What is the Cor-Ten B steel ASTM equivalent?

I know that Cor-ten B is equivalent to a588, but is it a588 grade a, a588 grade b or a588 grade c? Where does it say this?
 

Answer:

astmA588 has different grades means Cor-ten B is having different grades.
Following links are giving lot of information regarding Cor-ten B.

ASTM Corten B steel grade is a hot rolled products of structural steels in technical delivery conditions with improved atmospheric corrosion resistance.The steel grade Corten B is according to ASTM standard which with the yield strength of 355MPa and 345MPa which is based on the different thickness.The anti-corrosive properties of Corten B steel are better than those of other structural steels in many applications. Corten B steel is self-protecting. The rust layer on the surface becomes a tight oxide layer that slows down the progress of corrosion. Corten B steel is an economical, long-lasting and fully recyclable material.

ASTM CortenB is used for various types of welded, bolted and riveted constructions e.g. steel frame structures, building cladding, metal sculptures (Angel of the North), chimneys, bridges, tanks and containers, exhaust systems, vehicles and equipment constructions.

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