低炭素鋼のガス窒化特性におよぼすSi量の影響

抄録

The elements such as Al, Cr and Ti that form the stable nitride on the process of gas nitriding are necessary to obtain higher surface hardness and larger nitrided depth, as standarized in the chemical composition of nitriding steel.
Similarly, Si is an element to form nitride. Therefore, the authors have shown in the previous paper that a higher surface hardness, Hv 800, is obtained in the gas nitrided spheroidal graphite cast iron and considered that its hardening mechanism depends on the formation of Si₃N₄.
A more detailed study of the effect of Si content on the gas nitriding characteristics was conducted in this work.
The 0.2%C steels containing 0.37∼1.49%Si were gas nitrided at 530∼620°C for 20 hr using a circular type furnace.
It was found that the surface hardness of nitrided specimens increases in propotion to the increase of Si content, and that the surface hardness reaches a maximum value, about Hv 400. The nitrided depth increases with increasing of Si content and nitriding temperature. The maximum value of this depth is about 0.4 mm.
Moreover, it was found that tempering the nitrided specimens increases both the surface hardness and the nitrided depth.
From these results, we concluded that the hardening mechanism in those gas nitrided specimens was due to the precipitation or growth of Si₃N₄.