Melting the iron in the graphite crucible. Does the graphite in the crucible turn into carbon and it melts into the steel?
Graphite is a very pure substance, and graphite is a transition crystal. The carbon atoms in each layer of graphite are bonded by non-polar covalent bonds, and the molecular layers of graphite are joined by intermolecular forces. The melting point of the graphite crucible is 3652 to 3697 degrees (sublimation), so the graphite crucible is high temperature resistant.
Graphite burns at least 3000 degrees above the oxygen level. The ignition point in the air is even higher. There is no fire at such high temperatures in the air, so the graphite cannot be ignited.
In addition to carbon, charcoal contains hydrogen, oxygen, nitrogen, and a small amount of other elements. Carbon in charcoal is not a transition crystal like graphite, but amorphous carbon and no C-C covalent bonds. Charcoal ignition is 320-370 DEG C, the general fire than the high temperature, so the charcoal can be lit.
