Abstract: Inject ammonia and argon into the ion nitriding furnace, the ammonia flow rate of 0.5 L/min was maintained, and the furnace pressure was controlled by changing the argon flow rate (argon flow rates of 0, 0.45, 0.60 and 0.85 L/min, respectively) to study the effect of furnace pressure on the uniformity and microstructure of the nitrided layer of small modulus gears. The results show that as the argon gas flow rate increases, the uniformity of the ion nitrided layer also increases. Under an ion nitriding process at 540 ℃ for 8 h, when the furnace pressure is below 180 Pa, nitrogen cannot penetrate into the root area of gear teeth. When the furnace pressure is higher than 330 Pa, due to the thin glow thickness inside the furnace, the probability of arcing increases and the uniformity of furnace temperature deteriorates. With the increase of argon gas input, the thickness of the compound layer decreases and to some extent improves the nitriding rate, but has no significant effect on the looseness of the nitriding layer and the level of vein like nitrides.

Key words: iron nitriding, gear, glow thickness, furnace pressure