Thin Wall Ductile Iron Castings Research Articles

Effect of Inoculants on the Structure and Properties of Thin-Walled Ductile Iron Castings

Effect of Inoculants on the Structure and Properties of Thin-Walled Ductile Iron Castings

Технологія одержання тонкостінних виливків з високоміцного чавуну в облицьованих кокілях з використанням внутрішньоформового модифікування розплаву

Технологія одержання тонкостінних виливків з високоміцного чавуну в облицьованих кокілях з використанням внутрішньоформового модифікування розплаву

Mechanical Properties of Thin Wall Ductile Iron: Experimental Correlation Using ANOVA and DOE

The present study was undertaken to investigate the effect of different metallurgical parameters such as casting techniques, wall thickness, inoculant technique, carbon equivalent, nodule count, ferrite and pearlite percent on the mechanical properties of thin wall ductile iron castings (TWDI). Understanding of the effect of chemistry, casting techniques, melting and molten treatment on the mechanical properties and microstructural features of TWDI castings would help in selecting conditions required to achieve optimum mechanical properties and alloy high strength to weight ratio. The use of the design of experiment (DOE) and the analysis of variance (ANOVA) can be a useful methodology to reach this objective. The analysis of the effects of each variable and their interaction on the mechanical properties of TWDI castings using green sand, green sand with insulation and investment casting techniques plays a key role in improved materials performance.The results indicate that nodule count, pearlite content and the interaction between carbon equivalent, nodule count and pearlite content have a significant effect on the tensile strength of TWDI castings. The impact toughness values decrease with smaller section thickness and increased nodule count. Using investment casting technique, decreasing the pearlite percent and nodule count, and increasing the wall thickness and ferrite percent reduce the values of ultimate tensile strength and yield strength. The results of percent elongation and impact toughness show a reverse trend compared with those of ultimate tensile strength and yield strength in terms with different metallurgical parameters.

Performance of kaolin and cassava starch as replacements for bentonite in moulding sand used in thin wall ductile iron castings

Thin Wall Ductile Iron (TWDI) casting presents macroscopic and microscopic challenges using bentonite bonded moulding sand. In this study, moulding properties of bentonite, cassava starch and kaolin bonded silica sand were evaluated using various binder/sand formulations (6%, 9%, and 12%). TWDI samples of 3 mm thickness were cast using dry compression strength as criteria for each binder type. Cast samples were subjected to macroscopic, microscopic and Vickers hardness analysis. Kaolin bonded sand gave superior dry strength property of 650 KN/m 2 at 6 % addition. Samples showed nodularity and nodule counts of 96.2%, 587 nodules/mm 2 , 76.2%, 61 nodules/mm 2 and 96.5%, 985 nodules/mm 2 using kaolin, cassava starch and bentonite bonded sand respectively. Thickness deviations were observed in all samples, bentonite bonded samples being most significant. This study has shown that adopting kaolin as alternative binder for production of TWDI casting should be encouraged as properties of cast TWDIs samples were greatly improved. Keywords: Thin wall ductile iron (TWDI), binder/sand formulations, moulding sand properties, macroscopic and microscopic properties

The Influence of Wall Thickness and Mould Temperature on Structure and Properties of Thin Wall Ductile Iron Castings

The Influence of Wall Thickness and Mould Temperature on Structure and Properties of Thin Wall Ductile Iron Castings

Primary Structure and Graphite Nodules in Thin-Walled High-Nickel Ductile Iron Castings

