To form a nitrided case with high efficiency by a method wherein in low temperature nitriding treatment for an aluminum material to form a nitrided case, a flow rate of introduction nitrogen gas and a discharge area of the gas are regulated by a specified temperature in the middle of the increase of temperature, and an oxygen gas partial pressure in the furnace and a furnace pressure are held at a specified temp..
A horizontal type cylindrical heating furnace 1 having one end being opening is provided on the inner peripheral surface of a furnace wall with an electric heater 10 and a horizontal type cylindrical muffle 2 having an base end opening being opened is contained in the heating furnace 1 in a state to be separated away from the inner surface of the heating furnace 1 by a given distance. Gas for nitriding is introduced in the furnace 1 containing an aluminum material coated with nitriding auxiliaries and the interior of the furnace 1 is held at a positive pressure, the aluminum material is heated to 400-600°C, and a nitrided case is formed on the surface part of the aluminum material. In this case, at a high temperature stage from a given temperature to reaction completion, an oxygen gas partial pressure in the furnace 1 is held at 2.0Pa or less and a furnace pressure at a positive pressure of 0.5mmH2O to form the excellent nitrided case.
MATSUBARA EIKICHI
YAMADA YASUHIRO
MATSUNAGA HIROBUMI
NIPPON TOKUSHU KIKAI KK
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