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1
Content available Thin Wall Ductile Iron Castings as Substitutes for Aluminium Alloy Castings
Fraś E., Górny M., Lopez H.
Archives of Metallurgy and Materials
|
2014
|
Vol. 59, iss. 2
459--465
EN
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.
PL
W pracy omówiono przyczyny aktualnego trendu zastępowania odlewów z żeliwa przez odlewy ze stopów aluminium. W szczególności wykazano, że możliwe jest wytworzenie odlewów cienkościennych (wahacze, wsporniki, wirniki), wykonanych z żeliwa sferoidalnego bez zabieleń, niedolewów i niespawów oraz posiadających wskaźnik wytrzymałości (stosunek wytrzymałości do gęstości) wynoszący do 87 MPa cm3/g. Ponadto zastosowanie obróbki cieplnej polegającej na austenityzacji w temperaturze 900°C przez 20 minut oraz hartowaniu izotermicznemu w kąpieli solnej w temperaturze 350°C przez 15 minut powoduje otrzymanie osnowy austerrytycznej w odlewach cienkościennych, co zwiększa wskaźnik wytrzymałości do 154 MPa cm3/g. Z przeprowadzonych badań wynika, że odlewy z żeliwa sferoidalnego mogą być lżejsze od ich substytutów ze stopów aluminium, a przy tym charakteryzować się podobnymi lub lepszymi właściwościami mechanicznymi.
2
Content available Thin wall ductile iron castings: technological aspects
Fraś E., Górny M., Kapturkiewicz W.
Archives of Foundry Engineering
|
2013
|
Vol. 13, iss. 1
23--28
EN
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.
3
Content available An inoculation phenomenon in cast iron
Fraś E., Górny M.
Archives of Metallurgy and Materials
|
2012
|
Vol. 57, iss. 3
768-777
EN
The paper presents a solidification sequence of graphite eutectic cells of A and D types, as well as globular and cementite eutectics. The morphology of eutectic cells in cast iron, the equations for their growth and the distances between the graphite precipitations in A and D eutectic types were analysed. We observed a critical eutectic growth rate at which one type of eutectic transformed into another. A mathematical formula was derived that combined the maximum degree of undercooling, the cooling rate of cast iron, eutectic cell count and the eutectic growth rate. One type of eutectic structure turned smoothly into the other at a particular transition rate, transformation temperature and transformational eutectic cell count. Inoculation of cast iron increased the number of eutectic cells with flake graphite and the graphite nodule count in ductile iron, while reducing the undercooling. An increase in intensity of inoculation caused a smooth transition from a cementite eutectic structure to a mixture of cementite and D type eutectic structure, then to a mixture of D and A types of eutectics up to the presence of only the A type of eutectic structure. Moreover, the mechanism of modification of cast iron was studied.
PL
W pracy podano sekwencję krystalizacji ziaren eutektyki grafitowej typu A i D oraz kulkowej a także eutektyki cementytowej. Przeanalizowano morfologię tych ziaren w żeliwie oraz równania na prędkość wzrostu ziaren oraz odległość miedzy wydzieleniami grafitu typu A i D. Wykazano, że istnieją krytyczne prędkości wzrostu eutektyki, przy których jeden rodzaj eutektyki przekształca sie w drugi. Wyprowadzono ogólne równanie wiążące stopień przechłodzenia eutektyk z szybkością stygnięcia żeliwa, liczba ziaren eutektycznych i prędkością ich wzrostu. Wykazano, że istnieje prędkość transformacji, temperatura transformacji i transformacyjna liczba ziaren, przy których jeden rodzaj eutektyki przechodzi płynnie w drugi. Modyfikacja żeliwa zwiększa liczbę ziaren eutektycznych w żeliwie z grafitem płatkowym i liczbę kulek grafitu w żeliwie sferoidalnym oraz zmniejsza przechłodzenie. Powiększenie intensywności modyfikacji powoduje płynne przejście od eutektyki cementytowej poprzez mieszaniny eutektyk typu D i cementytowej, eutektyk typu D i A aż do wyłącznie eutektyki typu A. Podano mechanizm modyfikacji żeliwa.
