I am not sure that there is an equivalent ASTM grade for this steel alloy. None of the standards that I reviewed (ASTM A 193, A 194, ASTM A 540) reference an equivalent grade. Perhaps ASTM A 437 or A 453 list an equivalent, but I do not have either of these standards. Corus Enngineering Steels is one of the producers of this grade, and they do not list an ASTM standard either: