Method for hot-dip coating chromium-bearing steel

A method of pretreating and hot-dip coating steel strip containing at least 6% chromium in a molten bath of aluminum or aluminum alloy to provide an improved coating comprising the steps of:

• a) annealing the final gauge steel strip in an atmosphere of at least 3% excess oxygen to produce a chromium rich oxide on the surface,
• b) electrolytically descaling the strip in an aqueous salt solution to remove the oxide to expose a chromium depleted surface of the strip,
• c) introducing the previously annealed and descaled strip having the chromium depleted surface into the entry end of a coating line,
• d) heating the strip in a first nonoxidizing atmosphere,
• e) passing the strip to an intermediate stage where the temperature of the strip is brought at or above the temperature of the bath,
• f) maintaining a second nonoxidizing atmosphere of substantially hydrogen in the intermediate stage and over the bath while maintaining the dew point of the atmosphere in the intermediate stage below minus 35.degree. C., and
• g) drawing the strip having the chromium depleted surface through the bath.