Effect of Titanium on Microstructure and Solidification Behavior of Gray Irons

This study investigates the microstructure and the solidification behavior of titanium-alloyed gray irons. Thermal analysis technique was used to identify the Temperature of Liquidus Arrest (TLA), the Temperature of Eutectic Undercooling (TEU) and the Temperature of the Eutectic Recalescence (TER). It was found that the titanium addition promoted the formation of the primary austenite causing the larger difference in TLA and TEU. In addition, titanium encouraged the refining of eutectic mixture. The SEM showed the graphite particles were refined with increasing titanium. Fine particles of titanium-containing compound were readily observed throughout the microstructure. The hardness as high as 176 HB was achieved at 0.495%Ti addition.

Influence of the Magnesium Treatment in a Georg Fischer Converter

With up-to-date thermal analysis equipment, it is possible to control and regulate the melting and treatment process of ductile iron, more or less at every step of the process. Changes in the composition can be handled by controlling and then regulating each single step. The complete process, starting with the melting in a cupola furnace, followed by the holding process in an induction channel furnace and finally the magnesium treatment in a converter has been analysed. A correlation to control and regulate the eutectic undercooling of the melt has been developed.

Competitive Nucleation in Grey Cast Irons

Cast irons are good examples of materials which are more sensitive to chemical composition and production conditions. In this research to improve casting quality, solidification and nucleation process in grey cast iron was investigate. In particular, attempts have been made to rationalize variation in eutectic cells with nucleation sites and eutectic solidification undercooling. Four castings with different diameter and similar chemical composition and pouring temperature and different inoculant percentage was casted. The cooling curve and maximum and minimum undercooling for each castings was measured. Also optical metallography and image analyzer has been used to determine the average eutectic cells diameter, and linear and surface densities, and volume density was calculated. The results of this research show a competitive behavior between nucleation sites and eutectic undercooling. Higher nucleation sites and higher eutectic undercooling cause higher eutectic cell density. But increasing nucleation sites by introducing inoculants to molten metal, is accompanied with reduction in eutectic undercooling. It means that inoculation and undercooling have opposite effect on each other. So, to achieve maximum cell density, it is necessary to create an optimization between these parameters.

Modification of Eutectic Si in Hypoeutectic Al-Si Alloys with Erbium Addition

Effect of erbium (Er) on the eutectic Si morphologies in hypoeutectic Al-Si based alloys was investigated using thermal analysis and microstructure examination. The microstructural observations show that the addition of Er causes significant modification of the eutectic silicon morphology from a coarse plate-like to a fine fibrous one. Furthermore, the results of thermal analysis reveal that the addition of Er decreased the temperatures of eutectic nucleation and growth, and increased the eutectic undercooling. The eutectic undercooling caused by the presence of Er plays an important role in the modification of eutectic silicon.

Thermal Analysis to Optimize and Control the Cast Iron Solidification Process

The cooling curve and its derivatives display patterns that can be used to predict the characteristics of a cast iron. The effects of melting, superheating and holding in an acid lined coreless induction furnace were explored, as they affect the role of preconditioning and / or inoculation to restore solidification with low eutectic undercooling. Increased chill (iron carbides amount) in the experimental irons correlates well with certain thermal analysis parameters, such as the degree of eutectic undercooling. Preconditioning of the molten base iron before tapping led to improved solidification parameters in both untreated and inoculated irons as measured by the most significant thermal analysis cooling curve events. A double treatment incorporating preconditioning with inoculation improved the thermal analysis parameters, and consequently, the quality of the cast iron. If standard Ca-FeSi alloys do not have sufficient inoculation potential, the addition of the inoculant enhancing alloy (S, O and oxy-sulphides forming elements) will greatly enhance inoculation, well illustrated by changes to the thermal analysis parameters. A newly defined Inoculation Specific Factor [inoculation effect / inoculant consumption which led to that beneficial effect ratio] of different alloys is illustrated by thermal analysis, with good correlation with microstructural characteristics.

