USING MELT HIGH-TEMPERATURE TREATMENT FOR PROCESSING FOUNDRY WASTES OF HEAT-RESISTANT ALLOY

At present time, metallurgical wastes are used in metallurgical alloys production more and more. The volume accumulation and increase of return age effect on charge pollution by undesirable elements and nonmetallic inclusions. As a result, structure and properties of the casting inevitably get worse. This circumstance must influence on polytherm’s character of physical properties of the melt, necessary temperature and time parameters of the heat-resistant alloy’s melting accordingly. We have researched the temperature dependences of electrical resistance and kinematic viscosity of liquid heat-resistant composites based оn Ni – Nb – Cr – Mo systems. The critical temperatures were determined for the EP902 alloy. Heating up to these temperatures leads to irreversible changes in direction of the melt improving. Interaction was found between the amount of foundry waste and features of temperature dependences of the melt physico-chemical properties. An increase in the amount of foundry waste using in remelting results in the critical temperatures increasing. Influence of the melt conditions on crystallization process and on the structure of hard metal has been studied. The process of alloy EР902 solidification was researched by differential thermal analysis method. It has shown that the crystallization process starts with extraction of solid solution on the base of γ-phases and ends with forming of the eutectic based on the Ni₃Nb intermetallic compound. Heating of the melt over the critical temperature leads to an increase of supercooling and does not effect on the eutectic temperature. The processing mode of the high temperature melt treatment was proposed based on the research results of physico-chemical properties of the liquid metal and process of the melt crystallization. It allows obtaining the highest quality of casting of heat-resistant EР902 alloy, which contains significant amount of foundry waste in the charge. The mechanical tests were implemented for experimental samples melted out by the optimal mode of high-temperature melt treatment (HTTM). Application of HTTM for the melts, contained 50 % of foundry waste in charge, allows obtaining the level of strength and plastic properties exceeding the technical requirements, stabilizing and combining it from melt to melt.

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