Engineering Reference

Duplex stainless

A stainless family with a mixed austenitic-ferritic structure, giving roughly double the yield strength of 304.

Definition

The two-phase structure buys high strength plus excellent resistance to chloride stress-corrosion cracking — the failure mode that limits ordinary austenitic grades in warm chloride service.

It is also roughly twice as hard on tooling. The ferrite phase is abrasive and the austenite phase work-hardens, so a tool suffers wear and notching at the same time, from different mechanisms.

Common misuse

Treating duplex as a stronger 316 for machining purposes. It needs different tooling and feeds, and the standard stainless approach will not work.

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