SiMo Ductile Iron Crystallization Process

The determination of silicon and carbon contents by thermal analysis is based on the recording of a cooling curve of a melt whose eutectic solidification takes place in the metastable system. The temperatures of the austenite and eutectic arrests are evaluated and then related to the carbon and silicon contents by linear relationships that would be defined by the phase diagram if there were no undercoolings. However, published experimental values of austenite liquidus arrest and metastable eutectic arrest both show significant undercoolings when compared to the equilibrium metastable Fe–C–Si phase diagram. The undercooling of the austenite observed in hypo-eutectic alloys can be explained by tip undercooling during dendritic growth. On the other hand, it is pointed out that alloys with a composition close to the stable eutectic—either slightly hypo- or slightly hypereutectic—can show much higher undercoolings than expected if some stable eutectic precipitates. For such compositions, the thermal analysis could hardly be reproducible enough if the alloy does not solidify completely in the metastable system. Furthermore, the published experimental information on the temperature of the metastable eutectic is here supplemented by new results for silicon contents up to nearly 4 wt%. Both previous and new results show a similar undercooling of 5 to 15 °C compared to the calculated equilibrium metastable eutectic. Each foundry wishing to use thermal analysis for carbon and silicon evaluation must determine its own relationships for austenite liquidus and metastable eutectic to account for the specificity of its melting process and casting system. Care should be taken to avoid any graphite precipitation in the thermal cup, and testing should be performed to improve reproducibility as this defines the accuracy of the composition determination.

The influence of nitriding on the fatigue resistance of grey and nodular (ductile) cast iron piston rings was studied for six chemical compositions. The selected materials include three grey cast irons: one with a mixed initial microstructure (martensite plus bainite), the second martensitic and another martensitic alloyed with niobium; and three nodular cast irons: one common nodular cast iron, the second alloyed with Nb and another alloyed with Al and V. These materials were gas nitrided for 3 and 6 h. The relationship between the mechanical behaviour and the treatment time (depth of nitrided layer) was established. Samples were tested under a cyclical bending load. The stresses were determined in the cross-section, where the biggest moment was experienced. Results were statistically treated by means of Weibull analysis. Nitriding showed that fatigue resistance of grey cast iron with a martensitic structure is higher than that of a mixed structure. Fatigue resistance of nodular cast irons is red...

ABSTRACTUsing a dilatometer the isothermal transformation of austenite to bainite has been studied in ductile cast iron with 0.05 % Mn and a silicon content varying from 2.4 to 3.8 %. The alloys were austenitized to a carbon content in the matrix of 0.65 %. It appears that silicon retards the formation of carbides in the upper bainite region (400 °C), resulting in an amount of retained austenite up to 40 % present in the final structure at room temperature. Silicon improves the strength; in the lower bainite region the yield strength in particular. An elongation up to 10 % or more is obtained after austempering at 400 0C independent of the silicon content.

Corrosion behavior of ductile and austempered ductile cast iron in 0.01M and 0.05M NaCl Environments.

Characterization and modeling of the mechanical behavior of high silicon ductile iron

Thermodynamic and experimental study of C-S system and C-S-Mo system

A model to predict the solidification of spheroidal graphite (SG) cast iron during cooling process was developed. The model treated the problem of the ternary Fe-C-Si system and aimed at simulating the evolution of the solidifying microstructure. When the eutectic temperature is reached, eutectic grains are formed. The rate of nucleation depends on the melt characteristics and supercooling. The nucleation rate was assumed to be presented by power law function of undercooling. The growth of the austenite grain was controlled by carbon diffusion through austenite. Carbon and silicon concentrations at different interfaces are calculated from the Fe-C-Si equilibrium ternary phase diagram and Sheil equation was applied to calculate the silicon content in the bulk liquid and the concentration of carbon in the liquid was determined to keep the eutectic reaction. The model was applied to a four-step cylindrical sand casting which has a different diameter. The simulated results were compared with the experimental ones using a post processing program which was also developed to simulate the microstructural evolution graphically. The results showed relatively good agreement and the usefulness of the proposed model was confirmed.

