Alloy 20 (commercially known as Incoloy Alloy 20 or Carpenter 20Cb-3, corresponding to UNS N08020 / W.Nr. 2.4660) is an austenitic nickel-iron-chromium alloy. With the addition of copper, molybdenum, and niobium, it offers excellent resistance to sulfuric, phosphoric, and nitric acids, as well as chloride-containing environments. Originally developed specifically to combat sulfuric acid corrosion, it also provides outstanding resistance to stress corrosion cracking, pitting, and crevice corrosion. Known as the "sulfuric acid killer," Alloy 20 is widely used in demanding corrosive environments across the chemical, food, and pharmaceutical industries.
Click to get an Inconel 20 product quote
Alloy 20 (Incoloy 20) – a nickel-iron-chromium alloy specifically developed to resist corrosion in sulfuric acid environments.
Alloy 20 (Incoloy 20) – a nickel-iron-chromium alloy specifically developed to resist corrosion in sulfuric acid environments.
Alloy 20 (UNS N08020) is a nickel-iron-chromium austenitic superalloy stabilized with niobium and fortified with copper and molybdenum. It is specially designed to withstand strong acid environments and exhibits excellent resistance to sulfuric acid environments, chloride stress corrosion cracking, and intergranular corrosion.
What is the Alloy 20 material standard?
Alloy 20 (UNS N08020) is an austenitic nickel-iron-chromium-based superalloy with added copper and molybdenum, giving it excellent resistance to harsh environments, pitting corrosion, and crevice corrosion. Furthermore, it contains niobium for stabilization treatment to minimize carbide precipitation during welding.
1. Alloy 20 Chemical Composition
The chemical composition (weight percentage) of Alloy 20 is shown in the table below. Its precise proportioning is the foundation of its excellent corrosion resistance.
| Element | Content Range (Min - Max, %) | Primary Function |
|---|---|---|
| Nickel (Ni) | 32.0 - 38.0 | Stabilizes the austenitic matrix, providing excellent resistance to oxidation and corrosion cracking. |
| Chromium (Cr) | 19.0 - 21.0 | Forms a dense chromium oxide protective film, providing oxidation and corrosion resistance. |
| Iron (Fe) | Balance (approx. 29.85 - 44.0) | Primary matrix element, balancing cost and performance. |
| Copper (Cu) | 3.0 - 4.0 | Critical element, greatly improves resistance to reducing media such as dilute sulfuric acid and phosphoric acid. |
| Molybdenum (Mo) | 2.0 - 3.0 | Enhances resistance to pitting and crevice corrosion, especially in halide-containing environments. |
| Niobium (Nb) | 8 × C% - 1.0 (max) | Stabilizing element; preferentially combines with carbon to form NbC, preventing chromium carbide precipitation at grain boundaries, thus avoiding intergranular corrosion in the weld heat-affected zone. |
| Carbon (C) | ≤ 0.07 | Strictly controlled to reduce carbide precipitation and ensure corrosion resistance. |
| Manganese (Mn) | ≤ 2.0 | Improves hot workability. |
| Silicon (Si) | ≤ 1.0 | Impurity control. |
| Phosphorus (P) | ≤ 0.045 | Impurity control. |
| Sulfur (S) | ≤ 0.035 | Impurity control. |
2. Physical properties of Alloy 20
| Property | Typical Value / Range | Unit |
|---|---|---|
| Density | 8.08 - 8.14 | g/cm³ |
| Melting Range | 1357 - 1443 (typically 1370-1430) | °C |
| Coefficient of Thermal Expansion (20-200°C) | 13.9 - 15.0 | ×10⁻⁶/°C |
| Thermal Conductivity (room temperature) | 12.3 - 12.5 | W/(m·K) |
| Specific Heat Capacity (room temperature) | approx. 500 | J/(kg·K) |
| Electrical Resistivity (room temperature) | approx. 1.08 | μΩ·m |
| Modulus of Elasticity (room temperature) | approx. 200 - 214 | GPa |
| Poisson's Ratio | approx. 0.31 | - |
| Magnetic Permeability (annealed) | approx. 1.002 (non-magnetic) | - |
3. Alloy 20 room temperature mechanical properties (solution annealing, minimum values)
| Property | Value (Minimum) | Unit |
|---|---|---|
| Tensile Strength (Rm) | 550 - 620 (commonly ≥ 620) | MPa |
| 0.2% Yield Strength (Rp0.2) | 240 - 310 (commonly ≥ 300) | MPa |
| Elongation (A) | 30 - 40 (commonly ≥ 40) | % |
| Hardness | ≤ 217 HB (Brinell hardness) | - |
Click to download the Alloy 20 PDF file now
4. Alloy 20 Key Corrosion Resistance Properties
The most outstanding feature of Alloy 20 is its broad and excellent corrosion resistance, especially in sulfuric acid environments.
