Oxidation resistant ferrous base foil and method therefor

A method of making an aluminum coated ferrous base metal foil having improved oxidation resistance at elevated temperatures, improved wet corrosion resistance, and surfaces adapted to bond securely to a ceramic, heat resistant catalyst support material, comprising the steps of:

• hot dip coating a ferritic base metal strip in a bath of molten aluminum, said strip having a thickness of at least 0.25 mm and containing from 10% to about 35% chromium, up to 3% aluminum, up to 1% silicon, and balance essentially iron;
• finishing the molten aluminum coating to provide a coating thickness ranging from 0.013 to 0.13 mm on each side and a total aluminum content of at least 4% by weight;
• cold reducing the aluminum coated strip to a foil having a thickness not greater than 0.13 mm without intermediate annealing wherein the ratio of total aluminum coating thickness to base metal thickness is at least 1:10;
• and
• heating said foil in an oxidizing atmosphere within the range of about 600.degree. to about 1200.degree. C. with a time at temperature ranging from about 1 second to about 1 hour in accordance with the relationship:
• 1210>temperature (.degree.C.)+1/6.times.time (seconds)>600,
• whereby to produce a porous surface having a matte gray appearance.