Abstract: A passivated film on a surface of a high-alloy steel member makes it difficult to apply diffusion treatment, such as gas nitriding or gas carburizing, that forms a nitrided layer, carburized layer or carbonitrided layer on the surface of the steel member. An activating treatment method is provided for the surface of the metal member. This method is not accompanied by problems of conventional activation treatment with a halide, such as furnace deposits, furnace wall erosion and effluent gas detoxification treatment, and is useful as pretreatment for diffusion treatment. According to this method, the passivated surface of the high-alloy steel member can be activated by using a gas commonly employed in gas heat treatment, and forming HCN gas in a heating furnace while making use of catalytic action of the steel member or a surface of the furnace.

Abstract: A new nitriding process by using a salt bath to produce iron and steel parts having excellent abrasion resistance and corrosion resistance includes forming an iron lithium complex oxide layer at the outermost surface of the iron part by immersing the iron and steel parts in a salt bath containing cationic component of Li, Na and K and anionic components of CNO?and CO32?, where hydroxide compound selected from lithium hydroxide, sodium hydroxide and potassium hydroxide are added to the salt bath. Materials being in a hydrated state or in a free water containing state can be used for preparation or replenishing of the salt bath. Moistened air of (1×10?2 kg·H2O)/(1 kg dry air) can be used for mixing the salt bath. Containing ratio of Li, Na, K is preferable where a solidifying temperature of the mixture of carbonates of Li, Na, K in that ratio is lower than 500° C.

Abstract: A metal member is produced with enhanced corrosion resistance by salt bath nitriding. Specifically, in a nitriding salt bath containing Li+, Na+ and K+ ions as cation components and CNO? and CO3?? ions as anion components and enhanced in oxidizing power by addition of an oxidizing-power-enhancing substance selected from the group consisting of alkali metal hydroxides, bound water, free water and moist air, the metal member is immersed such that an nitrided layer is formed on a surface of the metal member and concurrently, an oxide film is formed on an outermost layer of the nitrided layer. As a subsequent step to the immersion in the nitriding salt bath, the metal member is immersed in a displacement cleansing salt bath which contains an alkali metal nitrate.

Abstract: A metal member is produced with enhanced corrosion resistance by salt bath nitriding. Specifically, in a nitriding salt bath containing Li+, Na+ and K+ ions as cation components and CNO− and CO3−− ions as anion components and enhanced in oxidizing power by addition of an oxidizing-power-enhancing substance selected from the group consisting of alkali metal hydroxides, bound water, free water and moist air, the metal member is immersed such that an nitrided layer is formed on a surface of the metal member and concurrently, an oxide film is formed on an outermost layer of the nitrided layer. As a subsequent step to the immersion in the nitriding salt bath, the metal member is immersed in a displacement cleansing salt bath which contains an alkali metal nitrate.