In modern times, there are increasing requirements for products quality in every part of manufacturing industry and in foundry industry it
is not different. That is why a lot of foundries are researching, how to effectively produce castings with high quality. This article is dealing
with search of the influence of using different types of risers or chills on shrinkage cavity production in ductile iron castings. Differently
shaped risers were designed using the Wlodawer´s modulus method and test castings were poured with and without combination of chills.
Efficiency of used risers and chills was established by the area of created shrinkage cavity using the ultrasound nondestructive method.
There are introduced the production process of test castings and results of ultrasound nondestructive reflective method. The object of this
work is to determine an optimal type of riser or chill for given test casting in order to not use overrated risers and thus increase the cost
effectiveness of the ductile iron castings production.
Austenitization is the first step of heat treatment preceding the isothermal quenching of ductile iron in austempered ductile iron (ADI)
manufacturing. Usually, the starting material for the ADI production is ductile iron with more convenient pearlitic matrix. In this paper we
present the results of research concerning the austenitizing of ductile iron with ferritic matrix, where all carbon dissolved in austenite must
come from graphite nodules. The scope of research includedcarrying out the process of austenitization at 900o
Cusing a variable times
ranging from 5 to 240minutes,and then observations of the microstructure of the samples after different austenitizing times. These were
supplemented with micro-hardness testing. The research showed that the process of saturating austenite with carbon is limited by the rate
of dissolution of carbon from nodular graphite precipitates.
In this study, a preliminary evaluation was made of the applicability ofthe signalsof the cutting forces, vibration and acoustic emission in
diagnosis of the hardness and microstructure of ausferritic ductile iron and tool edge wear rate during its machining. Tests were performed
on pearlitic-ferritic ductile iron and on three types of ausferritic ductile iron obtained by austempering at 400, 370 and 320⁰C for 180
minutes. Signals of the cutting forces (F), vibration (V) and acoustic emission (AE) were registered while milling each type of the cast iron
with a milling cutter at different degrees of wear. Based on individual signals from all the sensors, numerous measures were determined
such as e.g. the average or maximum signal value. It was found that different measures from all the sensors tested depended on the
microstructure and hardness of the examined material, and on the tool condition. Knowing hardness of the material and the cutting tool
edge condition, it is possible to determine the structure of the material .Simultaneous diagnosis of microstructure, hardness, and the tool
condition is probably feasible, but it would require the application of a diagnostic strategy based on the integration of numerous measures,
e.g. using neural networks.
The paper presents the results of investigations of the growth of protective coating on the surface of ductile iron casting during the hot-dip
galvanizing treatment. Ductile iron of the EN-GJS-600-3 grade was melted and two moulds made by different technologies were poured to
obtain castings with different surface roughness parameters. After the determination of surface roughness, the hot-dip galvanizing
treatment was carried out. Based on the results of investigations, the effect of casting surface roughness on the kinetics of the zinc coating
growth was evaluated. It was found that surface roughness exerts an important effect on the thickness of produced zinc coating
The paper discusses the reasons for the current trend of substituting ductile iron castings by aluminum alloys castings. However, it has been shown that ductile iron is superior to aluminum alloys in many applications. In particular it has been demonstrated that is possible to produce thin wall wheel rim made of ductile iron without the development of chills, cold laps or misruns. In addition it has been shown that thin wall wheel rim made of ductile iron can have the same weight, and better mechanical properties, than their substitutes made of aluminum alloys.
The combination of the austempered ductile iron mechanical properties strongly depend on the parameters used on the austempering cycle. On this study, the influence of austempering time and austenitizing temperature on the properties of a ductile iron were evaluated. A metallic bath of Zamak at 380°C was used as an austempering mean. A set of ductile iron blocks were austenitized at 900°C for 90 minutes and submitted to different austempering times in order to determine the best combination of microstructural and mechanical properties. After the definition of the time of austempering, the reduction of the austenitizing temperature was evaluated. The best combination of properties was obtained with austenitizing at 860°C and austempering during 60 minutes.
The excellent property combination of thin wall ductile iron castings (TWDI), including thin wall alloyed cast iron (e.g. austenitic TWDI) has opened new horizons for cast iron to replace steel castings and forgings in many engineering applications with considerable cost benefits. TWDI is considered as a potential material for the preparation of light castings with good mechanical and utility properties, the cost of which is relatively low. In this study, unalloyed and high Ni-alloyed (25% Ni) spheroidal graphite cast iron, with an austenitic metallic matrix were investigated. The research was conducted for thin-walled iron castings with 2, 3 and 5mm wall thickness, using different mould temperature (20°C, and 160°C) to achieve various cooling rates. The metallographic examinations i.e. characteristic of graphite nodules, metallic matrix, and primary grains of austenite dendrites (in high-nickel NTWDI) and mechanical properties were investigated. The study shows that homogeneity of the casting structure of thin-walled castings varies when changing the wall thickness and mould temperature. Finally, mechanical properties of thin-walled ductile iron castings with ferritic-pearlitic and austenitic metallic matrix have been shown.
