free carbides for Al-bearing Ca-FeSi inoculant addition. The both positions were obtained also for Al-FeSi preconditioning of the base iron melt. As the base metal matri, it was considered that Ferrite (F) + Pearlite (P) = 1%. GRAPHITE CHARACTERISTICS More than 8% nodularity was generally obtained, typically for commercial ductile irons, at a medium level of nodules compactness, specific for synthetic base iron. As eperimental procedure pointed out, selected steel scrap was used as metallic charge, to obtain a strong controlled base iron melt in foundry conditions charge. No detrimental influence of residual aluminium on the graphite nodularity was identified in these eperiments (Fig. 6b). Nodule count appears to be beneficially influenced by the residual aluminium level in inoculated irons. The upper level of this parameter (more than 1 N/mm 2 ) is typically for Al-bearing Ca-FeSi inoculation. The intermediary position was found for Al-FeSi preconditioning, while the lowest nodule count is typically for as Al source (Fig. 6c). SHRINKAGE TENDENCY Ductile iron shrinkage tendency was evaluated by shrinkage cross bar sample (1184mm,.86cm cooling modulus), which was cast in horizontal position, without risers. In this case, the main objective has focused on the obtaining of shrinkage with as much as possible concentration to a more precise evaluation. Numerical simulation of sample solidification was applied in order to establish the optimum radius between the cross arms. By this way, it was established that 12 mm radius between the cross arms ensures a controlled solidification (moving the shrinkage towards to the center of the cross bar). Encouraging of the directional solidification of the sample, which ensures the shrinkage concentration in the upper side of the cross section center and forestalls the chaotic spreading of the shrinkage was also considered. In this reason, 23 mm thermal insulation disc was inserted in the mold on the upper side of the cross section favoring the late solidification of the skin in this region. By this way, a very concentrated macro-shrinkage was obtained for each sample that has permitted high accuracy of its measurement. The shrinkage tendency has been evaluated by the following parameters: V csh -open concentrated shrinkage volume, cm 3 or %; d 1 -the relative density of the sample (shrinkage porosity is included), g/cm 3 ; d 2 -the apparent density of the sample (the total shrinkage is included): d 2 = Sample mass/sample apparent volume, g/cm 3 ; d s -the relative density of the sound piece (it can also include micro-porosity): d s = mass of the sound piece/volume of the sound piece, g/cm 3. K s =d s /d 2 -the rating of the sample soundness (it shows the deviation of the sample containing defects density from the density of the sound piece). The optimum value is K s =1 for a complete sound sample. The sample volumes were measured based on the Archimedes principle weighing the samples, both in air and water with a precision on.1g. In the calculation, water density was considered unity ( W =1 g/cm 3 ). Table 6 and Figure 7 illustrate the sensitiveness of cast irons to contraction defects formation. Open concentrated shrinkage volume (V csh ), the apparent density of samples, which include shrinkage (d 2 ) and the K s factor were found the most representative parameters. At lower carbon content ( %C) and lower equivalent carbon level ( %CE), Mg-treated irons are characterized by higher shrinkage level after inoculation compared to un-inoculated irons in all of cases (Fig. 7a). Higher residual aluminium content, lower shrinkage amount, for both un-inoculated and inoculated irons, but without a visible influence of the Al-source. The specific density of the cross samples, which included concentrated shrinkage (d 2 ), is accorded to found shrinkage level: higher d 2 values in un-inoculated irons (Fig. 7b). No visible influence of the residual aluminium content was found in inoculated irons, but with beneficial effect in un-inoculated irons. The d s /d 2 specific ratio could be also an important parameter, to illustrate the incidence of the contraction defects in ductile cast irons (Fig. 7c): lower level in un-inoculated irons according to lower shrinkage level. The increasing of residual aluminium content appears to have a positive influence on this parameter, but without visible influence of the Al-source: -the more narrow range in inoculated irons; -the decreasing level in un-inoculated irons.

