EFFECT OF ELECTRIC FIELD ON GAS CONTENT OF CAST IRON

Abstract

The effect of electric field on the gas content of cast iron has been experimentally established on the basis of electrochemical studies in the system “liquid cast iron – slag – gas phase”. The author has carried out the studies aimed at obtaining cast iron sparingly alloyed with nickel, equal to Ni-resist cast iron in its mechanical and performance characteristics. For this purpose, austenitic cast irons melted in induction furnace with electrocorundum lining have been studied. Samples prepared from the obtained cast iron have been subjected to further treatment with electric field in order to research the influence of static electric field on fixation of atomic nitrogen in the alloy, and ultimately, on the structure of metal matrix. According to the experimental data, the effect can be enhanced by application of electric field. The application of negative charge to metal appears to be more effective, although, in case of anode metal, certain “capture” of nitrogen in cast iron also occurs. This may be explained by the fact that, at the initial moment of time, there is a stationary electric field between the movable (free) electrode and surface of the melt, where the charged particles are stationary in this reference frame, which is registered as no current by ampere-meters integrated in the circuit. The application of static electric field facilitates is capture of nitrogen in cast iron. According to further experiments, at 8 – 9 % of Ni, it is necessary to apply significant voltage for the manifestation of this influence. The studies have shown that the issue of stabilizing austenite with nitrogen in cast iron was not so simple, and, apparently, the influence of the field in case of the introduction of nitrided ferrochrome affected decomposition of nitrides, recharging of nitrogen ions, and non-equilibrium conditions of their diffusion and transition to gaseous phase. It was confirmed by a wide variation of the results of nitrogen analyses. Some samples have shown 0.04 – 0.05 % of N (with the introduction of nitrided ferrochrome, and a “minus” applied to metal), but most analyses have indicated considerably lower values. For foundry industry, electrochemical deoxidation of alloys that are difficult to deoxide by other methods, e.g. aluminum cast iron alloy, is of particular interest. Aluminum is an active element, which, in case of unfavorable arrangement of mass flows, is difficult to remove even using calcium. It leads to the emergence of Al2O3 inclusions in metal with the density close to melt, which complicates their coagulation and emersion. A double deoxidation has been tried. After the melt’s exposure lasted for 1 hour, its EMF has almost “returned” to its initial state (0.8 V). The subsequent deoxidation of melt for 15 minutes facilitated three-fold decrease in oxidation degree as compared to the initial one. Thus, the possibility of electrochemical deoxidation of iron-carbon melts and expediency of double deoxidation have been experimentally proved. As a result, the method of applying electric field in order to change the gas content of cast iron, as well as the method of practical application of electrochemical deoxidation of iron-carbon alloys have been suggested.