| abstract |
A method for protecting low-carbon steel and stainless steel, and particularly high temperature stainless steel, from coking and corrosion at elevated temperatures in corrosive environments, such as during ethylene production by pyrolysis of hydrocarbons or the reduction of oxide ores, by coating the stainless steel with a coating of MCrAlXSiT in which M is nickel, cobalt, iron or a mixture thereof, X is yttrium, hafnium, zirconium, lanthanum, scandium or combination thereof, and T is tantalum, titanium, platinum, palladium, rhenium, molybdenum, tungsten, niobium, boron or combination thereof. A blended powder composition to produce a desired MCrAlXSiT surface alloy may be applied to the substrate. The overlay coating and stainless steel substrate preferably are heat-treated at about 1000 to 1200° C. for about 10 minutes or longer effective to metallurgically bond the overlay coating to the substrate and to form a multiphased microstructure. The obtained surface alloyed structure is preferably aluminized by depositing a layer of aluminum thereon and subjecting the resulting coating to oxidation at a temperature above about 1000° C. for a time effective to form an alumina surface layer. Also, the coating may be deposited onto and metallurgically bonded to the substrate by plasma transferred arc deposition of atomized powder of MCrAlXT, obviating the need for a separate heat treatment. Alternatively, a blended powder composition to produce a desired MCrAlXT alloy may be applied to the substrate. |