What Is Hot Forging and How the Process Works

Hot forging is a process that shapes steel after it has been heated above its recrystallization temperature. Above that point, new grains form as the steel is worked, so it does not work-harden during forging and flows under less force than cold steel. The part can still be hardened afterward by heat treatment, such as quench and temper. The Forging Industry Association puts the normal hot working range for steel at 1,900 to 2,300°F (about 1,040 to 1,260°C). In that range, a press can turn a solid slug of steel into a gear blank, a bearing race, or a wheel nut in a few blows.

Hot forging is worth evaluating when a steel part is machined from bar or cast today and the annual volume is high enough to cover the cost of dies. MacLean-Fogg's hot forging and machining business in Savanna, Illinois, forges those blanks on horizontal presses and takes them through the machining and secondary operations a finished part needs.

Table of Contents

• What Is Hot Forging?
• Types of Forging by Temperature
• How the Hot Forging Process Works, Step by Step
• What Hot Forging Does for Strength and Fatigue Life
• Near Net Shape and Material Use
• Secondary Operations That Finish a Hot Forged Part
• Hot Forged Parts and the Industries That Use Them
• Disadvantages of Hot Forging and When It Is the Wrong Fit
• How MacLean-Fogg Hot Forges Components
• Frequently Asked Questions

Key Takeaways

• Hot forging shapes steel above its recrystallization temperature, where it flows under less force and does not work-harden while it is being forged. The Forging Industry Association lists the normal hot working range for steel as 1,900 to 2,300°F.
• On a horizontal hot forging press, heated steel moves through several forging stations in one machine and leaves close to its finished shape.
• Forging develops grain flow that improves tensile strength, ductility, impact toughness, fracture toughness, and fatigue strength (Forging Industry Association).
• In University of Toledo testing of crankshafts, forged steel showed 36% higher fatigue strength than ductile cast iron (New Equipment Digest).
• Hot forging pays for its dies at higher annual volumes. At lower volumes, machining from bar may cost less.

What Is Hot Forging?