10 Paper 7-8(5).pdf, Page 1 of 11 SHRINKAGE, Vcsh, % Un-inoculated irons 1 a) d2, g/cm Un-inoculated irons b) Ks = ds / d Un-inoculated irons 1.1 c) Fig. 7 Influence of the Al level in iron melt on the concentrated shrinkage (a), samples density in the shrinkage area (b) and the densities ratio (c) (d s -density of samples, without contraction defects) Al source Base Conditions (No precond.) Preconditioner, AlFeSi Nodulariser (No precond.) Inoculant (No precond.) Treatment (Al level) (Med.Al) (High Al) Table 6. The Density and Shrinkage Characteristics Ca-FeSi Sample Al G sa Densities, g/cm 3 K s = V csh Inoculation (%) (g) d 1 d 2 d s d s /d 2 cm 3 % (Al level) Un Ca-FeSi Un Ca-FeSi Un Ca-FeSi Un Ca-FeSi Ca-FeSi (Med.Al) Ca-FeSi (High Al)

11 Paper 7-8(5).pdf, Page 11 of 11 CONCLUSIONS The presumptive role of residual aluminium proceeded from different sources, in low carbon equivalent level ( %) ductile iron, melted in acid lined induction furnace, was investigated. The conclusions drawn in the present paper based mainly on the thermal analysis, carbides sensitivity, graphite characteristics and shrinkage tendency. In the conditions of high purity charge materials and synthetic base iron, a large range of final residual aluminium was obtained (.2 -.5%Al), depending on the Al-source: less than.5%al without aluminium addition, %Al as preconditioning addition, %Al by inoculation contribution and %Al by Mg-FeSi treatment source. Generally, Al-residual was found as an important, medium potency graphitizing influencing factor, in both un-inoculated and inoculated ductile irons. As for solidification pattern, the most representative parameters of thermal analysis were improved by residual aluminium, such as higher eutectic temperatures and lower undercooling degree, higher temperature at the end of solidification and greater peak of the first derivative at this temperature etc. In lower carbon equivalent conditions, Al had not capacity to influence chill tendency as wedge chill test samples evaluation, but it may be efficient to control free carbides amount in conventional castings, especially by inoculation addition. There was a visible beneficial effect of Al-content on increasing the nodule count; and the most effective means was to add Al within the inoculant. shown higher shrinkage occurrence and lower correspondent density, as compared to un-inoculated irons. Al-content appears to have a beneficial influence, as casting compactness increased. Recommendations to ductile iron production practice: wt.%Al residual is beneficial to improve ductile iron characteristics without the incidence of pinholes - The greatest benefits were achieved when Al was introduced into the iron via the inoculant. - The net best was to have Al present in the base iron, added as an Al bearing preconditioner. - Al added via the provided the minimum benefit. ACKNOWLEDGMENTS This research was conducted with the funds provided by the Elkem s Foundry Products Division, Norway. In addition Torbjorn Skaland and Svein Olsen are to be thanked for their contribution to the work. REFERENCES 1. Chisamera, M., Riposan, I., Stan, S. and Skaland, T., Undercooling-Chill Size-Structure Relationship in the Ca/Sr Inoculated Grey Irons under Sulphur/Oygen Influence, 64th World Foundry Congress, Paris, Paper RO-62, (2). 2. Chisamera, M., Riposan, I., Stan, S. and Skaland, T., Effects of Residual Aluminum on Solidification Characteristics of Un-Inoculated and Ca/Sr Inoculated Grey Irons, AFS Transactions, vol. 112, pp , (24). 3. Riposan, I., Chisamera, M., Stan, S., Skaland, T. and Onsoien, M.O., Analyses of Possible Nucleation Sites in Ca/Sr Over Inoculated Grey Irons, AFS Transactions, V19, pp , (21). 4. Riposan, I., Chisamera, M., Stan, S. and Skaland, T., A New Approach on the Inoculated Grey Irons, Proceedings of AFS Inoculation Conference, Schaumburg, IL, pp.31-41, (25). 5. Solberg, J.K., and Onsoien, M.I., Nuclei for Heterogeneous Formation of Graphite Spheroids in Ductile Cast Iron, Materials Science and Technology, vol. 17, pp , (21). 6. Nakae,H. and Igarashi, Y., Influence of Sulfur on Heterogeneous Nucleus of Spheroidal Graphite, Materials Transactions, Vol. 43, No. 11, pp , (22). 7. Igoraski, V. and Okade, S., Observation and analysis of the nucleus of spheroidal graphite in Mg-treated ductile iron, Int. J.Cast Metals Res., 11, pp.83-88, (1998). 8. Lalich, M.J. and Hitching, J.R., Characterization of Inclusions as Nuclei for Spheroidal Graphite in Ductile Cast Irons, AFS Transactions, V84, pp , (1976). 9. Skaland, T., Doctoral Thesis, Metallurgiski Institut, Trondheim, Norway, (1992). 1. Sillen, R.V., Nova Cast Technologies, (26).