This paper investigates the effects of silicon content above 3 wt% and different cooling rates on the graphite morphology and the mechanical properties of ductile cast iron. To research and determine these effects, three grades of high-silicon ductile iron were cast with silicon content of 3 wt%, 3.5 wt% and 4.5 wt%. In order to investigate the effect of different cooling rates during solidification, four sections with different thicknesses were cast in the same mold, i.e., cube with wall thickness 180 mm and standard Y2, Y3 and Y4 keel blocks. Microstructure analysis and tensile test were performed on the as-cast samples. In the second step of analysis, detailed metallographic observations on specially prepared samples were performed in order to investigate the risk of graphite degeneracy appearance, especially chunky graphite formation due to high silicon content and its effect on mechanical properties. The results showed that graphite content, ferrite fraction, yield strength and tensile strength were increased by increasing the silicon content. On the other hand, elongation decreases with increasing silicon content. Also, based on the metallographic observations of the present work, the risk of chunky graphite formation increases with increase in silicon content and with decrease in the cooling rate. Chunky graphite formation affects negatively mechanical properties, especially elongation in ductile cast irons with silicon content higher than 3.5 wt%.

Effect of spheroidization of cementite in ductile cast iron

The processes of crystallization and solid deposit formation that led to the shutdown of the 2H evaporator operation at the Savannah River Site (SRS) and that could possibly cause similar problems in the future or in other evaporators need to be better understood. Through experimentation, thermodynamic modeling, and correlation of scaling to historical tank farm operations, progress has been made in developing guidelines as to the concentrations of silicon and aluminum that can be processed by evaporators while avoiding unacceptable levels of scale formation. However, because of limitations of the thermodynamic model and an insufficient amount of operational data at slightly supersaturated concentration levels, uncertainty still exists regarding acceptable feed concentrations. The objective of this effort is to provide information that can be used in defining acceptable levels of silicon and aluminum in evaporator feed solutions. Data collected previously showed that particle formation reactions can be rapid at evaporator temperatures for elevated silicon and aluminum concentrations. However, insufficient data exists to estimate the silicon and aluminum concentrations above which solids will form in the time frame of evaporator processing. The work described in this report was designed to determine the induction period for solutions of decreasing aluminum and silicon concentration such that the supersaturation level corresponding to a 4-h induction time for particle nucleation/growth in bulk solution can be estimated. In addition, experiments were conducted to explore the supersaturation levels that can result in deposition of solids on metal surfaces at varying aluminum-to-silicon concentration ratios. Laboratory studies of particle growth in solution were conducted at relatively low supersaturation levels. Dynamic-light-scattering (DLS) studies and deposition tests, similar to those performed in FY 2001, were conducted with solutions at relatively low supersaturation levels and at elevated temperatures to explore the formation of solids under conditions similar to those encountered in evaporator processing. The deposition of solids on stainless steel samples placed in the solutions during the experiments was simultaneously investigated. In addition, the deposition of solids on stainless steel surfaces was investigated in laboratory-scale batch evaporation experiments. Completion of this effort will aid the development of operating strategies to mitigate or avoid solid scale formation on surfaces in evaporator systems. The results are expected to benefit plant operations by helping to determine acceptable silicon and aluminum feed concentrations.

Two types of compacted vermicular graphite (CVG) cast iron having ferritic and pearlitic structures have been studied to determine the effects of CVG on fatigue strength, fatigue crack growth rate and fracture appearance of cast iron. The results obtained were compared with those of two types of spheroidal graphite (SG) cast iron (corresponding to JIS FCD) having ferritic and pearlitic structures. The significant conclusions obtained are as follows: The fatigue limit of the CVG cast iron was lower than that of the SG cast iron independent of matrix structure. This tendency was prominent for ferrite matrix. However, the fatigue limit ratio of the CVG cast iron was not less than that of the SG cast iron regardless the shape of graphite. The fatigue crack growth rate of the CVG cast iron was higher than that of the SG cast iron. This trend was significant for the CVG cast iron having ferritic matrix. This could be due to the fact that the fatigue crack propagation in the CVG cast iron occurs through a zig-zag path between graphites more than that in the SG cast iron when compared at the same level of Kmax.

