高周波加熱による高温ガス浸炭

Abstract

For the purpose of rapid carburizing of steel, we studied induction high temperature carburizing for Ni-Cr-Mo case hardening steel SNCM 23, in the atmosphere of propane-butane gas (JIS LPG No. 3) only or in the atmosphere diluted by nitrogen, and examined the influence of heating temperature (950°∼1300°C), holding time (below 90 min), gas flow (0.5∼1.51/min), dilute ratio of gas (propane-butane gas: nitrogen gas……1:4, 1:8, 1:16) on the rate of carburizing and microstructure. The results were as follows: (1) When the atmosphere was propane-butane gas only, the soot deposited at the surface of the specimen, and with prolongation in carburizing time, carburizing was injured. Under this condition, the rate of carburizing was a little larger than that obtained by the conventional gas carburizing at the same temperature.(2) When the atmosphere was diluted by nitrogen gas, the soot did not deposit and for the dilute ratio adopted in this experiment, the rate of carburizing was about 1.4 times larger than that obtained in the propane-butane gas only at the same temperature. Under this condition, the depth of the carburized layer was 2.0 mm at 1200°C for 30 min or 1.8 mm at 1300°C for 10 min. (3) The surface of the carburized layer had a carbon content which was rich enough to obtain the hardness above Hv 700, and the carbon content distribution curve became more gentle with increase in heating temperature. (4) The flow rate or the dilute ratio of gas did not affect the rate of carburizing so far as this experiment was concerned. (5) No grain growth was observed at the core of the specimen carburized at temperatures 1000°∼1300°C for only 30 min. For the carburized layer and core of the specimen, a normal microstructure and gentle hardness distribution curve were obtained by quenching and tempering.