A forged iron is made using a singular block of solid metal that’s heated red hot, stretched, hammered, formed to the iron’s specific head shape, and cooled. A cast iron golf club’s head is made by pouring liquid metal into a mold of the desired shape.
By using a liquified metal in the cast iron creation process, club head engineers and designers are able to be more aggressive in the “game improvement iron” head shapes leading to more forgiving “cavity back style” designs in the cast iron genre of club head.
This could be why we often recognize forged irons as the “better players clubs.” (Less game-improvement style head shapes)