International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Due to the mechanical properties (toughness, elongation, tensile strength) that characterize ductile iron, its application in foundry technology is becoming more pronounced every day. The chemical composition and heat treatment of ductile iron have a great influence on the required mechanical properties. Given the operating conditions, the main purpose of heat treatment of ductile iron is to change the desired mechanical properties. Since the specific mechanical properties of ductile iron are generally related to the regularity of the mined graphite nodules, the main objective in production is to produce ductile iron with the highest possible percentage of ductility. In the experimental part of the paper, microstructure and hardness tests were carried out on specimens of ductile iron NL 400 and NL 700 before and after heat treatment by soft annealing (ferritization) and improvement. It was found that the type and corresponding parameters of heat treatment significantly affect the microstructure and the achieved hardness values of the ductile iron test specimens.

This paper analyses the oxidation resistance of ductile irons containing 2.11, 3, 4.28, 4.49 and 4.81 wt.% Si that were held at 850 °C for 32 hours. A scale was formed on all the samples and their weight increased. The scale thickness and increase in weight were decreased with increase of the silicon content, especially when the silicon content > 4 wt.%. The compactness of the scale on the sample surface is significantly higher at higher silicon contents. The results obtained indicate that the resistance of ductile iron to high-temperature oxidation increases with increasing silicon content.

This paper deals with the effects of the addition of 0.00031, 0.00064, 0.001 and 0.0042 wt.% Bi on the matrix structure of ductile iron castings consisting of 7 sections of different thicknesses (3, 12, 25, 38, 50, 75 and 100 mm) and contain low content of Si (2.11 wt.%) and pearlite promoting element (0.018 wt.% Cu, 0.0055 wt.% Sn, 0.00041 wt.% Sb, 0.098 wt.% Mn). The Bi contents of 0.00031, 0.00064 and 0.001 wt.% were not significantly affected the share of ferrite and pearlite in the section thicknesses of 12, 25, 38, 50, 75 and 100 mm compared to the casting which does not contain Bi. In all these sections the share of pearlite was increased and the share of ferrite was decreased by the addition of 0.0042 wt.% Bi. All of the above-mentioned Bi contents were resulted in the formation of iron carbides in the section thickness of 3 mm. The share of carbides increases with increasing Bi content.

In this study, the effects of matrix structure (pearlitic, tempered martensitic, lower ausferritic, and upper ausferritic), boronizing temperature (800, 825, and 850°C) and time (3, 4.5 and 6 hours) on the wear behaviour of Cu-Ni-Mo alloyed ductile iron were investigated. Wear tests were performed on ball-on-disc type wear tester under the load of 6.8 N, at sliding speed of 6.5 mm/s, at room temperature and dry sliding conditions. The mass losses were measured after wear tests and the friction coefficients were obtained during wear tests. The hardnesses and thicknesses of boride layers, microstructures and worn surface examinations (SEM) of the matrix structures and borided layers were performed. The surface hardnesses of borided samples were obtained three or four times more than that of the matrix structures. The best wear performance was observed for the sample borided at 850°C for 6 h. The mass loss of this boronizing condition is 0,2 mg and this value is nine times less compared with that of the as-cast pearlitic structure.