ASTM B637/B637M is the standard specification by ASTM International covering precipitation-hardenable nickel alloys in the form of hot-finished and cold-finished rod, bar, and forgings. The most widely used grade is UNS N07718 (Alloy 718 / Inconel 718), renowned for its exceptional high-temperature strength up to 704°C (1300°F). The companion specification ASME SB-637 adopts identical requirements.
Zhengzhou Huitong (HT Pipe) supplies ASTM B637 / SB-637 compliant precipitation-hardenable nickel alloy rods, bars, and forgings with full Mill Test Certificates (MTC) per EN 10204 3.1.
1. Standard Scope & Designation
ASTM B637 covers the following precipitation-hardenable nickel grades:
| UNS No. |
Common Name |
Alloy Type |
Key Features & Application |
| UNS N07718 |
Alloy 718 / Inconel 718 |
Ni-50-55%, Cr-17-21%, Fe-balance, Nb+Ta-4.75-5.5%, Mo-2.8-3.3% |
Aerospace, gas turbines, high-strength fasteners |
| UNS N07725 |
Alloy 725 |
Ni-55-59%, Cr-19-22.5%, Mo-7-9.5%, Ti-1.2-1.6% |
Oil & gas, high-strength downhole components |
| UNS N07716 |
Alloy 716 |
Ni-40-45%, Cr-19-22%, Mo-2.8-3.3%, Nb+Ta-4.75-5.5% |
High-temperature bolting, aerospace |
| UNS N09946 |
Alloy 946 |
Ni-38-44%, Cr-19-22%, Mo-2.8-3.3%, Nb+Ta-4.75-5.5% |
Similar to 718 with controlled composition |
Scope Statement: "This specification covers precipitation-hardenable nickel alloys (UNS N07718, UNS N07725, UNS N07716, and UNS N09946) in the form of hot-finished and cold-finished rounds, squares, hexagons, rectangles, and forgings for high-strength and high-temperature service."
| Designation |
Issuing Body |
Unit System |
Latest Edition |
| ASTM B637 |
ASTM International |
Inch-Pound |
B637/B637M-21 |
| ASTM B637M |
ASTM International |
SI (Metric) |
B637/B637M-21 |
| ASME SB-637 |
ASME (BPVC Sec. II Part B) |
Both |
2025 Edition |
2. Alloy Grades Covered by ASTM B637
ASTM B637 covers precipitation-hardenable nickel alloys that achieve high strength through controlled heat treatment:
| UNS No. |
Commercial Designation |
Alloy Type |
Key Features & Typical Application |
| UNS N07718 |
Alloy 718 / Inconel 718 |
Ni-50-55%, Cr-17-21%, Fe-balance, Nb+Ta-4.75-5.5%, Mo-2.8-3.3% |
Aerospace, gas turbines, high-strength fasteners |
| UNS N07725 |
Alloy 725 |
Ni-55-59%, Cr-19-22.5%, Mo-7-9.5%, Ti-1.2-1.6% |
Oil & gas, high-strength downhole components |
| UNS N07716 |
Alloy 716 |
Ni-40-45%, Cr-19-22%, Mo-2.8-3.3%, Nb+Ta-4.75-5.5% |
High-temperature bolting, aerospace |
| UNS N09946 |
Alloy 946 |
Ni-38-44%, Cr-19-22%, Mo-2.8-3.3%, Nb+Ta-4.75-5.5% |
Similar to 718 with controlled composition |
3. Chemical Composition — Key Grades (ASTM B637)
Values are maximum unless shown as a range. Heat analysis per ASTM B637.
| Grade |
Ni% |
Cr% |
Mo% |
Nb+Ta% |
Ti% |
Al% |
Fe% |
C% |
| N07718 |
50.0–55.0 |
17.0–21.0 |
2.80–3.30 |
4.75–5.50 |
0.65–1.15 |
0.20–0.80 |
Balance |
0.08 |
| N07725 |
55.0–59.0 |
19.0–22.5 |
7.00–9.50 |
— |
1.20–1.60 |
— |
8.0 max |
0.03 |
| N07716 |
40.0–45.0 |
19.0–22.0 |
2.80–3.30 |
4.75–5.50 |
0.65–1.15 |
0.20–0.80 |
Balance |
0.08 |
Note: Product analysis tolerances per ASTM B637 apply.
4. Mechanical Property Requirements (ASTM B637)
All values are minimum requirements unless otherwise stated. Tensile testing per ASTM E8.
| Grade |
UNS |
Tensile Strength
min MPa (ksi) |
Yield Strength 0.2%
min MPa (ksi) |
Elong.
min % |
Hardness
max |
| Alloy 718 (ST) |
N07718 |
1034 (150) |
690 (100) |
12 |
331 HB |
Solution Treated + Aged |
| Alloy 718 (HW) |
N07718 |
1241 (180) |
1034 (150) |
6 |
363 HB |
Hot-Worked + Aged |
| Alloy 725 (ST) |
N07725 |
1207 (175) |
1000 (145) |
15 |
331 HB |
Solution Treated + Aged |
| Alloy 716 (ST) |
N07716 |
1034 (150) |
690 (100) |
12 |
331 HB |
Solution Treated + Aged |
Note: Hardness testing per ASTM E10 (Brinell) or ASTM E18 (Rockwell). Cold-worked bar may exhibit higher strength due to cold work.
