The exploitation and processing of lignite in the Bełchatów region is connected with the formation of various mineral waste materials: varied in origin, mineral and chemical composition and raw material properties of the accompanying minerals, ashes and slags from lignite combustion and reagipsum from wet flue gas desulphurisation installations. This paper presents the results of laboratory tests whose main purpose was to obtain data referring to the potential use of fly ashes generated in the Bełchatów Power Plant and selected accompanying minerals exploited in the Bełchatów Mine in the form of self-solidification mixtures. The beidellite clays were considered as the most predisposed for use from the accompanying minerals , due to pozzolanic and sorption properties and swelling capacity. Despite the expected beneficial effects of clay minerals from the smectite group on the self-settling process as well as the stability of such blends after solidification, the results of physical-mechanical tests (compressive strength and water repellence) were unsatisfactory. It was necessary to use Ca (OH)2, obtained from the lacustrine chalk as an activator of the self-settling process It was necessary to use lacustrine chalk as an activator of the self-solidification process. The presence of calcium will allow the formation of cement phases which will be able to strongly bond the skeletal grains. Also, the addition of reagipsum to the composition of the mixture would contribute to the improvement of the physico-mechanical parameters. The elevated SO4 2– ion in the mixture during the solidification allows for the crystallization of the sulphate phases in the pore space to form bridges between the ash and clay minerals. The use of mixtures in land reclamation unfavourably transformed by opencast mining in the Bełchatów region would result in measurable ecological and economic benefits and would largely solve the problem of waste disposal from the from the operation and processing of lignite energy.
Directional solidification of ledeburite was realised out using a Bridgman’s device. The growth rate for movement sample v=83.3 μm/s was used. In one sample the solidification front was freezing. The value of temperature gradient in liquid at the solidification front was determined. Interfacial distance λ on the samples was measured with NIS-Elements application for image analysis.
A vertical cut at the mid-depth of the 15-ton forging steel ingot has been performed by curtesy of the CELSA – Huta Ostrowiec plant. Some metallographic studies were able to reveal not only the chilled undersized grains under the ingot surface but columnar grains and large equiaxed grains as well. Additionally, the structural zone within which the competition between columnar and equiaxed structure formation was confirmed by metallography study, was also revealed. Therefore, it seemed justified to reproduce some of the observed structural zones by means of numerical calculation of the temperature field. The formation of the chilled grains zone is the result of unconstrained rapid solidification and was not subject of simulation. Contrary to the equiaxed structure formation, the columnar structure or columnar branched structure formation occurs under steep thermal gradient. Thus, the performed simulation is able to separate both discussed structural zones and indicate their localization along the ingot radius as well as their appearance in term of solidification time.
The investigations were inspired with the problem of cracking of steel castings during the production process. A single mechanism of decohesion – the intergranular one – occurs in the case of hot cracking, while a variety of structural factors is decisive for hot cracking initiation, depending on chemical composition of the cast steel. The low-carbon and low-alloyed steel castings crack due to the presence of the type II sulphides, the cause of cracking of the high-carbon tool cast steels is the net of secondary cementite and/or ledeburite precipitated along the boundaries of solidified grains. Also the brittle phosphor and carbide eutectics precipitated in the final stage solidification are responsible for cracking of castings made of Hadfield steel. The examination of mechanical properties at 1050°C revealed low or very low strength of high-carbon cast steels.
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.
Directionally solidified sample of Fe-Fe3C eutectic alloy were produced under an argon atmosphere in a vacuum Bridgman-type furnace to study the eutectic growth with v = 167 μm/s pulling rate and constant temperature gradient G = 33.5 K/mm. Since how the growth texture of eutectic cementite is related to its growth morphology remains unclear, the current study aims to examine this relationship. The technique such as X-ray diffraction, have been used for the crystallographic analysis of carbide particles in white cast irons.
In this paper, the deviation from eutectic composition in boundary layer for eutectic growth is studied by phase-field method. According to a series of artificial phase diagram, the lamellar eutectic growth of these alloy is simulated during directional solidification. At steady state, average growth velocity of eutectic lamella is equal to the pulling velocity. With the increasing of the liquidus slope of β phase, the average composition in boundary layer would deviate from eutectic composition and the deviation increases. The constitutional undercooling difference between both solid phases caused by the deviation increases with the increasing of the deviation. The β phase would develop a depression under the influence of the deviation.
