Alloy 20 / 020,Carpenter 20Cb-3,UNS N08020,E FORU

### **Alloy 20 / UNS N08020 / Carpenter 20Cb-3® - A Comprehensive Technical Overview** **Introduction** Alloy 20, also known by its UNS designation N08020 and the trade name Carpenter 20Cb-3®, is a nickel-iron-chromium super-austenitic stainless steel. It was originally developed to resist sulfuric acid corrosion and has since become a benchmark material for handling a wide range of aggressive corrosive media. Its excellent resistance is derived from a carefully balanced chemical composition that includes the addition of copper and molybdenum, stabilized with columbium (niobium) to prevent sensitization (carbide precipitation) during welding. This alloy offers superior resistance to stress corrosion cracking (SCC), pitting, and crevice corrosion compared to conventional stainless steels like Type 304 and 316, making it a prime choice for demanding chemical process industries. --- #### **1. Chemical Composition** The key to Alloy 20's performance lies in its precise chemistry. The composition for Carpenter 20Cb-3® is typically as follows (weight %): | Element | Content (%) | Role & Benefit | | :--- | :--- | :--- | | **Nickel (Ni)** | 32.0 - 38.0 | Base element providing inherent corrosion resistance and ductility. | | **Chromium (Cr)** | 19.0 - 21.0 | Confers resistance to oxidizing environments and general corrosion. | | **Iron (Fe)** | Balance | The base metal of the alloy. | | **Molybdenum (Mo)** | 2.0 - 3.0 | Enhances resistance to pitting and crevice corrosion in chloride environments. | | **Copper (Cu)** | 3.0 - 4.0 | Provides exceptional resistance to sulfuric acid and reducing chemicals. | | **Manganese (Mn)** | ≤ 2.0 | Aids in deoxidation during melting. | | **Silicon (Si)** | ≤ 1.0 | Improves resistance to oxidation. | | **Columbium (Cb) + Tantalum (Ta)**| 8 x %C min. to 1.00 max. | Stabilizes the alloy against sensitization by forming carbides, preventing chromium depletion at grain boundaries. | | **Carbon (C)** | ≤ 0.07 | Kept low to minimize carbide precipitation. | | **Phosphorus (P)** | ≤ 0.045 | Impurity, controlled to prevent embrittlement. | | **Sulfur (S)** | ≤ 0.035 | Impurity, controlled to improve hot workability and corrosion resistance. | *Note: "Carpenter 20Cb-3" is a registered trademark of Carpenter Technology Corporation, representing a specific, optimized version of UNS N08020.* --- #### **2. Physical Properties** The physical properties of Alloy 20 make it suitable for various engineering applications. | Property | Value | | :--- | :--- | | **Density** | 8.08 g/cm³ (0.292 lb/in³) | | **Melting Range** | 1443 - 1499 °C (2625 - 2730 °F) | | **Specific Heat (20°C)** | 500 J/kg·K | | **Electrical Resistivity** | 0.95 μΩ·m | | **Thermal Conductivity** | 12.9 W/m·K (at 100°C) | | **Coefficient of Thermal Expansion** | 15.1 μm/m·°C (20-100°C) | | **Modulus of Elasticity (Tensile)** | 186 GPa (27 x 10⁶ psi) | | **Magnetic Permeability** | Typically < 1.02 (Annealed condition, essentially non-magnetic) | --- #### **3. Mechanical Properties (Typical for Annealed Condition)** The mechanical properties demonstrate its excellent combination of strength and ductility. | Property | Room Temperature Value | | :--- | :--- | | **Tensile Strength** | 620 MPa (90 ksi) min. | | **Yield Strength (0.2% Offset)** | 300 MPa (44 ksi) min. | | **Elongation (in 2 inches / 50mm)** | 30% min. | | **Hardness (Rockwell B)** | ≤ 95 HRB | --- #### **4. Product Applications** Alloy 20 is extensively used in industries where corrosion resistance is paramount. Key applications include: * **Chemical Processing Industry (CPI):** Tanks, reactors, heat exchangers, distillation columns, and piping systems for producing and handling sulfuric acid, phosphoric acid, and other aggressive chemicals. * **Pharmaceutical Industry:** Process vessels, mixing tanks, and transfer lines where high purity and corrosion resistance are critical. * **Food and Dairy Industry:** Evaporators, vessels, and piping, particularly in applications involving acidic products like vinegar and citrus juices. * **Plastic and Synthetic Fiber Manufacturing:** Components in processes involving chloride catalysts and other corrosive intermediates. * **Pulp and Paper Industry:** Digesters, bleach plants, and chemical recovery systems. * **Oil and Gas Refining:** Heat exchangers and piping handling sour gas and corrosive crudes. --- #### **5. International Standards** Alloy 20 / UNS N08020 is covered by numerous international standards for different product forms. | Product Form | Standard Specification | | :--- | :--- | | **Plate, Sheet, Strip** | ASTM B463, ASME SB463, UNS N08020 | | **Seamless Pipe & Tube** | ASTM B729, ASME SB729 | | **Welded Pipe & Tube** | ASTM B775, ASME SB775 | | **Fittings (Butt-weld)** | ASTM B366, ASME SB366 | | **Forgings** | ASTM B462, ASME SB462 | | **Bar, Rod, Wire** | ASTM B473, ASME SB473 | | **Flanges & Forged Fittings** | ASTM B462, ASME SB462 | | **European Designation** | **EN 2.4660** (NiCr20CuMo) | --- **Summary** **Alloy 20 (UNS N08020 / Carpenter 20Cb-3®)** stands as a versatile and highly reliable corrosion-resistant alloy. Its unique combination of nickel, chromium, molybdenum, and copper, stabilized with columbium, provides an outstanding defense against a wide spectrum of corrosive attacks, particularly from sulfuric acid and chloride-induced stress corrosion cracking. Governed by strict ASTM/ASME and other international standards, it remains a material of choice for critical equipment in the chemical, pharmaceutical, and other process industries where equipment longevity and reliability are essential.

Packing of Standard Packing: Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and steel drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 1702 gallon liquid totes Special package is available on request.