5. Heat Treatment Requirements
| Grade |
Condition |
Heat Treatment |
Cooling |
| UNS N07718 (Alloy 718) |
Solution + Age |
954–996°C ST, then 718°C / 621°C double age |
Air cool (ST), Air cool (age) |
| UNS N07725 (Alloy 725) |
Solution + Age |
760°C ST, then 732°C age 8h + 621°C age 8h |
Air cool |
| UNS N07716 (Alloy 716) |
Solution + Age |
954–996°C ST, then 718°C / 621°C double age |
Air cool (ST), Air cool (age) |
Important: Alloy 718 achieves its exceptional strength through a two-stage precipitation hardening heat treatment: solution treatment at 1750–1825°F (954–996°F) followed by double aging at 1325°F (718°C) for 8 hours and 1150°F (621°C) for 8 hours. The niobium (columbium) addition forms gamma double-prime (Ni₃Nb) precipitates that provide the primary strengthening.
6. Testing & Inspection Requirements
| Test |
Requirement |
Reference Standard |
| Chemical Analysis (Heat) |
One per heat / melt; all elements per Table 1 |
ASTM E1473 / E354 |
| Tensile Test |
One per lot (same heat, same condition, same diameter group) |
ASTM E8 / E8M |
| Hardness Test |
Brinell or Rockwell; one per lot |
ASTM E10 / E18 |
| Stress Rupture |
When specified by purchaser |
ASTM E292 |
| Impact Testing (Charpy) |
When specified by purchaser |
ASTM E23 |
| Visual & Dimensional |
Surface condition, straightness, diameter tolerance |
ASTM B637 Tables |
7. Rod & Bar Dimensions — Available Sizes
ASTM B637 covers various rod and bar forms. Common commercial size ranges:
| Form |
Diameter / Width |
Typical Length |
Tolerance |
| Hot-Finished Round |
12.7 – 300 mm (1/2–12 in.) |
3.0 – 6.0 m random |
±0.13 mm typical |
| Cold-Finished Round |
6.35 – 150 mm (1/4–6 in.) |
3.0 – 6.0 m random |
±0.05 mm typical |
| Forgings |
Up to 500 mm (20 in.) |
Per drawing |
As-forged + machined tolerances |
| Hot-Finished Hexagon |
12.7 – 100 mm (AF) |
3.0 – 6.0 m random |
±0.25 mm typical |
Note: Diameter tolerances per ASTM B637 tables. Cut-to-length available on request.
8. Industries & Applications
| Industry |
Recommended Grades |
Typical Applications |
| Aerospace |
N07718, N07716 |
Turbine discs, shafts, casings, bolts, engine mounts, rocket components |
| Gas Turbines |
N07718 |
Turbine discs, blades, compressor wheels, shafts |
| Oil & Gas |
N07725, N07718 |
Downhole tools, fasteners, completion equipment, HPHT components |
| Automotive / Racing |
N07718 |
High-performance engine components, turbocharger wheels |
| Nuclear Industry |
N07718 |
Reactor internals, high-strength structural components |
| Tooling & Fixtures |
N07718 |
High-temperature molds, dies, and fixtures |
9. B637 vs B670 vs B808 — Precipitation-Hardenable Ni Alloy Specifications Compared
| Criteria |
ASTM B637 |
ASTM B670 |
ASTM B808 |
| Product Form |
Rod, Bar, Forgings |
Forgings |
Forgings (Discs, Rings) |
| Key Grades |
N07718, N07725, N07716 |
N07718, N07725 |
N07718, N07725 |
| Strength Level |
TS≥1241 MPa (718 HW+Aged) |
TS≥1241 MPa |
TS≥1241 MPa |
| Max Service Temp |
718: 704°C (1300°F) |
718: 704°C (1300°F) |
718: 704°C (1300°F) |
| Heat Treatment |
ST + Double Age |
ST + Double Age |
ST + Double Age |
| Primary Use |
Bars, shafts, fasteners, machined parts |
Large forged components |
Turbine discs, rings |
Key Distinction: ASTM B637 covers precipitation-hardenable nickel alloy rod, bar, and forgings. ASTM B670 covers similar alloys specifically as forgings. ASTM B808 covers precipitation-hardenable nickel alloy discs and rings. All share the same UNS grades (primarily N07718) and heat treatment requirements, but differ in product form and testing emphasis.
