Table of content
Introduction
Alloy 20 is a type of alloy steel. This article mainly introduces the uses and properties of Alloy 20. It will also compare it with other stainless steels.
Alloy 20 is mostly used in the chemical, food processing and pharmaceutical industries.
What Is Alloy 20?
Alloy 20 is a nickel-iron-chromium austenitic alloy with copper and molybdenum as the main elements. It has excellent corrosion resistance and sulfuric acid resistance. This super alloy steel has the corrosion resistance and durability of stainless steel.
Chemical Composition of Alloy 20
The element table of Alloy 20 is as follows:
| Element | Content (Approx.) | Purpose |
|---|---|---|
| Nickel (Ni) | 32–38% | Corrosion resistance and toughness |
| Chromium (Cr) | 19–21% | Forms passive layer, resists rust |
| Iron (Fe) | Balance | Base metal |
| Copper (Cu) | 3–4% | Improves resistance to sulfuric acid |
| Molybdenum | 2–3% | Resists pitting and crevice corrosion |
| Niobium | ≤1% | Prevents intergranular corrosion |
This alloy steel has strong tolerance in acidic and chloride-rich environments.
Key Properties of Alloy 20
Corrosion resistance
Sulfuric acid resistance
High strength
Easy to process and weld
Non-magnetic
Applications of Alloy 20
Alloy 20 was originally used in nucleic acid environments, but with the improvement of its corrosion resistance, it can be used in a variety of industries:
Chemical and petroleum industries
Food processing industries
Pharmaceutical industries
Power generation equipment
Typical Components:
Heat exchangers
Industrial piping systems
Valves and pumps
Pickling equipment
Reaction vessels
Alloy 20 has higher corrosion resistance than 316 stainless steel, so it is mostly used in strong acid environments or highly corrosive parts.
Alloy 20 vs 316 Stainless Steel
316 stainless steel is widely used and has good corrosion resistance, but Alloy 20 has relatively stronger corrosion resistance. The following is a performance comparison between the two:
| Property | Alloy 20 | 316 Stainless Steel |
|---|---|---|
| Sulfuric acid resistance | Excellent | Moderate |
| Chloride resistance | Good | Moderate to good |
| Price | Higher | Lower |
| Weldability | Good | Excellent |
| General corrosion | Excellent | Good |
From the above, it can be seen that if it needs to be used in strong acid or high temperature environments, Alloy 20 can be optimized.
Forms of Alloy 20 Available
Like other metals, Alloy 20 is available in a variety of forms to meet different needs:
- Plate and bar
- Seamless and welded pipes
- Castings and forgings
- Flanges and fittings
Products that meet ASTM specifications such as ASTM B463, B464, B729 can be produced.
Weldability and Fabrication
Alloy 20 can be welded using the following methods:
- Gas Tungsten Arc Welding (GTAW/TIG)
- Gas Metal Arc Welding (GMAW/MIG)
- Shielded Metal Arc Welding (SMAW)
The niobium element added to the alloy is stable and is not prone to cracking after welding, so heat treatment is not required.
It can also:
- Formed using standard tools
- Work hardening, this feature needs attention during processing
- Cold working can increase its strength
ASTM and UNS Designations
The industry code of Alloy 20 is as follows:
| Designation | Description |
|---|---|
| UNS N08020 | Unified Numbering System code |
| ASTM B463/B464 | Plate, Sheet, Strip, and Welded Pipe |
| ASTM B468/B729 | Seamless Pipe and Tube |
| ASME SB-462/SB-464 | Boiler and pressure vessel applications |
| Trade Names | Carpenter® 20, Incoloy® 20 |
Corrosion Resistance in Detail
Alloy 20 also has good corrosion resistance in the following environments:
Sulfuric acid (H₂SO₄) — even at high concentrations
Nitric acid and phosphoric acid
Sodium hydroxide (caustic environments)
Chloride-containing environments (moderate)
Summary
Alloy 20 is a highly corrosion-resistant material, a nickel-rich alloy designed for harsh environments involving sulfuric acid, chlorides and corrosive chemicals. Its corrosion resistance is slightly higher than that of stainless steel. It is mostly used in chemical processing, pharmaceutical and food industries.
This article introduces the performance and application of alloy 20. I hope it will be helpful to those who need to understand this material.
