Blueing

blueing [′blü·iŋ]

(metallurgy)

bluing

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Blueing 

the process of obtaining a layer of iron oxides (Fe₃0₄ and others) 1-10 microns thick on the surface of components made of carbon or low-alloy steel and cast iron. The coating has a fine crystalline, microporous structure. Blueing is used for decorative finishing. The protective properties of the layers formed during blueing are weak; therefore, after blueing the components are covered with grease to increase their corrosion resistance.

There are various methods of blueing: alkaline blueing, in alkaline solutions with oxidizers at temperatures of 135°-150° C; acid blueing, in acidic solutions by chemical or electrochemical means; and thermal blueing, which is the oxidation of steel at high temperatures—in an atmosphere of superheated water vapor at 200°-480° C, in vapors of an ammonia-alcohol mixture at 520°-880° C, in melted salts at 400°-600° C, or in an air atmosphere at 310CM50° C after first covering the surface of the components with a thin layer of asphalt or oil varnish.

REFERENCES

Vainer, la. V., and M. A. Dasoian. Tekhnologiia elektrokhimicheskikh pokrytii. Moscow-Leningrad, 1962.
Bakhvalov, G. T. Zashchita metallov ot korrozii. Moscow, 1964.

V. V. BONDAREV