10. Related Standards
| Standard |
Scope |
Relationship |
| ASTM B670 |
Precip. Hardenable Ni Alloy Forgings |
Forging companion specification |
| ASTM B808 |
Precip. Hardenable Ni Alloy Discs & Rings |
Disc and ring specification |
| ASTM B880 |
General Requirements for Nickel Alloys |
Governs tolerances, testing, certification |
| ASTM E8 / E8M |
Tension Testing of Metallic Materials |
Tensile test method required by B637 |
| ASTM E1473 |
Chemical Analysis of Ni & Ni Alloys |
Chemical analysis method |
| AMS 5662 |
Alloy 718 Bar & Forging (SAE) |
Aerospace equivalent specification |
| ASME SB-637 |
BPVC Section II Part B |
ASME adoption with CMTR |
| DIN EN 10204 |
Metallic Products — Inspection Documents |
3.1 CMTR certification |
11. How to Order — Required Information
| No. |
Item |
Requirement / Example |
| 1 |
Specification |
ASTM B637 / ASME SB637 |
| 2 |
Grade / UNS |
e.g., UNS N07718 (Alloy 718) or UNS N07725 (Alloy 725) |
| 3 |
Shape |
Round, Square, Hexagon, Rectangle, Forging |
| 4 |
Processing |
Hot-finished (HF) or Cold-finished (CF) |
| 5 |
Diameter / Size |
e.g., 50 mm round |
| 6 |
Length |
Random (RL ~3–6 m) or Cut-to-length |
| 7 |
Condition |
Solution Treated + Precipitation Hardened (ST+Age) |
| 8 |
Supplementary Tests |
PMI, intergranular corrosion, UT, impact testing |
| 9 |
Certification |
EN 10204 3.1 Certified Mill Test Report |
| 10 |
Quantity |
Pieces or total weight (kg / metric tons) |
Download ASTM B637/B637M Standard (PDF)
The official ASTM B637/B637M-21 PDF is available from our HT Pipe Download Center. The document includes full chemical composition, mechanical property requirements (multiple heat treatment conditions), dimensions and tolerances, testing methods, and supplementary requirements.
Go to Download Center | Request MTC / Quotation
12. Frequently Asked Questions
Q: What is ASTM B637 precipitation-hardenable nickel alloy?
ASTM B637/B637M is the standard specification for precipitation-hardenable nickel alloys in the form of hot-finished and cold-finished rod, bar, and forgings. It covers UNS N07718 (Alloy 718/Inconel 718), UNS N07725 (Alloy 725), UNS N07716 (Alloy 716), and UNS N09946 (Alloy 946). These alloys achieve high strength through controlled heat treatment with precipitation hardening.
Q: What is Alloy 718 (UNS N07718 / Inconel 718)?
Alloy 718 (UNS N07718) is a precipitation-hardenable nickel-chromium-iron alloy with additions of niobium (columbium), molybdenum, titanium, and aluminum. It is the most widely used nickel superalloy, offering exceptional yield strength (≥1000 MPa) and creep resistance up to 704°C (1300°F). Its gamma double-prime strengthening mechanism provides a unique combination of high strength, good weldability, and excellent fatigue resistance.
Q: What are the mechanical properties of Alloy 718 rod per ASTM B637?
In the hot-worked + aged condition, UNS N07718 rod must meet: minimum tensile strength 1241 MPa (180 ksi), minimum yield strength 1034 MPa (150 ksi), and minimum elongation 6%. In the solution-treated + aged condition: minimum tensile strength 1034 MPa (150 ksi), minimum yield strength 690 MPa (100 ksi), and minimum elongation 12%. Hardness maximum is 363 HB (hot-worked) or 331 HB (solution-treated).
Q: What heat treatment is required for Alloy 718?
Alloy 718 requires a two-stage precipitation hardening treatment: (1) solution treatment at 954–996°C (1750–1825°F) for 1 hour minimum followed by air cooling, (2) first aging at 718°C (1325°F) for 8 hours, furnace cool to 621°C (1150°F), (3) second aging at 621°C for 8 hours total, air cool.
Q: What is the difference between Alloy 718 and Alloy 725?
Alloy 718 (N07718) is a Ni-Fe-Cr-Nb alloy with TS≥1241 MPa, primarily used in aerospace and gas turbines. Alloy 725 (N07725) is a Ni-Cr-Mo-Ti alloy with even higher strength (TS≥1207 MPa with YS≥1000 MPa) and superior corrosion resistance, designed specifically for oil and gas downhole applications requiring both high strength and H₂S/corrosion resistance.
Q: Is ASTM B637 the same as ASME SB-637?
Technically identical in chemistry and mechanical properties. ASME SB-637 is ASTM B637 adopted into ASME BPVC Section II Part B. SB-637 additionally requires Certified Material Test Reports (CMTR) with full traceability and authorized inspection for ASME Code-stamped equipment.
Request a Quote — ASTM B637 Precipitation-Hardenable Nickel Alloy Rod & Bar
Zhengzhou Huitong (HT Pipe) supplies ASTM B637 / SB-637 compliant precipitation-hardenable nickel alloy rods, bars, and forgings in UNS N07718 (Alloy 718), UNS N07725 (Alloy 725), UNS N07716 (Alloy 716), and other grades. Full EN 10204 3.1 CMTRs and competitive lead times from affiliated mills.
