Alloy 20 UNS N08020, 2.4660 Incoloy 20 Alloy Steel Pipe Fittings

1. Definition & Material Overview

Alloy 20, also known as 20Cb-3 or Carpenter 20, is a niobium-stabilized nickel-iron-chromium-molybdenum-copper austenitic corrosion-resistant alloy. Its equivalent designations include DIN 2.4660 and Chinese standard NS143.

Positioned between high-grade stainless steels and premium Hastelloy alloys, it delivers outstanding cost performance. This material is widely recognized as a professional grade for sulfuric acid service, and it outperforms common stainless steels like 316L and 904L in harsh corrosive environments.

2. Global Grade Standards

UNS Number: N08020

Trade Names: Alloy 20, Carpenter 20Cb-3, Incoloy 20

DIN Standard: 2.4660

Chinese Standard: NS143 (0Cr20Ni35Mo3Cu4Nb)

3. Chemical Composition (wt%) & Function

Element	Content Range	Main Function
Carbon (C)	≤ 0.07	Reduce sensitization risk after welding
Chromium (Cr)	19.0 – 21.0	Form protective passive film, resist oxidation and nitric acid corrosion
Nickel (Ni)	32.0 – 38.0	Improve ductility and resistance to chloride stress corrosion cracking
Molybdenum (Mo)	2.0 – 3.0	Enhance resistance to pitting and crevice corrosion
Copper (Cu)	3.0 – 4.0	Key element for excellent resistance to dilute sulfuric acid
Niobium + Tantalum (Nb+Ta)	8×C ~ 1.0	Stabilize microstructure, prevent intergranular corrosion
Iron (Fe)	Remainder	Base matrix, balance cost and mechanical properties
Manganese (Mn)	≤ 2.0	Deoxidation, improve workability
Silicon (Si)	≤ 1.0	Boost high-temperature oxidation resistance
Phosphorus & Sulfur (P, S)	Trace	Strictly controlled as impurities

4. Physical Properties

Item	Parameter
Density	8.08 g/cm³
Melting Range	1357 – 1430 °C
Specific Heat Capacity	0.45 J/g·°C
Thermal Conductivity	14 W/m·K
Coefficient of Linear Expansion	15.6 × 10⁻⁶ /°C
Magnetism	Non-magnetic
Maximum Continuous Service Temperature	530 °C

5. Mechanical Properties (Solution Annealed Condition)

Item	Parameter
Tensile Strength	≥ 550 MPa (Typical: 620 MPa)
Yield Strength	≥ 240 MPa (Typical: 300 MPa)
Elongation	≥ 30% (Typical: 40%)
Hardness	HB ≤ 217 / HRB ≤ 95

This alloy features high strength, excellent ductility and good anti-cracking performance, suitable for various forming processes

UNS N08020 fitting — ALLOY 20 PIPE FITTINGS

6. Corrosion Resistance

Superior resistance to sulfuric acid: Performs exceptionally well in 20% to 40% boiling sulfuric acid, serving as the preferred material for sulfuric acid processing equipment.

Good tolerance to mixed acids: Resists phosphoric acid, nitric acid and hydrochloric acid, as well as complex corrosive media containing fluorides and chlorides.

Excellent local corrosion resistance: Effectively resists pitting, crevice corrosion and chloride-induced stress corrosion cracking, far superior to conventional duplex and austenitic stainless steels.

No post-weld sensitization: Niobium stabilizes carbon elements, so no additional heat treatment is required after welding to avoid intergranular corrosion.

7.Workability & Heat Treatment

· Hot working: Suitable for hot forging, hot rolling, hot extrusion and hot forming. The recommended hot working temperature range is 900 – 1150 °C.

· Cold working: Good formability. Cold rolling, bending and stamping can be conducted with standard equipment. Work hardening will occur during cold processing.

· Weldability: Compatible with GTA/TIG, GMA/MIG and SMA welding methods. Matching filler metals are required. Welded joints retain good corrosion resistance.

· Solution annealing: The standard annealing temperature is 1010 – 1090 °C, followed by rapid water quenching to restore full corrosion resistance and mechanical properties.

8. Main Applications

Alloy 20 is widely applied in chemical, pharmaceutical, food processing and fertilizer industries. Typical products and equipment include pipes, elbows, tees, flanges, pressure vessels, reaction tanks, pickling lines and wet-process phosphoric acid production facilities. It is the ideal choice for long-term service in moderate to severe corrosive environments.