Inconel 718 N07718 ASTM B637 vs AMS 5662 vs AMS 5663: Differences and Connections Explained

Inconel 718, also known by its UNS designation N07718, is a precipitation-hardenable nickel-chromium alloy that exhibits exceptional tensile strength, creep resistance, and corrosion resistance at elevated temperatures. As one of the most widely used superalloys in the aerospace, oil and gas, and power generation industries, Inconel 718 is covered by several standards — each offering different requirements depending on the intended application.

Among these standards, ASTM B637, AMS 5662, and AMS 5663 are the most commonly referenced. However, while they all relate to the same base alloy — Inconel 718 — there are significant differences between them in terms of mechanical properties, heat treatment, and application requirements.

This article will delve into the distinctions and correlations between these specifications to help engineers, buyers, and procurement professionals make informed decisions when sourcing Inconel 718 products.

What Is Inconel 718 (UNS N07718)?

Inconel 718 is a high-strength, corrosion-resistant nickel-based alloy that is known for its excellent weldability, oxidation resistance, and performance in cryogenic and high-temperature environments.

Key chemical components include:

• Nickel (50-55%)

• Chromium (17-21%)

• Iron (Balance)

• Niobium + Tantalum (4.75-5.5%)

• Molybdenum (2.8-3.3%)

• Titanium and Aluminum (combined 1.0-1.5%)

It is precipitation-hardenable through the addition of niobium, which forms the γ″ phase — a key strengthening mechanism of the alloy. This property enables Inconel 718 to maintain its mechanical strength even at temperatures up to 700°C (1290°F).

Overview of Standards: ASTM B637 vs AMS 5662 vs AMS 5663

ASTM B637

ASTM B637 is a general material specification covering wrought nickel-based alloys like Inconel 718 in the form of bars, forgings, and forging stock. It outlines acceptable chemical composition ranges, mechanical properties, heat treatment conditions, and permissible variations in dimensions and quality.

This standard is commonly used across industries such as power generation, aerospace, and chemical processing. However, it provides flexibility in mechanical property ranges, making it suitable for a broad range of applications.

Key Takeaways:

• General-purpose specification

• Allows different heat treatment states

• Suitable for both high and medium-strength applications

• Provides baseline chemical and mechanical requirements

AMS 5662

AMS 5662 is an aerospace material specification that defines the requirements for Inconel 718 in the solution-annealed (annealed) condition. This means the material is supplied in a soft state, ideal for subsequent forming or machining operations before it is aged to achieve final strength.

The solution-annealed state facilitates better machinability and workability but does not exhibit the high strength associated with fully heat-treated material.

Applications:

• Components requiring significant post-machining

• Forgings and billets to be later aged by the end user

• Aerospace parts requiring dimensional stability before heat treatment

Key Characteristics:

• Supplied in solution-annealed condition only

• Lower strength as compared to aged versions

• Requires additional aging to achieve full mechanical properties

AMS 5663

AMS 5663 defines Inconel 718 in the precipitation heat-treated condition (solution annealed + age hardened). This is the most commonly specified condition for aerospace and high-performance parts, where maximum strength and fatigue resistance are required.

The material in this condition has been heat-treated using a specific aging cycle to produce a finely distributed γ″ and γ′ precipitate structure, providing superior mechanical strength, creep resistance, and fatigue life.

Applications:

• Turbine engine components

• Fasteners

• High-strength structural parts

• Subsea oil and gas components

Key Characteristics:

• Delivered in fully heat-treated condition

• High tensile and yield strength

• Excellent fatigue and stress corrosion resistance

Differences at a Glance

While all three specifications involve Inconel 718 (N07718), the primary differences lie in mechanical properties, heat treatment condition, and intended applications:

Heat Treatment Distinctions

AMS 5662 Heat Treatment:

• Solution Annealing: 1700–1850°F (927–1010°C)

• Cooling: Typically rapid air or oil quenching

• No aging included in this spec

This condition prepares the material for subsequent aging, allowing users to perform post-forming heat treatments tailored to specific application needs.

AMS 5663 Heat Treatment:

• Solution Annealing: Same as AMS 5662

• Aging Treatment:

  • Step 1: 1325°F (718°C) for 8 hours, furnace cooled to 1150°F (621°C)

  • Step 2: Hold at 1150°F (621°C) for 8 more hours, then air cool

The double aging process results in peak precipitation of γ′ and γ″, which dramatically increases strength and stability.

Which Specification Should You Choose?

Choose ASTM B637 If:

• You need a flexible standard covering bars and forgings

• You’re working in general engineering applications

• Your project allows for custom heat treatment strategies

Choose AMS 5662 If:

• You require Inconel 718 in the soft solution-annealed condition

• Your components will be aged or heat-treated after complex machining

• You are producing preforms or semi-finished parts for aerospace

Choose AMS 5663 If:

• Your parts require immediate high strength and fatigue resistance

• You need material that meets stringent aerospace requirements

• You are building parts for turbines, jet engines, or high-pressure systems

Importance of Choosing the Right Standard

Incorrect specification can lead to:

• Poor mechanical performance

• Premature failure in high-stress environments

• Costly rework or rejection from customers

For example, using AMS 5662 material in a project requiring AMS 5663 strength may result in underperformance and safety risks. On the other hand, over-specifying AMS 5663 when not needed can drive up costs unnecessarily.

At sasaalloy, we help our clients choose the correct specification for their application by evaluating operating environment, loading requirements, and processing constraints.

Product Availability at sasaalloy

At sasaalloy, we offer Inconel 718 products compliant with:

• ASTM B637 (bars, forgings, rings)

• AMS 5662 (solution annealed condition)

• AMS 5663 (precipitation-hardened condition)

Our Inconel 718 products are available in:

• Round Bars

• Forging Billets

• Rings

• Custom Machined Parts

We support third-party testing, ultrasonic inspection, and full traceability including EN10204 3.1 or 3.2 certificates, ensuring your procurement meets both technical and regulatory standards.

Final Thoughts

While ASTM B637, AMS 5662, and AMS 5663 all apply to Inconel 718 (UNS N07718), they serve different purposes in the manufacturing and supply chain process. The choice of specification should be based on heat treatment condition, final application, and mechanical property requirements.

Always consult with your engineering team or trusted suppliers like sasaalloy to ensure the correct specification is used — especially when dealing with critical components in aerospace, oil and gas, or high-temperature applications.

By understanding the differences between these specifications, engineers and buyers can avoid costly errors, improve performance, and ensure long-term reliability of their parts.