Chill (Carbide) Control in Low Sulphur Electric Melt Grey Cast Irons

Ca, Ba and Ca-Ba bearing FeSi alloys were compared for their effectiveness in chill (carbide) control, using iron chemistries with critical element levels [< 0.035%S, (%Mn) x (%S) < 0.02, <0.003%Al]. Relative clear and total chill measurements were employed, for chill wedges with different cooling modulii (CM = 0.11 – 0.35 cm). Previous experiments illustrated that the eutectic undercooling of this type of base iron is excessively high, demonstrating a relatively high need for inoculation. Under these conditions, Ca inoculation had a significant effect compared to Ba inoculation, while a Ca-Ba combination improved most of the solidification parameters. The results also illustrate the importance of residual Al and confirm its key role in graphite nucleation in grey irons. The content of the active elements (Al, Ca, Ba) in FeSi based alloys appears to be more important if they inoculate low sulphur irons, more so than increasing the addition rate of an unsuitable inoculant composition.

Effects of Iron Powder Addition on the Solidification Behaviour of Hypereutectic Grey Cast Iron

The purpose of the present paper is to investigate the solidification pattern of slightly hypereutectic grey irons (CE = 4.35 - 4.45%) after an addition of a commercial iron powder, and also in a double treatment with inoculation. Chill wedges with a 0.11 - 0.43 cm cooling modulus (CM), from using resin sand and metal moulds, were used along with different thermal analysis cups (CM = 0.75 and 0.43 cm). Relative clear/mottled/total chill measurement criteria were applied. Unfavourable Mn and S contents [(%Mn) x (%S) = 0.016] and a reduced Al residual (0.0015%) led to relatively high eutectic undercooling and chill in the base iron, especially at high cooling rates (CR). With the lower CM of cups, there was more undercooling in the entire solidification range and more difference between irons. Thermal analysis and chill parameter relationships are normal, except only for iron powder treatment and resin mould solidification, where chill is higher for a relatively lower undercooling. Conventional inoculation after addition of iron powder (double treatment) showed a strong graphitizing effect, as these irons had the lowest undercooling and chill levels, in all the irons tested. It reflects the improved properties of (Mn,X)S compounds as nucleation sites for graphite [10]. This paper is the first of two papers reporting on this study.

Thermal Analysis and Microstructure Comparison Between A356 Aluminum Alloy and A356/15%vol. SiCP Cast Composite Modified with Strontium

A study of the effect of strontium on some solidification parameters, such as eutectic nucleation temperature, eutectic growth temperature, eutectic undercooling temperature and eutectic undercooling time, has been carried out using thermal analysis for a composite reinforced with 15 vol. % SiCP and, for comparison, for an A356 aluminum alloy. The composite is prepared by the melt stirring technique with a SiC particle size of 38 μm. Thermal analysis results show that the presence of SiCP in the unmodified A356 aluminum alloy increases the eutectic growth temperature (TE) and the eutectic nucleation temperature (TNucl); on the contrary, SiCP decreases the eutectic undercooling temperature (θ) and the eutectic undercooling time (tE). These phenomena suggest that SiC particles give favorable conditions for the growth of eutectic silicon. On the other hand, the modification with strontium of the composite material, although showing basically the same effect on the eutectic parameters as the one described for the A356 aluminum alloy, brings about certain differences due to the presence of the SiC particles. Microstructural analysis shows that the eutectic structures in the composite are coarser than those of the matrix alloy and they do not have the classic fibrous eutectic shape obtained in the matrix alloy. For the matrix alloy, when the Sr concentration increases beyond the quantity required to obtain a well-modified structure, the eutectic structure suffers a gradual coarsening or a reversion from fine fibrous silicon to coarser silicon; subsequently, when the Sr concentration is higher than 0.068%, Al2Si2Sr particles are produced. In the composite material there is also a gradual coarsening of the eutectic structure, although the appearance of Al2Si2Sr particles is just seen when the Sr concentration reaches 0.106%.

Undesirable Graphite Morphologies Incidence in Inoculated Grey Irons

Successful inoculation is not guaranteed and effects may even be deleterious. The main risks are the appearance of types B and D graphite, associated with ferrite and/or carbides due to lack of control of undercooling during eutectic solidification. Alternatively coarse type C graphite in hypo to eutectic grey irons may result from inadequate or excessive inoculation. Sulphur and aluminium content in a molten iron are considered to be the main factors to control the degree of eutectic undercooling, graphite morphology and inoculation efficiency. Thermal conditions, such as superheating, inoculation and pouring temperature play an important role in controlling these effects. Cooling rates due to different mould materials and casting thickness were also considered. In order to resolve individual problems, different inoculant systems have to be considered, such as Sr-FeSi, Ca-FeSi, Ti,Ca-FeSi, Zr,Ca-FeSi, Ba,Ca-FeSi, RE-FeSi (Ca). The present paper made a synthesis of other published papers by the authors, but also added many original un-published results.