Title: Chromizing of steels by gaseous method

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Abstract: The object of the present invention is an improvement in chromizing methods, constituted by a method of chromizing steels to a depth e greater than 30 microns, usable for steels with a carbon content of at least 0.2%, especially for steels for construction work and steels for tools, characterized by the combination of three successive treatments, the first of these three treatments consisting of an ionic nitriding of a surface layer between 100 and 350 microns thick, this ionic nitriding being realized in an atmosphere constituted by a mixture of nitrogen and hydrogen, at a temperature of between 450.degree. C. and 650.degree. C., for between 5 and 40 hours, so as to obtain between 1.5% and 2.5% nitrogen in the nitrided layer, the second of these treatments consisting of a chromizing by gaseous method forming chromium carbides, lasting between 5 and 30 hours, and realized at temperatures of between 850.degree. C. and 1,100.degree. C., the third of these three treatments being a thermal treatment comprising a quenching in oil of the chromized piece followed by a tempering at a temperature of between 600.degree. C. and 650.degree. C., lasting between 30 minutes and 10 hours, depending on the size of the piece treated.


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