2021 Volume 62 Issue 5 Pages 596-602
Pure iron and Fe–M (M = Mo, Si, Mn, Cr, Al, V) binary ferritic alloys were nitrided at 843 K for various times. Phase constituent, hardness distribution and growth rate of the compound layer are investigated by means of X-ray diffraction, EBSD, EPMA, 3DAP and nanoindentation. In pure iron, ε and γ′ (beneath ε) form on the surface, and voids form along the interface. The hardness of γ′ is higher than ferrite matrix, while void formation causes softening of compound layer. Although alloying effects on the hardness of compound layer are small, Si, V and Al additions suppress the formation of voids, and therefore the softening is also contained. All the elements investigated increase growth rate of compound layers. Especially the Si, V and Al additions significantly accelerate their growth rate due to the presence of excess nitrogen in compound layer. However, in the case of Al-added specimen, the growth layer becomes sluggish at longer nitriding time, presumably because of the extensive precipitation of AlN into the diffusion layer.
This Paper was Originally Published in Japanese in Netsu-shori 59 (2019) 336–343.
