Hi All,  As I discovered during my research, 'plates with the best
acoustic qualities are those in which a soft gray iron has been formed
during the casting process.  This soft iron dampens metallic ringing
sounds and hammer noise more than any other type of ferrous metal.

The dampening ability is maximized when the casting cools slowly.  Slow
cooling also produces a soft metal, which significantly reduces string
breakage at the plate termination point.

Piano wire will break prematurely if the termination point is as hard
or harder than the wire.  (from "The Educated Piano", by E. J. McMarrow)

Musically,
John A Tuttle
Player-Care.com
Brick, New Jersey, USA