4
Content available Inoculation effects of cast iron
Fraś E., Górny M.
Archives of Foundry Engineering
|
2012
|
Vol. 12, iss. 4
39-46
EN
The paper presents a solidification sequence of graphite eutectic cells of A and D types, as well as globular and cementite eutectics. The morphology of eutectic cells in cast iron, the equations for their growth and the distances between the graphite precipitations in A and D eutectic types were analyzed. It is observed a critical eutectic growth rate at which one type of eutectic transformed into another. A mathematical formula was derived that combined the maximum degree of undercooling, the cooling rate of cast iron, eutectic cell count and the eutectic growth rate. One type of eutectic structure turned smoothly into the other at a particular transition rate, transformation temperature and transformational eutectic cell count. Inoculation of cast iron increased the number of eutectic cells with flake graphite and the graphite nodule count in ductile iron, while reducing the undercooling. An increase in intensity of inoculation caused a smooth transition from a cementite eutectic structure to a mixture of cementite and D type eutectic structure, then to a mixture of D and A types of eutectics up to the presence of only the A type of eutectic structure. Moreover, the mechanism of inoculation of cast iron was studied.
5
Content available Forming of the microstructure in Fe-C-V alloys
Kawalec M., Fraś E.
Metallurgy and Foundry Engineering
|
2011
|
Vol. 37, no. 1
17-24
EN
The study presents the results of microstructural examinations of the volume solidifying Fe-C-V alloys containing carbon in the range of 1.45-2.23% and vanadium in the range of 7.33-15.08%. Attention was focussed on near-eutectic alloys. The Fe-C-V eutectic crystallising in these alloys is composed of ferrite and vanadium carbides of VC1-x type, and as such is included in the group of fibrous eutectics. During research, the experimental eutectic lines were plotted for Fe-C-V alloys, and a formula enabling calculation of the eutectic saturation ratio of these alloys was proposed.
PL
W pracy przedstawiono wyniki badań mikrostruktury stopów Fe-C-V, o zawartości węgla w zakresie 1,45-2,23% i wanadu w zakresie 7,33-15,08%, krystalizujących w sposób objętościowy, przy czym szczególną uwagę zwrócono na stopy okołoeutektyczne. Krystalizująca w stopach Fe-C-V eutektyka składa się z ferrytu i węglików wanadu typu VC1-x i jest zaliczana do grupy eutektyk włóknistych. W pracy określono eksperymentalnie przebieg linii eutektycznej dla stopów Fe-C-V oraz wyznaczono zależność na stopień nasycenia eutektycznego dla tych stopów.
6
Content available remote Computer modelling of ductile iron solidification using FDM and CA methods
Kapturkiewicz W., Burbelko A. A., Fraś E., Górny M., Gurgul D.
Journal of Achievements in Materials and Manufacturing Engineering
|
2010
|
Vol. 43, nr 1
310--323
EN
Purpose: The purpose of the work was the presentation of tool for modelling of solidification process, for prediction of some structure parameters in DI by the given chemical composition of alloy and for given boundary condition of casting. Design/methodology/approach: Two mathematical models and methods developed by authors have been presented: micromodelling with using of finite difference method (FDM) and mesomodelling with using of cellular automaton method (CA). Findings: The FDM was used for solving the DI solidification model, including heat conductivity equation with source function, boundary condition for casting, equations for austenite and eutectic grains nucleation depended on the changing undercooling, the Weibull’s formula for graphite nodule count, Kolmogorov’s equation for calculation of volume fraction of phases (eutectics and austenite). A set of equations, after transformation to a difference form, were solved by the finite difference method, using an iteration procedure. The correctness of the mathematical model has been experimentally verified in the range of most significant factors, which include temperature field, the value of maximum undercooling, and the graphite nodule count interrelated with the casting cross-section. Literature offers practically no data on so confronted process model and simulation program. The CA model was used for the simulation of the grains’ shapes in connection with FD for temperature field and solute redistribution in the grain scale. Practical implications: FDM modeling gives the possibility of statistical description of microstructure but the geometrical shape of grains is assumed a priori. In CA modeling the grain shape is not assumed, but this is the result of modeling. The use of FDM gives results quantitatively comparable to the process in real casting, particularly according to temperature fields and number of graphite spheroids. Originality/value: The CA method gives on the present stage credible qualitative results but this method is more perspective for good reproducing of the real process of solidification.
