Papers by Keyword: Nodular Iron

Abstract: This article focuses on research into thermal shock fatigue resistance and oxidation resistance of as-cast ferritic nodular iron. The results show that the number of cycles required to crack nodular iron under the action of thermal stress is significantly higher than that of grey cast iron, and the rate at which cracks spread is lower compared with that of grey cast iron. When graphite is transformed from flakes into nodules, its decreased connectivity impedes the flow of oxygen during oxidization, thereby improving its oxidation resistance.

Abstract: By way of alloying, a sort of low-chromium heat-resistant ductile iron material was developed. Through the observation of microstructure, testing of mechanical properties and process performance, heat-resistant test, the microstructure and properties of heat resistant ductile iron of low chromium was studied. The results show that microstructure of the developed heat-resistant ductile iron is spherical graphite distributed regularly on matrix of pearlite and a small amount of ferrite; mechanical properties, processing performance and high-temperature heat resistance of samples of different chrome composition are preferable, but 1.6% of chromium component possess the best performance.

Abstract: The microstructure and properties of austempered ductile iron with carbides was studied to increase the abrasive resistance of ADI. It was proven that the austempering temperature influences greatly the microstructure, impact toughness, hardness and abrasion resistance of CADI. With increase of austempering temperature, the acicular ferrite becomes thicker and bigger, the impact toughness rises, and the hardness decreases. But there is a complicated effect of austempering temperature on wet abrasion resistance. In addition, the CADI grinding balls were cast and the field testing was performed. The CADI ball is one third of abrasion loss of low chromium cast iron, zero rate of breakage and no loosing round.

Abstract: The present paper deals with residual stress and strain changes in thin flat specimens of nodular cast iron during laser remelting process. In laser remelting process of a workpiece we have used several laser beam passages across the workpiece surface. The state of internal stress in the workpiece changes because of different ways of guiding the laser beam across the workpiece surface, and consequently strain of the workpiece may occur. In the process of gradual remelting of the specimen surface, i.e. during its heating and cooling, volume changes in the specimen surface layer occur due to thermal and microstructural changes. To find out more about volume changes in the thin surface layer of specimens, the latter were monitored by measuring the strain at the lower side of the specimens during and after the remelting process, and also by residual stress measurement in the thin surface layer. The results obtained confirm that the laser remelting process could be successfully optimised on the basis of knowing the residual stresses and the strain generated during the remelting process.

Abstract: Parameters that affect chunky graphite formation in heavy-section castings have been studied in previous works which showed that inoculation and cerium addition both increase the tendency for this degenerate graphite. This suggested that laboratory study on chunky graphite formation could be performed on small castings by over-treating the melt. Though the role of silicon was not ascertained, it appeared of potential interest to also investigate its effect in relation with the carbon equivalent of the iron and the nucleation potential of the melt. Keel-blocks were thus cast using Ce or Ce-Mg treated melts, with increased silicon content (up to 4.0 wt.%) and inoculation rate as compared to usual practice. It was observed that chunky graphite systematically appeared in more or less extended areas centred on the upper part of the keel-blocks. The as-cast microstructure (graphite shape and distribution) has then been studied in relation to melt composition and additions (Ce treatment and inoculation) in both affected and non-affected areas. Finally, microanalysis of oxides and other minor phases showed them to be similar to those appearing in heavy-section castings. It may then be concluded that chunky graphite appears in light-section castings in the same way than in heavy-section castings when using over-treated melts.

Abstract: Laser remelting process is a very promising hardening method for ferrous and nonferrous alloys, which do not show a homogeneous microstructural state after having been heattreated in a traditional way. Consequently, the alloys concerned do not achieve the required hardness of the surface layer and do not provide the required wear resistance either. The paper deals with residual stresses of thin flat specimens of nodular cast iron 500-7 in the laser remelting process. In the process of gradual remelting of the specimen surface, that is during its heating and cooling, volume changes of the specimen occur due to thermal and microstructural changes. For a better knowledge of volume changes in the thin surface layer of the specimen, the latter were evaluated by residual-stress measurement in the thin modified surface layer after the remelting process. In laser remelting of a workpiece such remelting conditions should be ensured that a uniform thickness of the modified layer could be obtained in spite of several laser-beam passages across the workpiece surface. Because of a multiple laser-beam passage across the workpiece surface, the state of internal stress in the workpiece changes. Optimal laser surface remelting conditions on the basis of knowing the residual stresses were chosen, while the way of guiding the laser beam over the surface of flat samples and degree of overlapping were varied.

Abstract: The paper presents the study of the microstructure and ultrasound measurments by proeminent part of the nodular iron castings. The experiment has been made in the Havy Machine Factory in Clausenburg. The crossing speed of the ultasound increases near the edge of the castings. Analising the nodular iron microstructure by smoler castings, there occurs no graphite change. By bigger mouldings the shape of the graphite can change to a vermicular graphite near the edges. The thickness of the transformed stratum is of 0,1-0,3 mm. In the nodular graphite iron are acting the forces in the frontier-surface. After casting the evaporation of the magnezium increases near the edge of the castings. The changes of forces on frontier surface can be caused by the changes of the innere tension, and also by the interacting of moulding materials. Opinions regarding these two effects are contardictory in the technical literature. Our experiments have been made in the Heavy Machine Combinat (C.U.G) in Kolozsvar, on nodular iron containing different ferrit-pearlite proportions. The weight of castings varried between 0,5 kg and 8000 kg. The metalic melt necessary to nodulisation was produced inductive furnaces of 6,3 and 12 tons. Before treatment by magnezium alloy, the chemical composition of the iron melt varried between the following parameters, according to the different types of irons: 3,7-3.9% C, 0,2-1,4% Si, 0,1-1,0% Mn, max. 0,025% S, max. 0,05% P, 0,1-1,4% Cr,%, 0,05-0,3% Mo, 0,2-0,8% Cu, 0,2-2,0% Ni. The globularisation has been made in the Tundich-pot. The work-temperature was between 1450 and 1600 C. We used 1,8 – 2,2% FeSiMg and 0,4-1,6% FeSi for the nodulisation. Our target was the examination of the surface strata on the castings, using for mould mixtures with different chemical effect.