Discussion of cementite layer formation and sooting

A thermodynamic explanation was recently proposed for the formation of massive layers of cementite without any graphite by gas carburization of steels at 550 °C if the gas contains NH3. That explanation is now criticized. It is proposed that a kinetic factor, based on the difficulty of precipitating graphite inside a solid matrix, may contribute to the inhibition of metal dusting in the presence of NH3.