Naming rules and common grades of duplex stainless steel

Duplex stainless steel is a kind of stainless steel with both austenite and ferrite phases.

It is widely used in chemical industry, marine engineering, pressure vessels, bridge construction and other fields due to its high strength and excellent corrosion resistance (especially resistance to chloride ion stress corrosion).

Common grades such as 2205, 2304, 1.4462, S32205, etc., have the logic of material composition, performance level and standard system behind their naming rules.

This article will systematically analyze the naming method of duplex stainless steel from the aspects of classification, naming rules, international standard comparison and typical grade analysis.

1. Classification of duplex stainless steel

1. Classification by composition ratio

Standard duplex stainless steel:

Austenite and ferrite each account for about 50%.

Typical grades such as 2205 (22%Cr+5%Ni) have moderate corrosion resistance and are suitable for most corrosive environments.

High molybdenum duplex stainless steel:

Contains 2%-3% molybdenum (Mo), such as 2507 (25%Cr+7%Ni), has stronger resistance to pitting and crevice corrosion, and is used in extreme corrosive environments (such as seawater desalination, acidic media).

Super duplex stainless steel:

Cr content ≥25%, Mo content ≥3%, such as 2507, 254SMO, with better comprehensive performance, used in harsh scenarios such as deep-sea oil and gas extraction.

2. Classification by use

Structural duplex stainless steel: Such as 2205, 2304, used for load-bearing structures such as buildings, bridges, and storage tanks.

DSS for corrosion resistance: Such as 2507 and S32760, used for chemical equipment, offshore platforms, and pipelines in acidic environments.

Duplex stainless steel for low temperature: Some grades (such as 2205) can be used in low temperature environments after special treatment.

2. Naming rules for duplex stainless steel

1. Naming rules for national standards (GB)

Composition representation: Take “022Cr19Ni13Mo3” as an example:

022: Carbon content ≤ 0.02% (expressed in thousandths).

Cr19: Chromium (Cr) content is about 19%.

Ni13: Nickel (Ni) content is about 13%.

Mo3: Molybdenum (Mo) content is about 3%.

Use: For example, “022Cr19Ni13Mo3” in GB/T 20878 corresponds to American Standard 2205.
Uniform digital code: Starting with “U”, such as the unified digital code of 2205 is U22052.

2. Naming rules of American Standard (ASTM/ASME)

Serial numbering method: named as “2205”, “2304”, “2507”, etc. The numbers represent the approximate chromium content:

2205: about 22%Cr, corresponding to American Standard ASTM A890 Grade 22.

2304: about 23%Cr (low nickel version), low cost, used in general corrosion-resistant scenarios.

2507: about 25%Cr, super DSS, corresponding to ASTM A998 Grade 6.

Grade extension: such as “S32205” means 2205 stainless steel that meets American Standard ASTM A240.

3. Naming rules of European Standard (EN)

EN number + component code: such as “1.4462” and “1.4501”:

1.4462: corresponding to 2205, the composition contains Cr22% and Ni5%.

1.4501: Corresponds to 2304, containing 23% Cr and 4.5% Ni.

4. Japanese Standard (JIS) naming rules

SUS+four-digit number: For example, SUS32940 corresponds to 2205, and SUS35500 corresponds to super duplex steel.

3. Comparison of international standards

4. Analysis of common duplex stainless steel grades

1. 2205 (S32205, 1.4462, 022Cr19Ni13Mo3)

Standards: ASTM A240, EN 1.4462, GB/T 20878.

Composition: 22%Cr, 5%Ni, 3%Mo.

Applications: chemical storage tanks, seawater desalination equipment, bridge structures.

2. 2304 (1.4501, 023Cr21Ni5Mo3)

Standards: ASTM A890 Grade 32, EN 1.4501.

Composition: 23%Cr, 4.5%Ni, 3%Mo.

Applications: architectural decoration, automotive exhaust systems (low-cost alternative to 2205).

3. 2507 (S32760, 1.4501, 025Cr25Ni7Mo4)

Standard: ASTM A998 Grade 6, EN 1.4410.

Composition: 25%Cr, 7%Ni, 4%Mo.

Application: deep-sea oil and gas pipelines, acidic medium reactors.

4. 254SMO (025Cr25Ni6Mo4)

Standard: ASTM A240, EN 1.4547.

Composition: 25%Cr, 6%Ni, 4%Mo.

Application: extreme corrosive environments (such as pulp bleaching equipment, seawater filtration systems).

5. 1.4435 (F51)

Standard: ASTM A890 Grade 5, EN 1.4435.

Composition: 25%Cr, 6%Ni, 3%Mo.

Application: Petrochemical equipment, sulfuric acid storage tanks.

5. Advantages and Challenges of Duplex Stainless Steel

Duplex stainless steel achieves the following advantages through the synergistic effect of ferrite and austenite:

High strength: The yield strength can reach 500-800MPa, which is twice that of 304 stainless steel.

Excellent corrosion resistance: Especially in chloride environment, its resistance to stress corrosion cracking is better than that of austenitic stainless steel.

Economical efficiency: Compared with super austenitic stainless steel or nickel-based alloy, it has lower cost.

However, its welding performance is poor, and the heat treatment process is strict, and the risk of intergranular corrosion needs to be avoided.

6. Summary

Although the naming rules of duplex stainless steel are complex, they follow the logic of composition, standards and uses.

Whether it is the national standard “022Cr19Ni13Mo3”, the American standard “2205” or the European standard “1.4462”, each grade corresponds to a specific chemical composition, mechanical properties and application scenarios.

Understanding these naming rules will help to accurately match requirements in engineering material selection, procurement and quality control, and maximize the performance advantages of materials.