ASTM B473 is the standard specification by ASTM International covering nickel alloys UNS N08020, UNS N08024, and UNS N08026 in the form of hot-worked and cold-worked bar and wire. The most widely used grade is UNS N08020 (Alloy 20 / Carpenter 20Cb-3), an iron-nickel-chromium-molybdenum-copper alloy with exceptional resistance to sulfuric acid. The companion specification ASME SB-473 adopts identical requirements.
Zhengzhou Huitong (HT Pipe) supplies ASTM B473 / SB-473 compliant Alloy 20 nickel alloy bars and wire with full Mill Test Certificates (MTC) per EN 10204 3.1.
1. Standard Scope & Designation
ASTM B473 covers the following nickel alloy (alloy 20 family) grades:
| UNS No. |
Common Name |
Alloy Type |
Key Features & Application |
| UNS N08020 |
Alloy 20 / Carpenter 20Cb-3 |
Ni-32-38%, Cr-19-21%, Mo-2-3%, Cu-3-4%, Cb-8xC min |
Sulfuric acid, phosphoric acid — chemical processing |
| UNS N08024 |
Alloy 20Mo-4 |
Ni-33-38%, Cr-19-22%, Mo-3.5-5%, Cu-1.5-3% |
Enhanced molybdenum for chlorides |
| UNS N08026 |
Alloy 20Mo-6 |
Ni-33-38%, Cr-19-22%, Mo-5-6.5%, Cu-1.5-3% |
Maximum molybdenum for aggressive service |
Scope Statement: "This specification covers nickel alloys (UNS N08020, UNS N08024, and UNS N08026) in the form of hot-worked and cold-worked bar and wire for corrosion-resistant service, particularly in sulfuric acid environments."
| Designation |
Issuing Body |
Unit System |
Latest Edition |
| ASTM B473 |
ASTM International |
Inch-Pound |
B473-21 |
| ASME SB-473 |
ASME (BPVC Sec. II Part B) |
Both |
2025 Edition |
2. Alloy Grades Covered by ASTM B473
ASTM B473 covers three nickel alloy grades in the Alloy 20 family, all designed for sulfuric acid and general corrosive service:
| UNS No. |
Commercial Designation |
Alloy Type |
Key Features & Typical Application |
| UNS N08020 |
Alloy 20 / Carpenter 20Cb-3 |
Ni-32-38%, Cr-19-21%, Mo-2-3%, Cu-3-4%, Cb-8xC min |
Sulfuric acid, phosphoric acid — chemical processing |
| UNS N08024 |
Alloy 20Mo-4 |
Ni-33-38%, Cr-19-22%, Mo-3.5-5%, Cu-1.5-3% |
Enhanced molybdenum for chlorides |
| UNS N08026 |
Alloy 20Mo-6 |
Ni-33-38%, Cr-19-22%, Mo-5-6.5%, Cu-1.5-3% |
Maximum molybdenum for aggressive service |
3. Chemical Composition — Key Grades (ASTM B473)
Values are maximum unless shown as a range. Heat analysis per ASTM B473.
| Grade |
Ni% |
Cr% |
Mo% |
Cu% |
Cb% |
C% |
Fe% |
Mn% |
| N08020 |
32.0–38.0 |
19.0–21.0 |
2.0–3.0 |
3.0–4.0 |
8×C min |
0.07 |
Balance |
2.00 |
| N08024 |
33.0–38.0 |
19.0–22.0 |
3.5–5.0 |
1.5–3.0 |
— |
0.03 |
Balance |
1.00 |
| N08026 |
33.0–38.0 |
19.0–22.0 |
5.0–6.5 |
1.5–3.0 |
— |
0.03 |
Balance |
1.00 |
Note: Product analysis tolerances per ASTM B473 apply.
4. Mechanical Property Requirements (ASTM B473)
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 20 |
N08020 |
586 (85) |
241 (35) |
30 |
217 HB |
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 |
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 N08020 (Alloy 20) |
Annealed |
927–1010°C (1700–1850°F) |
Water quench |
| UNS N08024 (Alloy 20Mo-4) |
Solution Annealed |
1010–1093°C (1850–2000°F) |
Water quench |
| UNS N08026 (Alloy 20Mo-6) |
Solution Annealed |
1010–1093°C (1850–2000°F) |
Water quench |
Important: Alloy 20 (N08020) requires stabilization with columbium (Nb) at a minimum of 8× the carbon content to prevent chromium carbide precipitation and intergranular corrosion. The low-carbon variants N08024 and N08026 do not require columbium stabilization due to their ultra-low carbon content (≤0.03%), which eliminates carbide formation risk.
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 |
ASTM A262 Practice A or equivalent |
ASTM A262 |
| Visual & Dimensional |
Surface condition, straightness, diameter tolerance |
ASTM B473 Tables |
| PMI (Positive Material ID) |
When specified by purchaser |
ASTM E1473 |
7. Rod & Bar Dimensions — Available Sizes
ASTM B473 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 B473 tables. Cut-to-length available on request.
