I need to repair a cast iron pully and i was wondering if i could i build up the damaged area with 0.6 mild steel wire. The area is just a small chipped area.
Almost certainly not. You could maybe braze a piece of steel onto the pulley and machine it back (or file, or grind), or you could maybe stickweld with a ni/fe rod to build up material.
Or use some epoxy metal filler style material. There are some very tough epoxys available.
Good advice - mild steel wire will stick, but it shrinks as it cools and the tension built up on cooling might crack the cast iron. And a pulley isn't normally the sort of thing you'd want cracks in. Probably get away with it if you heat the pulley to dark red hot for welding, then let it cool very very slowly.
Soft filler metals are good - theres the braze, and nickel is commonly used with arc welders.