4. CHARACTERISTICS OF FORGING ALLOYS

The material specification on a product drawing occupies a very small part of the total space. However it is a very important part of the specification, in some cases as important as the dimensioned views.

The product designer has a wide variety of alloys from which to choose. Most forging grades of ferrous or non-ferrous alloys are selected based on their inherent property levels as bar or billet materials, usually after heat treatments are performed. The forging process tends to improve some of the mechanical properties, such as impact toughness, fatigue strength, and tensile ductility, which are dependant on the grainflow patterns developed during forging. For example:

• Forgings are usually selected for applications requiring high ductility, impact toughness, fracture toughness and fatigue strength; therefore, forging alloys with inherently high ductility and tensile strength are generally selected.
• Alloys that cannot withstand very high rates of deformation are restricted to slower speed presses, and can not be forged readily on equipment such as hammers and high-speed presses.
• Alloys selected for cold forging must be able to undergo the required deformations at room temperature without excessive work hardening.

Another factor in alloy selection is the ability of the alloy to be forged; that is its forgeability. Some alloys are relatively easy to forge and may be used to make components with very intricate features. Grades that are more difficult to forge require distinct design approaches. The effects of differences in forgeability on design are described in this and other sections. Individual forging firms are in the best position to describe how such designs are affected.

The majority of forging alloys are in one of seven primary alloy groups:

Carbon, microalloy and alloy steels
Stainless steels
Aluminum
Copper
Iron, nickel, or cobalt based heat resistant alloys
Titanium
Magnesium

Some refractory alloys such as tungsten, molybdenum, tantalum and columbium (niobium), and some light reactive alloys such as zirconium, beryllium, hafnium have been forged on a limited basis. These materials are considered outside the scope of this design guide.