Abstract
Investigations were made on the relation between salt bath nitriding and crystal grain size of steel, which had been annealed at various temperatures and refined.
The results obtained were summarized as follows.
(1) The relation between nitriding temperature and hardness was as follows.
After some specimens of SACM 1 and S45C steels, having various crystal grain sizes, were subjected to nitriding, the change in their surface hardness did not depend on their initial grain sizes, but was found to be almost in the same trend for every size.
However, the depth of hardened layer was decreased with the increase in crystal grain size.
(2) The surface of every specimen was mose rough with the rise in nitriding temperature.
(3) The surface hardness after re-heating for diffusion was indifferent to the crystal grain size, but was in the same trend for every specimen.
(4) The fatigue limit was more improved when the grain size was finer.