7
Content available remote Thin wall ductile and austempered iron castings
Fraś E., Górny M.
Archives of Foundry Engineering
|
2010
|
Vol. 10, iss. 3
5--10
EN
It has been shown that it is possible to produce thin wall castings made of ductile iron with wall thickness in the range of 1.2 to 2.9 mm (without chills, cold laps and misruns). Thin wall ductile iron castings can be lighter (380 g) than their substitutes made of aluminium alloys (580 g). The kinetics of austenitising transformation was studied in unalloyed ductile iron. The advance of transformations during austenitising was monitored by measurement the fraction of martensite and also by dilatometic studies. It has been shown that in thin wall ductile iron castings austenitising at 880 oC for 20 minutes is adequate to obtain the austenite matrix at the end of the first stage of austempering heat treatment cycle.
8
Content available remote The morphology of TiC carbides produced in surface layers of carbon steel castings
Fraś E., Olejnik E., Janas A., Kolbus A.
Archives of Foundry Engineering
|
2010
|
Vol. 10, iss. 4
39--42
EN
The study presents the results of investigations of the process of in situ fabrication of TiC carbides in a surface layer of carbon steel casting. Carbides were produced by SHS reaction taking place between the substrates deposited on mould surface and cast molten alloy. The thickness of the obtained layer was up to 700 μm, and the size of carbides was comprised in a range of 1-10μm. During alloy solidification in mould, a thermal analysis was carried out; its results were used in evaluation of the morphology of the obtained titanium carbides. It has been found that, at the moment of reaction, the temperature of the reaction layer and the temperature of the central part of casting differed by 93 K. This difference has changed the morphology of the obtained carbides. In the region of reaction layer, where the temperature amounted to 1955 K, the crystals assumed an oval and coagulated shape, while at the layer-casting interface, TiC carbides in the form of cuboids were formed.
9
Content available remote Shaping of the microstructure in neareutectic Fe-C-V alloys
Kawalec M., Fraś E.
Archives of Foundry Engineering
|
2010
|
Vol. 10, iss. 4
83--88
EN
The study presents the results of microstructural examinations of the volume solidifying Fe-C-V alloys containing carbon in the range of 1.45÷2.23% and vanadium in the range of 7.33÷15.08%. Attention was focussed on near-eutectic alloys. The Fe-C-V eutectic crystallising in these alloys is composed of ferrite and vanadium carbides of VC1-x type, and as such is included in the group of fibrous eutectics. During research, the experimental eutectic lines were plotted for Fe-C-V alloys, and a formula enabling calculation of the eutectic saturation ratio of these alloys was proposed.
10
Content available remote Multiphysics and multiscale modelling of ductile cast iron solidification
Gurgul D., Burbelko A., Fraś E., Guzik E.
Archives of Foundry Engineering
|
2010
|
Vol. 10, iss. 1 spec.
35--40
EN
The presented model of ductile cast iron solidification is a typical sample of multiphysics and multiscale engineering system. This model takes into consideration the different time and spatial scales of accounted phenomenon of microstructure formation: heat diffusion, components mass diffusion in the liquid and solid phases, thermodynamic of phase transformation under the condition of inhomogeneous chemical composition of growing and vanishing phases, phase interface kinetics and grains nucleation. The results of two-dimensional modelling of the microstructure formation in the ductile cast iron (so called - Ductile Iron - DI) are presented. The cellular automaton model (CA) was used for the simulation. Six states of CA cells were adopted to three phases above mentioned (liquid, austenite and graphite) and to three two-phase interfaces. For the modelling of concentration and temperature fields the numerical solution was used. The parabolic nonlinear differential equations with a source term were solved by using the finite difference method and explicit scheme. The overlapping lattices with the same spatial step were used for the concentration field modelling and for the CA. The time scale of the temperature field for this lattice is about 104 times shorter. Due to above reasons the another lattice was used with a multiple spatial step and the same time step.
