Directional Solidification of Ductile Iron under Continuous Casting Conditions

摘要

Unidirectional solidification of ductile iron under continuous casting conditions was carried out using an experimental model, where primary and secondary cooling phases were applied, Mg treatment was carried out using sandwich method. Two Mn levels were added, namely, 0.1 and 0.6% to the chemical composition of 3.3% C, 2.3% Si, 0.003% S, 0.02% P and 0.04% Mg. Metallographic investigations, hardness and cooling curves were studied. Nodularity and microstructure of ground matrix were thoroughly investigated as related to cooling conditions, solidification rate and Mn addition. Deep microstructure investigation was directed to solidified shell. Good nodularity (80%) and higher nodules count (350-400 nodules/mm~2) were obtained with higher solidification rate (0.25-0.35 mm/sec) under early application of secondary cooling (30 sec dwell time). Manganese deteriorates solidification so progress, therefore, nodularity and nodules count were reduced consequently. Massive carbides or martensite followed with branched eutectic carbides were the main constituents of shell zone. Upgraded pearlitic-ferritic structure were observed along the ingot axis related to cooling conditions.