We are looking for SA508 Class 2 made in 1970 years.
Its possible,the steel name has changed ?
We had found in ASME Code that the name has changed in
SA508 Grade 2 Class 1.
Does anyone know anything about that ?

You are probably going to have to correspond with the ASTM directly. I checked their web site and the farthest back their on-line historical records go is the 1999 revision of the 1995 standard.

Many standards for steels that I am more familiar with were reclassified in the 90's to account for changes in steel making technology. It looks like this one met the same fate.

You might also be able to get a copy of ASME BPVC SA-508 from that era much more easily, since it will be a part of the BPVC. It will be much more expensive, though. I am not sure whether the BPVC SA specifications mimic the ASTM A specifications, or vice versa, but they track each other very well. The ASTM is primarily an organization made up of materials fabricators and the ASME is for those using the materials to fabricate (in this case) pressure containment systems. Logically, therefore, one would expect the ASTM specs to be the primary documents and the ASME specs to be the derived documents, but I don't know for sure.

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You might find this link useful.