FabDigitFabDigit

Duplex Stainless Steel

Duplex stainless steels are balanced — 22–25 % chromium, 4–7 % nickel, up to 4 % molybdenum and 0.15–0.3 % nitrogen — to solidify as roughly half ferrite and half austenite. The mixed structure gives about twice the yield strength of 316L (2205: 450 MPa minimum against 170) together with far better resistance to chloride pitting and to the stress-corrosion cracking that limits the 300 series, at a lower nickel content. They are magnetic, weldable with the right filler, and confined to about −50 to 300 °C in service.

Popular duplex stainless grades

Compare in the explorer
GradeYield, MPaTensile, MPaDensity, g/cm³MachinabilityWeldabilityBest for
22055407907.8PoorVery goodThe default duplex; seawater, brine, chemical plant
25076208807.8PoorGoodSuper-duplex for hot seawater; 550 MPa yield
23044606807.75FairVery goodLean duplex; 316L corrosion at twice the strength
21015307507.8FairVery goodLow-nickel lean duplex for tanks and rebar
2556108307.81PoorVery goodCopper-bearing super-duplex for sulfuric acid
Zeron 1006208307.8PoorGoodOffshore piping and castings; PREN above 40
S327078009807.8PoorGoodHyper-duplex, PREN above 45

All 56 duplex stainless grades

Choose duplex stainless for

Seawater and brine piping, pump and valve bodies, heat-exchanger tubing, chemical and pulp-mill vessels, storage tanks, umbilicals, bridge and pool structures near salt — anywhere 316L pits or cracks, or where twice its strength lets the wall get thinner. 2205 for most of it, 2507 or Zeron 100 when the chloride service is hot.

Look elsewhere when

The part runs above about 300 °C (sigma phase and 475 °C embrittlement take the toughness — 316L, 310S or a nickel alloy) or below about −50 °C (austenitic grades stay tough to cryogenic temperatures), the environment is a hot reducing acid or wet chlorine (Hastelloy C276, 254 SMO), the design needs a non-magnetic grade, the part is deep-drawn or spun (304), or corrosion is mild and 304 does the job with easier machining and forming.

Yield strength against max service temp, Duplex & super-duplex among every stainless steel grade

No materials in view have both of these properties.

Loading the library…

Duplex stainless by application

Seawater and brine systems
2205 for piping, pumps and heat exchangers in seawater below about 40 °C; 2507 or Zeron 100 where the water is hot, chlorinated or stagnant enough for crevice attack. Cast pump and valve bodies use CD3MN or CE3MN.
Pressure vessels and tanks
2205 plate lets a vessel wall come down 30–40 % against 316L at the same design pressure; 2304 and 2101 for storage tanks, water tanks and digesters where the chemistry is mild but chloride stress cracking rules out 304.
Oil and gas and sour service
2205 for flowlines and manifolds within the NACE MR0175 limits; 2507 and Zeron 100 for umbilicals, downhole tubing and injection systems with higher chloride and hydrogen-sulfide loading.
Structures near salt
2205 and 2304 for bridge hangers, swimming-pool structure and coastal architecture, where 304 and 316L have stress-cracked; the strength allows lighter sections.

Working with duplex stainless

Machining
Harder work than 316L — the high yield strength and nitrogen make 2205 cut about 20 % slower, and super-duplex slower still — with tough chips and heavy tool pressure. Rigid setups, sharp positive carbide with a chip breaker, moderate speed and a steady feed; drilling and tapping want plenty of coolant, because the material springs back on the tool.
Welding
Welds well by TIG, MIG, SMAW and SAW, but the phase balance has to be kept: over-alloyed 2209 filler for 2205 and 2594 for 2507 and Zeron 100, no autogenous welds without a post-weld anneal, heat input of about 0.5–2.5 kJ/mm, interpass below 150 °C (100 °C for super-duplex) and nitrogen-bearing shielding gas for the root. Weld ferrite should measure 30–70 %. No preheat, no post-weld heat treatment.
Heat treatment and service limits
Not hardenable. Solution-anneal at 1,020–1,100 °C (2507 slightly hotter) and water-quench to lock in the 50 / 50 balance; anything slower through 700–950 °C forms sigma phase and destroys toughness and corrosion resistance. Service stays below about 300 °C — 250 °C for super-duplex — and above −50 °C.
Forming
Bends and rolls with roughly twice the force of 304 and more springback, so inside radii are larger. Deep drawing and spinning are limited; heavily cold-formed parts may need a solution anneal to restore toughness and corrosion resistance.

Other stainless steel series

Duplex Stainless Steel — frequently asked

What is duplex stainless?

Duplex stainless steels are balanced — 22–25 % chromium, 4–7 % nickel, up to 4 % molybdenum and 0.15–0.3 % nitrogen — to solidify as roughly half ferrite and half austenite. The mixed structure gives about twice the yield strength of 316L (2205: 450 MPa minimum against 170) together with far better resistance to chloride pitting and to the stress-corrosion cracking that limits the 300 series, at a lower nickel content. They are magnetic, weldable with the right filler, and confined to about −50 to 300 °C in service.

Which grade of duplex stainless should I use?

2205 unless there is a reason not to: it is the duplex grade every mill, filler supplier and design code covers, with a pitting resistance number around 35 that handles brine, ambient seawater, organic acids and most chemical-plant duty. 2507 (25 % Cr, 4 % Mo, 0.28 % N, PREN above 40) is the super-duplex for hot seawater, desalination, umbilicals and sour wells, with 550 MPa yield. Zeron 100 adds copper and tungsten to the same base for offshore piping and pump castings; 255 (Ferralium) uses copper for sulfuric-acid service. At the lean end, 2304 (no molybdenum) and 2101 (manganese replacing much of the nickel) match 316L or 304 in corrosion at twice the strength, for tanks, rebar and structural sections. Cast equivalents are CD3MN for 2205, CE3MN for 2507 and CD3MWCuN for Zeron 100.

Which grade of duplex stainless is the strongest?

S32707 has the highest yield strength in the series at 800 MPa; 1.4658 follows at 750 MPa. Values are for each grade's default condition.

Which grade of duplex stainless is easiest to machine?

1.4669 (machinability fair, 45/100), then 1.4655 (42/100).

Is duplex stainless heat-treatable?

No. These grades are strengthened by cold work and softened by annealing, not by heat treatment; the conditions are listed on each grade page.

2205 or 2507?

2205 for ambient seawater and brine, chemical plant, tanks and structure: its critical pitting temperature in the standard ferric-chloride test is around 35 °C, and every fabricator knows it. 2507 raises that to about 70 °C or more and the yield strength from 450 to 550 MPa, which is what hot seawater, desalination brine, chlorinated cooling water and sour wells need. It costs more, has a tighter welding window and is limited to about 250 °C in service, so it is specified only when 2205 would pit.

Can I use 2205 to make the part thinner than 316L?

Yes — that is usually why it is chosen. With a minimum yield of 450 MPa against 170 for 316L, pressure vessels, tanks and tubing designed to code come out 30–40 % thinner and lighter, with better chloride pitting resistance and far less risk of the stress-corrosion cracking that troubles 316L above about 60 °C. Three things change: the service temperature must stay under about 300 °C, the part will be magnetic, and welded joints need 2209 filler with controlled heat input.