The results of examinations of the influence of titanium-boron inoculant on the solidification, the microstructure, and the mechanical properties of AlZn20 alloy are presented. The examinations were carried out for specimens cast both of the non-modified and the inoculated alloy. There were assessed changes in the alloy overcooling during the first stage of solidification due to the nuclei-forming influence of the inoculant. The results of quantitative metallographic measurements concerning the refinement of the grain structure of casting produced in sand moulds are presented. The cooling rate sensitivity of the alloy was proved by revealing changes in morphology of the α-phase primary crystals. Differences in mechanical properties resulting from the applied casting method and optional inoculation were evaluated.
The mathematical model of the globular eutectic solidification in 2D was designed. Proposed model is based on the Cellular Automaton Finite Differences (CA-FD) calculation method. Model has been used for studies of the primary austenite and of globular eutectic grains growth during the ductile iron solidification in the thin wall casting. Model takes into account, among other things, non-uniform temperature distribution in the casting wall cross-section, kinetics of the austenite and graphite grains nucleation, and non-equilibrium nature of the interphase boundary migration. Calculation of eutectic saturation influence (Sc = 0.9 - 1.1) on microstructure (austenite and graphite fraction, density of austenite and graphite grains) and temperature curves in 2 mm wall ductile iron casting has been done.
The paper presents the cellular automaton (CA) model for tracking the development of dendritic structure in non-equilibrium solidification conditions of binary alloy. Thermal, diffusion and surface phenomena have been included in the mathematical description of solidification. The methodology for calculating growth velocity of the liquid-solid interface based on solute balance, considering the distribution of the alloy component in the neighborhood of moving interface has been proposed. The influence of solidification front curvature on the equilibrium temperature was determined by applying the Gibbs Thomson approach. Solute and heat transfer equations were solved using the finite difference method assuming periodic boundary conditions and Newton cooling boundary condition at the edges of the system. The solutal field in the calculation domain was obtained separately for solid and liquid phase. Numerical simulations were carried out for the Al-4 wt.% Cu alloy at two cooling rates 15 K/s and 50 K/s. Microstructure images generated on the basis of calculations were compared with actual structures of castings. It was found that the results of the calculations are agreement in qualitative terms with the results of experimental research. The developed model can reproduce many morphological features of the dendritic structure and in particular: generating dendritic front and primary arms, creating, extension and coarsening of secondary branches, interface inhibition, branch fusion, considering the coupled motion and growth interaction of crystals.
It is well-known that the better the control of the liquid aluminium allows obtaining of better properties. One of the most important defects that is held responsible for lower properties has been the presence of porosity. Porosity has always been associated with the amount of dissolved hydrogen in the liquid. However, it was shown that hydrogen was not the major source but only a contributor the porosity. The most important defect that causes porosity is the presence of bifilms. These defects are surface entrained mainly due to turbulence and uncontrolled melt transfer. In this work, a cylindrical mould was designed (Ø30 x 300 mm) both from sand and die. Moulds were produced both from sand and die. Water cooled copper chill was placed at the bottom of the mould in order to generate a directional solidification. After the melt was prepared, prior to casting of the DC cast samples, reduced pressure test sample was taken to measure the melt quality (i.e. bifilm index). The cast parts were then sectioned into regions and longitudinal and transverse areas were investigated metallographically. Pore size, shape and distribution was measured by image analysis. The formation of porosity was evaluated by means of bifilm content, size and distribution in A356 alloy.
Paper present a thermal analysis of laser heating and remelting of EN AC-48000 (EN AC-AlSi12CuNiMg) cast alloy used mainly for casting pistons of internal combustion engines. Laser optics were arranged such that the impingement spot size on the material was a circular with beam radius rb changes from 7 to 1500 m. The laser surface remelting was performed under argon flow. The resulting temperature distribution, cooling rate distribution, temperature gradients and the depth of remelting are related to the laser power density and scanning velocity. The formation of microstructure during solidification after laser surface remelting of tested alloy was explained. Laser treatment of alloy tests were perform by changing the three parameters: the power of the laser beam, radius and crystallization rate. The laser surface remelting needs the selection such selection of the parameters, which leads to a significant disintegration of the structure. This method is able to increase surface hardness, for example in layered castings used for pistons in automotive engines.
