Search

Nodularity is one of the key indexes to evaluate compacted graphite cast iron, and the vermicularizing effect is related to the active oxygen of molten iron. In this study, the active oxygen including oxygen activity and oxygen potential was measured by NSP3603 with disposable oxygen probe, and the nodularity was measured by quantitative metallography. The influence of active oxygen on vermicularizing effect and the influence of temperature on active oxygen during the fading process were analyzed and discussed. The results showed that the smaller the oxygen activity and oxygen potential are, the higher the nodularity becomes. When the oxygen activity is 0.1 ppm and the oxygen potential is − 237 mV, it has the best deoxidation effect, and the nodularity is 87%, which belongs to ductile cast iron. When the oxygen activity is more than 0.8 ppm and the oxygen potential is higher than – 166 mV, it has suitable deoxidation effect, and the nodularity is less than 15%. The oxygen potential of – 107 mV and oxygen activity of 0.8 ppm are taken as thresholds for the vermicularizing state. If lower than those, the vermicularizing effect remains unchanged. Once higher than those, the vermicularizing effect declines. A method was proposed to evaluate the vermicularizing effect of molten iron by the oxygen activity αO, oxygen potential EO and temperature TC after ladle treatment, and the corresponding criteria were established. Namely, if αO < 0.1 ppm, the nodularity is more than 80%; if 0.1 ppm < αO≤ 0.3 ppm, the nodularity is 45–80%; if 0.3 ppm< αO ≤0.6 ppm, the nodularity is 30–45%; if 0.6 ppm< αO ≤0.8 ppm, the nodularity is 20–30%; if 0.8 ppm< αO< 1.3 ppm, the nodularity is below 20% and mostly lower than 15%; if αO ≥ 1.3 ppm, the nodularity suddenly increases and the tendency to precipitate flake graphite increases. According to the criteria, the nodularity of molten iron can be evaluated by oxygen activity αO, oxygen potential EO and temperature TC after the ladle treatment. [ABSTRACT FROM AUTHOR]

The contribution summarises the results of application of thermodynamic calculation obtained from oxygen activities measurements in cast irons with various type of graphite microstructure. The results were used to find the relationship between natural logarithm of oxygen activities and reverse value of thermodynamic temperature 1/T.From obtained regression line the calculation of oxygen activities value for significant temperature of molten metal was achieved. Each material has its proper typical oxygen activities range for analysing and controlling graphite quality. Practical implication was successfully tested in a Czech foundry producing centrifugally poured cast iron rolls designed for hot strip mills with spheroidal graphite iron core.

The contribution summarises the results of application of thermodynamic calculation obtained from oxygen activities measurements in cast irons with various type of graphite microstructure. The results were used to find the relationship between natural logarithm of oxygen activities and reverse value of thermodynamic temperature 1/T. From obtained regression line the calculation of oxygen activities value for significant temperature of molten metal was achieved. Each material has its proper typical oxygen activities range for analysing and controlling graphite quality. Practical implication was successfully tested in a Czech foundry producing centrifugally poured cast iron rolls designed for hot strip mills with spheroidal graphite iron core. [ABSTRACT FROM AUTHOR]

Ferric iron is present in all metamorphic rocks and has the ability to significantly affect their phase relations. However, the influence of ferric iron has commonly been ignored, or at least not been considered quantitatively, mainly because its abundance in rocks and minerals is not determined by routine analytical techniques. Mineral equilibria calculations that explicitly account for ferric iron can be used to examine its effect on the phase relations in rocks and, in principle, allow the estimation of the oxidation state of rocks. This is illustrated with calculated pseudosections in NCKFMASHTO for mafic and pelitic rock compositions. In addition, it is shown that ferric iron has the capacity to significantly increase the stability of the corundum + quartz assemblage, making it possible for this assemblage to exist at crustal P– T conditions in oxidized rocks of appropriate composition. [ABSTRACT FROM AUTHOR]

Lately, the present authors published a study where oxygen activities were measured using a commercial sensor, which became recently available. In ductile cast iron melts with ferritic and pearlitic structure, optimal properties occur for a well-defined oxygen activity. Castings poured in these circumstances present maximal modularity, elongation and ferrite content combined with lowest hardness. Additionally, the first results for compacted graphite cast iron were published. The present contribution examines in much more detail the effect of sulfur and oxygen activity on several phenomena important during production of compacted graphite cast iron. These phenomena are the limit for which mechanical properties as defined in ISO16112 are met, the transition from compacted graphite to lamellar graphite and the point at which 20 percent nodularity occurs. [ABSTRACT FROM AUTHOR]