UNS K23010 – ASTM A470 – ASTM A470M – ASTM A293 – Grade D – Class 8
ASTM A470 is a set of vacuum treated CrMoV carbon and alloy steels. The alloy has a resistance to elevated temperatures and is of USA-origin grade. In particular Grade D is specified more commonly for industrial and energy applications and often VAR / ESR processed.
ASTM A470, formerly ASTM A293, is a specification commonly used for steam turbine rotor shafts and disks. It covers various grades (A-E) with different chemical compositions and subdivided into classes (1-8) with different applications.
For example, Grade D Class 8 is typically used for HP rotors which endure elevated operating temperatures while Grade B&C Classes 2-7 are typically utilized for LP rotors with somewhat lower temperatures but higher resistance to wet (steam) erosion, with various heat treatment options depending on the application and grade / class required.
In Europe a common equivalent grade selected is 1.7709 – 21CrMoV5-7, which has better availability but similar chemical composition and mechanical properties, in particular to ASTM A470 Grade D Class 8.
