New forms of carbon in Fe-C alloys that had been obtained experimentally or may be produced in the future are discussed. Carbyn, as the "linear" allotropic form of crystalline carbon, has not yet been obtained in them and allegations to the contrary are seemingly false. The electron diffraction patterns, published in Russia, pertain to austenite. Small diamond crystals in "diamond cast iron" have been produced experimentally, but assertions of their formation inside graphite nodules in SG-iron at atmospheric pressure seem to be erroneous. An international quest into these problems is probably necessary.