In this paper, an algorithm will be presented that enables solving the two-phase inverse Stefan problem, where the additional information consists of temperature measurements in selected points of the solid phase. The problem consists in the reconstruction of the function describing the heat transfer coefficient, so that the temperature in the given points of the solid phase would differ as little as possible from the predefined values. The featured examples of calculations show a very good approximation of the exact solution and stability of the algorithm.
In order to determine the leading phase of the Fe - 4.25% C eutectic alloy, the method of directional crystallization, which allows to study the character of the solid / liquid growth front, was used. Examined eutectic was directionally solidified with a constant temperature gradient of G = 33,5 K/mm and growth rate of v = 125 μm/s (450 mm/h). The Bridgman technique was used for the solidification process. The sample was grown by pulling it downwards up to 30 mm in length. The alloy quenched by rapid pulling down into the Ga-In-Sn liquid metal. The sample was examined on the longitudinal section using a light microscope and scanning electron microscope. The shape of the solid/liquid interface and particularly the leading phase protrusion were revealed. The formation of the concave – convex interface has been identified in the quasi-regular eutectic growth arrested by quenching. The cementite phase was determined to be a leading phase. The total protrusion d is marked in the adequate figure.
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.
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.
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.
There has been a growing interest in the peritectic due to increasing productivity, quality, and alloy development. Differential scanning calorimetry (DSC) has traditionally been used to study steel solidification but suffers significant limitations when measuring the solidus and peritectic. This work covers a new thermal analysis system that can characterize the peritectic reaction. Heats of AISI/SAE 1030 and 4130 steel were poured to provide some benchmarking of this new technique. The peritectic was detected and the reaction temperature measured. Measurements agree reasonably well with reference information. A review of the literature and thermodynamic calculations did find some disagreement on the exact temperatures for the peritectic and solidus. Some of this difference appears to be related to the experimental techniques employed. It was determined that the system developed accurately indicates these reaction temperatures. The system provides a unique method for examining steel solidification that can be employed on the melt deck.
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.
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.
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.
In the aluminium alloy family, Al-Zn materials with non-standard chemical composition containing Mg and Cu are a new group
of alloys, mainly owing to their high strength properties. Proper choice of alloying elements, and of the method of molten metal treatment
and casting enable further shaping of the properties. One of the modern methods to produce materials with submicron structure is a method
of Rapid Solidification. The ribbon cast in a melt spinning device is an intermediate product for further plastic working. Using the
technique of Rapid Solidification it is not possible to directly produce a solid structural material of the required shape and length.
Therefore, the ribbon of an ultrafine grain or nanometric structure must be subjected to the operations of fragmentation, compaction,
consolidation and hot extrusion.
In this article the authors focussed their attention on the technological aspect of the above mentioned process and described successive
stages of the fabrication of an AlZn9Mg2.5Cu1.8 alloy of ultrafine grain structure designated for further plastic working, which enables
making extruded rods or elements shaped by the die forging technology. Studies described in the article were performed under variable
parameters determined experimentally in the course of the alloy manufacturing process, including casting by RS and subsequent
fragmentation.
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.
The mold temperature of the downward continuous unidirectional solidification (CUS) cannot be controlled higher than the liquidus of alloys to be cast. Therefore, the continuous casting speed becomes the main parameter for controlling the growth of columnar crystal structure of the alloy. In this paper, the tin bronze alloy was prepared by the downward CUS process. The microstructure evolution of the CUS tin bronze alloy at different continuous casting speeds was analysed. In order to further explain the columnar crystal evolution, a relation between the growth rate of columnar crystal and the continuous casting speed during the CUS process was built. The results show that the CUS tin bronze alloy mainly consists of columnar crystals and equiaxed crystals when the casting speed is low. As the continuous casting speed increases, the equiaxed crystals begin to disappear. The diameter of the columnar crystal increases with the continuous casting speed increasing and the number of columnar crystal decreases. The growth rate of columnar crystal increases with increasing of the continuous casting speed during CUS tin bronze alloy process.