Duplex stainless steels have a microstructure of nearly equal proportions of austenite and ferrite. This microstructure ensures that they are much more resistant to stress corrosion cracking than conventional austenitic stainless steels such as 304L/1.4307 or 316L/1.4404.

Duplex stainless steels are also tough in gauges up to 40mm and can be successfully welded in these thick gauges. This is in contrast to common ferritic stainless steels, which tend to be brittle in thick gauges, particularly if welded, which limits their use to applications requiring gauges up to 3mm. Duplex stainless steels remain tough between -20°C or lower, depending on the gauge, and 300°C.

Corrosion Resistance:
The adjacent figure shows the Pitting Resistance Equivalent (PRE) of the duplex stainless steels compared to the conventional austenitic stainless steels. The PRE is a measure of the pitting resistance in chloride environments.

In most environments, S32001/1.4482 has a similar corrosion resistance to 304L/1.4307, while S32304/1.4362 has a similar corrosion resistance to 316L/1.4404.

S32205/1.4462 has significantly better corro - sion resistance than 316L/1.4404 in most environments. It thus stands to reason that S32001/1.4482 can be seen as a 304L/1.4307 substitute, while S32304/1.4362 can be seen as a 316L/1.4404 substitute.

Strength:
The specification 0.2% Proof Stress of duplex stainless steels is about double that of conventional austenitic stainless steels. This often allows down gauging in the design (dependant on buckling and Young's Modulus limitations), with associated cost benefits.

Applications:
S32001/1.4482 has good strength, toughness, corrosion resistance and resistance to stress corrosion cracking. Applications include process and storage tanks, ducting and structural applications.

S32001/1.4482 is also suitable for pipe supports, walkways, cable racking, strapping, clamps, etc. in aggressive environments. S32304/1.4362 has a higher chromium and nitrogen content than S32001/1.4482. The resultant composition gives the steel much improved corrosion resistance in many aggressive environments. The higher chromium and nitrogen contents ensure more resistance to pitting and crevice corrosion in chloride containing media and chemical environments such as sulphuric acid compounds as well as phosphoric and acetic acids. The lower rate of general corrosion in mildly corrosive environments gives the steel good atmospheric corrosion resistance in polluted marine atmospheres.

S32205/1.4462 is a highly suitable material for service in environments containing chlorides and hydrogen sulphide such as marine environments and the oil and gas extraction and processing industries. Typical appli - cations also include the chemical industry (processing, transport and storage, e.g. pressure vessels, tanks and piping), the pulp and paper industry (digesters and liquor tanks) and the mining industry. S32205/1.4462 has thus found widespread use in production tubing and flowlines for the extraction of oil and gas from sour wells, in refineries and in process solutions contaminated with chlorides. S32205/1.4462 is also particularly suitable for heat exchangers where chloride bearing water or brackish water is used as the cooling medium.