Inconel 718 Large-Diameter Bars — Engineered for High Temperatures and High Mechanical Stress

Core Positioning of Inconel 718 Large-Diameter Bars

Inconel 718 is currently the world’s most widely produced, broadly applied, and comprehensively balanced precipitation-strengthened nickel-chromium-iron-based superalloy; its Chinese equivalent designation is GH4169/GH169. Based on a Ni-Cr-Fe matrix, this alloy achieves strengthening primarily through the formation of composite γ” (Ni₃Nb) and γ’ (Ni₃(Al,Ti)) phases—driven predominantly by niobium (Nb)—supplemented by trace additions of Mo, C, and B to facilitate grain boundary and solid-solution strengthening. Large-diameter bars constitute one of the alloy’s most critical supply forms, specifically designed for the manufacture of large-scale, critical load-bearing components such as aircraft engine turbine discs, compressor discs, shafts, nuclear power main pump shafts, and deep-sea oil and gas equipment.

Industries and Environments Suitable for Inconel 718 Large-Diameter Bars

• Anti-rust (extremely hot): Can be used for long-term service in a red-hot environment ranging from 650°C to 700°C, and the yield strength remains firmly locked at ≥725 MPa or higher. Suitable for gas turbine hot-end components, rocket engine combustion chambers, aviation fasteners, and high-load anti-rust heavy-duty structures.
• Anti-cryogenic cold brittleness (extremely cold): Exhibits no tendency to crack even when exposed to an ultra-low temperature deep cryogenic environment of -253°C, demonstrating excellent plasticity toughness and mechanical anti-fatigue performance. Applicable to liquid hydrogen/liquid oxygen aerospace fuel systems, LNG ultra-low temperature equipment, and deep cryogenic engineering.
• High concentration nickel-chromium matrix: Exhibits extremely strong inertness towards non-oxidizing acids (such as sulfuric acid and hydrochloric acid), and constructs a natural defense against chloride stress corrosion cracking (SCC) in high-salinity acidic fluid environments. Applicable to deep-sea high-pressure downhole tools, high-acidic oil and gas extraction, and chemical complex acid gas neutralization reactors.
• Spontaneous passivation protective film: When the environment surges to 1000°C, the chromium element in the matrix rapidly forms a highly consistent and dense Cr₂O₃ film on the surface, suppressing the annual oxidation rate to within 0.1 mm. Applicable to industrial waste gas treatment, high-temperature sulfide atmosphere environments, and key components of heat treatment furnaces.
• Solid solution + two-stage precipitation aging: Through Double Aging grain boundary strengthening treatment, a large amount of γ” strengthening phase is precipitated in the matrix, ultimately raising the tensile strength to ≥1275 MPa or higher. Applicable to deep-sea wellhead devices (Wellhead), high-pressure oil and gas conversion joints (X-Over), and extreme high-pressure difference and cyclic stress conditions.

Product Application Forms of Inconel 718 Across Various Industries

Features and Advantages of TIPTOP’s Inconel 718 Large-Diameter Bars

1. Ultra-high strength:

The yield strength below 650℃ ranks first among deformation high-temperature alloys. After solution treatment and aging, the tensile strength is ≥ 1275 MPa, and the yield strength is ≥ 1035 MPa.

2. Wide temperature range adaptability:

Maintains stable performance within the range of -250℃ to 700℃, featuring both low-temperature toughness (-196℃ impact toughness ≥ 54 J) and high-temperature creep resistance.

3. Outstanding corrosion resistance:

Resistant to oxidation (below 980℃), acid and alkali, and chloride stress corrosion cracking (SCC). Exhibits excellent corrosion resistance in weak corrosive media such as seawater.

4. Good processing formability:

Can be formed through various methods such as forging, rolling, and mechanical processing. The processing performance is good in the solution state, and the heat treatment process window is wide, with good dimensional stability.

5. Long-term microstructure stability:

The δ phase at the grain boundaries can effectively anchor the grain boundaries, preventing excessive grain growth at high temperatures, ensuring long-term service reliability.

6. Cost controllable:

With iron as the excess element, it reduces the cost of raw materials and has a higher cost-performance ratio among similar high-temperature alloys.

Physical and Mechanical Properties

Chemical Composition

Physical Properties

Mechanical Properties (Typical Values — Solution-Treated + Aged Condition)

TIPTOP Inconel 718 Products: Supply Forms and Size Ranges

Product Forms:

• Bars: Round Bars (Bright/Black Finish), Hexagonal Bars, Square Bars, Flat Bars, Billets, Ingots. Round Bar Diameter: 3.17–500 mm (Large-diameter forged bars available in the 50–500 mm range).
• Plates & Sheets: Medium-to-Thick Plates, Thin Sheets, Strips. Thickness: 0.5–200 mm; Width and Length: Customizable.
• Tubes & Pipes: Seamless Tubes, Welded Tubes, U-Tubes. Customizable according to client requirements.
• Forgings: Forged Bars, Forged Rings, Forged Discs, Shafts, Flanges. Forged Bar Diameter: 50–500 mm, Length: ≤6000 mm; Irregular-shaped parts are customized based on technical drawings.
• Wire Rods/Wires: Suitable for applications such as welding wire, springs, etc.

