Abstract
The present study highlights the effect of the cooling rate on the microstructure formation of Si–Mo ductile iron. In this study, experiments were carried out for castings with different wall thicknesses (i.e., 3, 5, 13, and 25 mm) to achieve various cooling rates. The simulation of the cooling and solidification was performed through MAGMASOFT to correlate the cooling conditions with the microstructure. The phase diagram of the investigated alloy was calculated using Thermo-Calc, whereas the quantitative metallography analyses using scanning electron microscopy and optical microscopy were performed to describe the graphite nodules and metallic matrix morphologies. The present study provides insights into the effect of the cooling rate on the graphite nodule count, nodularity, and volumetric fractions of graphite and ferrite as well as the average ferritic grain size of thin-walled and reference Si–Mo ductile iron castings. The study shows that the cooling rates of castings vary within a wide range (27 °C–1.5 °C/s) when considering wall thicknesses of 3 to 25 mm. The results also suggest that the occurrence of pearlite and carbides are related to segregations during solidification rather than to cooling rates at the eutectoid temperature. Finally, the present study shows that the longitudinal ultrasonic wave velocity is in linear dependence with the number of graphite nodules of EN-GJS-SiMo45-6 ductile iron.
Highlights
IntroductionDuctile iron (especially of the Si–Mo, ADI, and Ni–Resist grades) should, be treated as a potential material to produce light castings with good mechanical and operational properties and at a relatively small cost
The ongoing development of high-quality cast iron mainly concerns ductile iron, which can be used to produce high-tech components that have an attractive combination of mechanical and usable properties that can compete with the so-called light alloys [1,2,3,4,5].Ductile iron should, be treated as a potential material to produce light castings with good mechanical and operational properties and at a relatively small cost
The diagramTransformation of the investigated Si–Mo ductile iron is shown in Figure 2a,b,The which illustrates the formation of of its the structure during Si–Mo the cooling andiron solidiThermo-Calc phase diagram investigated ductile is shown ficationintoFigure room 2a,b, temperature
Summary
Ductile iron (especially of the Si–Mo, ADI, and Ni–Resist grades) should, be treated as a potential material to produce light castings with good mechanical and operational properties and at a relatively small cost. Si–Mo ductile irons have been widely used for high-temperature automotive components such as exhaust manifolds as well as turbine castings and many types of furnace applications [6,7,8,9,10,11,12]. The use of Si–Mo ductile iron is closely related to the thermal stability of the structure and is important in the design of cast components (especially in automotive production, where structural stability and functional properties are of key importance when choosing a given material). In the case of castings with different wall thicknesses, the key issue in attaining homogeneous structures and properties is the sensitivity of cast iron to the cooling rate, especially when we “enter” the range of the high cooling rates that take place in the production of thin-walled castings
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