This paper considers the most important quality factors in processing spheroidal graphite cast iron; namely, primary grains and graphite nodules in thin-walled ductile iron castings (TWDI). In the present study, the effect of grain refinement (by means of Ti, Nb and Zr) and of the holding time after spheroidization and inoculation on effecting the primary grains and eutectic structure in TWDI castings was investigated. Moreover, metallographic examinations (including electron backscattering diffraction, EBSD) were carried out to reveal the macro- and micro-structural features during the primary and eutectic solidification of the cast iron. EBSD results indicate that, within a single dendritic grain, there are numerous boundaries that split the grain into numerous smaller areas. In particular, it is found that the graphite nodules are in contact with the boundaries inside the primary dendritic grain. In turn, crystallization of highly branched dendrites is observed, which seems to “push” the graphite nodules into the interdendritic regions during their growth. The present work investigates the dominant mechanism that gives rise to the primary spheroidal graphite cast iron (SGI) structure. In addition, this work shows that the melt quality is closely associated with the resultant morphology and number of austenite dendrites, graphite nodules, and matrix structure.

Effect of some inoculants on the structure and properties of thin wall ductile iron

The production of ductile iron parts as thin as (2-3 mm), known generally as Thin Wall Ductile Iron (TWDI) casting. Inoculants play a great role in changing the structure–properties of ductile iron. In the present work, the effect of inoculation on thin wall ductile iron castings is analyzed. Three types of potent inoculants were used namely Ce-Ca-Al-S-O-FeSi, Zr-Mn-Ca-Al-Ba-FeSi and Sr-Al-Ca-FeSi. The in-mould inoculation was done. It is observed that Ce-Ca-Al-S-O-FeSi inoculant provides highest nodule count and a unique wide distribution of nodule size in comparison to thin wall ductile iron (TWDI) inoculated with Zr-Mn-Ca-Al-Ba-FeSi and Sr-Al-Ca-FeSi. By increasing the weight of Ce-Ca-Al-S-O-FeSi from 0.2% to 0.4% for in-mould inoculation leads to increase in the nodule count. It was also observed that thin wall ductile iron (TWDI) samples inoculated with Ce containing 0.2% to 0.4% inoculant contain pearlitic matrix, whereas the samples inoculated with 0.6% inoculant have ferritic matrix. The as-cast microstructure of thin wall ductile iron (TWDI) containing 0.6% inoculants contain islands of pearlite in ferritic matrix whereas the samples inoculated by 0.2% to 0.4% inoculants had ferrite in the form of concentric shells around graphite nodules.

Effect of carbon equivalent on impact toughness for the thin-walled ductile cast iron

Effect of carbon equivalent on impact toughness for the thin-walled ductile cast iron

Strength Characteristics of Inoculated and Nodularised Thin Wall Ductile Iron Castings

Carbide precipitates in Thin Wall Ductile Iron (TWDI) used for automotive applications needs to be eliminated or reduced for improved strength, ductility, crack propagation resistance and good machinability. Ductile iron thin section profiles (≤3 mm) present danger of massive carbide precipitations in the as-cast sample. Precipitated carbide phase is brittle and negatively affects the mechanical properties of the iron matrix. The suppression of carbide formation is associated with the nucleating properties of the nodularizer and innoculant alloys. This treatment is vital in ensuring that carbide precipitation, flake graphite structure and non-nodular graphite phases are reduced or completely eliminated in the TWDI castings. Therefore, the temperature and technique of treatment would influence the yield of the process, and ultimately the mechanical properties. In this study, the effect of nodularization and inoculation treatment temperature on the microstructure and mechanical properties of TWDI castings is examined. The results indicate that good nodularity and nodule count with better percent elongations are achieved using low treatment temperatures in descending order of 1490°C, 1470°C and 1450°C, but have negative effect at lower treatment temperature of 1430°C. However, TWDI castings have superior properties in terms of nodule counts and nodularity at 1450°C. Treatment temperature does not produce significant influence on ultimate tensile strength (UTS) and hardness of TWDI castings. TWDI castings show poor nodularity, nodule count and ductility at higher inoculation treatment temperatures of 1550°C, 1530°C and 1510°C.

