How Are Golf Irons Made? Forged vs. Cast Manufacturing

Forged iron begins life as a solid billet of carbon steel. The specific grade of steel varies by manufacturer and is a bigger factor in performance than most golfers realize.

The most common grades are 1025 carbon steel (used across much of the industry), 8620 carbon steel (favoured by several Cobra and Srixon models for its balance of softness and strength), and Mizuno’s proprietary S20C, which is softer and purer than standard alternatives. 

S20C is the reason Mizuno forged irons have a distinct feel that other manufacturers have struggled to replicate for decades.

The billet is heated to roughly 1,200°C until it becomes malleable, then placed between precision dies and pressed or stamped under extreme force. 

This is not a single hit. Depending on the head design, the billet may go through three to five stamping stages, each progressively refining the shape toward the final product.

What this process creates inside the metal is a uniform grain structure. The steel’s internal crystalline grain flows in a consistent, aligned direction, which is what produces that cohesive, responsive sensation at impact. 

When you strike a forged iron cleanly, the vibration travels through a dense, uniform internal structure and reaches your hands with minimal signal loss. That is the physics behind “feel.”

After forging, the head goes through CNC milling for precision on the face, sole, and topline. This finishing step is what delivers the tight tolerances that better players expect from a forged iron.

The constraint of forging is a design limitation. Because you are shaping a single piece of solid metal, there are limits to how much mass you can redistribute. 

Internal cavities, channels, and extreme perimeter weighting configurations that cast irons achieve easily are difficult or impossible to replicate through forging alone.

Cast irons use a method called investment casting, sometimes known as the lost-wax process. It is an ancient technique (jewellers and weapons makers used it for centuries) adapted for modern precision manufacturing.

The process starts with a wax replica of the clubhead, crafted to exact specifications. That wax model is coated in layers of ceramic slurry, building up a hard shell around it. Once the ceramic hardens, the assembly goes into an oven where the wax melts and drains out, leaving a hollow ceramic mold in the exact shape of the intended clubhead.

Molten metal is then poured into this mold. The most common alloys for cast irons are 17-4 PH stainless steel (precipitation-hardened, strong, and corrosion-resistant) and 431 stainless steel. 

These are harder than the carbon steels used in forging, which contributes to the firmer feel at impact but also to the superior durability and groove longevity of cast irons.

After cooling, the ceramic shell is broken away, and the raw head goes through finishing: grinding, polishing, and quality inspection.

The critical advantage of casting is design freedom. Because you are pouring liquid metal into a mold, manufacturers can engineer undercut cavities, internal speed channels, tungsten weighting pockets in precise locations, and multi-material constructions that would be physically impossible to forge from a single billet. 

This is why the vast majority of game improvement irons, players’ distance irons, and high-MOI designs use casting. The process lets engineers put mass exactly where the physics says it should go.