May 2026 Volume 8

MATERIALS

Summary The guidelines for selecting a Nickel Alloy forging are: 1. Exceptional High-Temperature Strength and Stability a. Creep Resistance b. High Melting Point c. Oxidation and Scaling Resistance d. Resistance to Carburization (embrittlement) 2. Outstanding Corrosion Resistance a. Reducing Acids b. Chloride Pitting/Crevice Corrosion c. Caustic/Alkaline d. Marine Environment Resistance 3. Superior Mechanical Properties

• Alloy 718 - The heat treatment consists of solution treatment followed by a double aging treatment. Depending on the mechanical properties desired, one of the following two heat treatments is utilized: • Recommended for optimum impact properties: Solution treat at 1,950° F (1,066° C) for 1 to 2 hours. Air cool. Age at 1400° F (760° C) for 10 hours. Furnace cooling to 1,200° F (649° C). Hold for total elapsed time of 20 hours. Air cool. • Recommended for optimum tensile and creep-rupture properties: Solution treat at 1,700-1,850° F (927 - 1,010° C) for 1 hour. Air cool. Age at 1,325-1,400° F (718 - 760° C) for 8 hours. Furnace cooling at 100° F (38° C) per hour to 1,150-1,200° F (621 - 649° C). Hold for 8 hours followed by air cooling. • Alloy 625 • Annealing at 1,600-1,900° F (927 - 1,038° C) for high hardness, tensile and fatigue strength are desired. • Solution annealing at 2,000-2,200° F (1,093 - 1,204° C) for optimum creep-rupture strength is desired. • Not as common - lower carbon versions of the alloy can be precipitation strengthened by aging up to 120 hours at temperatures from 1,050° F to 1,350° F (566 - 732° C). Mechanical and thermal processing dictate the properties. Grain size is an important microstructural parameter. Fine grain sizes normally provide superior room-temperature properties, such as toughness, strength, and fatigue resistance. Coarse grain sizes generally yield better creep resistance at elevated temperatures, although properties under other types of loading may suffer. Duplex grain structures generally are undesirable. Grain size also affects carbide precipitation at the grain boundaries. Coarse grain sizes have less grain-boundary surface area; therefore, carbide precipitation will be more continuous and thicker, thus impairing properties. Due to these problems, a uniform, intermediate grain size is generally preferred. Following heat treatment, the forgings are typically surface inspected by both visual (VT) and fluorescent penetrant (PT) and Macroetch; and, volumetrically inspected by ultrasonic testing (UT) methods (Figure 13).

a. High Toughness and Ductility (even at cryogenic temps) b. Strength allows for thinner sections c. Fabrication and Weldability (even precipitation hardened grades – Figure 14)

Figure 14: Weldability Rating of High Strength Ni Alloys [7]

Free RFQ Submission Program If you have a need for a forged Nickel Alloy part, you can use FIA’s Request for Quote (RFQ) page for fast access to the many producer members who forge Nickel Alloy. Once you answer a few short questions about your component requirements, click submit, and contacts from all FIA forging producer members will automatically be emailed your RFQ.

Figure 13: Immersion Ultrasonic Testing (UT) of metal

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