ASTM B649/B649M is the standard specification by ASTM International covering nickel-iron-chromium-molybdenum-copper-nitrogen low-carbon alloys and chromium-nickel-iron-nitrogen low-carbon alloys in the form of hot-worked and cold-worked bar and wire. Key grades include UNS N08925 (Alloy 25-6MO), UNS N08024, UNS N08026, and UNS N08031 (Alloy 31). The companion specification ASME SB-649 adopts identical requirements.
Zhengzhou Huitong (HT Pipe) supplies ASTM B649 / SB-649 compliant nickel alloy bars and wire with full Mill Test Certificates (MTC) per EN 10204 3.1.
1. Standard Scope & Designation
ASTM B649 covers the following ni-fe-cr-mo-cu-n low-c grades:
| UNS No. |
Common Name |
Alloy Type |
Key Features & Application |
| UNS N08925 |
Alloy 25-6MO / 1925 hMO |
Ni-24-26%, Cr-19-21%, Mo-6-7%, Cu-0.8-1.5%, N-0.14-0.20% |
Seawater, HCl, H₂SO₄ — offshore, chemical |
| UNS N08024 |
Alloy 20Mo-4 |
Ni-33-38%, Cr-19-22%, Mo-3.5-5.0%, Cu-1.5-3.0% |
Sulfuric acid, phosphoric acid service |
| UNS N08026 |
Alloy 20Mo-6 |
Ni-33-38%, Cr-19-22%, Mo-5.0-6.5%, Cu-1.5-3.0% |
Aggressive reducing acid environments |
| UNS N08031 |
Alloy 31 |
Ni-30-34%, Cr-26-28%, Mo-6-7%, Cu-1.0-1.4% |
Highly aggressive chloride and acid environments |
Scope Statement: "This specification covers nickel-iron-chromium-molybdenum-copper-nitrogen low-carbon alloys and chromium-nickel-iron-nitrogen low-carbon alloys in the form of hot-worked and cold-worked bar and wire for high-performance corrosion-resistant service."
| Designation |
Issuing Body |
Unit System |
Latest Edition |
| ASTM B649 |
ASTM International |
Inch-Pound |
B649/B649M-21 |
| ASTM B649M |
ASTM International |
SI (Metric) |
B649/B649M-21 |
| ASME SB-649 |
ASME (BPVC Sec. II Part B) |
Both |
2025 Edition |
2. Alloy Grades Covered by ASTM B649
ASTM B649 covers several high-performance nickel alloy grades designed for aggressive corrosion environments:
| UNS No. |
Commercial Designation |
Alloy Type |
Key Features & Typical Application |
| UNS N08925 |
Alloy 25-6MO / 1925 hMO |
Ni-24-26%, Cr-19-21%, Mo-6-7%, Cu-0.8-1.5%, N-0.14-0.20% |
Seawater, HCl, H₂SO₄ — offshore, chemical |
| UNS N08024 |
Alloy 20Mo-4 |
Ni-33-38%, Cr-19-22%, Mo-3.5-5.0%, Cu-1.5-3.0% |
Sulfuric acid, phosphoric acid service |
| UNS N08026 |
Alloy 20Mo-6 |
Ni-33-38%, Cr-19-22%, Mo-5.0-6.5%, Cu-1.5-3.0% |
Aggressive reducing acid environments |
| UNS N08031 |
Alloy 31 |
Ni-30-34%, Cr-26-28%, Mo-6-7%, Cu-1.0-1.4% |
Highly aggressive chloride and acid environments |
3. Chemical Composition — Key Grades (ASTM B649)
Values are maximum unless shown as a range. Heat analysis per ASTM B649.
| Grade |
Ni% |
Cr% |
Mo% |
Cu% |
N% |
C% |
Fe% |
Mn% |
| N08925 |
23.0–28.0 |
19.0–21.0 |
6.0–7.0 |
0.8–1.5 |
0.14–0.20 |
0.02 |
Rem |
2.00 |
| N08024 |
33.0–38.0 |
19.0–22.0 |
3.5–5.0 |
1.5–3.0 |
— |
0.03 |
Rem |
1.00 |
| N08026 |
33.0–38.0 |
19.0–22.0 |
5.0–6.5 |
1.5–3.0 |
— |
0.03 |
Rem |
1.00 |
| N08031 |
30.0–34.0 |
26.0–28.0 |
6.0–7.0 |
1.0–1.4 |
0.15–0.25 |
0.015 |
Rem |
2.00 |
Note: Product analysis tolerances per ASTM B649 apply.
