What is Grey Cast iron ? How it is made ?

This is obtained by allowing the molten metal to cool and solidify slowly. On Solidifying , The iron contains the greater part of carbon in the form of graphic flakes.

Grey cast Iron contains large quantities of carbon and relatively small quantities of the other element, e.g., silicon phosphorous , Sulphur and manganese.

It presents a dull grey crystalline or granular structure and a strong light will give a glistering effect due to the reflection of the free graphite flakes. The presence of this free graphite is also seen when filing or machining cast iron as it makes hands black.

The Cast Iron is brittle and may easily be broken if a heavy hammer is used. The strength of Iron is much greater in compression than in tension. The ultimate tensile strength of Cast Iron varies between 12 to 13 kg-f per mm2 (120 to 300 Newton per mm2) and depends on the composition of the Iron. In compression , Gray cast Iron will withstand about 60 to 75 kg-f per mm2 (600 to 750 Newton per mm2) before fracturing, whilst in shear its strength is approximately 15 to 22 kg-f per mm2 (150 - 225 Newton per mm2). The hardness ranges from 150 - 240 BHN.

The main advantages in favor of its use are : (1) its cheapness, (2) its low melting temperature (1,150*C to 1200*C), and fluidity when in the molten condition , and (3) it is easily machined. A further good property of cast Iron is that the free graphite in its structure seems to act as a lubricant , and when large machine slides are made of it a very free-working action is obtained. The fluidity Analysis of the iron enables it to be used widely for making castings of parts having intricate shapes and in almost all cast Iron Forms.

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