In the high-alloy, ferritic - austenitic (duplex) stainless steels high tendency to cracking, mainly hot-is induced by micro segregation processes and change of crystallization mechanism in its final stage. The article is a continuation of the problems presented in earlier papers [1 - 4]. In the range of high temperature cracking appear one mechanism a decohesion - intergranular however, depending on the chemical composition of the steel, various structural factors decide of the occurrence of hot cracking. The low-carbon and low-alloy cast steel casting hot cracking cause are type II sulphide, in high carbon tool cast steel secondary cementite mesh and / or ledeburite segregated at the grain solidified grains boundaries, in the case of Hadfield steel phosphorus - carbide eutectic, which carrier is iron-manganese and low solubility of phosphorus in high manganese matrix. In duplex cast steel the additional factor increasing the risk of cracking it is very "rich" chemical composition and related with it processes of precipitation of many secondary phases.
The paper presents a new numerical model of solidification processes in hypoeutectic alloys. The model combines stochastic elements, such as e.g. random nucleation sites and orientation of dendritic grains, as well as deterministic methods e.g. to compute velocity of dendritic tips and eutectic grains. The model can be used to determine the temperature and the size of structure constituents (of both, the primary solid phase and eutectics) and the arrangement of individual dendritic and eutectic grains in the consecutive stages of solidification. Two eutectic transformation modes, typical to modified and unmodified hypoeutectic alloys, have been included in the model. To achieve this, cellular automata and Voronoi diagrams have been utilized.
The paper presents results of measuring heat diffusivity and thermal conductivity coefficients of used green foundry sand in temperature range ambient – 600 o C. During the experiments a technical purity Cu plate was cast into the green-sand moulds. Basing on measurements of the mould temperature field during the solidification of the casting, the temperature relationships of the measured properties were evaluated. It was confirmed that the obtained relationships are complex and that water vaporization strongly influences thermal conductivity of the moulding sand in the first period of the mould heating by the poured and solidified casting
Mg-0.5Si-xSn (x=0.95, 2.9, 5.02wt.%) alloys were cast and extruded at 593K (320 ºC) with an extrusion ratio of 25. The microstructure and mechanical properties of as-cast and extruded test alloys were investigated by OM, SEM, XRD and tensile tests. The experimental results indicate that the microstructure of the Mg-0.5Si-xSn alloys consists of primary α-Mg dendrites and an interdendritic eutectic containing α-Mg, Mg2Si and Mg2Sn. There is no coarse primary Mg2Si phase in the test alloys due to low Si content. With the increase in the Sn content, the Mg2Si phase was refined. The shape of Mg2Si phase was changed from branch to short bar, and the size of them were reduced. The ultimate tensile strength and yield strength of Mg-0.52Si-2.9Sn alloy at the temperature of 473K (200 ºC) reach 133MPa and 112MPa respectively. Refined eutectic Mg2Si phase and dispersed Mg2Sn phase with good elevated temperature stability are beneficial to improve the elevated temperature performance of the alloys. However, with the excess addition of Sn, large block-like Mg2Sn appears around the grain boundary leading to lower mechanical properties.
The aim of the present work is to verify a numerical implementation of a binary fluid, heat conduction dominated solidification model with a novel semi-analytical solution to the heat diffusion equation. The semi-analytical solution put forward by Chakaraborty and Dutta (2002) is extended by taking into account variable in the mushy region solid/liquid mixture heat conduction coefficient. Subsequently, the range in which the extended semi-analytical solution can be used to verify numerical solutions is investigated and determined. It has been found that linearization introduced to analytically integrate the heat diffusion equation impairs its ability to predict solidus and liquidus line positions whenever the magnitude of latent heat of fusion exceeds a certain value.
In this paper, the mathematical model and numerical simulations of the molten steel flow by the submerged entry nozzle and the filling process of the continuous casting mould cavity are presented. In the mathematical model, the temperature fields were obtained by solving the energy equation, while the velocity fields were calculated by solving the momentum equations and the continuity equation. These equations contain the turbulent viscosity which is found by solving two additional transport equations for the turbulent kinetic energy and its rate of dissipation. In the numerical simulations, coupling of the thermal and fluid flow phenomena by changes in the thermophysical parameters of alloy depending on the temperature has been taken into consideration. This problem (2D) was solved by using the finite element method. Numerical simulations of filling the continuous casting mould cavity were performed for two variants of liquid metal pouring. The effect of the cases of pouring the continuous casting mould on the velocity fields and the solid phase growth kinetics in the process of filling the continuous casting mould was evaluated as these magnitudes have an influence on the high quality of the continuous cast steel slab.
In Part I of this article, two-stage solidification model was presented. In this part we use our model to simulate solidification of the Al 7% Si alloy for two cooling rates and . Simulations have been performed for two eutectic transformation modes, typical for modified and unmodified alloys. Obtained cooling curves are qualitatively consistent with the typical cooling curves for modified and unmodified alloys. Moreover, evolution of cooling-curve characteristics is compared with the analytical model and found to be in close agreement.
