One has to distinguish between black body and black body radiation (see, e.g., the discussion in Black body vs. Thermal radiation thread.) The latter is radiation in thermal equilibrium, which, in modern physics, can be derived without recourse to the concept of black body - e.g., simply by starting from the Boltzmann distribution of a photon gas.

Black body is an object that absorbs all the radiation incident on it and then re-emits it - thus, it finds itself in equilibrium with the surrounding radiation, which provides another way of deriving black body radiation spectrum.

A piece of metal heated to 3000K is obviously not in equilibrium with its environment, and hence it is not a black body. It can be however viewed as a body in internal thermal equilibrium, and the radiation wondering inside (emitted by some atoms and absorbed and reemitted by the other) is in thermal equilibrium, i.e., it can be described as black body radiation. The radiation emitted by such an object (during a short observation time) constitutes only a small fraction of the radiation energy stored inside. Of course, if we look at this object for a long enough time, the quasi-equilibrium description for the radiation in it doe snot hold - the object will gradually lose more and more energy, eventually coming to equilibrium with its surroundings.

A more interesting case is Sun with internal sources of energy - see How does radiation become black-body radiation? for more discussion.

One has to distinguish between black body and black body radiation (see, e.g., the discussion in Black body vs. Thermal radiation thread.) The latter is radiation in thermal equilibrium, which, in modern physics, can be derived without recourse to the concept of black body - e.g., simply by starting from the Boltzmann distribution of a photon gas.

Black body is an object that absorbs all the radiation incident on it and then re-emits it - thus, it finds itself in equilibrium with the surrounding radiation, which provides another way of deriving black body radiation spectrum.

A piece of metal heated to 3000K is obviously not in equilibrium with its environment, and hence it is not a black body. It can be however viewed as a body in internal thermal equilibrium, and the radiation wandering inside (emitted by some atoms and absorbed and reemitted by the other) is in thermal equilibrium, i.e., it can be described as black body radiation. The radiation emitted by such an object (during a short observation time) constitutes only a small fraction of the radiation energy stored inside. Of course, if we look at this object for a long enough time, the quasi-equilibrium description for the radiation in it does not hold - the object will gradually lose more and more energy, eventually coming to equilibrium with its surroundings.

A more interesting case is Sun with internal sources of energy - see How does radiation become black-body radiation? for more discussion.