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چكيده انگليسي :

93 Single stage semi solid casting of gray cast iron in a sand mold Safar rostamzadeh s rostamzadeh@ma iut ac ir Department of Materials Engineering Isfahan University of Technology 84156 8311 isfahan iran Degree M Sc Language FarsiSupervisors Dr Behzad Niroumand behzn@cc iut ac irDr Ali Maleki maleki110@cc iut ac irAbstractSemi solid casting is one of the new methods of manufacturing metalic parts In manysemisolid casting methods the parts are produced by applying shear to a solidifying melt tomake a slurry of suspended non dendritic primary particles in the melt Most popular semi solid casting processes involve two stages The first stage includes producing a semi solidslurry which is formed in a high strength metallic die in the second stage of the process Because of high pressures applied on the semi solid slurry during the second stage the dieshould be made of expensive alloy steels Also most of the studies have been conducted onlow melting point alloys such as aluminium or magnesium and high melting point alloyshave attracted less attention Gray cast iron is a high melting point alloy used in manyindustrial applications and is suitable for products requiring good heat transfer machinablity damping capacity and wear resistance By increasing the carbon content flake graphites in the microstructure become coarser and mechanical properties are reduced Therefore reducing the size of flake garphite in high carbon cast irons may results insuperior physical and mechanical properties This research investigated the possibility oflow cost single stage semi solid casting of a high melting point alloy i e gray cast iron insand molds using centrifugal force For this purpose a specially designed runner chilledsand mold rigged to a vertical centrifugal casting machine was used The hypereutectic graycast iron was poured in the sand mold at 1270 1275 and 1285 C and at rotation speeds of200 and 400 rpm The effects of different parameters on microstructure as well asmechanical and physical properties of the specimens were characterized In order tocompare the results control samples were cast in the same mold at 1275 C by traditionalmethods of gravity and centrifuged casting Mold filling and temperature and solid fractionchanges during solidification were also simulated by Procast simulation software Theresults showed that the average length and thickness of eutectic and Kish flake graphites insemi solid centrifuged castings were smaller than those in the castings prepared byconventional gravity or centrifuged casting methods Reducing the pouring temperature insemi solid casting method led to smaller size and thickness of eutectic and Kish graphiteflakes Hardness and tensile strength of the semi solid cast samples were higher than thoseof the control samples Improvment of the microstructure by semi solid casting resulted inincrease of tensile strength and hardness of control samples from 128 MPa and 166 vickers respectively to 154 MPa and 192 vickers for semi solid samples respectively The resultshowed that semi solid casting of hypereutectic gray cast iron in sand mold using the newsingle stage semi solid centrifuged casting method was successful Key words Centrifuged Semi Solid Casting Hypereutectic Gray Cast Iron Kish graphite Sand Mold Mechanical peroperties Simulation

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