8. Industries & Applications
| Industry |
Recommended Grades |
Typical Applications |
| Chemical Processing |
N08020, N08024, N08026 |
H₂SO₄ production, pickling tanks, acid storage, reactors |
| Pharmaceutical |
N08020 |
Reaction vessels, mixing tanks, piping systems |
| Food Processing |
N08020 |
Acid-resistant equipment, heating coils, storage tanks |
| Oil & Gas |
N08020, N08026 |
Sour gas service, downhole equipment, manifold piping |
| Pulp & Paper |
N08020 |
Digester components, bleach plant equipment |
| Plastics / Synthetic |
N08020 |
Reactors for resin and plastic production |
9. B473 vs B462 vs B729 — Alloy 20 Specifications Compared
| Criteria |
ASTM B473 |
ASTM B462 |
ASTM B729 |
| Product Form |
Bar, Wire |
Plate, Sheet, Strip |
Seamless Pipe & Tube |
| Key Grades |
N08020, N08024, N08026 |
N08020, N08024, N08026 |
N08020, N08024, N08026 |
| Stabilization |
Cb (N08020), Low-C (N08024/26) |
Cb (N08020), Low-C (N08024/26) |
Cb (N08020), Low-C (N08024/26) |
| Mechanical Props |
TS≥586 MPa (N08020) |
TS≥586 MPa (N08020) |
TS≥517 MPa (N08020) |
| General Requirements |
ASTM B880 |
ASTM B880 |
ASTM B880 |
| Primary Use |
Machined parts, fasteners, pump shafts |
Pressure vessels, heat exchangers |
Process piping, tubing |
Key Distinction: ASTM B473, B462, and B729 form a complementary family of specifications for Alloy 20-type materials across all product forms. B473 covers bar and wire, B462 covers flat products (plate, sheet, strip), and B729 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 B462 |
Ni Alloy Plate, Sheet, Strip |
Flat product companion specification |
| ASTM B729 |
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 B473 |
| ASTM A262 |
Intergranular Corrosion Testing |
Detection of sensitization |
| ASTM E1473 |
Chemical Analysis of Ni & Ni Alloys |
Chemical analysis method |
| ASME SB-473 |
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 B473 / ASME SB473 |
| 2 |
Grade / UNS |
e.g., UNS N08020 (Alloy 20) or UNS N08026 (Alloy 20Mo-6) |
| 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 |
Annealed / 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) |
12. Frequently Asked Questions
Q: What is ASTM B473 nickel alloy bar?
ASTM B473 is the standard specification for nickel alloys UNS N08020 (Alloy 20/Carpenter 20Cb-3), UNS N08024 (Alloy 20Mo-4), and UNS N08026 (Alloy 20Mo-6) in the form of hot-worked and cold-worked bar and wire. These alloys are specifically designed for sulfuric acid and general corrosive service.
Q: What is Alloy 20 (UNS N08020)?
Alloy 20 (UNS N08020), also known as Carpenter 20Cb-3, is an iron-nickel-chromium-molybdenum-copper alloy with approximately 29% Ni, 20% Cr, 2.5% Mo, and 3.5% Cu. It was originally developed for sulfuric acid service and offers excellent resistance to stress corrosion cracking, pitting, and general corrosion.
Q: What are the mechanical properties of Alloy 20 bar per ASTM B473?
In the annealed condition, UNS N08020 (Alloy 20) bar must meet: minimum tensile strength 586 MPa (85 ksi), minimum yield strength 241 MPa (35 ksi), and minimum elongation 30%. Hardness maximum is 217 HB.
Q: What is the difference between N08020, N08024, and N08026?
UNS N08020 (Alloy 20) is the standard grade with 2–3% Mo and columbium stabilization. UNS N08024 (Alloy 20Mo-4) has higher molybdenum (3.5–5%) with ultra-low carbon (0.03% max) for improved chloride resistance. UNS N08026 (Alloy 20Mo-6) has the highest molybdenum (5–6.5%) with low carbon for the most aggressive environments.
Q: What is the difference between ASTM B473 and ASTM B462?
ASTM B473 covers Alloy 20 nickel alloy bar and wire. ASTM B462 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 B473 the same as ASME SB-473?
Technically identical in chemistry and mechanical properties. ASME SB-473 is ASTM B473 adopted into ASME BPVC Section II Part B. SB-473 additionally requires Certified Material Test Reports (CMTR) for ASME Code-stamped equipment. Most mills supply dual-certified B473/SB-473 material.
Request a Quote — ASTM B473 Alloy 20 Nickel Alloy Bar & Wire
Zhengzhou Huitong (HT Pipe) supplies ASTM B473 / SB-473 compliant Alloy 20 nickel alloy bars and wire in UNS N08020, UNS N08024, and UNS N08026. Full EN 10204 3.1 CMTRs and competitive lead times from affiliated mills.
