Think of duplex stainless steel as a “special forces soldier”—highly capable yet temperamental, requiring precise command to unleash its full potential.

Core Requirements (Key to Mastering It)

Professional welding is paramount.

Specialized Welding Rods: Must be welded using specialized rods that are “higher grade” than the material itself.

Temperature Control: Welding should be like “simmering over low heat”—neither too slow (insufficient heat) nor too intense (excessive heat), or its internal structure will be compromised.

Avoid Critical Temperature Range: Remember that 300°C to 1000°C is its “deadly zone.” Prolonged exposure at these temperatures causes embrittlement and increased corrosion susceptibility. Thus, it is unsuitable for equipment operating continuously at high temperatures (e.g., boiler liners).

Primary Limitations (Its Weaknesses)

Poor Cryogenic Performance: Unlike standard austenitic stainless steels (e.g., 304), it lacks cryogenic toughness and is unsuitable as a core material for cryogenic equipment handling liquid nitrogen, liquid oxygen, etc.

Susceptibility to strong acids and hydrogen:

In highly reducing acids like hydrochloric acid or dilute sulfuric acid, its performance is only marginally better than 316L.

In environments with cathodic protection or hydrogen sulfide, it readily absorbs hydrogen and becomes brittle (hydrogen embrittlement).

High strength and toughness make machining difficult: Due to its exceptional strength, cutting and bending are more challenging than with standard stainless steels, requiring specialized equipment.

The continuous operating temperature range of duplex stainless steel is -50°C to 250°C. The lower limit is determined by the brittle transition temperature of the stainless steel, while the upper limit is determined by the brittle transition temperature of 475°C. The upper limit temperature must not exceed 300°C.

Duplex stainless steel needs to be cooled quickly after solution treatment. Slow cooling will cause the precipitation of brittle phases, thereby reducing toughness and local corrosion resistance of the steel.

Proficiently master the welding rules of duplex stainless steel. The safe use of duplex stainless steel equipment is closely related to the correct mastery of welding technology. Some equipment failures are usually related to welding.

In order to ensure the best overall performance, the phase ratios in duplex stainless steels need to be controlled. If the two-phase ratio is out of balance, single-phase ferrite is easily formed in the weld heat-affected zone (HAZ), which may lead to stress corrosion cracking sensitivity in certain media.

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