2304 (UNS S32304) duplex stainless steel
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General Properties
Alloy 2304 is a 23% chromium, 4% nickel, molybdenum-free duplex stainless steel. The Alloy 2304 has corrosion resistance properties similar to 316L. Furthermore, its mechanical properties, i.e., yield strength, are twice those of 304/316 austenitic grades. This allows the designer to save weight, particularly for properly designed pressure vessel applications.

The alloy is particularly suitable for applications covering the -50C/+300C (-58F/572F) temperature range. Lower temperatures may also be considered but need some restrictions, particularly for welded structures.

With its duplex microstructure and low nickel and high chromium contents, the alloy has improved stress corrosion resistance properties compared to 304 and 316 austenitic grades.

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Applications
Generally where 304 and 316L are used
Pulp and paper industry (chip storage tanks, white and black liquor tanks, digestors)
Caustic solutions, organic acids (SCC resistance)
Food industry
Pressure vessels (weight savings)
Mining (abrasion/corrosion)
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Standards
ASTM/ASME.......... A240 - UNS S32304
EURONORM...........1.4362 - X2 Cr Ni 23.4
AFNOR...................Z3 CN 23.04 Az
DIN.........................W. Nr 1.4362

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Corrosion Resistance
General Corrosion
Because of its high chromium content (23%) the corrosion resistance properties of 2304 are almost equivalent to those of 316L.

Localized Corrosion Resistance
The 23% chromium and 0.1% nitrogen additions explain why 2304 duplex stainless steel behaves much better than Alloy 316L when considering pitting and crevice corrosion resistance.

Stress Corrosion Resistance
Stress corrosion resistance test results in chloride containing aqueous solutions ((8ppm 02) PH =7, >1000 h, applied stresses higher than the yield strength) show that Alloy 2304 outperforms Alloys 304L and 316L, due to its high chromium additions and low nickel contents.

This is a typical feature of duplex stainless steels. Alloy 2205 performs still better than 2304 in similar conditions.

Other Corrosion Resistance Properties
Alloy 2304 duplex stainless steel successfully passes most of the standard IC test procedures such as ASTM, A262E, and C tests. Its corrosion rate in boiling nitric acid (65%) is higher than that of Alloy 316L. Due to its high yield strength, the alloy performs well in abrasion/corrosion applications.

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Chemical Analysis
Typical values (Weight %)

C Cr Ni Mo N Others
0.020 23 4 0.2 0.1 S = 0.001
PREN (Cr%) + 3.3 (Mo%) = 16 (N%) ≥ 24