Features of the formation of endogenic inoculants in the metal stream during the casting of large ingots

• Published in: Metallurgist (New York) 2001-05, Vol.44 (9-10), p.530-533
• Main Authors: Zyuban, N A, Zhul'ev, S I
• Format: Article
• Language: English
• ISSN: 0026-0894

A promising method of controlling the structure of metal in production of ingots and large castings is introduction of highly dispersed cooling particles (inoculants) into the melt, but iron particles for inoculants are not always compatible with the chemical composition of the alloy. Also, the outer surface of the inoculant may become oxidized which diminishes the cooling effect on the crystallization of the ingot. It is more efficient to form droplets inside the metal stream during casting which would solidify as they fall in the stream and so act as cooling additives having the same chemical composition as the metal being cast. There is little chance that an isolated drop will separate spontaneously from the melt because of the strong surface tension of the liquid melt, but the stream can be atomized to form smaller droplets when Weber's criteria exceeds 11. Owing to the relatively small size of the inoculants in the melt some will undergo melting but the determining criterion becomes the amount of the solid phase present in the flow of inoculants introduced. The optimum combination of the volume of solid phase and the temperature of the particles introduced will create favorable conditions for crystallization and structure formation. This process can be applied to fabrication of high-quality vacuum castings as well as large ingots and castings (circular forgings for propellor shafts). Formation of favorable structure in ingots cast with inoculants has sharply reduced the scatter of measured values of mechanical properties (yield point, UTS, impact toughness and elongation) resulting in stronger, more reliable castings.