Study of the Ion-Carbo-Nitriding of Iron and Steel with the City Gas

Abstract

Some kinds of metals are hardened by ion-bombarding with the reactive gas in glow discharge. This technique is being applied to surface hardening of some metals. In most cases, however, metals have been hardened by ion-nitriding using a nitrogen-hydrogen gas mixture as a bombarding gas. In this work iron and some steels were bombarded in the city gas (the reformed naphtha which have a combustion heat of 3600 kcal/m²) in the temperature range from 400 fo 700°C in order to ion-carbo-nitriding. The gas seems to be useful for carbo-nitriding, because it consists of CH₄, CO, CO₂, N₂, H₂, H₂O, etc. The change on ion-bombarded specimens were investigated by means of optical microsrcopy, hardness measurement, X-ray analysis, etc. The following results were obtained.
In α-iron and S 15 C steel, the surface layers of cementite are formed at 650 to 700°C and their maximum hardnesses are higher than Hv 1000.
In SCM 21 and SACM 1 steels, the same layer is not observed clearly by the optical microscope but the reflections from the cementite are obtained on X-ray diffraction. They are soft in comparison with α-iron and S 15 C steels.
SUS 304 steel could not be carbo-nitrided.