Claims
- 1. In an article having a metal alloy component containing chromium, a method of protecting the metal alloy component against metal embrittlement by carburization or sulfidation when the metal alloy component is exposed to carbon or sulfur at an elevated temperature, the method comprising providing a metal alloy component containing chromium, coating a surface of the metal alloy component with a dry, porous layer of a pulverized glass that is thermally crystallizable and that is capable of combining with chromium oxide, heating the coated metal alloy component in an atmosphere containing oxygen to cause a layer of chromium oxide to form at the interface between the coating and the metal alloy component, thermally softening the glass coating and combining the layer of chromium oxide at the coating-metal alloy interface with an inner portion of the thermally softoned glass adjacent thereto to form a vitreous layer that is tightly adherent to the metal alloy surface, that contains chromium oxide, and that resists crystallization, the outer portion of the thermally softened glass remaining essentially uncombined, and cooling the coated metal alloy component to a lower temperature at which the outer portion of the glass layer that is essentially chromium-free crystallizes, holding at that temperature for a sufficient time to crystallize the glass, and then cooling the metal alloy component with a bi-layer coating of glass and glass-ceramic.
- 2. A method in accordance with claim 1 which further comprises producing a glass that is thermally crystallizable and that is capable of combining with chromium oxide, pulverizing the glass, mixing the pulverized glass with a vehicle to form a slurry, applying the slurry to the surface of the metal component to be coated, and drying the coating to a porous layer through which oxygen is accessible to the metal alloy surface.
- 3. A method in accordance with claim 2 in which the glass to be pulverized has a composition selected from a group of glass families consisting of alkaline earth metal silicates, aluminoborosilicates and aluminoborates.
- 4. A method in accordance with claim 2 in which the step of forming the pulverized glass layer on the metal alloy component surface comprises applying the coating in such amount that, when dry, the coating has a thickness of at least 10 microns, but not over about 0.25 mm.
- 5. A method in accordance with claim 1 which comprises heating the coated metal alloy component to a temperature of about 1200.degree. C. to form the chromium oxide-containing glass and adhere it to the metal alloy surface, cooling the coated metal alloy component to about 1050.degree. C. and holding at that temperature for about 4 hours to crystallize the chromium free glass layer and then cooling the metal alloy component with the bi-layer coating.
- 6. A method of protecting a metal alloy element of a thermal cracking furnace from embrittlement due to exposure of the element to carbon particles during operation of the furnace, the method comprising providing an iron-nickel-chromium alloy furnace element, coating a surface of the furnace element with a dry, porous layer of a pulverized, barium aluminosilicate, thermally crystallizable glass that is capable of combining with chromium oxide, heating the coated furnace element in the presence of oxygen. to a temperature of about 1200.degree. C. in an oxygen-containing atmosphere while chromium migrates to the furnace element surface to form an oxidized layer of chromium at the interface between the coating and the metal alloy, continuing to supply heat to thermally soften the pulverized glass layer and to cause at least a portion of the layer adjacent to the interface to form a vitreous layer that contains chromium oxide and that forms a continuous adherent layer on the metal alloy surface, and cooling the coated metal alloy furnace element, to about 1050.degree. C., holding at that temperature to crystallize that portion of the pulverized glass coating that is chromium-free, and cooling the furnace element to ambient, whereby the metal alloy furnace element is isolated from contact with the carbon particles.
Parent Case Info
This application is a continuation-in-part of Ser. No. 08/427,381 filed Apr. 24, 1995 by T. R. Kozlowski, F. E. Noll, J. M. Quintal and M. H. Wasilewski under the title METHOD OF PROTECTING METAL and assigned to the same assignee as this application.
US Referenced Citations (8)
Foreign Referenced Citations (1)
Number |
Date |
Country |
2066696 |
Jul 1981 |
GBX |
Non-Patent Literature Citations (1)
Entry |
Barnes, J. et al., "Sulfur Effects on the Internal Carbuization of Fe-Ni-Cr Alloys," Oxidation of Metals, vol. 26, No. 5/6, p. 333-349, 1986. |
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
427381 |
Apr 1995 |
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