Excellent Corrosion Resistance of Alloy 20
Alloy 20 is a highly corrosion-resistant austenitic nickel-iron-chromium alloy developed for superior performance in sulfuric acid and aggressive chemical environments. It also shows excellent resistance to chloride stress corrosion cracking, pitting, and crevice corrosion. Designed as a cost-effective alternative to higher-priced alloys, Alloy 20 combines high strength, good weldability, and excellent mechanical properties.
This article introduces the composition, characteristics, and applications of Alloy 20 to help guide better material selection in engineering projects.
What is Alloy 20?
Alloy 20 (UNS N08020), also known as Carpenter 20, is a corrosion-resistant alloy designed primarily for sulfuric acid service but also performs well in phosphoric acid, nitric acid, and chloride environments.
It bridges the gap between stainless steels and high-nickel alloys, offering enhanced resistance to pitting and stress corrosion without the cost of fully nickel-based alloys.
Alloy 20 Equivalent Grades
| Standard / System | Equivalent Designation |
| UNS | N08020 |
| ASTM / ASME | ASTM B473 (bars), B464 (plate), B468 (pipe), B462 (forgings) |
| EN / DIN | 2.466 |
| ISO | NiCr20CuMo |
| Trade Name | Carpenter 20, Incoloy® Alloy 20 |
Alloy 20 Chemical Composition
| Element | Content (%) |
| Nickel (Ni) | 32.0 – 38.0 |
| Chromium (Cr) | 19.0 – 21.0 |
| Iron (Fe) | Balance |
| Molybdenum (Mo) | 2.0 – 3.0 |
| Copper (Cu) | 3.0 – 4.0 |
| Carbon (C) | ≤ 0.06 |
| Manganese (Mn) | ≤ 2.0 |
| Silicon (Si) | ≤ 1.0 |
| Niobium (Cb + Ta) | 8 × C min – 1.0 |
Alloy 20 Mechanical Properties
| Property | Typical Value |
| Tensile Strength | 551 – 758 MPa |
| Yield Strength | ≥ 241 MPa |
| Elongation | ≥ 30% |
| Hardness (HBW) | ≤ 21 |
Alloy 20 Physical Properties
| Property | Value |
| Density | 8.1 g/cm³ |
| Melting Point | 1357 – 1430 °C |
| Thermal Conductivity | ~10.8 W/m·K (at 20°C) |
| Electrical Resistivity | ~0.98 µΩ·m |
| Modulus of Elasticity | ~195 GPa |
| Service Temperature Range | -50°C to ~550°C |
Applications of Alloy 20
- Sulfuric Acid Processing: Highly resistant to all concentrations of sulfuric acid at varying temperatures.
- Chemical and Petrochemical Plants: Used in reactors, tanks, piping, and heat exchangers.
- Food and Pharmaceutical Industry: Excellent corrosion resistance in clean, controlled processes.
- Marine and Offshore Equipment: Good resistance to chloride pitting and crevice corrosion.
- Plastics and Synthetic Fiber Production: Exposure to acids, chlorides, and oxidizing environments.
Advantages of Alloy 20
- Outstanding resistance to sulfuric acid, phosphoric acid, nitric acid, and chlorides.
- Excellent weldability and mechanical strength without post-weld heat treatment.
- Lower cost than many nickel-based superalloys while offering similar corrosion resistance.
- Resists chloride stress corrosion cracking better than 316L or 317L.
- Non-magnetic in the annealed condition, suitable for instrumentation and process control.
Limitations of Alloy 20
- More expensive than standard stainless steels due to high nickel and copper content.
- Not suitable for strong oxidizing agents like nitric acid at high concentrations.
- Cold forming requires care due to work hardening behavior.
- Welding may require controlled heat input to avoid hot cracking or sensitization.
- Limited availability in some markets compared to standard grades like 304 or 316.
Alloy 20 vs Other Stainless Alloys
| Feature | 316L | Alloy 20 | Hastelloy C276 |
| PREN (Pitting Index) | ~25 | ~38 | ~45–52 |
| Molybdenum Content | ~2.0% | ~2.5% | ~16% |
| Chloride Resistance | Moderate | High | Very High |
| Strength | Medium | Medium-High | High |
| Cost | Low | Moderate | High |
FAQ About Alloy 20
Alloy 20 is often referred to as a superaustenitic stainless steel, but it is technically a nickel alloy due to its high nickel content (32–38%).
It offers excellent resistance to stress corrosion cracking, pitting, and crevice corrosion in chloride-containing environments, thanks to its high nickel, chromium, and copper content.
Yes. Alloy 20 has good weldability and formability using standard shop fabrication techniques, including TIG, MIG, and stick welding.
For sulfuric acid environments, Alloy 20 typically outperforms 316L and 904L due to its higher resistance to acid attack and stress corrosion.
Summary
This article explores Alloy 20, its corrosion-resistant features, chemical and mechanical properties, and performance advantages over other stainless alloys. It is ideal for sulfuric acid service, chloride-bearing systems, and pharmaceutical applications.
MT.BOLTS supplies Alloy 20 fasteners, bolts, and custom parts tailored to your engineering needs. Contact our team or visit our website to learn more or request a quote.
