Abstract
Sintered Cr-steels containing 1-3% Cr were prepared from the mixtures of iron powder, Cr3C2 powder and graphite powder, by compacting and sintering at 1250°C in vacuum. Specimens were nitrided at 500°C in an ammonia gas atmosphere, and the nitrided layer was examined. The results obtained are as follows:
(1) Specimens containing more than 2%Cr give nearly same hardness distribution pattern after nitriding for 1 hr, compared with that of conventional Cr-steel nitrided for long time.
(2) Rapid nitriding is due to the penetration of nitriding gas through pores of specimen, therefore nitrides are formed on the inner surface of pores and grain boundaries connecting with pores.
(3) Although sintered specimens absorb large amounts of nitrogen, an X-ray diffraction pattern of the surface layers clearly shows a phase peak. This peak shifts to lower angle direction with an increase of Cr content, which shows lattice strain of a phase, and may contribute to the hardness increase.
