@abhi7183,
In any real life situation, the hot sphere will lose heat to the environment. The hotter the sphere, the faster it will lose heat. This means it would reach a temperature equilibrium at the point that the heat added to the sphere equals the heat lost.
If you are going to continually raise the temperature of the surroundings, you are limited by the melting point of iron.
I don't think there is anything that complicated here.