| Corrosive Media | Description of Corrosion Resistance |
|---|---|
| Sulfuric Acid (H₂SO₄) | Excellent corrosion resistance. In 10-80% concentration sulfuric acid up to boiling temperature, the corrosion rate is far lower than that of stainless steels such as 316L. In ≤50% concentration, ≤80°C sulfuric acid, the corrosion rate is typically <0.5 mm/year. |
| Phosphoric Acid (H₃PO₄) | Excellent corrosion resistance. Includes wet-process phosphoric acid containing fluoride impurities; widely used in the fertilizer industry. |
| Nitric Acid (HNO₃) | Good corrosion resistance. Chromium provides resistance to oxidizing acids. |
| Chloride Environments | Excellent resistance to stress corrosion cracking (SCC). High nickel content provides near-total immunity to chloride-induced SCC, far exceeding 300 series stainless steels. Additionally, the addition of molybdenum provides good resistance to pitting and crevice corrosion. |
| Mixed Acids | Excellent performance in mixed acids such as nitric-sulfuric acid (e.g., in nitration processes). |
| Other Media | Good resistance to alkalis such as sodium/potassium hydroxide, hydrofluoric acid (all concentrations at room temperature, ≤10% at 70°C), seawater (moderate pitting/crevice corrosion resistance), and sour environments containing hydrogen sulfide (meets NACE MR0175 standard). |
Limitations: Not suitable for high-temperature concentrated sulfuric acid (such as fuming sulfuric acid) or highly reducing acids (such as boiling hydrochloric acid). Its corrosion resistance is also limited in nitric-hydrofluoric acid mixtures.
5. Welding and Heat Treatment
Heat Treatment (Solution Annealing):
Temperature: Heat to 925°C – 1010°C (typically around 1066°C).
Cooling: Water quench or rapid air cool. It is critical to pass quickly through the carbide precipitation sensitive temperature range (540°C – 900°C) to maintain optimal corrosion resistance.
Welding:
Weldability: Excellent. Suitable for conventional processes such as TIG, MIG, SMAW, and SAW.
Filler Metal Selection: Matching filler metals are recommended, such as ERNiCrMo-3 (AWS A5.14 ER320LR) wire or ENiCrMo-3 (AWS A5.11) electrode.
Process Control: No preheating required. Interpass temperature should be kept below 100–120°C. Use low heat input, multi-layer and multi-pass welding, along with high-purity shielding gas.
Post-Weld Heat Treatment (PWHT): Due to the presence of niobium as a stabilizing element, solution treatment is generally not required after welding. For large or complex structures, stress relief annealing at 870°C for 1 hour may be applied to eliminate welding stress.
6. Alloy 20 – Key Material Property Summary
1. Superior Sulfuric Acid Resistance: Specifically designed for sulfuric acid environments, with excellent performance over a wide range of concentrations and temperatures.
2. Broad Corrosion Resistance Spectrum: Outstanding resistance to phosphoric acid, nitric acid, chloride-induced stress corrosion cracking (SCC), pitting, and crevice corrosion.
3. Excellent Weldability and Workability: Good hot and cold formability, excellent weldability, and generally no post-weld heat treatment required.
4. Stable Microstructure: Stabilized with niobium, effectively preventing sensitization and intergranular corrosion.
7. Alloy 20 – Applications
Thanks to its comprehensive corrosion resistance, Alloy 20 is widely used across various industrial sectors:
| Industry | Applications |
|---|---|
| Chemical & Petrochemical | Equipment for sulfuric acid, phosphoric acid, and nitric acid production (reactors, heat exchangers, piping, pumps, valves) Mixed acid handling equipment Nitration process equipment |
| Food & Pharmaceutical | Production equipment for food additives (e.g., phosphoryl chloride, phosphorus trichloride) Pharmaceutical reactors and piping systems |
| Energy & Environmental Protection | Flue gas desulfurization (FGD) systems Wastewater treatment equipment |
| Marine & Oil & Gas | Seawater cooling systems Sour oil and gas environments containing hydrogen sulfide (NACE MR0175 compliant) |
| General Equipment | Mixing tanks Pickling equipment Synthetic rubber manufacturing equipment Various flanges, bolts, and fasteners |
Why Choose Gnee as Your Nickel-Based Alloy Supplier
✅ Over 18 years of export experience, products sold to more than 80 countries
✅ Certified by ISO, SGS, and BV
✅ Global inventory of Inconel, Hastelloy, Incoloy, and Monel alloy tubing, plates, and bars
✅ Custom processing services available – including cutting, polishing, CNC machining, and packaging
✅ Fast delivery within 7-15 days, supported by global logistics partners
Gnee Alloy Alloy 20 Certificate
📦 Packaging and Shipping
All Nickel Based Alloy products are packaged using the following methods:
Wooden pallets or crates
Moisture-proof packaging
Labels with furnace number, standard, and size labels
Shipped worldwide by sea, air, or express
Gnee Alloy incoloy 020 Product Packing
Contact us for the latest export price quote for Alloy 20
FAQ
Q：Are Alloy 20, Incoloy 20, and 20Cb-3 the same?
A：Yes, they generally refer to the same material (UNS N08020). Incoloy is a registered trademark of Special Metals Corporation, and 20Cb-3 is a registered trademark of Carpenter Technology.
Q：What is its maximum service temperature?
A：Its strength lies in corrosion resistance rather than high-temperature strength. For long-term structural use, the temperature is typically recommended below 425°C. Short-term exposure can be higher, but oxidation and loss of strength should be considered.
Q：Can it completely replace 316L stainless steel?
A：In environments involving sulfuric acid, phosphoric acid, and severe chloride-induced stress corrosion cracking (SCC), it is an excellent upgrade alternative to 316L. However, in strongly oxidizing or strongly reducing extreme environments, evaluation should be based on the specific service conditions.
Q：Is post-weld heat treatment required?
A：Thanks to the presence of niobium as a stabilizing element, post-weld solution heat treatment is generally not required to meet the requirements of most corrosive environments. Only for large or complex structures is stress relief annealing recommended.
Q：What international standards cover this alloy?
A：Common standards include: UNS N08020, W.Nr. 2.4660, ASTM B463 / B473 / B729, ASME SB463 / SB473, and others.