Thin Wall Ductile Iron Castings as Substitutes for Aluminium Alloy Castings

Abstract The paper discusses the reasons behind current trends for substituting cast iron castings by aluminum alloys. In particular it is shown that it is possible to produce thin wall castings (control arms, cantilevers and rotors) made of ductile iron without the development of chills, cold laps or misruns, and with a strength to weight ratio of up 87 MPa cm3/g. In addition, austenitizing at 900 °C for 20 minutes and then austempering in a salt bath at 350 °C for 15 minutes promotes the development of a fully ausferritic matrix in thin wall castings with a the strength to weight ratio increase of up to 154 MPa cm3/g. Finally, it is shown that thin wall castings made of ductile or austemperded cast iron can be lighter and with superior mechanical properties then their substitutes made of aluminum alloy.

Undercooling, Cooling Curves and Nodule Count for Near-eutectic Thin-walled Ductile Iron Castings

A solidification model for ductile iron, including Weibull formula for nodule count, has been presented. The principal assumptions of the kinetic nature of growth, depending on undercooling in respect of the eutectic equilibrium temperature and austenite liquidus line, have been adopted, disregarding the diffusion processes, which was justified by the rapid course of the crystallization process in a thin-walled casting. From this model, the following parameters can be determined: cooling curves, kinetics of austenite and eutectic nucleation, austenite and eutectic growth velocity, and volume fraction.The correctness of the mathematical model has been experimentally verified by comparison with literature data in the range of the most significant factors, which include temperature field, the value of maximum undercooling, the value of minimum and maximum temperature on a cooling curve, maximum undercooling, the recalescence and graphite nodule count interrelated with the casting cross-section.

Effects of Silicon and Carbon Contents on Microstructure of 2mm-thick Thin-walled Ductile Cast Iron

Effects of Silicon and Carbon Contents on Microstructure of 2mm-thick Thin-walled Ductile Cast Iron

Effects of Silicon Content on Microstructure and Impact Fracture Properties with Miniature Specimens for Thin-walled Ductile Cast Iron

Effects of Silicon Content on Microstructure and Impact Fracture Properties with Miniature Specimens for Thin-walled Ductile Cast Iron

Solidification behaviour and mechanical properties of ductile iron castings with varying thickness

Achieving the desired mechanical properties in thin wall ductile iron castings poured in industrial production foundries is a challenge. In this work, the effect of copper addition (up to 0·74%) and melt processing (Ba based stream inoculation) on the matrix structure, mechanical properties and fracture behaviour of ductile iron castings with varying section thickness (4–16 mm) were investigated in a regular jobbing foundry. It was possible to obtain 80% pearlitic structure without carbides in 4 mm sections, giving a tensile strength of 658 MPa with 2·5% ductility and 264 Brinell hardness. The solidification behaviour represented by the cooling curves helped in checking the effectiveness of the melt treatment by observing the amount of undercooling. Fractography studies of tensile specimens showed the change in fracture mechanisms due to increase in copper content on fracture paths. The increased amount of pearlite in the matrix exhibited brittle fracture with river pattern.

Effect of nodule count on austenitising and austempering kinetics of ductile iron castings and mechanical properties of thin walled iron castings

In the present work, the potential for producing thin walled ductile iron castings with an ausferritic matrix is presented. Experimentally, thin walled iron castings of 2 mm in thickness were obtained and characterised by a nodule count of 1992 mm−2. In addition, a reference casting was produced with a 25 mm thick wall and a nodule count of 330 mm−2. Austenitising was carried out at 920°C, whereas austempering was implemented in the 300–400°C temperature range. The austenitising and austempering transformation rates were determined by dilatometry, and the results were confirmed by microstructural analyses. It was found that in thin walled castings, the austenitising and austempering times were reduced by either one-half or one-third of the ones corresponding to the reference casting. The exhibited mechanical properties of the thin walled castings were also determined as a function of austempering time and temperature. It was found that austempering at 300°C for 1200 s leads to thin walled castings with a tensile strength of 1500 MPa. Accordingly, from this work, it is plausible to produce high strength thin walled castings that satisfy all the ASTM 897M grades of ausferritic ductile iron through proper heat treating.