4. Mechanical Property Requirements (ASTM B649)
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 25-6MO |
N08925 |
650 (94) |
300 (44) |
40 |
223 HB |
Solution Annealed |
| Alloy 20Mo-4 |
N08024 |
550 (80) |
240 (35) |
35 |
217 HB |
Solution Annealed |
| Alloy 20Mo-6 |
N08026 |
550 (80) |
240 (35) |
35 |
217 HB |
Solution Annealed |
| Alloy 31 |
N08031 |
650 (94) |
300 (44) |
40 |
223 HB |
Solution Annealed |
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 N08925 |
Solution Annealed |
1050–1150°C (1920–2100°F) |
Water quench |
| UNS N08024 |
Solution Annealed |
1066–1121°C (1950–2050°F) |
Water quench |
| UNS N08026 |
Solution Annealed |
1066–1121°C (1950–2050°F) |
Water quench |
| UNS N08031 |
Solution Annealed |
1093–1149°C (2000–2100°F) |
Water quench |
Important: All grades covered by ASTM B649 are low-carbon, nitrogen-strengthened alloys that require solution annealing followed by rapid water quenching to dissolve precipitates and homogenize the microstructure. This is critical for achieving optimal resistance to intergranular corrosion and stress corrosion cracking in chloride environments.
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 |
| Intergranular Corrosion |
Required; ASTM A262 Practice A or G28 |
ASTM A262 / G28 |
| Visual & Dimensional |
Surface condition, straightness, diameter tolerance |
ASTM B649 Tables |
| PMI (Positive Material ID) |
When specified by purchaser |
ASTM E1473 |
7. Rod & Bar Dimensions — Available Sizes
ASTM B649 covers various rod and bar forms. Common commercial size ranges:
| Form |
Diameter / Width |
Typical Length |
Tolerance |
| Hot-Worked Round Bar |
12.7 – 200 mm (1/2–8 in.) |
3.0 – 6.0 m random |
±0.13 mm typical |
| Cold-Worked Round Bar |
6.35 – 100 mm (1/4–4 in.) |
3.0 – 6.0 m random |
±0.05 mm typical |
| Wire |
0.50 – 12.7 mm |
Coil or cut lengths |
±0.025 mm typical |
| Hot-Worked Hexagon |
12.7 – 100 mm (AF) |
3.0 – 6.0 m random |
±0.25 mm typical |
Note: Diameter tolerances per ASTM B649 tables. Cut-to-length available on request.
8. Industries & Applications
| Industry |
Recommended Grades |
Typical Applications |
| Chemical Processing |
N08925, N08031 |
H₂SO₄, HCl, H₃PO₄ acid service, pickling tanks, scrubbers |
| Marine / Offshore |
N08925, N08031 |
Seawater heat exchangers, subsea piping, desalination plants |
| Oil & Gas |
N08925 |
Sour gas service, downhole tubulars, manifold piping |
| Flue Gas Desulfurization |
N08925, N08031 |
FGD absorber towers, ductwork, stack liners |
| Pharmaceutical |
N08925 |
High-purity corrosion-resistant equipment, reactors |
| Pulp & Paper |
N08925 |
Digester components, bleach plant equipment |
9. B649 vs B622 vs B674 — Ni-Fe-Cr-Mo-Cu-N Alloy Specifications Compared
| Criteria |
ASTM B649 |
ASTM B622 |
ASTM B674 |
| Product Form |
Bar, Wire |
Plate, Sheet, Strip |
Seamless Pipe & Tube |
| Key Grades |
N08925, N08024, N08026, N08031 |
N08925, N08024, N08026, N08031 |
N08925, N08024, N08026, N08031 |
| Mechanical Props |
TS≥650 MPa (N08925) |
TS≥650 MPa (N08925) |
TS≥650 MPa (N08925) |
| Corrosion Focus |
Pitting, crevice, SCC |
Pitting, crevice, SCC |
Pitting, crevice, SCC |
| General Requirements |
ASTM B880 |
ASTM B880 |
ASTM B880 |
| Primary Use |
Machined parts, fasteners, shafts |
Pressure vessels, heat exchangers |
Process piping, tubing |
Key Distinction: ASTM B649, B622, and B674 form a complementary family of specifications for high-performance nickel alloys across all product forms. B649 covers bar and wire, B622 covers plate, sheet, and strip, and B674 covers seamless pipe and tube. All share the same UNS grades designed for aggressive corrosion resistance.
