ASTM B463/B463M is the standard specification by ASTM International covering UNS N08020 nickel-iron-chromium alloy plate, sheet, and strip — commonly known as Alloy 20 (or Alloy 20Cb-3). This niobium-stabilized austenitic alloy delivers outstanding resistance to sulfuric acid across a wide range of concentrations and temperatures, with excellent resistance to intergranular corrosion in the as-welded condition. The companion specification ASME SB463 adopts identical requirements for ASME Code-stamped equipment.

Zhengzhou Huitong (HT Pipe) supplies ASTM B463 / ASME SB463 compliant plate, sheet & strip with full Mill Test Certificates (MTC) per EN 10204 3.1. 

1. Standard Scope & Designation

ASTM B463/B463M covers UNS N08020 (Alloy 20) plate, sheet, and strip for general corrosion-resistant applications, particularly in sulfuric acid environments. Alloy 20, stabilized with columbium (niobium), provides excellent resistance to intergranular corrosion in the as-welded condition without post-weld heat treatment.

2. Grades Covered by ASTM B463

ASTM B463 covers the following grades. Each grade is defined by its UNS number and specific chemistry targeted at different service environments.

3. Chemical Composition

Values are weight percent maximum unless shown as a range. Heat analysis. Per ASTM B463 Table 1.

4. Mechanical Property Requirements

All values are minimum requirements. Tensile testing per ASTM E8/E8M.

5. Heat Treatment Requirements

6. Testing & Inspection Requirements

7. Dimensions & Dimensional Tolerances

ASTM B463 covers plate, sheet, and strip in standard mill thicknesses from thin strip (~0.010 in) to plate up to 3 in (76 mm). Widths and lengths per mill capability; standard widths 48–96 in (1220–2440 mm). Cold-rolled sheet typically available 0.018–0.187 in (0.46–4.75 mm).

8. Industries & Applications

9. ASTM B463 vs ASTM B625 (Ni-Fe-Cr-Mo-Cu Alloy Plate — UNS N08904 / 904L) — Comparison

10. Related Standards

11. How to Order — Required Information

12. Frequently Asked Questions

Q: What is ASTM B463 Alloy 20 used for?

ASTM B463 Alloy 20 (UNS N08020) plate is primarily used in sulfuric acid service — including storage tanks, reaction vessels, heat exchanger tube sheets, and process piping — across concentrations from dilute to 98% at moderate temperatures. It is also specified for phosphoric acid, nitric acid, organic acids, and mixed acid systems in chemical processing, pharmaceutical, and petrochemical industries. Its niobium stabilization ensures excellent intergranular corrosion resistance in the as-welded condition, eliminating the need for post-weld heat treatment in many applications.

Q: What is the difference between Alloy 20 and 316L stainless steel?

Alloy 20 contains significantly higher nickel (32–38% vs 10–14%) and copper (3–4% vs none) than 316L, giving it dramatically superior resistance to sulfuric acid at all concentrations. While 316L is rapidly attacked by sulfuric acid at concentrations above 5%, Alloy 20 maintains excellent corrosion resistance up to approximately 40% H₂SO₄ at boiling point. Additionally, Alloy 20's niobium stabilization prevents sensitization during welding, whereas 316L can still experience intergranular attack in certain environments despite its low-carbon designation.

Q: Can ASTM B463 Alloy 20 plate be welded without PWHT?

Yes, this is one of Alloy 20's key advantages. The niobium (columbium) stabilization — minimum 8× carbon content, maximum 1.00% — precipitates NbC preferentially during welding, preventing chromium carbide (Cr₂₃C₆) formation at grain boundaries. This makes Alloy 20 highly resistant to intergranular corrosion (sensitization) in the as-welded condition, eliminating the mandatory post-weld heat treatment required for unstabilized austenitic stainless steels. Recommended filler metal: ERNiCrMo-3 (AWS A5.14) or E/ERNiCrMo-3 for GTAW/SMAW.

Q: What is PREN and where does Alloy 20 rank?

PREN (Pitting Resistance Equivalent Number) = %Cr + 3.3×%Mo + 16×%N. For Alloy 20 (Cr 19–21%, Mo 2–3%, N ~0.04% typical), PREN ≈ 27–30 — comparable to 316L (~24–27) but lower than 904L (~34–39) or super-austenitics like AL-6XN (~43–48). Alloy 20 should not be selected purely for chloride pitting resistance; its strength is sulfuric acid service, where PREN is not the controlling parameter. For seawater or high-chloride service, consider ASTM B688 (AL-6XN, PREN ~43–48) or ASTM B575 (Alloy C-276, PREN ~64+).

Q: What is the temperature limit for ASTM B463 Alloy 20?

For continuous service in sulfuric acid environments, Alloy 20 is typically limited to approximately 170°C (338°F) depending on acid concentration. In general corrosive service without sulfuric acid, it can be used up to approximately 540°C (1000°F), though mechanical properties begin to decrease above 400°C (750°F). For elevated-temperature structural applications, Alloy 800H/800HT (ASTM B409) or Alloy 625 (ASTM B443) should be considered. Cryogenic service is acceptable — Alloy 20 retains good toughness down to −196°C (−320°F).

Request a Quote — ASTM B463 Alloy 20 (UNS N08020) Plate, Sheet & Strip

Zhengzhou Huitong (HT Pipe) supplies ASTM B463 / SB463 UNS N08020 Alloy 20 plate, sheet, and strip for sulfuric acid and general corrosive service. Full EN 10204 3.1 CMTRs with IGC testing per ASTM A262 when specified. Competitive lead times from qualified nickel alloy mills.