The regularities of carbonyl iron powder nitriding were investigated using Ti + C “chemical oven” mixture and urea as a source of atomic nitrogen. Increasing the urea content was found to lower maximum nitriding temperatures and decelerate cooling rates, the latter being attributed to the exothermic nature of iron–nitrogen reaction. Although maximum temperatures decreased as sample diameter was reduced, the phase composition exhibited minimal sensitivity to these geometric variations.
Barinova et al. (Sun,) studied this question.