10. Related Standards
| Standard |
Scope |
Relationship |
| ASTM B622 |
Ni Alloy Plate, Sheet, Strip |
Flat product companion specification |
| ASTM B674 |
Ni Alloy Seamless Pipe & Tube |
Tubular product companion 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 B649 |
| ASTM A262 |
Intergranular Corrosion Testing |
Detection of sensitization in stainless alloys |
| ASTM E1473 |
Chemical Analysis of Ni & Ni Alloys |
Chemical analysis method |
| ASME SB-649 |
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 B649 / ASME SB649 |
| 2 |
Grade / UNS |
e.g., UNS N08925 (Alloy 25-6MO) or UNS N08031 (Alloy 31) |
| 3 |
Shape |
Round, Hexagon, Wire |
| 4 |
Processing |
Hot-worked (HW) or Cold-worked (CW) |
| 5 |
Diameter / Size |
e.g., 50 mm round |
| 6 |
Length |
Random (RL ~3–6 m) or Cut-to-length |
| 7 |
Condition |
Solution Annealed (default) |
| 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 B649/B649M Standard (PDF)
The official ASTM B649/B649M-21 PDF is available from our HT Pipe Download Center. The document includes full chemical composition, mechanical property requirements, heat treatment, dimensions and tolerances, testing methods, and supplementary requirements.
Go to Download Center | Request MTC / Quotation
12. Frequently Asked Questions
Q: What is ASTM B649 nickel alloy bar?
ASTM B649/B649M is the standard specification for nickel-iron-chromium-molybdenum-copper-nitrogen low-carbon alloys and chromium-nickel-iron-nitrogen low-carbon alloys in the form of hot-worked and cold-worked bar and wire. Key grades include UNS N08925 (Alloy 25-6MO), UNS N08024 (Alloy 20Mo-4), UNS N08026 (Alloy 20Mo-6), and UNS N08031 (Alloy 31).
Q: What is UNS N08925 (Alloy 25-6MO)?
UNS N08925 is a super-austenitic nickel alloy with approximately 20% Cr, 6% Mo, and 0.15% N. It offers excellent resistance to pitting, crevice corrosion, and stress corrosion cracking in chloride-containing environments. The nitrogen addition increases strength and improves pitting resistance, making it a cost-effective alternative to nickel-based alloys like Hastelloy C276 in many seawater applications.
Q: What are the mechanical properties of N08925 bar per ASTM B649?
In the solution-annealed condition, UNS N08925 bar must meet: minimum tensile strength 650 MPa (94 ksi), minimum yield strength 300 MPa (44 ksi), and minimum elongation 40%. Hardness maximum is 223 HB.
Q: What is the difference between N08925 and N08031?
UNS N08925 (Alloy 25-6MO) has 19–21% Cr, 6–7% Mo, and 0.14–0.20% N. UNS N08031 (Alloy 31) has higher chromium (26–28%) with similar molybdenum and nitrogen content. Alloy 31 offers better resistance to highly oxidizing acids and higher pitting resistance equivalent number (PREN > 42), while Alloy 25-6MO offers better economy for seawater service.
Q: What is the difference between ASTM B649 and ASTM B622?
ASTM B649 covers nickel alloy bar and wire. ASTM B622 covers the same alloy family in plate, sheet, and strip form. Both share the same UNS grades and similar chemical and mechanical requirements.
Q: Is ASTM B649 the same as ASME SB-649?
Technically identical in chemistry and mechanical properties. ASME SB-649 is ASTM B649 adopted into ASME BPVC Section II Part B. SB-649 additionally requires Certified Material Test Reports (CMTR) for ASME Code-stamped equipment.
Request a Quote — ASTM B649 Nickel Alloy Bar & Wire
Zhengzhou Huitong (HT Pipe) supplies ASTM B649 / SB-649 compliant nickel alloy bars and wire in UNS N08925 (Alloy 25-6MO), UNS N08024, UNS N08026, UNS N08031, and other grades. Full EN 10204 3.1 CMTRs and competitive lead times from affiliated mills.