Fluidity and Temperature Profile of Ductile Iron in Thin Sections

It has been shown that it is possible to produce thin wall ductile iron (TWDI) castings of considerable length using an Archimedes spirals with a wall of 1, 2 or 3 mm in thickness. The fluidities for different moulding materials [(classical mould, chemically bonded silica sand and chemically bonded low-density alumina-silicate ceramic sand (LDASC)], chemical composition, and pouring temperature were estimated. There is a significant temperature drop in thin sections (contrary to typical sections) during the mould filling. A profile of real temperature drop is presented along with theoretical predictions. The high temperature drop of liquid iron results in an increased cooling rate (before the eutectic equilibrium solidification temperature), which in turn affects the solidification and microstructure of TWDI castings. Microstructures were characterized quantitatively using an image analyser. Structure parameters for different wall thicknesses and moulding materials (graphite nodule count, ferrite and cementite fraction) are plotted, which is versus distance from the entrance to the mould cavity. It has been shown that the thin wall castings have a gradient structure. Moreover, a strong influence of LDASC sand (material with low ability to absorb the heat) on the structure parameters of TWDI castings is presented.

Effect of Cooling Rate on Microstructure and Mechanical Properties of Thin-Walled Ductile Iron Castings

This article addresses the effect of cooling rate on microstructure and mechanical properties as determined by changing molding media and section size. The research was conducted for thin-walled iron castings with 2-5-mm wall thickness and for the reference casting with 13-mm wall thickness, using different molding materials (silica sand and insulating sand “LDASC”) to achieve various cooling rates. Thermal analysis was performed to determine the real cooling rate at the beginning of the graphite eutectic solidification. In general, it was found that the predictions based on theoretical analysis of the solidification process of ductile iron are in good agreement with the experimental outcomes. Finally, the present study provides insights into the effect of cooling rate on the graphite nodule count, the ferrite fraction and mechanical properties of thin-walled ductile iron castings. The study shows that the cooling rate of thin-walled castings varies in a wide range (80-15 °C/s) when changing the wall thickness from 2 to 5 mm, accompanied by significantly changing the mechanical properties of ductile iron. The cooling rate can be effectively reduced by applying an insulating sand to obtain the desired properties of thin-walled castings practically in the whole range of ductile iron grades in accordance with the ASTM Standard.

Effect of carbon equivalent on microstructure of thin-walled ductile cast iron

Effect of carbon equivalent on microstructure of thin-walled ductile cast iron

Fatigue propagation of long cracks in ferritic thin wall ductile iron castings

The present work focuses on the fatigue propagation of long cracks in ferritic ductile iron parts of varied thickness. Samples were taken from thin wall ductile iron plates and standard 'Y' blocks with nodule counts ranging from 250 to 2200 nod/mm2 and ferrite grain sizes from 70 to 150 μm. Fatigue crack propagation threshold ΔKth and Paris law constants C and m were measured, and the influence of the microstructure refinement (established through nodule count and grain size) on the characteristics of the fatigue fracture surface was analysed. The results show that, once the crack is initiated, the fatigue crack growth threshold diminishes as the microstructure is refined, while the rate of growth remains practically unaltered. The crack path preferentially intersects graphite nodules and is mostly transgranular through the ferrite grains. Nevertheless, at low levels of ΔK, a low percentage of intergranular fracture was also observed.

Solidification of Thin Wall Ductile Iron Castings with Hypereutectic Composition

Numerical calculations are presented describing the solidification of a thin wall ductile iron castings with a hypereutectic composition. Numerical model was implemented in Matlab–Simulink environment. The model takes into account the presence of off-eutectic austenite as well as primary graphite. Experimental verification was made using casting with the shape of Archimedes spiral. Thermal analysis showed that there is high temperature drop of liquid metal due to intensive heat transfer between the flowing metal stream—the mould material. Thermal analysis along with microstructure observations were made and show reasonable agreement of numerical calculations with experimental measurements.