Abstract

Bainitic structure can be made on nodular cast iron by giving a Nickel and Molibdenum as an alloying. The bainitic structure should be homogen without any other structure in its matrices. In practice the bainitic structure formation is not fully homogen. Another undesirable structure such as ferrit and ledeburit structure can be found in the matrices of its microstructure. The microstructure formation is associated with the thickness (module) of casting which could influence the cooling rate. Ledeburit formation could be occur when the cooling rate is relatively fast and in contrary a ferritic formation could be occur because of slow cooling. The addition of Silicon (Si) content is used particularly to promote graphite formation. Silicon also can influence the formation of the matrices structure. That depend on carbon content left behind on the matrices and the thickness of the casting. Ferit and ledeburit formation can be avoided or minimized by controlling the Si content. The addition of more Si content on the thin casting sample will reduce the possibility of ledeburit formation. The Si content must be controlled and reduced on the thick sample to make sure that the ferrit formation is not too much present. The research has been done by make a casting sample with a three variation of its thickness which is represent its casting module. The casting module is made to 0,33, 0,78 and 1,22. The melting of nodular cast iron is done with a composition of C 3,2%, Mn 0,3%, Mo 0,7%, Ni 2,6% and Mg rest 0,03%. The Silicon is given by three variation of 2,0 %, 2,3 % and 2,6%. The research find a conclusion that at the addition of 2.3 % Si could omit the ledeburit formation at thin module and the ferrit formation is relatively reduced to a small amount at thick module.

Keywords: cast iron, Bainitic structure, Module, Cooling rate, Si alloying

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