ASTM B446/B446M is the standard specification by ASTM International covering nickel-chromium-molybdenum-columbium alloys in the form of hot-finished and cold-drawn rod, bar, and shapes. The most widely used grade is UNS N06625 (Alloy 625 / Inconel 625). The companion specification ASME SB-446 adopts identical requirements for ASME Boiler and Pressure Vessel Code (BPVC) compliance.
Zhengzhou Huitong (HT Pipe) supplies ASTM B446 / SB-446 compliant nickel alloy rods and bars with full Mill Test Certificates (MTC) per EN 10204 3.1.
1. Standard Scope & Designation
ASTM B446 covers the following ni-cr-mo-cb (columbium/niobium) grades:
| UNS No. |
Common Name |
Alloy Type |
Key Features & Application |
| UNS N06625 |
Alloy 625 / Inconel 625 |
Ni-58% min, Cr-20-23%, Mo-8-10%, Nb+Ta-3.15-4.15%, Fe-5% max |
General corrosion — aerospace, marine, chemical, nuclear, FGD |
| UNS N06219 |
Haynes 625 variant |
Ni-58% min, Cr-20-23%, Mo-8-10%, Si-2.0-3.0%, Al-1.0-2.0% |
High-temperature oxidation resistance |
| UNS N06686 |
Inconel 686 |
Ni-57% min, Cr-19-23%, Mo-15-17%, W-3-4.4%, Ti-0.02-0.25% |
Aggressive chemical & flue gas environments |
| UNS N06652 |
Inconel 665 |
Ni-58% min, Cr-19-23%, Mo-8-10%, Nb+Ta-3.15-4.15%, Ti-0.3-0.6% |
Enhanced crevice corrosion resistance |
Scope Statement: "This specification covers nickel-chromium-molybdenum-columbium (niobium) alloys (UNS N06625, UNS N06219, UNS N06686, and UNS N06652) in the form of hot-finished and cold-drawn rounds, squares, hexagons, and rectangles for general corrosive and high-temperature service."
| Designation |
Issuing Body |
Unit System |
Latest Edition |
| ASTM B446 |
ASTM International |
Inch-Pound |
B446/B446M-20 |
| ASTM B446M |
ASTM International |
SI (Metric) |
B446/B446M-20 |
| ASME SB-446 |
ASME (BPVC Sec. II Part B) |
Both |
2025 Edition |
2. Alloy Grades Covered by ASTM B446
ASTM B446 covers four nickel-chromium-molybdenum-columbium alloys:
| UNS No. |
Commercial Designation |
Alloy Type |
Key Features & Typical Application |
| UNS N06625 |
Alloy 625 / Inconel 625 |
Ni-58% min, Cr-20-23%, Mo-8-10%, Nb+Ta-3.15-4.15%, Fe-5% max |
General corrosion — aerospace, marine, chemical, nuclear, FGD |
| UNS N06219 |
Haynes 625 variant |
Ni-58% min, Cr-20-23%, Mo-8-10%, Si-2.0-3.0%, Al-1.0-2.0% |
High-temperature oxidation resistance |
| UNS N06686 |
Inconel 686 |
Ni-57% min, Cr-19-23%, Mo-15-17%, W-3-4.4%, Ti-0.02-0.25% |
Aggressive chemical & flue gas environments |
| UNS N06652 |
Inconel 665 |
Ni-58% min, Cr-19-23%, Mo-8-10%, Nb+Ta-3.15-4.15%, Ti-0.3-0.6% |
Enhanced crevice corrosion resistance |
3. Chemical Composition — Key Grades (ASTM B446)
Values are maximum unless shown as a range. Heat analysis per ASTM B446.
| Grade |
Ni% |
Cr% |
Mo% |
Nb+Ta% |
Fe% |
Si% |
C% |
Mn% |
S% |
| N06625 |
58.0 min |
20.0–23.0 |
8.0–10.0 |
3.15–4.15 |
5.0 max |
0.50 |
0.10 |
0.50 |
0.015 |
| N06219 |
58.0 min |
20.0–23.0 |
8.0–10.0 |
3.15–4.15 |
5.0 max |
2.0–3.0 |
0.10 |
0.50 |
0.015 |
| N06686 |
57.0 min |
19.0–23.0 |
15.0–17.0 |
— |
5.0 max |
0.50 |
0.01 |
0.50 |
0.02 |
Note: Product analysis tolerances per ASTM B446 apply.