11
Content available remote Morphology of graphite solidified in Ni3Al/C intermetallic
Fraś E., Janas A., Olejnik E., Kawalec M., Kolbus A.
Archives of Foundry Engineering
|
2010
|
Vol. 10, iss. 1 spec.
169--174
EN
The study presents the results of microstructural examinations of the Ni-Al-C alloy forming a natural Ni3Al/C composite, in which the precipitates of graphite are acting as a lubricating, slip phase. Different forms of graphite were described, starting with the fibrous shapes and ending in spheroidal forms, identical with the spheroidal graphite present in cast iron. The morphologies of graphite precipitates in the Ni3Al phase were compared to similar precipitates observed in ferrous alloys with high carbon content.
12
Content available remote Mechanism of free sulfur influence on the eutectic cell count and transition from graphite to cementite eutectic in cast iron Part I. Theoretical background
Fraś E., Górny M.
Archives of Foundry Engineering
|
2010
|
Vol. 10, iss. 1 spec.
53--56
EN
In this work an analytical solution of general validity is used to explain the mechanism of free sulfur influence on the cell count and on the transition from graphite to cementite eutectic in cast iron. It is found that this transition can be related to the nucleation potential of graphite (represented by eutectic cell count Nv), the growth rate coefficient of graphite eutectic cell, μ the temperature range, ΔTsc and the pre-eutectic austenite volume fraction, fγ.
13
Content available remote Mechanism of free sulfur influence on the eutectic cell count and transition from graphite to cementite eutectic in cast iron. Part II. Experimental verification
Fraś E., Górny M.
Archives of Foundry Engineering
|
2010
|
Vol. 10, iss. 1 spec.
57--62
EN
In this work the mechanism of free sulfur influence on the transition from graphite to cementite eutectic in cast iron is experimentally verified. It has been shown that the main impact of free sulfur on the transition from graphite to cementite eutectic consist in reducing the growth rate of graphite eutectic cell.
14
Content available remote Mechanism of carbon influence on the transition from graphite to cementite eutectic in cast iron
Fraś E., Górny M.
Archives of Foundry Engineering
|
2010
|
Vol. 10, iss. 2
51--56
EN
In this work an analytical solution is used to explain mechanism of carbon influence on the transition from graphite to cementite eutectic in cast iron. It is found that this transition can be related to (1) the nucleation potential of graphite (characterized directly by the cell count, N and indirectly by nucleation coefficients Ns and b) (2) the growth rate coefficient of graphite eutectic cell, [mi] (3) the temperature range, [delta]Tsc = Ts - Tc (where Ts and Tc is the equilibrium temperature of the graphite eutectic and formation temperature of the cementite eutectic respectively) and (4) the liquid volume fraction, fl after solidification of the pre-eutectic austenite. Method of estimation of Ns b and [mi] values was presented. It has been shown that the main impact of carbon on the transition from graphite to cementite eutectic consist in increasing the eutectic cell count and growth rate of graphite eutectic cell. Analytical equations were derived to describe the absolute, CT relative chilling tendency, CTr and chill, w of cast iron.
15
Content available remote Fabrication of in situ composite layer on cast steel
Fraś E., Olejnik E., Janas A., Kolbus A.
Archives of Foundry Engineering
|
2010
|
Vol. 10, iss. 1 spec.
