This paper presents the results of studies of high-alloyed white cast iron modified with lanthanum, titanium, and aluminium-strontium. The samples were taken from four melts of high-vanadium cast iron with constant carbon and vanadium content and near-eutectic microstructure into which the tested inoculants were introduced in an amount of 1 wt% respective of the charge weight. The study included a metallographic examinations, mechanical testing, as well as hardness and impact resistance measurements taken on the obtained alloys. Studies have shown that different additives affect both the microstructure and mechanical properties of high-vanadium cast iron.
High-vanadium cast iron is the white cast iron in which the regular fibrous γ + VC eutectic with the volume fraction of vanadium carbide amounting to about 20% crystallises. This paper presents the results of studies on high-vanadium cast iron subjected to the inoculation treatment with magnesium master alloy. The aim of this operation is to change the morphology of the crystallising VC carbides from the fibrous shape into a spheroidal one. The study also examines the effect of the amount of the introduced inoculant on changes in the morphology of the crystallising VC carbides. To achieve the goals once set, metallographic studies were performed on high-vanadium cast iron of eutectic composition in base state and after the introduction of a variable content of the inoculant. The introduction of magnesium-based master alloy resulted in the expected changes of microstructure. The most beneficial effect was obtained with the introduction of 1.5% of magnesium master alloy, since nearly half of the crystallised vanadium carbides have acquired a spheroidal shape.
The paper presents the results of tests on the spheroidising treatment of vanadium carbides VC done with magnesium master alloy and mischmetal. It has been proved that the introduction of magnesium master alloy to an Fe-C-V system of eutectic composition made 34% of carbides crystallise in the form of spheroids. Adding mischmetal to the base alloy melt caused 28% of the vanadium carbides crystallise as dendrites. In base alloy without the microstructure-modifying additives, vanadium carbides crystallised in the form of a branched fibrous eutectic skeleton. Testing of mechanical properties has proved that the spheroidising treatment of VC carbides in high-vanadium cast iron increases the tensile strength by about 60% and elongation 14 - 21 times, depending on the type of the spheroidising agent used. Tribological studies have shown that high-vanadium cast iron with eutectic, dendritic and spheroidal carbides has the abrasive wear resistance more than twice as high as the abrasion-resistant cast steel.
In this paper the effects of titanium addition in an amount up to 0.13 wt.% have been investigated to determine their effect on the microstructure and mechanical properties of Thin Wall Vermicular Graphite Iron Castings (TWVGI). The study was performed for thinwalled iron castings with 3-5 mm wall thickness and for the reference casting with 13 mm. Microstructural changes were evaluated by analyzing quantitative data sets obtained by image analyzer and also using scanning electron microscope (SEM). Metallographic examinations show that in thin-walled castings there is a significant impact of titanium addition to vermicular graphite formation. Thinwalled castings with vermicular graphite have a homogeneous structure, free of chills, and good mechanical properties. It may predispose them as a potential use as substitutes for aluminum alloy castings in diverse applications.
The paper presents the results of abrasive wear resistance tests carried out on high-vanadium cast iron with spheroidal VC carbides. The cast iron of eutectic composition was subjected to spheroidising treatment using magnesium master alloy. The tribological properties were examined for the base cast iron (W), for the cast iron subjected to spheroidising treatment (S) and for the abrasion-resistant steel (SH). Studies have shown that high-vanadium cast iron with both eutectic carbides and spheroidal carbides has the abrasion resistance twice as high as the abrasion-resistant cast steel. The spheroidisation of VC carbides did not change the abrasion resistance compared to the base high-vanadium grade.
The cast alloys crystallizing in Fe-C-V system are classified as white cast iron, because all the carbon is bound in vanadium carbides. High vanadium cast iron has a very high abrasion resistance due to hard VC vanadium carbides. However, as opposed to ordinary white cast iron, this material can be treated using conventional machining tools. This article contains the results of the group of Fe-C-V alloys of various microstructure which are been tested metallographic, mechanical using an INSTRON machine and machinability with the method of drilling. The study shows that controlling the proper chemical composition can influence on the type and shape of the crystallized matrix and vanadium carbides. This makes it possible to obtain a high-vanadium cast iron with very high wear resistance while maintaining a good workability.
The present research was conducted on thin-walled castings with 5 mm wall thicknesses. This study addresses the effect of the influence of different master alloys, namely: (1) Al-5%Ti-1%B, (2) Al-5%Ti and (3) Al-3%B, respectively on the structure and the degree of undercooling (ΔTα = Tα-Tmin, where Tα - the equilibrium solidification temperature, Tmin - the minimum temperature at the beginning of α(Al) solidification) of an Al-Cu alloy. The process of fading has been investigated at different times spent on the refinement treatment ie. from 3, 20, 45 and 90 minutes respectively, from the dissolution of master alloys. A thermal analysis was performed (using a type-S thermocouple) to determine cooling curves. The degree of undercooling and recalescence were determined from cooling and solidification curves, whereas macrostructure characteristics were conducted based on a metallographic examination. The fading effect of the refinement of the primary structure is accompanied by a significant change in the number (dimension) of primary grains, which is strongly correlated to solidification parameters, determined by thermal analysis. In addition to that, the analysis of grain refinement stability has been shown with relation to different grain refinements and initial titanium concentration in Al-Cu base alloy. Finally, it has been shown that the refinement process of the primary structure is unstable and requires strict metallurgical control.
A eutectic reaction is a basic liquid-solid transformation, which can be used in the fabrication of high-strength in situ composites. In this study an attempt was made to ensure directional solidification of Fe-C-V alloy with hypereutectic microstructure. In this alloy, the crystallisation of regular fibrous eutectic and primary carbides with the shape of non-faceted dendrites takes place. According to the data given in technical literature, this type of eutectic is suitable for the fabrication of in-situ composites, owing to the fact that a flat solidification front is formed accompanied by the presence of two phases, where one of the phases can crystallise in the form of elongated fibres. In the present study an attempt was also made to produce directionally solidifying vanadium eutectic using an apparatus with a very high temperature gradient amounting to 380 W/cm at a rate of 3 mm/h. Alloy microstructure was examined in both the initial state and after directional solidification. It was demonstrated that the resulting microstructure is of a non-homogeneous character, and the process of directional solidification leads to an oriented arrangement of both the eutectic fibres and primary carbides.
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.
The resistance of cast iron to abrasive wear depends on the metal abrasive hardness ratio. For example, hardness of the structural constituents of the cast iron metal matrix is lower than the hardness of ordinary silica sand. Also cementite, the basic component of unalloyed white cast iron, has hardness lower than the hardness of silica. Some resistance to the abrasive effect of the aforementioned silica sand can provide the chromium white cast iron containing in its structure a large amount of (Cr, Fe)7C3 carbides characterised by hardness higher than the hardness of the silica sand in question. In the present study, it has been anticipated that the white cast iron structure will be changed by changing the type of metal matrix and the type of carbides present in this matrix, which will greatly expand the application area of castings under the harsh operating conditions of abrasive wear. Moreover, the study compares the results of abrasive wear resistance tests performed on the examined types of cast iron. Tests of abrasive wear resistance were carried out on a Miller machine. Samples of standard dimensions were exposed to abrasion in a double to-and-fro movement, sliding against the bottom of a trough filled with an aqueous abrasive mixture containing SiC + distilled water. The obtained results of changes in the sample weight were approximated with a power curve and shown further in the study.