4. Mechanical Property Requirements (ASTM B446)
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 625 |
N06625 |
828 (120) |
414 (60) |
30 |
241 HB |
Annealed |
| N06219 |
N06219 |
758 (110) |
345 (50) |
30 |
223 HB |
Annealed |
| N06686 |
N06686 |
690 (100) |
276 (40) |
40 |
200 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 N06625 (Alloy 625) |
Annealed |
1093–1204°C (2000–2200°F) |
Water quench or rapid air cool |
| UNS N06219 |
Annealed |
1093–1204°C (2000–2200°F) |
Water quench or rapid air cool |
| UNS N06686 |
Solution Annealed |
1121–1177°C (2050–2150°F) |
Water quench |
Important: Alloy 625 is a solid-solution strengthened alloy that derives its strength from the molybdenum and columbium additions. It does not require precipitation hardening. The alloy maintains excellent corrosion resistance in annealed condition. It should not be used in the age-hardened condition for corrosive service.
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 |
Supplementary requirement when specified |
ASTM G28 |
| Visual & Dimensional |
Surface condition, straightness, diameter tolerance |
ASTM B446 Tables |
| PMI (Positive Material ID) |
When specified by purchaser |
ASTM E1473 |
7. Rod & Bar Dimensions — Available Sizes
ASTM B446 covers various rod and bar forms. Common commercial size ranges:
| Form |
Diameter / Width |
Typical Length |
Tolerance |
| Hot-Finished Round |
12.7 – 200 mm (1/2–8 in.) |
3.0 – 6.0 m random |
±0.13 mm typical |
| Cold-Drawn Round |
6.35 – 100 mm (1/4–4 in.) |
3.0 – 6.0 m random |
±0.05 mm typical |
| Hot-Finished Square |
12.7 – 150 mm |
3.0 – 6.0 m random |
±0.25 mm typical |
| Hot-Finished Hexagon |
12.7 – 100 mm (AF) |
3.0 – 6.0 m random |
±0.25 mm typical |
Note: Diameter tolerances per ASTM B446 tables. Cut-to-length available on request.
8. Industries & Applications
| Industry |
Recommended Grades |
Typical Applications |
| Aerospace |
N06625, N06219 |
Aircraft exhaust systems, thrust reversers, engine mounts, fuel nozzles |
| Marine / Offshore |
N06625, N06686 |
Subsea fasteners, seawater heat exchangers, umbilicals, propeller blades |
| Chemical Processing |
N06625, N06686 |
H₂SO₄, HCl acid service, reactor vessels, scrubber systems |
| Power Generation (FGD) |
N06625, N06686 |
Flue gas desulfurization, stack liners, ductwork, dampers |
| Nuclear Industry |
N06625 |
Nuclear fuel reprocessing, radioactive waste handling, reactor internals |
| Oil & Gas |
N06625 |
Downhole components, manifold piping, choke valves, flow lines |
9. B446 vs B443 vs B444 — Ni-Cr-Mo-Cb Alloy Specifications Compared
| Criteria |
ASTM B446 |
ASTM B443 |
ASTM B444 |
| Product Form |
Rod, Bar, Shapes |
Plate, Sheet, Strip |
Seamless Pipe & Tube |
| Processing |
Hot-finished, Cold-drawn |
Hot-rolled, Cold-rolled |
Hot-finished, Cold-drawn |
| UNS Grades |
N06625, N06219, N06686, N06652 |
N06625, N06219, N06686 |
N06625, N06219, N06686 |
| Mechanical Props |
TS≥828 MPa, YS≥414 MPa (N06625) |
TS≥758 MPa, YS≥345 MPa (N06625) |
TS≥828 MPa, YS≥414 MPa (N06625) |
| General Requirements |
ASTM B880 |
ASTM B880 |
ASTM B880 |
| Primary Use |
Machined parts, fasteners, shafts |
Pressure vessels, heat exchangers |
Process piping, heat exchanger tubes |
Key Distinction: ASTM B446, B443, and B444 form a complementary family of specifications for Alloy 625-type materials across all product forms. B446 covers rod/bar (solid long products), B443 covers flat products (plate, sheet, strip), and B444 covers tubular products (seamless pipe and tube). All share the same UNS grades and similar chemical/mechanical requirements.
