Nitrogen Contents of Iron Compacts Sintered in Atmospher of Cracked Ammonia

Abstract

Nitrogen contents of iron powder compacts sintered in cracked ammonia were determined by direct chemical analysis. At the sintering temperature of 1200°C, maximum solubility of nitrogen in compacts seems to be reached at the earliest stage of sintering. Since the solubility of nitrogen in a-iron is considerably less than that in r-iron, the nitrogen content of sintered compact decreases drastically, during the relatively slow cooling from Ar3 down to 500°C after sintering. This desorption of nitrogen proceeds most rapidly at about 550°C for the low density compact, probably due to the catalytic effect of hydrogen on the inner surface of pore. In order to decrease the final content of nitrogen down to about 10 p.p.m. for the compact of 6.2 and 7.1 g/ee, the slow cooling rate below 100 and 2°C/min in the temperature range of 500-900°C are required respectively.