A forged iron contains a clubhead that’s heated and molded from a single piece of metal. Unless you’re an expert, you probably won't be able to look at an iron and determine whether it’s been forged or created via a different manufacturing process. But the differences between forged and non-forged irons might be felt when you swing the clubs on a golf course.
Forging techniques differ between club manufacturers, but the basic idea of forging has been around for centuries – metal is heated up, then hammered or pressed into shape. For example, the process used by Mizuno – which has been forging clubs since the 1930s – begins with a bar of 1025 or 1025E steel that is heated to a red-hot temperature. The steel is bent into the correct angle for the particular club being made, then placed in a primary forging mold, where an air hammer presses it into its basic shape. After another machine trims the excess metal from around the edges, the future clubhead is re-heated and placed into a second mold, where the metal is pressed slowly to create the final shape, including the grooves. The clubhead’s sides are then smoothed on a grinder before it’s attached to a shaft.
Forged irons were the only option for high-level golfers for most of the 20th century. The main alternative to forged clubs are those made from cast irons, which are made by pouring hot liquid metal into a mold and allowing the metal to cool. As casting techniques and designs improved, cast irons gained greater popularity, largely due to the development of “game improvement” clubs that were more forgiving of mis-hits. By the mid-1990s, only about half the players on the PGA Tour were using forged irons. In the 21st century, however, many forged irons incorporate design ideas made popular by cast-iron clubs. Even some cavity-back clubs, formerly the sole province of cast-iron manufacturers, are now being forged. As of 2010, approximately 80 percent of PGA Tour golfers carried forged irons in their bags.
Because a forged iron is constructed from a single piece of steel, a forged clubhead is more consistently solid than a cast-iron club. The casting process inevitably creates tiny air bubbles that are trapped in the mold and become part of the finished clubhead. Highly skilled golfers tend to prefer the greater feel they receive with forged irons, which typically allow top players to produce more accurate shots, provided they hit the forged iron’s smaller sweet spot in the middle of the clubface.
The average golfer will benefit from using game-improvement clubs, many of which are still manufactured using the casting process. Game-improvement clubs have larger sweet spots, are more tolerant of mis-hit shots and give beginning golfers a better chance to hit with reasonable accuracy. However, a forged game-improvement club constructed with the same design as a cast-iron club should produce the same results.