Changes of gas pressure in the moulding sand in the zone adjacent to mould cavity were analysed during pouring of cast iron. No significant effect of pressure on the surface quality of castings was observed. In the second series of tests, the concentration of hydrogen in the gas atmosphere was measured. It has been found that the value of this concentration depends on metal composition and is particularly high in cast iron containing magnesium. This is due to the reduction of water vapour with the element that has high affinity to oxygen. The presence of hydrogen causes the formation of gas-induced defects on the casting surface.
The work presents the research results of the silumin coat structure applied on the carbidic alloy ductile iron with the metal matrix: pearlitic, bainitic and martensitic. The coats were made in the AlSi5 silumin bath at the temperature tk = 750±5°C. The holding time of cast iron element in the bath was τ = 180s. Irrespective of the kind of tested ductile iron the obtained coat consisted of three layers with a different phase composition. The first layer from the cast iron ground “g1`” is built from Fe4CSi carbide which contains selected alloy additives of the cast iron. On it the second layer “g1``” crystallizes. It consists of the AlFeSi inter-metallic phase which can appear in its pure form or contain a small quantity of the alloy additives of the cast iron. The last external part of the layer “g2” mainly consists of the hypo-eutectic phases of silumin. The AlFeSi inter-metallic phases in the form of free precipitations with a lamellar or faceted morphology can also appear there. These phases also can contain a small quantity of the alloy additives of the cast iron. More than that, in all the layers of the coat there are graphite precipitations. The phenomenon of graphite movement to the coat is caused by intensive dissolving of the cast iron element surface by the aluminum of the silumin bath.
The paper presents recent developments concerning the formation of surface layer in austempered ductile iron castings. It was found that the traditional methods used to change the properties of the surface layer, i.e. the effect of protective atmosphere during austenitising or shot peening, are not fully satisfactory to meet the demands of commercial applications. Therefore, new ways to shape the surface layer and the surface properties of austempered ductile iron castings are searched for, to mention only detonation spraying, carbonitriding, CVD methods, etc.
The presence of the chunky graphite is unwanted in the cast iron with the spheroidal graphite for this significantly lowers the properties of
the ductile iron. This shape of the graphite is formed as the result of the slow cooling rate of the castings with large thermal point and also
due to the presence of the elements which suppress the formation of the spheroidal graphite and support formation of the chunky graphite.
The spheroidal graphite present in the ductile iron assures the excellent mechanical properties, while the chunky graphite significantly
reduces those properties of the ductile iron. Therefore it is of importance to assume conditions under which prevented is the formation of
the chunky graphite. The casts were carried out under the conditions of the regular operation of the foundry and tested were various types
of modifiers and inoculators and also pre-inoculators containing the elements suppressing the formation of the chunky graphite (Al, Sb a
Ba). Applied were also the chromium breaker core to suppress the formation chunky graphite which was present in the structure in the
places after the feeders elimination. As whole, executed were eight casts with various types of the modifiers and inoculators.
The paper attempts to analyze distortions of cast iron and cast steel rings, after heat treatment cycles. The factors influencing distortion are: chemical composition of material, sample geometry, manufacturing process, hardenability, temperature and heat treatment method. Standard distortion tests are performed on C-ring samples. We selected a ring-model, which approximate the actual part, so that findings apply to gear rings. Because distortion depends on so many variables, this study followed strictly defined procedures. The research was started by specifying the appropriate geometry of the samples. Then, the heat treatment was conducted and samples were measured again. The obtained results allow to determine the value of the resulting distortion and their admissibility. The research will be used to evaluate the possibility of using the material to produce parts of equipment operated under extreme load conditions.
Studies were conducted on a zinc coating produced on the surface of ductile iron grade EN-GJS-500-7 to determine the eutectic grain
effect. For this purpose, castings with a wall thickness of 5 to 30 mm were made and the resulting structure was examined. To obtain a
homogeneous metal matrix, samples were subjected to a ferritising annealing treatment. To enlarge the reaction surface, the top layer was
removed from casting by machining. Then hot dip galvanising treatment was performed at 450°C to capture the kinetics of growth of the
zinc coating (in the period from 60 to 600 seconds). Analysing the test results it was found that within the same time of hot dip
galvanising, the differences in the resulting zinc coating thickness on samples taken from castings with different wall cross-sections were
small but could, particularly for shorter times of treatment, reduce the continuity of the alloyed layer of the zinc coating.
