ASTM A588 covers high-strength low-alloy structural steel shapes, plates, and bars for welded, riveted, or bolted construction but intended primarily for use in welded bridges and buildings where savings in weight or added durability are important.
The atmospheric corrosion resistance of this steel in most environments is substantially better than that of carbon structural steels with or without copper addition.
When properly exposed to the atmosphere, this steel is suitable for many applications in the bare (unpainted) condition.
A606-4 is a type of high strength low alloy steel that is known for its rusted appearance. It’s popular because it can be made into metal panels and has a rusted appearance.
Corten flat sheets will not arrive pre-rusted. Weathering steel will rust naturally when exposed to the weather.