The materials used for the forging process must be able to achieve the required physical and mechanical properties. If several groups of alloys can meet the performance requirements, the alloy that is most economical in terms of material and processing costs should be selected. See the following summary of the initial selection of forging materials:

1. Carbon, micro-alloyed and alloy steels

The cost of carbon, micro-alloyed and alloy steels is low to medium. The main cost driver is processing and machining. These alloys are easy to hot forge, and some shapes of alloys can also be cold forged. When anticipating precision forgings or closed die forging, designers should be aware that the number of forgings ultimately purchased should be large enough to justify the usual increased die preparation expenses. Sometimes, regardless of the purchase quantity, the increased die cost is justified to eliminate difficult-to-machine shapes.

The alloy formula may also be controlled by the product size. As the cross-section size increases, higher alloy content is required to achieve hardenability.

2. Stainless steel

Stainless steel costs are higher than carbon, micro-alloyed and alloy steels. They can be hot forged into simple shapes and low-profile structural shapes, but high forging pressures limit net-shape forging to simpler shapes. When more complex shapes are encountered or more difficult-to-forge alloys are specified, the hot die forging process should be reconsidered. The forging pressure required for 300 series alloys is 20% to 40% higher than that for 400 series, mainly due to the higher nickel content.

3. Aluminum Alloys

Aluminum alloys are moderately costly, relatively light, and easy to hot forge because most tool materials retain adequate properties at the forging temperatures of aluminum alloys. Net-shape forgings can have a planar projection area of up to 400 square inches. Net-shape forging processes have been developed and mature. Forging design guidelines are available and are being continuously improved. When a combination of multiple properties such as corrosion resistance, load-bearing capacity, and moderate cost are required, they should be selected.

4. Copper-based alloys

Compared with other wrought alloys, copper-based alloys have moderate strength but are generally superior to castings made from equivalent alloys. These alloys can be forged into parts with close tolerances and maintain smooth surfaces. Low porosity, common in castings, contributes to an aesthetically pleasing surface.

5. Heat-resistant alloys of iron, nickel, and cobalt

Heat-resistant alloys of iron, nickel, and cobaltTitanium alloys are among the most expensive wrought alloys and are generally the most difficult to forge. They are usually chosen only when other alloy systems cannot achieve the required high-temperature properties. When the most heat-resistant alloys cannot be forged by conventional processes, superplastic forging is a process that forges the alloy at a temperature very close to the melting point. For "super" alloys such as IN100, MERL 76, and Rene 95, vacuum isothermal processing is the main method for forging high-quality parts.

6. Titanium alloys

Titanium alloys are suitable for applications that require high strength, low weight, high operating temperatures, or high corrosion resistance. Its specific strength is higher than that of steel. The density is about 55% of steel and 60% higher than that of aluminum alloys. The properties and cost of titanium alloys make them ideal for high-performance applications such as aerospace, chemical processing, and prosthetics.

7. Magnesium alloys

Magnesium alloys are sometimes considered as an alternative to aluminum alloys for applications that require minimal product weight. Compared with aluminum alloys, magnesium alloys have a weight advantage of about 30%. However, magnesium alloys are more susceptible to corrosion than aluminum alloys and require more attention to coating. Its mechanical properties, such as elastic modulus, tensile strength, and yield strength, are not as high as those of aluminum alloys, especially at high temperatures. Therefore, its strength-to-weight ratio is not ideal. Magnesium is a metal system that seems to have been replaced by reinforced plastics.

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