Gas Carburizing and Quenching of Sintered Iron-Nickel

Abstract

Sintered iron-3%nickel specimens prepared from the mixture of reduced iron and carbonyl nickel powders were gas carburized and oil-quenched. The effects of nickel addition were examined. The results obtained are as follows :1) The increase in sintered density by nickel addition was found to be effective in reducing the penetration of carburizing gas to the interior of the sintered specimens. The carbon decrease in the carburized specimens is remarkable owing to the high density of the specimen obtained by the prolonged sintering.2) The surface carbon content of carburized specimens tends to decrease as compared with sintered and carburized iron specimens owing to the density increase and the change of the carbon activity in austenite by the nickel addition.3) The increase in quench-hardening ability by the nickel addition depends on the diffusion of nickel into iron during the sintering. The depth of the hardened case increases in the early stage, and then decreases, with increasing sintering time. This decrease of depth is due to the above mentioned carbon decrease during the prolonged sintering.