Selective coating and carburisation of an earth boring drill bit.

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A portion 20 of a component 17 for an earth-boring drill bit (10, fig 1) is coated and the component as a whole is exposed to a carbon-rich environment at an elevated temperature. The areas that were uncoated originally are then coated and the component exposed to a second elevated temperature in a second environment with carbon present. In one embodiment, a drill leg 17 is coated everywhere apart from the journal pin 18 and exposed to a carbon-rich environment at an elevated temperature. The journal pin itself is then coated and the drill leg as a whole is exposed to an elevated temperature with a percentage of carbon that is less than the initial carbon-rich environment. An optional step of machining or drilling the drill bit may also be added.