Alloy 20 Fasteners: The Definitive Guide to Carpenter 20 Bolts, Chemistry, Properties & Applications

When sulfuric acid, phosphoric acid, or mixed‑acid environments attack standard stainless steels in hours, Alloy 20 fasteners step in as the proven solution. Originally developed for hot sulfuric acid service, this high‑nickel austenitic stainless steel—commonly known as Carpenter 20 or 20Cb‑3—provides exceptional resistance to a wide range of aggressive chemicals while maintaining good strength and fabricability. RAYCHIN LIMITED, a specialist global manufacturer and supplier of high‑performance alloy fasteners with decades of experience, provides the complete range of UNS N08020 fasteners. This guide covers everything engineers need to know about the material, its composition, properties, and why it is indispensable in chemical processing.

1. What Is Alloy 20 Material?

What is Alloy 20 material? Alloy 20, also known as Carpenter 20 or 20Cb‑3, is a high‑nickel (32–38%) austenitic stainless steel specifically designed for maximum resistance to sulfuric acid attack. The "Cb" in 20Cb‑3 stands for columbium (niobium), which is intentionally added to stabilize the alloy against intergranular corrosion. Unlike standard stainless steels, Alloy 20 bridges the gap between conventional austenitic grades and nickel‑base alloys, providing excellent resistance to a wide range of chemical environments—including sulfuric, phosphoric, nitric, and mixed acids—at a cost below Hastelloy or Inconel.

2. Alloy 20 Chemical Composition

The Alloy 20 chemical composition is carefully balanced to achieve its unique combination of acid resistance, strength, and weldability. The nominal chemistry per ASTM B473 (UNS N08020) is presented below.

3. Alloy 20 Properties – Mechanical and Physical

Alloy 20 properties in the solution‑annealed condition per ASTM B473 combine good strength with outstanding corrosion resistance. Typical room‑temperature mechanical properties are:

• Tensile Strength: ≥ 550 MPa (80 ksi)
• Yield Strength (0.2% offset): ≥ 240 MPa (35 ksi)
• Elongation: ≥ 30%
• Hardness: ≤ 95 HRB

Key physical properties include a density of 8.08 g/cm³, a melting range of 1370–1425°C, and a mean coefficient of thermal expansion of 14.7 µm/m·°C (20–100°C). The alloy is non‑magnetic in the annealed condition.

4. Alloy 20 Equivalent Grades and Nickel‑Copper Content

Alloy 20 equivalent grades include the cast version, ASTM A351 CN7M, often used for valve bodies. While Alloy 20 contains copper (3–4%), it is primarily a nickel‑iron‑chromium alloy, not a copper‑base alloy. The Alloy 20 nickel copper content gives it the unique ability to resist sulfuric acid while maintaining ductility and weldability. Common equivalent designations are UNS N08020 for wrought products and CN7M for castings.

5. RAYCHIN's Alloy 20 Fastener Product Range

RAYCHIN LIMITED supplies the complete line of Carpenter 20 fasteners for global chemical processing industries:

• Hex bolts – ASME B18.2.1, DIN 931/933, M6–M48, 1/4″–2″
• Stud bolts and threaded rod – ASME B16.5, DIN 976, M6–M64, 1/4″–2‑1/2″
• Socket head cap screws – ASME B18.3
• Heavy hex nuts and washers
• Custom parts – per your drawings; flanged bolts, stepped studs

All products are solution‑annealed, with full material certification, PMI testing, and EN 10204 3.1 as standard (3.2 available).