A cast iron is gradient material. This means that depending on the cooling rate it is possible, at the same chemical composition and the physicochemical state of molten metal, to obtain material with a different structure. The connection between the wall thickness of the casting and the speed of its cooling expresses the casting module. Along with the module escalation a cooling rate of the casting is reducing what can cause changes of the microstructure and the increased tendency to the crystallization of distorted graphite forms. Inspections of experimental castings from nodular cast iron with different modules were conducted to the graphite form.
The study presents a mathematical model of the crystallisation of nodular graphite cast iron. The proposed model is based on micro- and macromodels, in which heat flow is analysed at the macro level, while micro level is used for modelling of the diffusion of elements. The use of elementary diffusion field in the shape of an averaged Voronoi polyhedron [AVP] was proposed. To determine the geometry of the averaged Voronoi polyhedron, Kolmogorov statistical theory of crystallisation was applied. The principles of a differential mathematical formulation of this problem were discussed. Application of AVP geometry allows taking into account the reduced volume fraction of the peripheral areas of equiaxial grains by random contacts between adjacent grains. As a result of the simulation, the cooling curves were plotted, and the movement of "graphite-austenite" and "austenite-liquid” phase boundaries was examined. Data on the microsegregation of carbon in the cross-section of an austenite layer in eutectic grains were obtained. Calculations were performed for different particle densities and different wall thicknesses. The calculation results were compared with experimental data.
This paper presents the results of the abrasive wear resistance of selected types of nodular cast iron, including ADI, cooperating with quartz sand and 100 grit abrasive paper. It has been shown that carbides in nodular cast iron cause an increase in wear resistance of 6 to 12% depending on the surface fraction of the carbides and type of the matrix. For the same unit pressure the mass loss of the cast iron cooperating with quartz sand is many times larger than the cast iron cooperating with abrasive paper. For both abrasives the highest wear resistance showed nodular cast iron with upper and lower bainite and carbides.
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.
Effects of charge composition on microstructure, mechanical and fatigue properties of nodular cast irons have been studied. For experiments, five melts of nodular cast iron were used – three types of unalloyed nodular cast irons (with different ratio of steel and pig iron in a charge and different additives for regulation of the chemical composition) and two types of alloyed nodular cast irons (SiMo- and SiCu- nodular cast iron). The microstructure of the specimens was evaluated according to a norm and by automatic image analysis. The mechanical properties were investigated by the tensile test, impact bending test and Brinell hardness test. The fatigue tests were carried out at sinusoidal cyclic push-pull loading at ambient temperature. The best mechanical properties were reached in the nodular cast iron alloyed by Si and Cu, what is related to its microstructure.
The article presents the results of the research on the influence of the shape of reaction chamber on spheroidisation of cast iron produced with use of the inmold method. The amounts of nodular graphite precipitates in castings produced with the use of different reaction chambers have been compared.
The paper presents results of studies on the effect of the nodular cast iron metal matrix composition on the abrasive and adhesive wear resistance. Nodular cast iron with different metal matrix obtained in the rough state and ADI were tested. To research of abrasive and adhesive wear the pearlitic and bainitic cast iron with carbides and without this component were chosen. The influence of the carbides amount for cast iron wear resistance was examined. It was found, that the highest abrasive and adhesive wear resistance under conditions of dry friction has a nodular cast iron with carbides with upper and lower bainite. Carbides in bainitic and pearlitic cast iron significantly increase the wear resistance in these conditions. In terms of fluid friction the largest wear resistance had cast iron group with the highest hardness.
In this paper results of microsegregation in the newly developed nodular cast iron with carbides are presented. To investigate the pearlitic and bainitic cast iron with carbides obtained by Inmold method were chosen. The distribution of linear elements on the eutectic cell radius was examined. To investigate the microsegregation pearlitic and bainitic cast iron with carbides obtained by Inmold method were chosen. The linear distribution of elements on the eutectic cell radius was examined. Testing of the chemical composition of cast iron metal matrix components, including carbides were carried out. The change of graphitizing and anti-graphitizing element concentrations within eutectic cell was determined. It was found, that in cast iron containing Mo carbides crystallizing after austenite + graphite eutectic are Si enriched.
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.