The conducted work shows and confirms how thermal analysis of grey and ductile iron is an important source for calculating metallurgical data to be used as input to increase the precision in simulation of cooling and solidification of cast iron. The aim with the methodology is to achieve a higher quality in the prediction of macro– and micro porosity in castings. As comparison objects standard type of sampling cups for thermal analysis (solidification module M ≈ 0.6 cm) is used. The results from thermal analysis elaborated with the ATAS MetStar system are evaluated parallel with the material quality (including tendency to external and internal defects) of the tested specimen. Significant temperatures and calculated quality parameters are evaluated in the ATAS MetStar system and used as input to calibrate the density curve as temperature function in NovaFlow&Solid simulation system. The modified data are imported to the NovaFlow&Solid simulation system and compared with real results.
In sand moulds, at a distance of 3 mm from the metal- mould interface, the sensors of temperature, and of oxygen and hydrogen content were installed. Temperature and the evolution of partial gas pressure have been analysed in moulds bonded with bentonite with or without the addition of seacoal, water glass or furan resin. Moulds were poured with ductile iron. For comparison, also tests with the grey iron have been executed. It was found that the gas atmosphere near the interface depends mainly on the content of a carbonaceous substance in the mould. In the green sand moulds with 5% of seacoal or bonded with furan resin, after the mould filling, a sudden increase in the hydrogen content and the drop of oxygen is observed. This gas evolution results from the oxidation of carbon and reduction of water vapour in the mould material, and also from the reduction of water vapour and alloy reoxidation. In carbon-free sand, the evolution in the gas composition is slower because water vapour is reduced only at the interface. Changes of oxygen and hydrogen content in the controlled zone are determined by the transport phenomena.
In this paper, the effect of changes the parameters of heat treatment on the structure and the degree of elements segregation was
determined, in the context of corrosion resistance of ductile iron Ni-Mn-Cu, containing 7.2% Ni, 2.6% Mn and 2.4% Cu. In the condition
after casting, castings of austenitic matrix and 160HBW hardness were obtained. The achieved castings were soaked at 450, 550 and
650°C for 4, 8 and 12 hours, then cooled down at the ambient air. In most cases, the heat treatment resulted in a change in the castings
matrix, had the consequence of increasing their hardness in comparison to raw castings. Increasing the temperature and prolonging soaking
time resulted in increasing the degree of transformation of austenite, while reducing the degree of elements segregation. This led to the
formation of slightly bigger number of pitting due to corrosion, but not so deep and more evenly distributed in comparison to raw castings.
Wherein the results of corrosion tests show that heat treatment of castings did not significantly change their corrosion resistance in
comparison to raw castings, in contrast to the significant increase in mechanical properties.
In the family of iron-based alloys, ductile iron enjoys the highest rate of development, finding application in various industries. Ductile iron or the cast iron with spheroidal graphite can be manufactured by various methods. One of them is the Inmold spheroidization process characterized by different technological solutions, developed mainly to increase the process efficiency. So far, however, none of the solutions has been based on the use of a reactor made outside the casting mould cavity. The method of spheroidization inside the casting mould using a reaction chamber developed at the Foundry Research Institute is an innovative way of cast iron treatment. The innovative character of this method consists in the use of properly designed and manufactured reactor placed in the casting mould cavity. Owing to this solution, the Inmold process can be carried out in moulds with both horizontal and vertical parting plane. The study presents the results of examinations of the microstructure of graphite precipitates and metal matrix of castings after spheroidization carried out by the Inmold process using a reactor and mould with vertical parting plane. Special pattern assembly was made for the tests to reproduce plates with wall thicknesses of 3; 5; 7; 10; 20 and 30 mm. The content of residual magnesium was determined for all tested castings, while for castings of plates with a wall thickness equal to or larger than 10 mm, testing of mechanical properties was additionally performed.
The results presented in this paper are a continuation of the previously published studies. The results of hest treatment of ductile iron with
content 3,66%Si and 3,80% Si were produced. The experimental castings were subjected to austempering process for time 30, 60 and 90
minutes at temperature 300o
C. The mechanical properties of heat treated specimens were studied using tensile testing and hardness
measurement, while microstructures were evaluated with conventional metallographic observations. It was again stated that austempering
of high silicone ferritic matrix ductile iron allowed producing ADI-type cast iron with mechanical properties comparable with standard
ADI.
Production of spheroidal graphite cast iron is today quite mastered technology. There are many methods achieving the nodular graphite morphology. Each of these methods have specific characteristics and requirements to technical support, properties and the type of applied modifier. Selection of the spheroidization method is dependent on foundry disposition, production character, economic balance, quality requirements, etc. In case of centrifugally casting the core, which fills body and neck of the roll, is created by ductile iron. Considering the sophisticated production of centrifugally cast rolls for hot rolling mills it is necessary to ensure a high reproducibility and reliability of ductile cast iron production quality in the bulk range of 9-18 t per tapping. These conditions are in the Roll Foundry in Vítkovicke Slevarny, spol. s r.o. provided and verified mastered overpour method and the newly injection of cored wire in the melt.