The reason cast iron is so popular in machinery is damping
characreristic. steel pings, that is mechanical waves resonate and
propagate well through it.
The thing about cast iron is that it is supersaturated with carbon,
during cooling some of this precipitates out in a fine lath as
graphite. These flakes of graphite absorb acousti-mechanical waves,
and thus provide damping.
The welded steel may indeed be the better machine. These are just the
properties of the two materials.

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