抄録
Nitriding, heretofore in use, has many advantages such as eminent heat resistivity of the hardened layer and small-degree deformation by the treatment, but the main disadvantage is to take many hours for nitriding.
Therefore, noticing the presence of a conspicuous affinity of Ti to N2, the authors have carried out experiments to examine whether nitriding of steel can be achieved in a much shorter period of time by diffusing or alloying Ti.
At first, mild steel was heated in a mixed gas of H2 and TiCl4, but any favorable result could not be obtained. Next, mild steel was buried in ferro-titanium powder, the surface layer was enriched in Ti, and then nitrided. In this case, remarkable hardness was obtained in a shorter time, but the hardness or depth of this hardened layer could hardly be controlled and the surface condition was not desirable. Finally, Ti-steel, Ti-Cr-steel and Ti-Cr-Mo-steel were prepared and nitrided. As the result, the authors succeeded in producing a favorable, deep hardened layer (VPN: 1000; depth: 0.7 mm) by nitriding for a short time (9 hr at 650°C). Heat-resisting tests showed that the surface hardness of these specimens remained unchanged even after reheating at 500°∼600°C.
