According to Grandpa asiong:
CAST - will make use of cast so normally there will be a rough surface finish. Liquid material is poured int a casted shape and allowede to solidify.
FORGED- is shaped by deformation / use of suitable compressive force (e.g. hammer,press). It will refine the grain structure of metal and improves physical properties (strength, ductility, toughness)will produce a neat or smooth surface finish.
Based from articles (for Cars anyway) about which is better to use as engine parts, it is said that forged metals are the way to go and stonger than cast metals. And being more recently developed than the cast, which has a long history, Forged is really the newer tech of the two.
As an example," The cast piston is light and very dimensionally stable. It is found in high-rpm mass-produced engines that are not subject to modification or prone to detonation. This type of piston is however fairly brittle, and the cost of its manufacture has limited its availablity outside the OEM sources and applications.
On the other hand, the forged piston is inherently heavy and less dimensionally stable. It is a good choice for engines in which detonation is probable, and its wide availability has made it the choice of engine modifiers. The special demands of these end users has given the forged piston its own niche in the powersports market."-motorcycleproject.com