Semi-solid Processing of Cast Iron Under Low Convection Conditions

摘要

Cast irons are attractive engineering materials as they are easy to cast, have good compressive strength, hardness and are resistant to wear. Alloys with optimum combination of properties are finding increasing importance due to the low cost of the castings. The enhanced properties are achieved by adjusting the composition through proper alloy addition [1-6]. By adopting suitable heat treatment cycle, the micro- structural improvement have been reported [6, 7] which can also lead to castings of better quality. Such techniques not only include addition of costly elements: Nickel and Rare earths [3, 6] during processing, they also require the proper knowledge of detrimental effect of such elements on overall performance of the alloy. Many processing techniques have been engineered for modifying and improving the particle morphology. Few recent studies reported on the fundamental principles of processing plain cast iron in semisolid temperature range, using cooling plate technique [8-10] in a direction to achieve spherical grains in the final castings. Equiaxed structures in the cast iron due to fragmentation of dendrites have been reported. The disintegration of dendrites to small particles due to shearing can cause improvement in grain sphericity and lead to non-dendritic structure. In the present study, processing of hypereutectic alloy cast irons of various compositions with chromium and molybdenum as constituent under low convection conditions in the semi solid temperature range is carried out. An inclined slope furnace with provision of proper temperature control and thermal gradient has been used. Improvement in the ductility and toughness parameters for such alloys has been observed.