12%Crフェライト系ステンレス鋼粉圧粉体の窒素雰囲気における窒化および焼結機構

抄録

Sintering and nitriding behaviors of 12mass% Cr ferritic stainless steel (SUS410L) powder compacts in nitrogen gas atmosphere were investigated by means of optical microscopy and chemical analysis. Kinetics of the austenitization by nitriding was also discussed in terms of nitrogen diffusion within austenite grain and along grain boundaries.
The results obtained are as follows:
(1) At sintering temperature of 1473K in nitrogen gas atmosphere, about 0.26mass% of nitrogen is absorbed into the steel powders through open pores during heating to the sintering temperature, and ferritic phase changes to austenite owing to nitrogen absorption. Therefore, sintering proceeds in the state of austenitic structure at 1473K and then austenite transforms to martensite on cooling to room temperature after the sintering treatment.
(2) Grain boundaries within powder particles play a role of free path for nitrogen diffusion, so that the austenitization by nitriding in ferrite powder particles proceeds not only from the particle surface but also from grain boundaries within each powder particle.
(3) Nitriding rate greatly depends on the grain size within powder particles, although it is dependent on particle size itself when particles are of single crystal. As the grain size within powder particles becomes smaller, nitriding rate is increased.