The paper presents results of a study concerning an AlSi7Mg alloy and the effect of subjecting the liquid metal to four different processes: conventional refining with hexachloroethane; the same refining followed by modification with titanium, boron, and sodium; refining by purging with argon carried out in parallel with modification with titanium and boron salts and strontium; and parallel refining with argon and modification with titanium, boron, and sodium salts. The effect of these four processes on compactness of the material, parameters of microstructure, and fatigue strength of AlSi7Mg alloy after heat treatment. It has been found that the highest compactness (the lowest porosity ratio value) and the most favorable values of the examined parameters of microstructure were demonstrated by the alloy obtained with the use of the process including parallel purging with argon and modification with salts of titanium, boron, and sodium. It has been found that in the fatigue cracking process observed in all the four variants of the liquid metal treatment, the crucial role in initiation of fatigue cracks was played by porosity. Application of the process consisting in refining by purging with argon parallel to modification with Ti, B, and Na salts allowed to refine the microstructure and reduce significantly porosity of the alloy extending thus the time of initiation and propagation of fatigue cracks. The ultimate effect consisted in a distinct increase of the fatigue limit value.
Elaborated shapes of many car components are the reason for which the use of casting techniques to fabricate them is a solution wellfounded from the economical point of view. Currently applicable regulatory requirements concerning emissions of exhaust fumes force the carmakers to reduce the overall weight of their products, as this is a basic precondition for reducing fuel consumption. As a result, newly launched car models contain a continuously increasing share of thin-walled castings made of materials which ensure a satisfactory level of service properties. At the same time, developing new technological processes allowing to extend the service life of individual components by means of surface improving becomes more and more important.
The paper presents an analysis of factors affecting the wear of cylinder liners. The effect of the graphite precipitation morphology on the cylinder liner wear mechanism is presented. Materials used to cast cylinder liners mounted in a number of engines have been examined for their conformity with requirements set out in applicable Polish industrial standard. A casting for a prototype cylinder liner has been made with a microstructure guaranteeing good service properties of the part.
The paper proposes a methodology useful in verification of results of dilatometric tests aimed at determination of temperatures defining the start and the end of eutectoid transformation in the course of ductile cast iron cooling, based on quenching techniques and metallographic examination. For an industrial melt of ductile cast iron, the effect of the rate of cooling after austenitization at temperature 900°C carried out for 30 minutes on temperatures TAr1 start and TAr1 end was determined. The heating rates applied in the study were the same as the cooling rates and equaled 30, 60, 90, 150, and 300°C/h. It has been found that with increasing cooling rate, values of temperatures TAr1 start and TAr1 end decrease by several dozen degrees.
The study reported in this paper was aimed at establishing the effect of values of parameters characterizing the process of superficial remelting of a nodular iron casting on the quantity of introduced heat, geometry of remeltings as well as parameter λ and hardness of cementite eutectic. The remelting process was carried out using GTAW method, at electric arc length of 3 mm in argon atmosphere, welding current intensities I = 50, 130, 210, and 300 A, and electric arc scanning speeds vs = 200, 400, and 800 mm/min. The measurements included estimation of the quantity of heat introduced to the casting in the electric arc-induced remelting process with the use of flow calorimeter. Widths and depths of remetlings were assessed with the use of metallographic method. As a result of fast solidification, cementite eutectic was obtained in remelted material in which, in the course of cooling down to ambient temperature, austenite was subject to partial transformation into martensite. To characterize the cementite eutectic, value of the structural parameter λ was assessed. Values of the parameter were similar for areas of occurrence of both fibrous and laminated eutectic. Remeltings were examined at half of their depths. Micro-hardness measurements were taken in the same areas. The established quantitative relationships may prove to be useful in practice for the purpose of predicting values of parameter λ and hardness of remeltings in studies aimed at improving resistance of cast-iron castings to abrasive wear.
This study presents results of stress rupture test of MAR-M-509 cobalt alloy samples, as-cast and after surface refining with a concentrated stream of heat. Tests were conducted on samples of MAR-M-509 alloy castings, obtained using the lost-wax method. Casting structure refining was performed with the GTAW method in argon atmosphere, using the current I = 200 A and electrical arc scanning velocity vs = 100, 150, 200 and 250 mm/min. The effect of rapid resolidification of the MAR-M-509 alloy on the microstructure was examined and significant improvement in stress rupture test was observed.
The paper deals with susceptibility of nodular cast iron with ferritic -pearlitic matrix on cavitation erosion . Cavitation tests were carried out with the use of a cavitation erosion vibratory apparatus employing a vibration exciter operated at frequency of 20 kHz. The study allowed to determine the sequence of subsequent stages in which microstr ucture of cast iron in superficial regions is subject to degradation. The first features to be damaged are graphite precipitates. The ferritic matrix of the alloy turned out to be definitely less resistant to cavitation erosion compared to the pearlitic matrix component.
The paper presents results of metallographic examination of faults occurring in the course of founding thin-walled cast-iron castings in furan resin sand molds. A non-conformance of the scab type was Observed on surface of the casting as well as sand buckles and cold shots. Studied the chemical composition by means of a scanning electron microscope in a region of casting defects: microanalysis point and microanalysis surface. Around the observed defects discloses high concentration of oxides of iron, manganese and silicon. A computer simulation of the casting process has been carried out with the objective to establish the cause of occurrence of cold shots on casting surface. The simulation was carried out with the use of NovaFlow & Solid program. We analyzed the flowing metal in the mold cavity. The main reason for the occurrence of casting defects on the surface of the casting was gating system, which caused turbulent flow of metal with a distinctive splash stream of liquid alloy.
