| abstract |
Chromized nickel- and cobalt-based superalloys have alphachrome phase formed during chromizing, and the amount of that phase is diminished by one or more treatments with alkali-permanganate solution and intervening removal of permanganate reaction product film as by acid dip. A kit of such solutions can be prepared. Low-alloy steel steam boiler tubing can have chromized interior and aluminized exterior, and long lengths chromized without a perfectly sealed retort around it can have end caps fitted with extra pack to reduce oxygen penetration to interior. Chain saw cutter blades can be chromized and carburized. Stripping of aluminized coatings from superalloys with fluoride-containing nitric acid solution is improved by follow-up treatment with fluoride-free nitric acid solution. Smut that forms on ferrous surface during cleaning is chemically removed by first depositing a nickel flash plating on smut-containing surface, and then dissolving the nickel plating by treatment with aqueous nitric acid containing a little halide ion. |