Abstract
Billets from high-chromium steels possessing the necessary complex of mechanical and corrosion properties are widely used in the manufacture of critical products of heavy and power engineering. One of the effective technologies widely used in the manufacture of such work-pieces is electroslag remelting (ESR). ESR, included in the production process chain, for the management of refining and solidification processes allows to ensure a high homogeneity of metallurgical characteristics (chemical composition, structure, non-metallic inclusions, etc.) of the metal and, as a result, the complex of mechanical properties of the product. The choice of slag, maintaining its optimum oxidation-reduction potential at an optimum level, is a prerequisite for the effective refining of high-chromium steels at the ESR, since chromium and other elements present in the slag in various oxidation degree participate in the transport of oxygen from the gas phase to the liquid metal. From standpoint of the theory of electronic structure of slag systems, the effect of slag oxidation (equilibrium partial pressure of oxygen Р O 2 ) on the oxidation degree of chromium has been studied for widely used slags in Russia such as ANF-1, ANF-6, and ANF-29. Dependence of the ratio of Cr +3 /Cr +2 concentrations on the temperature, oxidation level and optical slag basicity is established. A thermodynamic model of changing the oxidation state of chromium in slag depending on its oxidation is presented. The calculated results are compared with the experimental data for slag systems at a temperature of 1873 K. It is shown that the average oxidation degree of chromium decreases with increasing temperature, decreasing of the oxygen partial pressure and the optical slag basicity. The presence of fluorine in the slag affects the varia- tion ratio Cr +3 /Cr +2 . It is shown that with decrease in the oxygen partial pressure from 10 -4 to 10 -12 Pa at a temperature of 1873 K, the average value of chromium oxidation degree in fluoride-oxide slags decreases from +3 to +2. A correlation is proposed, which makes it possible to estimate the Cr +3 /Cr +2 ratio in fluoride-oxide slags, taking into account the temperature and oxidation of slag.
Highlights
Billets from high-chromium steels possessing the necessary complex of mechanical and corrosion properties are widely used in the manufacture of critical products of heavy and power engineering
One of the effective technologies widely used in the manufacture of such work-pieces is electroslag remelting (ESR)
The choice of slag, maintaining its optimum oxidation-reduction potential at an optimum level, is a prerequisite for the effective refining of high-chromium steels at the ESR, since chromium and other elements present in the slag in various oxidation degree participate in the transport of oxygen from the gas phase to the liquid metal
Summary
Что средняя степень окисления хрома уменьшается с ростом температуры, понижением парциального давления кислорода и оптической основности шлака. Продемонстрировано, что с понижением парциального давления кислорода от 10–4 до 10–12 Па при температуре 1873 К средняя величина степени окисления хрома во фторидно-оксидных шлаках уменьшается от +3 до +2. Значительную роль при изготовлении заготовок ответственных металлоизделий играет электрошлаковый переплав (ЭШП), обеспечивающий необходимые характеристики химического состава, структуры, неметаллических включений и, в итоге, комплекс механических свойств металла за счет эффективного управления процессами рафинирования и затвердевания [1, 2]. Поэтому важной предпосылкой совершенствования технологии ЭШП является исследование влияния термодинамических параметров (температуры и окисленности), а также состава шлака, отражаемого синтетическим параметром его оптичес кой основности, на степень окисления хрома
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