The paper presents a research results concerning impact of volume modification (ceramic filter containning cobalt aluminate and hafniumpowder) and simultaneous surface and volume modification on solidification and stereological parameters of macrostructure of castingsmade from post-production scrap of nickel superalloy IN-713C. Research included investigation of the influence of chemical compositionon the temperature Tliq i Tsol and evaluation of following macrostructure parameters: the number of grains per mm2, average grain area andshape coefficient. Results indicate high influence of carbon content on Tliq. Macrostructure of sample castings indicate positive effect of surface and volume modification, however impact of surface modification is more pronounced.
In this study, solidification/stabilization (S/S) of electric arc furnace dust (EAFD) which is generated during the production of steel from scrap metals and classified as hazardous waste were investigated by using different ratios of cement and low grade MgO (LG MgO) as binding agents. Type I PC 42.5 R portland cement and LG MgO which contains 70–80% MgO were used. S/S blocks that contain different ratios of binding agents which have 1/0.5 – 1/1 – 1/2 – 1/3 – 1/4 – 1/5 cement/LG MgO ratio and S/S blocks which contain only cement and no LG MgO agents were prepared. These blocks, which contain 3 different waste ratios according to weight, 20%, 30% and 40% respectively, were produced and exposed to 28-day water purification. At the end of the purification process, S/S blocks were extracted using TCLP (Toxicity Characteristic Leaching Procedure) tests in order to determine the leaching behavior of Zn, Pb, and Cd in S/S blocks. By the end of this study, it was concluded that the recovery of EAFD is possible and applicable by immobilization. The findings of the study concluded that environmental performances or structural properties of blocks contain 30% waste by weight are suitable. This method is a proper one for recovering and treatment of EAFD with mixture of cement and LG MgO.
Investigation of the tensile and fatigue properties of cast magnesium alloys, created by the heated mold continuous casting process (HMC), was conducted. The mechanical properties of the Mg-HMC alloys were overall higher than those for the Mg alloys, made by the conventional gravity casting process (GC), and especially excellent mechanical properties were obtained for the Mg97Y2Zn1 -HMC alloy. This was because of the fine-grained structure composed of the -Mg phases with the interdendritic LPSO phase. Such mechanical properties were similar levels to those for conventional cast aluminum alloy (Al84.7Si10.5Cu2.5Fe1.3Zn1 alloys: ADC12), made by the GC process. Moreover, the tensile properties (UTS and f ) and fatigue properties of the Mg97Y2Zn1 -HMC alloy were about 1.5 times higher than that for the commercial Mg90Al9Zn1 -GC alloy (AZ91). The high correlation rate between tensile properties and fatigue strength (endurance limit: l ) was obtained. With newly proposed etching technique, the residual stress in the Mg97Y2Zn1 alloy could be revealed, and it appeared that the high internal stress was severely accumulated in and around the long-period stacking-order phases (LPSO). This was made during the solidification process due to the different shrinkage rate between α-Mg and LPSO. In this etching technique, microcracks were observed on the sample surface, and amount of micro-cracks (density) could be a parameter to determine the severity of the internal stress, i.e., a large amount to micro-cracks is caused by the high internal stress.
The paper presents results of measuring thermal conductivity and heat capacity of bentonite foundry sand in temperature range ambient – 900 OC. During the experiments a technical purity Cu plate was cast into the green-sand moulds. Basing on measurements of the mould temperature field during the solidification of the casting, the temperature relationships of the measured properties were evaluated. It was confirmed that water vaporization strongly influences thermal conductivity of the moulding sand in the first period of the mould heating by the poured casting.
The objective of the research was to determine the influence of boron on the crystallization process and microstructure of ductile cast iron. In the case of ductile cast iron it is a vital issue because even as little as trace presence of boron changes the properties of ductile cast iron in a significant way. With the use of a new ATD-4 (TDA) tester and CRYSTALDIGRPAH converter it was possible to measure the crystallization process parameters of the same alloy with four different contents of boron in one mould. Four samples with different boron contents were extracted, their microhardness was measured and quantitative analysis of microstructure was conducted. Obtained results allowed to state that with increasing content of boron the amount of graphite precipitates decreases, the amount of pearlite precipitates increases, the shape of graphite precipitates deteriorates and hardness increases. It is also planned to perform additional testings with boron contents between previously tested values.