The paper presents results of a study on the effect of the flux density of heat carried away for the remelting area to substrate in the course of surface remelting with concentrated heat stream on values of structural parameters λ1D and λ2D of α(Al) phase dendrites in C355 alloy. The remeltings were made with the use of GTAW method, at arc current intensity I = 200 A and concentrated heat stream scanning speed vs = 200, 400, 600, and 800 mm/min. The used protective gas was argon supplied at rate of 20 l/min. It has been found that the increase of the rate of scanning with concentrated heat stream results in a change of the remelting-substrate separation surface shape consisting in reduction of the remelting width and depth. This increases the value of the flux density of heat transmitted from the remelting area to substrate which in turn acts in favor of reduction of structural parameters λ1D and λ2D characterizing α(Al) phase dendrites in C355 alloy.
The paper is a presentation of a study on issues concerning degradation of protective paint coat having an adverse impact on aesthetic qualities of thin-walled cast-iron castings fabricated in furan resin sand. Microscopic examination and microanalyses of chemistry indicated that under the coat of paint covering the surface of a thin-walled casting, layers of oxides could be found presence of which can be most probably attributed to careless cleaning of the casting surface before the paint application process, as well as corrosion pits evidencing existence of damp residues under the paint layers contributing to creation of corrosion micro-cells
The paper deals with the effect of microstructure diversified by means of variable cooling rate on service properties of AlSi7Mg cast alloy refined traditionally with Dursalit EG 281, grain refining with titanium-boron and modified with sodium and a variant of the same alloy barbotage-refined with argon and simultaneously grain refining with titanium-boron and modified with strontium. For both alloy variants, the castings were subject to T6 thermal treatment (solution heat treatment and artificial aging). It turned out that AlSi7Mg alloy after simultaneous barbotage refining with argon and grain refining with titanium-boron and modified with strontium was characterised with lower values of representative microstructure parameters (SDAS – secondary dendrite arm spacing, λE, lmax) and lower value of the porosity ratio compared to the alloy refined traditionally with Dursalit EG 281 and grain refining with titanium-boron and modified with sodium. The higher values of mechanical properties and fatigue strength parameters were obtained for the alloy simultaneously barbotagerefined with argon and grain refining with titanium-boron and modified with strontium.
The cooling rate is one of the main tools available to the process engineer by means of which it is possible to influence the crystallisation process. Imposing a desired microstructure on a casting as early as in the casting solidification phase widens significantly the scope of technological options at disposal in the process of aluminium-silicon alloy parts design and application. By changing the cooling rate it is possible to influence the course of the crystallisation process and thus also the material properties of individual microstructure components. In the study reported in this paper it has been found that the increase of cooling rate within the range of solidification temperatures of a complex aluminium-silicon alloy resulted in a decrease of values of the instrumented indentation hardness (HIT) and the instrumented indentation elastic modulus (EIT) characterising the intermetallic phase occurring in the form of polygons, rich in aluminium, iron, silicon, manganese, and chromium, containing also copper, nickel, and vanadium. Increased cooling rate resulted in supersaturation of the matrix with alloying elements.
The paper discusses the possibility of improving resistance of heat exchangers made of gray cast iron with flake graphite to hightemperature corrosion by providing them with metallic coatings. A metallic coating containing 76.9% Ni, 19.8% Cr, 1.7% Si, 0.9% Fe, and 0.9% Mn was applied by means of the plasma spraying method and subjected to cyclically variable thermal loads in the atmosphere of solid fuels combustion products (oxygen, sulfur, chlorine, and sodium). In a 30-day thermal load test held at temperature 500°C it has been found that thickness of the metallic coating decreased from the initial (240 ± 6) μm to (231 ± 6) μm. The depth to which sulfur, chlorine, and sodium penetrated the coating was about 30 μm. Increased oxygen content occurred along the whole coating depth. In the coating area adjacent to the substrate surface, the content was twice as high compared to this observed in the initial coating material. Although presence of oxygen was found within the whole depth of the coating, i.e. (231 ± 6) μm, no signs of susceptibility of the sprayed metallic layer to separation from substrate of gray cast iron with flake graphite were found.
The present paper is a presentation of results of a study on morphology, chemical composition, material properties (HVIT, HIT, EIT), and nanoindentation elastic and plastic work for carbide precipitates in chromium cast iron containing 24% Cr. It has been found that the carbides differ in chemical composition, as well as in morphology and values characterizing their material properties. The carbides containing the most chromium which had the shape of thick and long needles were characterized with highest values of the analyzed material properties.
The paper presents results of assessment of the unit pressure force within the refractory material volume in the course press-moulding of stampings for refractory precast shapes. The force was evaluated with the use of physical simulation of deformation undergone by lead balls placed in the raw refractory mass subjected to pressing in a metal die. To determine the value of unit pressure force applied to the aggregate grains in the course of stamping press-moulding, physical model of deformation of a sphere induced by the uniaxial stress state was used.
The paper presents results of an analysis of material density distribution in stampings press-moulded in metal dies from raw refractory materials based on alumina-magnesia-carbon aggregate. The stampings, fabricated on LAEIS HPF 1250 pressing machine, are blanks from which refractory precast shapes are manufactured by means of drying and firing. Samples for material density evaluation were cut out from test stampings with the use of diamond-reinforced disc. Density of the material was determined in thirteen layers of stampings denoted with letters A through M.
NC11 steel, in view of the specificity of its manufacturing process, is characterised with band-like orientation of carbides. Depending on the direction of cutting the material for the inserts out of commercially available steel products, carbide bands can be oriented in parallel or perpendicularly to the direction in which aggregate grains move in the process of pressing stampings. It has been found that in case of scratches made in direction perpendicular to carbide bands, depth of the scratches is less than this observed when scratches are made in direction coinciding with prevailing orientation of carbide precipitates.