Abstract

The cast iron consists flakes graphite with ferrite and pearlite as matrix, addition of alloying element to cast iron could increase the strength and hardness of the material. This material is commonly applied in the otomotive industry such as in the case of cylinder liner. To enhance cast iron`s mechanical properties with a certain thickness with no any formation of carbide as of it doesn`t degrade the vibration resistant function, then an adding process of Molybdenum element is conducted. This research aims to analize the effect of Molybdenum element toward the micro structure and to increase the phase’s hardness in the variant of FC 250 material thickness without harm the graphite, and also to know the maximum level of thickness in the case of carbide formation. In this research, there will be some experiments by adding 0,53% Molybdenum on the thickness variant of 5, 10, 15, 20, and 25 mm speciment and 0% Molybdenum as proportion, while other variables such as non-Molybdenum alloy, sand mold, and temperature is intentionally set constant. A whole process of this research is started with the melting process which alloying Molybdenum element is added into ladle and other several experiments which are micro structure observation, brinell test method, microvickers test method, Scanning Electron Microscope test method, and Optical Emission Spectrometry test method. This research results the effect of adding 0,53% Molybdenum element towards FC 250 material micro structure which the amount of graphite less than a whole thickness, the size of smaller graphite, and the distribution of graphite turns to be type D with speciment thickness 10 and 15 mm and in the thickness of 5 mm but formed the ledeburite. The amount of phase ferrite increases around 9-12% and the amount of phase pearlite decreases around 9-12% if it`s compared to the same variant of 0% Mo thickness. The effect of adding 0,53% Molybdenum element towards FC 250 material thickeness which increases brinell hardness of 44,9 HBS, increases the strength value of microvickers of 46,06 HV in phase ferrite and 42,3 HV in the phase pearlite on each thickness compared to the same thickness in 0% Mo variant. By all the experiments of thickness that had been conducted, it could be concluded that addition Molybdenum element towards FC 250 material could increases the strenght of ferrite and pearlite.

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