FORMATION OF COMPOUND LAYERS ON IRON DURING GAS NITRIDING

Abstract

Gas nitriding experiments were carried out for two series of iron specimens at 575°C: one was preheatedin air at 300°C for 1 h before nitriding, the other was nitrided directly. It was found that the pretreatment has a significant effect on the formation of the nitrides. Without preoxidation, the rate of nitriding was inhibited by a slow surface reaction such that the nitrides were formed on the iron surface inhomogeneously. With preoxidation, a homogeneous compound layer developed rapidly on the iron surface during the subsequentnitriding. The kinetics of the compound layer formation and the effect of the preoxidation on the subsequent nitriding process are discussed together with the previous findings.