A process and reactor are disclosed for the thermal cracking of a charge containing at least one hydrocarbon with at least one carbon atom, in which the charge is circulated in a metal reaction zone which includes a pyrolysis zone whose external wall is in thermal exchange relationship with a heating liquid. The reaction zone consists of an alloy containing, by weight, 66-82% nickel, 14-18% chromium, and 4-6% aluminum. This alloy, which has already been preoxidized, may be covered, at least in the reaction zone, with at least one layer formed by an oxide of at least one metal and/or at least one metal carbide and/or at least one metal nitride and/or at least one metal silicide. The invention finds application for vapor-phase cracking and dehydrogenation of hydrocarbon charges.