Compacted graphite iron, also known as vermicular cast iron or semiductile cast iron is a modern material, the production of which is increasing globaly. Recently this material has been very often used in automotive industry. This paper reviews some findigs gained during the development of the manufacturing technology of compacted graphite iron under the conditions in Slévárna Heunisch Brno, Ltd. The new technology assumes usage of cupola furnace for melting and is beeing developed for production of castings weighing up to 300 kilograms poured into bentonite sand moulds.
This paper shows how it is possible to obtain an ausferrite in compacted graphite iron (CGI) without heat treatment of castings. Vermicular graphite in cast iron was obtained using Inmold technology. Molybdenum was used as alloying additive at a concentration from 1.6 to 1.7% and copper at a concentration from 1 to 3%. It was shown that ausferrite could be obtained in CGI through the addition of molybdenum and copper in castings with a wall thickness of 3, 6, 12 and 24 mm. Thereby the expensive heat treatment of castings was eliminated. The investigation focuses on the influence of copper on the crystallization temperature of the graphite eutectic mixture in cast iron with the compacted graphite. It has been shown that copper increases the eutectic crystallization temperature in CGI. It presents how this element influences ausferrite microhardness as well as the hardness of the tested iron alloy. It has been shown that above-mentioned properties increases with increasing the copper concentration.
The paper presents the results of the research on the effect of copper on the crystallization process, microstructure and selected properties
of the compacted graphite iron. Compacted graphite in cast iron was obtained using Inmold process. The study involved the cast iron
containing copper at a concentration up to approximately 4%. The effect of copper on the temperature of the eutectic crystallization as well
as the temperature of start and finish of the austenite transformation was given. It has been shown that copper increases the maximum
temperature of the eutectic transformation approximately by 5C per 1% Cu, and the temperature of the this transformation finish
approximately by 8C per 1% Cu. This element decreases the temperature of the austenite transformation start approximately by 5C per
1% Cu, and the finish of this transformation approximately by 6C per 1% Cu. It was found that in the microstructure of the compacted
graphite iron containing about 3.8% Cu, there are still ferrite precipitations near the compacted graphite. The effect of copper on the
hardness of cast iron and the pearlite microhardness was given. This stems from the high propensity to direct ferritization of this type of
cast iron. It has been shown copper increases the hardness of compacted graphite iron both due to its pearlite forming action as well as
because of the increase in the pearlite microhardness (up to approx. 3% Cu). The conducted studies have shown copper increases the
hardness of the compacted graphite iron approximately by 35 HB per 1% Cu.
This article presents the methodology for exploratory analysis of data from microstructural studies of compacted graphite iron to gain
knowledge about the factors favouring the formation of ausferrite. The studies led to the development of rules to evaluate the content of
ausferrite based on the chemical composition. Data mining methods have been used to generate regression models such as boosted trees,
random forest, and piecewise regression models. The development of a stepwise regression modelling process on the iteratively limited
sets enabled, on the one hand, the improvement of forecasting precision and, on the other, acquisition of deeper knowledge about the
ausferrite formation. Repeated examination of the significance of the effect of various factors in different regression models has allowed
identification of the most important variables influencing the ausferrite content in different ranges of the parameters variability.
The paper presents the effect of manganese on the crystallization process, microstructure and selected properties: cast iron hardness as well as ferrite and pearlite microhardness. The compacted graphite was obtained by Inmold technology. The lack of significant effect on the temperature of the eutectic transformation was demonstrated. On the other hand, a significant reduction in the eutectoid transformation temperature with increasing manganese concentration has been shown. The effect of manganese on microstructure of cast iron with compacted graphite considering casting wall thickness was investigated and described. The nomograms describing the microstructure of compacted graphite iron versus manganese concentration were developed. The effect of manganese on the hardness of cast iron and microhardness of ferrite and pearlite were given.
The paper presents the effect of tin on the crystallization process, microstructure and hardness of cast iron with compacted (vermicular) graphite. The compacted graphite was obtained with the use of magnesium treatment process (Inmold technology). The lack of significant effect of tin on the temperature of the eutectic transformation has been demonstrated. On the other hand, a significant decrease in the eutectoid transformation temperature with increasing tin concentration has been shown. It was demonstrated that tin narrows the temperature range of the austenite transformation. The effect of tin on the microstructure of cast iron with compacted graphite considering casting wall thickness has been investigated and described. The carbide-forming effect of tin in thin-walled (3 mm) castings has been demonstrated. The nomograms describing the microstructure of compacted graphite iron versus tin concentration have been developed. The effect of tin on the hardness of cast iron was given.
High temperature behavior of three compacted graphite iron (CGI) alloys on polycrystalline alumina substrates (99.7%, porosity <3%) were examined by the sessile drop method combined with classical contact heating procedure in flowing Ar. High-speed high-resolution CCD camera was used for continuous recording of the CGI/Al2O3 couples during melting alloy, heating to and holding the couples at the test temperature of 1450°C for 15 min and their subsequent cooling. The comparative studies were made with conventional CGI (in wt.%: 3.70 C, 2.30 Si, 0.44 Mn, 0.054 P, 0.017 Mg, 0.015 S) and two alloys additionally containing the same amounts of 0.25 Mo, 0.1 V, 0.045 Sn and 0.032 Sb with different concentrations of Mg + Cu additions, i.e. 0.01Mg + 0.33Cu and 0.02Mg + 0.83Cu. All three CGI alloys demonstrated non-wetting behavior on the Al2O3 substrates while the contact angle values slightly decreased with increase of the Mg + Cu content in the alloy, i.e. 131° (unalloyed CGI), 130° (0.01Mg + 0.33Cu) and 125° (0.02Mg + 0.83Cu). Structural characterization of solidified couples by light microscopy and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy revealed: 1) heterogeneous nucleation of discontinuous graphite layer at the drop-side interfaces and on the surface of the drops; 2) reactively formed Mg-rich oxide layer at the substrate-side interface; 3) the formation of satellite droplets on the surface of the drops during their solidification; 4) degeneration of initially compacted graphite to lamellar graphite after remelting and subsequent solidification of the drops, particularly in their surface layer.