Size Range:

Round Bar Diameter: 3.17 mm – 500 mm (Hot-rolled/Forged Round Bars)

Large-Diameter Forged Bars: Φ50 – 500 mm, Length ≤ 6000 mm

Hexagonal Bars: 18 – 57 mm (11/16″ – 2-3/4″)

Square Bars: 18 – 47 mm (11/16″ – 1-3/4″)

Hot-Rolled Round Bars: Dia. 20 – 100 mm

Cold-Drawn Round Bars: Dia. 8 – 80 mm

Length Range: 1 – 12 m; custom cut lengths available upon request

TIPTOP Inconel 718 Bar: Supply Status and Processing Techniques

Supply Condition:

• Solution-Treated: Rapidly cooled following a solution treatment at approximately 980°C; exhibits excellent ductility, facilitating subsequent processing and forming. Corresponds to AMS 5662.
• Age-Hardened: Undergoes a two-stage aging heat treatment following solution treatment to achieve maximum strength. Corresponds to AMS 5663.
• Solution-Treated + Aged (SHT+AGED): The complete heat treatment cycle has been completed prior to delivery, making the material ready for immediate use.

(Ⅰ) Melting

The process used is a dual or triple combination, which involves first conducting vacuum induction melting (VIM), followed by one round of electroslag remelting (ESR) or vacuum consumable electrode remelting (VAR). This series of operations aims to reduce the impurities such as sulfur and phosphorus to ≤ 0.015% and clean the material. The melting temperature is approximately between 1450°C and 1550°C. Throughout the process, one must closely monitor the atmosphere inside the furnace to prevent oxidation and ensure that no unwanted inclusions are introduced.

(Ⅱ) Hot processing (forging/rolling)

The heating temperature is controlled at 900–1150℃. The ideal forging temperature is 1000–1050℃. When the final rolling or forging process is completed, the temperature must not be lower than 870℃; otherwise, the grains are prone to become coarse. The main purposes of hot processing can be summed up as three things: to refine the grains, to eliminate the defects left during casting, and to improve the mechanical properties.

(III) Heat Treatment

Standard two-stage aging heat treatment, in accordance with AMS 5662/5663:

Solution treatment: Heat to 980℃ ± 10℃, hold for approximately 1 hour, then quench in oil, water or rapidly cool.

First stage duration: Heat to 720℃ ± 10℃, maintain for 8 hours, then cool down – the cooling rate is approximately 50℃ per hour, until it reaches 620℃.

Second stage holding time: Maintain at 620℃ ± 10℃ for 8 hours, then cool down slowly.

The differences between these two specifications: AMS 5662 only covers solidified rods, while AMS 5663 is after the aging hardening process. This “solidification + two-stage aging” approach is the key to making this alloy both strong and resistant to creep. The solidification treatment fully dissolves the strengthening phases into the matrix, and the two-stage aging precisely controls the size and distribution of the γ phase. Finally, the strength, toughness, and creep resistance are all balanced out for you.

(Ⅳ) Machining

Cutting speed: Low speed, 20–30 meters per minute.

Cutting tools: Hardened alloy or ceramic blades.

Cooling: Ensure that the coolant is adequately supplied and avoid overheating.

Processing method: Turning, milling, drilling and grinding are all acceptable. The key is to use the cutting fluid properly.

(Ⅴ) Welding

Welding methods: Tungsten Inert Gas Arc Welding (GTAW), Electron Beam Welding, Resistance Welding can all be used.

Weld wire: It is recommended to use ERNiFeCr-2 welding wire, or an Inconel 718 welding wire of the same grade as the base material.

Preparation before welding: Before welding, a solution treatment must be carried out first, and the surface must be cleaned thoroughly.

Post-weld treatment: After welding is completed, a complete aging heat treatment must be carried out again to restore the mechanical properties, and stress relief annealing must also be performed.

TIPTOP Inconel 718 bars: International Quality Standards and Company Assurance

Applicable Standards

Standard Selection Recommendations:

For aerospace and high-end industrial applications, priority should be given to AMS 5662 (solution-treated) or AMS 5663 (aged); for general industrial applications, ASTM B637 is a suitable choice.

Testing Standards:

Key Quality Control Points

Batch Traceability: Each batch is accompanied by the melting furnace number, heat treatment batch number, and a complete Material Test Certificate (MTC).

Third-Party Inspection: SGS or BV third-party inspection reports are available upon request.

Flaw Detection Certificates: Ultrasonic flaw detection certificates are provided for critical components.

Company Advantages

At TIPTOP METAL, we handle every stage of production in-house—from steelmaking and hot working through to heat treatment and precision machining. Our products demonstrate exceptional performance stability; indeed, we have successfully supplied materials to sectors with the most stringent quality demands, such as aerospace and nuclear power. In terms of product form, our comprehensive inventory includes bars, tubes, plates, rings, and forgings, available in a full range of specifications.

Available delivery conditions include hot-rolled, cold-rolled, solution-treated, and aged states. We also offer custom manufacturing based on technical drawings to produce specialized forgings—such as discs, rings, shafts, and other complex shapes. By employing multi-directional forging techniques, we refine grain structures to enhance transverse mechanical properties. Furthermore, every batch can be accompanied by a third-party inspection report (with SGS or BV options available).