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Definition Of Duplex Steels

Definition Of Duplex Steels


Duplex Stainless Steels Are Extremely Corrosion Resistant, Work Hardenable
Alloys. Their Microstructures Consist Of A Mixture Of Austenite And Ferrite
Phases. As A Result, Duplex Stainless Steels Display Properties Characteristic
Of Both Austenitic And Ferritic Stainless Steels. This Combination Of
Properties Can Mean Some Compromise When Compared With Pure Austenitic And Pure
Ferritic Grades.

Duplex Stainless Steels Are In Most Cases, Tougher Than Ferritic Stainless
Steels. Strengths Of Duplex Stainless Steels Can In Some Cases Be Double That
For Austenitic Stainless Steels.
Whilst Duplex Stainless Steels Are Considered Resistant To Stress Corrosion
Cracking, They Are Not As Resistant To This Form Of Attack As Ferritic
Stainless Steels. However, The Corrosion Resistance Of The Least Resistant
Duplex Stainless Steels Is Greater Than That For The Most Commonly Used Grades
Of Stainless Steels, I.E. 304 And 316.

Duplex Steels Are Also Magnetic, A Property That Can Be Used To Easily
Differentiate Them From Common Austenitic Grades Of Stainless.

Property Data Given In This Document Is Typical For Flat Rolled Products
Covered By Astm A240/A240m.
Astm, En Or Other Standards May Cover Products Sold. It Is Reasonable To Expect
Specifications In These Standards To Be Similar But Not Necessarily Identical
To Those Given In This Datasheet.


Corrosion Resistance :
When Adequately Heat Treated, The Materials, Depending On Their Composition,
Are Corrosion Resistant. For Chloride Pitting And Crevice Corrosion Resistance,
The Chromium-, Molybdenum- And Nitrogen Contents Are Very Important. Duplex
Stainless And Super-Duplex Steel Grades Have ARangeOfCorrosionResistance, Similar To The Range For Conventional Austenitic Stainless Steels
(E.G.V304 Or V316 To Vrc 254).

Heat Resistance :
The High Chromium Content Of Duplex Stainless Steels That Protects Against
Corrosion, Causes Embrittlement At Temperatures Over About300°C.
At Low Temperatures Duplex Stainless Steels Have Better Ductility Than The
Ferritic And Martensitic Grades. Duplex Grades Can Readily Be Used Down To At

Heat Treatment :
Duplex Stainless Steels Cannot Be Hardened By Heat Treatment. They Can However
Be Work Hardened. Solution Treatment Or Annealing Can Be Done By Rapid Cooling
After Heating To Around1100°C.

Applications :
Oil And Gas Exploration And Offshore Rigs
Oil And Gas Refining & Industry Equipment
Marine Environments, Desalination Plants, High Pressure Ro-Plant And Seawater
Pollution Control Equipment
Pulp & Paper Manufacturing
Chemical Process Industries, Heat Exchangers, Vessels, And Piping

Power Industry Fgd Systems, Utility And Industrial Scrubber Systems, Absorber
Towers, & Ducting
Mechanical And Structural Components, High Strength, Corrosion-Resistant Parts
Offshore Platforms, Heat Exchangers, Process And Service Water Systems,
Fire-Fighting Systems, Injection And Ballast

Water Systems
Exhaust Systems, Car Trim/Grilles, Road Tankers, Ship Containers, Ships
Chemical Tankers, Refuse Vehicles
Chemical Processing, Transport And Storage
Springs, Fasteners (Bolts, Nuts And Washers), Wire.

Duplex Characteristics & Benefits



High Inherent Corrosion Resistance

No Need To Protect By Surface Coating

Outstanding Pitting/Crevice Resistance

Ideal For Oil & Gas, Marine & Defence

Excellent Corrosion Resistance In Acids

Ideal For Chemical Industry

High Resistance To Stress Corrosion Cracking

Suitable For Highly Loaded Components In Chloride

High Resistance To Chloramines At High Temperature /

Suitable For Use In Safety Critical Supports In
Swimming Pools

High Mechanical Strength

Scope For Smaller Diameter And Hardware

Good Fatigue Strength

Applicable For Cyclically Loaded Assemblies

High Modulus Of Elasticity

Low Propensity To Stretch

* Available Specifications Of Duplex And Super Duplex Stainless Steel

Euro Specification

U.S Specification



En Astm1.4501 A135 F55

Uns S32760

Super Duplex Stainless Steel. 25% Chromium Super Duplex
(Austenitic/Ferritic) Steel With 0.75% Tungsten And Copper

Good Strength/Ductility Combined With High Corrosion

En Astm1.4462 A135 F51

Uns S31803

Duplex Stainless Steel. 22% Chromium Duplex
(Austenitic/ Ferritic) Steel (2205 Type)

Moderate/Good Strength And Good General Corrosion/
Stress Corrosion Cracking Resistance

En Astm1.4410 A135 F53

Uns S32750

Super Duplex Stainless Steel. 25% Chromium Copper-Free Super
Duplex (Austenitic/Ferri
tic) Steel (Also Known As 2507)

Good Strength And Ductility Combined With High Marine
Corrosion Resistance

En Astm1.4507 A135 F61

Uns S32550 Ferrinox® 255

Super Duplex Stainless Steel. High Performance 25%
Chromium Super Duplex (Austenitic/Ferritic) Steel With 1.75% Copper

Good Strength/Ductility Combined With High Resistance
To All Forms Of Corrosion


Fabrication Of All Stainless Steels Should Be Done Only With Tools
Dedicated To Stainless Steel Materials. Tooling And Work Surfaces Must Be
Thoroughly Cleaned Before Use. These Precautions Are Necessary To Avoid Cross
Contamination Of Stainless Steel By Easily Corroded Metals That May Discolour
The Surface Of The Fabricated Product.

Although Machinable, The High Strengths Of Duplex Stainless Steels Makes
Machining Difficult. As An Example, Machining Of 2205 Is Around 20% Slower Than
For 304.

Machining Can Be Enhanced By Using The Following Rules :
~ Cutting Edges Must Be Kept Sharp. Dull Edges Cause Excess Work
~ Cuts Should Be Light But Deep Enough To Prevent Work Hardening By Riding On
The Surface Of The Material.

~ Chip Breakers Should Be Employed To Assist In Ensuring Swarf Remains Clear Of
The Work
~ Low Thermal Conductivity Of Austenitic Alloys Results In Heat Concentrating
At The Cutting Edges. This Means Coolants And Lubricants Are Necessary And Must
Be Used In Large Quantities.

Weldability Duplex Stainless Steels Have Good Weldability. All
Standard Welding Processes Can Be Used. They Are Not Quite As Easily Welded As
The Austenitic Grades But Low Thermal Expansion In Duplex Grades Reduces
Distortion And Residual Stresses After Welding. The Recommended Filler Material
For 2205 Stainless Steel Is 2209


Duplex Stainless Steels Have Lower Nickel And Molybdenum Contents Than
Their Austenitic Counterparts Of Similar Corrosion Resistance.  Due To The
Lower Alloying Content, Duplex Stainless Steels Can Be Lower In Cost, Especially
In Times Of High Alloy Surcharges.  Additionally, It May Often Be Possible
To Reduce The Section Thickness Of Duplex Stainless Steel, Due To Its Increased
Yield Strength Compared To Austenitic Stainless Steel.  The Combination
Can Lead To Significant Cost And Weight Savings Compared To A Solution In
Austenitic Stainless Steels.

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