10. Related Standards
| Standard |
Scope |
Relationship |
| ASTM B443 |
Ni-Cr-Mo-Cb Alloy Plate, Sheet, Strip |
Flat product companion specification |
| ASTM B444 |
Ni-Cr-Mo-Cb 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 B446 |
| ASTM E1473 |
Chemical Analysis of Ni & Ni Alloys |
Chemical analysis method |
| ASTM G28 |
Intergranular Corrosion Testing for Ni Alloys |
Supplementary requirement |
| ASME SB-446 |
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 B446 / ASME SB446 |
| 2 |
Grade / UNS |
e.g., UNS N06625 (Alloy 625) or UNS N06686 |
| 3 |
Shape |
Round, Square, Hexagon, Rectangle |
| 4 |
Processing |
Hot-finished (HF) or Cold-drawn (CD) |
| 5 |
Diameter / Size |
e.g., 50 mm round |
| 6 |
Length |
Random (RL ~3–6 m) or Cut-to-length |
| 7 |
Condition |
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 B446/B446M Standard (PDF)
The official ASTM B446/B446M-20 PDF is available from our HT Pipe Download Center. The document includes full chemical composition Table 1, mechanical property Table 2, heat treatment requirements, dimensions and tolerances, testing methods, and supplementary requirements.
Go to Download Center | Request MTC / Quotation
12. Frequently Asked Questions
Q: What is ASTM B446 nickel alloy rod?
ASTM B446/B446M is the standard specification for nickel-chromium-molybdenum-columbium alloys in the form of hot-finished and cold-drawn rod, bar, and shapes. It covers UNS N06625 (Inconel 625/Alloy 625), UNS N06219 (Haynes 625 variant with Si and Al additions), UNS N06686 (Alloy 686), and UNS N06652 (Alloy 665). The most widely used grade is UNS N06625.
Q: What is Alloy 625 (UNS N06625 / Inconel 625)?
Alloy 625 (UNS N06625) is a nickel-chromium-molybdenum-columbium alloy with outstanding strength and corrosion resistance from room temperature up to 980°C (1800°F). The columbium and molybdenum additions provide excellent resistance to pitting, crevice corrosion, and stress corrosion cracking in chloride environments. It is a solid-solution strengthened alloy that does not require precipitation hardening.
Q: What are the mechanical properties of Alloy 625 rod per ASTM B446?
In the annealed condition, UNS N06625 (Alloy 625) rod and bar must meet: minimum tensile strength 828 MPa (120 ksi), minimum yield strength 0.2% offset 414 MPa (60 ksi), minimum elongation 30% in 50 mm (2 in.), and maximum hardness 241 HB.
Q: What is the difference between UNS N06625 and UNS N06219?
Both are nickel-chromium-molybdenum-columbium alloys covered by ASTM B446. UNS N06625 (Alloy 625) has ≤0.50% Si and no intentional Al addition. UNS N06219 has higher silicon (2.0–3.0%) and aluminum (1.0–2.0%) additions, which enhance its resistance to high-temperature oxidation and carburization, making it suitable for furnace components and high-temperature applications.
Q: What is the difference between ASTM B446 and ASTM B443?
ASTM B446 covers nickel-chromium-molybdenum-columbium alloy rod, bar, and shapes. ASTM B443 covers the same alloy family in plate, sheet, and strip form. Both share the same UNS grades and similar chemical and mechanical requirements. B446 is for solid long products (fasteners, shafts, machined parts); B443 is for flat products (pressure vessels, heat exchangers).
Q: Is ASTM B446 the same as ASME SB-446?
Technically identical in chemistry and mechanical properties. ASME SB-446 is ASTM B446 adopted into ASME BPVC Section II Part B. SB-446 additionally requires Certified Material Test Reports (CMTR) with full traceability and authorized inspection for ASME Code-stamped equipment. Most mills supply dual-certified B446/SB-446 material.
Request a Quote — ASTM B446 Nickel Alloy Rod & Bar
Zhengzhou Huitong (HT Pipe) supplies ASTM B446 / SB-446 compliant nickel alloy rods and bars in UNS N06625 (Alloy 625), UNS N06219, UNS N06686, and other grades. Full EN 10204 3.1 CMTRs and competitive lead times from affiliated mills.
