What is 2205 Duplex stainless steel and why do we use it?

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What is 2205 Duplex Stainless Steel and Why Do We Use it?

To begin, what is stainless steel?
2205 Duplex Stainless Steel

A: As the name suggests stainless steel is a stain/corrosion resistant metal and it’s corrosion resistance is due mainly to its chemical composition and namely the greater than 10% of chromium present in the composite of metals called an alloy.

There are five main types of stainless steel alloys,

Ferritic, Austenitic, Martensitic, Duplex and Precipitation Hardening.

Duplex stainless steel is approximately 50% ferritic and 50% austenitic offering the very best characteristics of strength and corrosion resistance.

Of the duplex grades, 2205 duplex stainless steel is the most widely used of its kind, found in industries where petrochemicals, oil, gas and chemicals are used due to the superior properties its microstructure contains. Only in recent years has 2205 become more readily available for construction hardware.

Able to withstand temperatures between -50 and 300 degrees Celsius, 2205 is composed of equal parts austenite and ferrite, leading to stronger, highly corrosion resistant steel that is also resistant to stress corrosion cracking and erosion.

Grade 2205 contains large amounts of chromium, molybdenum and nitrogen, and lower amounts of nickel, which further benefits the alloy by lowering cost and weight. 2205 is far superior to marine grade 316, in not only marine and tropical environments but in all common residential and industrial environments.

This is due to its low carbon content, which provides the steel with a high resistance to corrosion in the grain, as well as protection from pitting and crevicing. Its duplex properties make it less susceptible to stress cracking, though this also means it is unable to handle temperatures above 300 degrees Celsius for event short periods of time but not a consideration when used in construction applications of glass barriers.

The Facts

Material Properties

Mechanical Properties

2205 Duplex

316/316L

Tensile strength620 MPa min515Mpa min
Yield strength450 MPa min290 MPa min
Elongation25% min50% min
Brinell hardness293 HB max217HB max
Rockwell hardness31 HR C max95HRB max

Physical Properties

2205 Duplex

316/316L

Density7,805kg/m38,027kg/m3
Elastic Modulus450 MPa min200GPa
Mean coefficient of thermal expansion 0-100˚C13.7µm/m/˚C15.9µm/m/˚C

Composition


Grade

C%

Mn%

Si%

P%

S%

Cr%

Ni%

Mo%

N%

2205

0.030

2.00

1.00

0.030

0.020

21.0-23.0

4.5-6.5

2.5-3.5

0.08-0.20

316

0.08

2.0

0.75

0.045

0.03

16.0-18.0

10.0-14.0

2.0-3.0

0.1

Applicable Standards

  1. ASTM/ASME: A240 UNS S32205/S31803
  2. EURONORM: 1.4462 X2CrNiMoN 22.5.3
  3. AFNOR: Z3 CrNi 22.05 AZ
  4. DIN:W.Nr 1.4462

When it comes to fabricating grade 2205 the processes become more difficult, as greater capacity equipment is necessary than is required for the cold forming of most other austentic steels. Cutting speeds for machining and milling are usually at least 20% slower than grades 304 and 316

Care should be taken when stretch forming, spinning and deep drawing grade 2205, though welding can be undertaken, providing the following conditions are followed:

  • Heat input must be kept low before, during and after
  • The material must cool to below 150 degrees Celsius between passes
  • Filler grade 2209 must be used

Why use 2205 duplex stainless steel for glass balustrade and glass pool fence hardware?

Glass hardware requires a certain level of corrosion resistance to be present in the stainless steel used, more importantly one strong enough to withstand the extreme testing requirements of structural glass barriers to meet international building codes.

While 304 and 316/316L  grades of stainless steel were previously used for glass hardware, the strength characteristics of 304/316 stainless steel fall short when achieving the high requirement of test loads. Grade 2205 Duplex more easily passes load testing, and has become more commonly used grade to achieve high load capacity in structural balustrade and railings allowing the use of larger glass panel sizes than previously permitted using lesser grades.

The corrosion resistance properties are much better suited to coastal areas that if properly maintained can all but eliminate the risk of surface corrosion known as tea staining.

Key Points:

  • 2205 has twice the yield Strength of 304, 316 and 316L Stainless Steel
  • Demonstrates good fatigue stress
  • Superior resistance to corrosion cracking, crevice, pitting, erosion and general corrosion in severe environments when compared to 316, 316L and 304
  • Enables light weight yet incredibly strong components allowing more cost effective products
  • Stronger metal allows for thin wall investment castings offering more scope for new product designs

How can 2205 Duplex Stainless Steel be used in your business to give you the competitive edge?