Synopsis : Steels containing 0.3mass%C and various amount of Mn were nitrocarburized at 873 K for 2 h to investigate behavior of N and Mn in a nitrocarburized layer. Transmission electron microscopy observation showed that a part of Mn precipitated as nitrides η-Mn 3 N 2 in the ferrite matrix. To fix the state of N in the nitrocarburized layer, solution and aging treatments were carried out sequentially. Most N was presumed to exist as dissolved N or Mn nitrides in the solution treated specimen

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... and as iron or Mn nitrides in the aged specimen. Amount of the precipitation hardening with η-Mn 3 N 2 increased with the increasing Mn content, whereas amount of solid solution hardening in the steel with high Mn content was smaller than that with low Mn content. On the basis of measuring N concentration and thermodynamical calculation, it was estimated that the precipitation hardening ability of Mn nitrides was smaller than that of Cr, Al, Ti and V nitrides.