175--180
EN
The study describes the technology of fabrication of composite layers in cast steel reinforced with titanium carbides. In the process under discussion, the reinforcing TiC phase is formed in situ from the substrates deposited on mould cavity, where the said substrates under the effect of heat supplied by molten metal poured into mould (1823K) undergo a synthesis in the SHS reaction. An outcome of this process is the formation, within the casting surface, of a layer from 550 to 1200μm thick. Carbides produced in this synthesis have the size from 0,5 to 20μm and a non-typical spheroidal shape. The hardness of the produced layer examined in function of the distance from the casting surface is from 700 to 1134 HV, and is determined by volume fraction of the reinforcing TiC phase. To better document the type of microstructure obtained in the produced material, metallographic and structural examinations were carried out using the method of scanning electron microscopy (SEM), X-ray microanalysis (EDS/EDX), and phase analysis (XRD). To check the mechanical properties of the examined material, hardness was measured by the Vickers test.
16
Content available remote Cellular automata modeling of cooperative eutectic growth
Burbelko A., Gurgul D., Fraś E., Olejnik E.
Archives of Foundry Engineering
|
2010
|
Vol. 10, iss. 1 spec.
29--34
EN
The model and results of the 2D simulation of the cooperative growth of two phases in the lamellar eutectic are presented. The proposed model takes into account heat transfer, components diffusion and nonstationary concentration distribution in the liquid and solid phases, non-equlibrium nature of the phase transformation and kinetics of the growth, influence of the surface energy and interface curvature on the conditions of the thermodynamic equilibrium. For the determination of the phase interface shape the Cellular Automata technique (CA) was used. For the calculation of temperature and concentration distribution the numerical solution of the Fourier equation was used. The partial differential equations were solved by Finite Differences Method (FDM). The spatial position and cell sizes of CA lattice and FDM mesh are equal. Proposed model can predict the steady state growth with a constant interlamellar spacing in the regular plate eutectic, as well as some transient processes that bring to the changes of that parameters. Obtained simulation data show the solid-liquid interface changes result in the termination of lamella and enlargement of interlamellar spacing. Another simulation results illustrate a pocket formation in the center of one phase that forestalls nucleation (or intergrowth) of the new lamellae of another phase. The data of the solidification study of the transparent material (CBr4– 8,4% C2Cl6) obtained in the thin layer demonstrate the qualitative agreement of the simulation.
17
Dyfuzyjny i częściowo dyfuzyjny model wzrostu ziaren w żeliwie z grafitem kulkowym i płytkowym
Kapturkiewicz W., Fraś E., Burbelko A.
Zeszyty Naukowe. Mechanika / Politechnika Opolska
|
2009
|
z. 95
75-76
18
Content available remote Modeling the kinetics of solidification of cast iron with lamellar graphite
Kapturkiewicz W., Fraś E., Burbelko A. A.
Archives of Metallurgy and Materials
|
2009
|
Vol. 54, iss. 2
369-380
EN
The most important results of own studies on modeling the solidification kinetics in lamellar (flake) graphite cast iron were reviewed. A set of basic equations used for modeling the solidification process in macro- and micro-scales was given. A numerical solution of these model equations enables the determination of thermodynamic equilibrium temperature and actual temperature of cast iron solidification, the cooling rate, the heat flux generated during solidification, the fractions of the solidified structural constituents, the size of graphite eutectic grains and austenite dendrites, thickness of graphite lamellar, as well as the segregation of cast iron alloying constituents in liquid phase and in the forming grains. It has also been proved and confirmed by experiments that the grains of graphite eutectic are formed in a two-step process, that is, at the beginning and end of the solidification process. Some important differences in the size of graphite precipitates were observed to exist between the cast plate and cylinder.
PL
Zaprezentowano najistotniejsze rezultaty własnych prac, dotyczących modelowania komputerowego krystalizacji żeliwa z grafitem płatkowym. Przedstawiono zestaw podstawowych równań procesu, odnoszących się do mikro i makro skali. Rozwiązanie numeryczne zestawu równań w postaci programu symulacyjnego pozwoliło na wyznaczenie przebiegu temperatury w czasie stygnięcia odlewu wraz z rozkładem temperatury równowagowej, ciepła generowanego podczas krystalizacji, ilości frakcji zakrzepłej poszczególnych składników strukturalnych żeliwa, wymiaru ziaren austenitu i eutektyki grafitowej, wymiary płatków grafitu jak również mikrosegregacji składników stopu w ziarnach. Potwierdzono eksperymentalnie, że ziarna eutektyki grafitowej mogą zarodkować w dwóch etapach: na początku i pod koniec procesu krystalizacji. Istotne różnice zauważono w wymiarach grafitu w zależnosci od kształtu odlewu.