Elevated temperature brittleness (ETB) of spheroidal graphite (s-g) cast iron has been referred to as reduced ductility within an elevated temperature range and has been related to grain boundary brittleness. The phenomenon of ETB has not been yet clearly understood. In this study, the factor affecting on ETB was studied in terms of strain rate and chemical composition. A study was carried out on the influence of phosphorus on ETB by using laboratory-made heats containing different phosphorus contents. ETB indicated the marked decrease in ductility at around 673K. S-g cast iron containing low phosphorus content manifested ETB at temperatures between 650K and 700K. There was a consistent correlation between the fractional increases in intergranular fracture appearance and the decrease in elongation. The increase of phosphorus suppressed ETB and s-g cast irons containing phosphorus exceeding 0.030 % were found to be immune to ETB. It was found that ETB could be suppressed by reducing the ratio of magnesium and phosphorus to less than 1.5.

The determination of carbon activities in the Fe–C–Si system is important in thermodynamic calculations and in particular for predicting equilibrium compositions in slag–metal reactions. In this research, the interaction parameters required to describe the activity of carbon were calculated from previously published carbon solubility data. These parameters were referred to as ternary interaction parameters &phis; and were fitted to equations as a function of the carbon and silicon contents and temperature. Subsequently, the various interaction parameter formalisms were utilised to calculate the activity of carbon. In dilute solutions, all formalisms were in excellent agreement with a previously published regular solution model. At low silicon and high carbon contents, the unified formalism was in excellent agreement, while the substitutional formalism was in good agreement with the regular solution model. However, in high silicon alloys with low carbon contents, the substitutional and unified formalisms showed only limited agreement with the regular solution model.

Effects of high silicon contents on graphite morphology and room temperature mechanical properties of as-cast ferritic ductile cast irons. Part I – Microstructure

Leaf Blade Micromorphology and the Silicon Content in Phragmites Australis (Poaceae) are Correlated with Water Balance in the Environment The role of leaf blade micromorphology and the silicon (Si) content in the tolerance of Phragmites australis to changes in the soil water balance in natural conditions was examined. The features of leaf micromorphology and silicon distribution in leaf epidermis of Ph. australis emergent and terrestrial plants, which grew in the zone of Kiev (Ukraine), were studied by scanning electron microscopy, X-ray analysis, and laser confocal microscopy. Emergent (air-water) plants grew in riverside, along the shore of Venetian Strait of Dnipro River, Kiev, Ukraine. Terrestrial plants grew near 12-15 m far from the strain in a sandy soil. Rooted are emersed in the substrate of emergent plants, whereas leaves fully exposed to air (on-shore emergent). As far as terrestrial plants of the reed, the roots were in sandy soil, and the stems with leaves–are exposed over the land. It is established that change of soil humidity effect to leaf blade micromorphology, particularly the density of stomata and prickles. The investigation has shown that terrestrial environment leads to decrease of the density of stomata and prickles and increase of wax incrustation in the leaf epidermis. The comparison analysis of the presence of silicon ions, its content, and Si-bodies appearance in leaf blade of Ph. australis two ecotypes showed the images of the quantitative distribution of silicon bodies and silicon amorphous formations in the prickles, stomata and strands, and revealed the depending Si content on the cell type and environmental conditions of plant growth. The obtained results are documented in Ph. australis the plasticity for leaf micromorphology and silicon content in leaf epidermis depending on the water balance of the nature external environments. We discuss the important role of leaf micromorphology and silicon inclusions, the indicator of which depends on the water balance of the plant and light absorption.