19
Content available remote Mechanism of the silicon influence on absolute chilling tendency and chill of cast iron
Fraś E., Górny M., Lopez H. F.
Archives of Metallurgy and Materials
|
2009
|
Vol. 54, iss. 1
103-110
EN
In this work an analytical solution of general validity is used to explain mechanism of the silicon influence on the absolute chilling tendency (CT) and chill (w) of cast iron. It is found that CT can be related to nucleation potential of graphite (Nv), growth parameter (μ) of eutectic cells, temperature range (ΔTsc), where ΔTsc = Ts - Tc (Ts is graphite eutectic equilibrium temperature and Tc is cementite eutectic formation temperature) and the pre-eutectic austenite volume fraction (fϒ). It has been shown that silicon addition: 1) impedes the growth of graphite eutectic cells through decreasing the graphite eutectic growth coefficient (μ), 2) expands the temperature range (ΔTsc), 3) increases the nucleation potential of graphite (Nv), 4) lowers the pre-eutectic austenite volume fraction, (fϒ). In a consequence, the absolute chilling tendency (CT) decreases. The minimum wall thicknesses for chilled castings, or chill width (w) in wedge shaped castings is related to CT and as Si content increases, the chill width, w value decreases.
PL
W pracy przedstawiono wyniki rozwiązania analitycznego mechanizmu wpływu krzemu na bezwzględną skłonność żeliwa do zabieleń (CT) i zabielenia (w) w żeliwie. Wykazano, że CT jest uzależnione od potencjału zarodkowania grafitu (Nv), parametru wzrostu (μ) ziaren eutektycznych, zakresu temperatury (ΔTsc), gdzie ΔTsc = Ts - Tc (Ts jest równowagowa temperatura krystalizacji eutektyki grafitowej, a Tc jest temperatura tworzenia eutektyki cementowej) oraz udział przedeutektycznego austenitu (fϒ). Z przedstawionych badan wynika, ze dodatek krzemu: 1) utrudnia wzrost ziaren eutektycznych poprzez zmniejszenie współczynnika wzrostu eutektyki grafitowej (μ), 2) rozszerza zakres temperatury (ΔTsc), 3) zwieksza potencjał zarodkowania grafitu (Nv, 4) zmniejsza udział przedeutektycznego austenitu (fϒ) a w konsekwencji zmniejsza bezwzgledną skłonność żeliwa do zabieleń (CT). Wykazano ponadto, że minimalna grubość ścianki, powyżej której w odlewie występują zabielenia lub szerokość zabielenia klina (w) w odlewie o kształcie klina zależy od CT oraz zwiększenie zawartości krzemu prowadzi do zmniejszenia szerokości zabielania klina.
20
Content available remote Thin Wall Austempered Ductile Iron (TWADI)
Fraś E., Górny M.
Archives of Foundry Engineering
|
2009
|
Vol. 9, iss. 3
45-48
EN
In this paper the analysis of thin walled castings made of ductile iron is considered. It is shown that thin wall austempered ductile iron can be obtained by means of short-term heat treatment of thin wall castings without addition of alloying elements. Metallographic examinations of 2 mm thin walled castings along with casting with thicker wall thickness (20x28 mm) after different austempring conditions are presented. It has been proved that short-term heat treatment amounted 20 minutes of austenitizing at 880 oC followed by holding at 400 oC for 5 minutes causes ausferrite matrix in 2 mm wall thickness castings, while casting with thicker wall thickness remain untransformed and martensite is still present in a matrix. Finally there are shown that thin wall ductile iron is an excellent base material for austempering heat treatments. As a result high mechanical properties received in thin wall plates made of austempered ductile iron.
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