Super Duplex Stainless Steels

Centrifugally cast duplex stainless tubing offers the corrosion resistance of a 300 series at a lower cost

Duplex stainless steels are known for excellent corrosion resistance and high strength. And because of their chemical and mechanical properties, they can often minimize weaknesses at a lower cost. 

Advantages: 

  • Improved strength
  • Corrosion resistance
  • High toughness and ductility
  • Long-lasting
  • Increased heat transfer

The Duplex Structure

Duplex stainless steels are referred to as “duplex” because their microstructure consists of approximately equal combinations of ferrite and austenite. 

Using duplex stainless steels for a centrifugally cast metal tube creates a yield strength that is often twice as strong as the regularly austenitic or ferritic stainless. There’s no need to choose one over the other.

Super duplex stainless steel is fundamentally the same as duplex stainless steel. However, super duplex grades will possess more of each element, which can increase certain characteristics. 

Both have a formula that provides a corrosion resistance comparable to a 300 series stainless. However, there is far less nickel used than in the 300 series, and, therefore, costs less in general.

Centrifugally Cast Duplex Grades: Cast Equivalent to 2205 Stainless Steel and 2507 Stainless Steel

Spuncast centrifugally casts high-quality, easily repeatable duplex grade products that can meet the specs of specific industries. The results stand up to the mechanical properties of wrought 2205 and 2507 steels. 

Industry Standards

Spuncast centrifugal cast duplex grades equate to the following industry standards:

Spuncast Alloys1A
CD4MCu
4A
CD3MN
CD7MCuN1B
CD4MCUN
DPX-1B
MOD
5A
CE3MN
Similar Alloy2205Ferralium255®2507
Industry Standards
ASTM StandardA 890
A 995
A 890
A 995
A 890
A 995
A 890
A 995
UNSJ93370J92500S32550J93372J93404
Similar DIN1.44621.45071.441

Chemical Composition

Spuncast centrifugal cast duplex grades are composed of the following chemical specifications:

Spuncast Alloys1A
CD4MCu
4A
CD3MN
CD7MCuN1B
CD4MCUN
DPX-1B
MOD
5A
CE3MN
Carbon max0.040.030.040.040.040.03
Manganese max11.51.511.51.5
Silicon max11111.11
Phosphorus max0.040.040.040.040.040.04
Sulfur max0.040.020.030.040.040.04
Chromium24.5-26.521.0-23.524.0-27.024.5-26.524.5-26.524.0-26.0
Nickel4.75-6.004.5-6.54.5-6.54.7-6.04.5-6.06.0-8.0
Molybdenum1.75-2.252.5-3.52.9-4.01.7-2.32.5-4.04.0-5.0
OtherCu2.75-3.25Cu1.00 max
N.10-.30
Cu 1.5-2.5
N .10-.25
CU 2.7-3.3
N .10-.25
Cu 1.3-3.0
N .18-.26
N .10-.30

Mechanical Properties

Spuncast centrifugal cast duplex grades have the following mechanical properties:

Spuncast Alloys1A
CD4MCu
4A
CD3MN
CD7MCuN1B
CD4MCUN
DPX-1B
MOD
5A
CE3MN
Tensile (min) – KSI (MPa)100(690)90(620)105(725)100(690)110(758)100(690)
Yield (min) – KSI (MPa)70(485)60(415)70(485)70(485)70(485)75(515)
Elongation (2″ min)16%25%20%16%20%18%
Brinell Hardness (10mm – 3000Kg -) Typical Values235 typical235 typical235 typical235 typical235 typical218 typical
Density lbs/in0.280.280.280.280.280.28

Secondary Processes and Duplex Stainless Steel Tubing

The quality of a duplex grade stainless steel cast product is further enhanced by using the appropriate secondary processes.

Heat Treating

Heat treating further improves the strength, hardness, toughness, and corrosion resistance of your metal. Your metallurgist will select the most appropriate heat treatment for your material. For duplex stainless steel, Spuncast offers the following heat treatments:

  • Quenching and tempering to create better balance and stability.
  • Annealing for restoring ductility and allowing additional processing without cracking.

CNC Machining

Once cast, your product can be machined to quickly and selectively remove unneeded metal. CNC machining is a finishing process that works especially well with most metals in a centrifugal casting environment because it:

  • Requires fewer steps to deliver far more complexity
  • Creates highly repeatable components accurately
  • Adds improved performance to the design
  • Eliminates unnecessary waste

Typical Duplex Grade Applications

Because of its good engineering performance, an increasing number of industries request duplex grade steel that can stand up to specific environmental conditions. That includes ones with corrosive environments such as oil and gas, water treatment, and others using industrial operational equipment.

The industries that typically use duplex grades are: 

Water treatment

Requires improved resistance to chloride pitting and crevice corrosion 

Food processing

Needs to be hygienic and clean while being easy to weld and have excellent resistance to stress corrosion cracking

Medical

Needs enhanced hardness, yield strength, excellent corrosion resistance, and good biocompatibility

Spuncast Duplex Grades 

Spuncast centrifugally cast duplex stainless steels such as CD4MCu (J93370) are popular options with our customers. Because it has high mechanical strength, it allows us to reduce both weight and cost because it can be produced as a thinner tube. 

It’s also a material we have a lot of experience with because we’ve been manufacturing it for over 30 years! 

FAQ

Duplex stainless steels are two-phase alloys containing essentially equal parts ferritic and austenitic in their microstructure, which provides the corrosion resistance of austenitic stainless steels with greater strength.

Super duplex stainless steel is fundamentally the same as duplex stainless steel. However, super duplex grades will possess more of each element, which can increase certain characteristics.

Both have a formula that provides a corrosion resistance comparable to a 300 series stainless. However, there is far less nickel used than in the 300 series, and, therefore, generally costs less.

Centrifugal casting, investment casting, and wrought methods can each create super duplex stainless steel. The most appropriate foundry is chosen based on the product’s needs and what their processes provide to the result.

The excellent engineering performance of super duplex steel has led to an increasing number of industries requesting it when specific environmental conditions are involved. That includes industries with corrosive environments, such as oil and gas, water treatment, and others using industrial operational equipment.

Though highly resistant to rust, even duplex stainless steel can rust under certain environmental conditions. However, it is a material specifically designed to provide better corrosion resistance, particularly chloride stress corrosion and chloride pitting corrosion.

Duplex stainless steels have about two times the strength of austenitic stainless steels with a much better resistance to corrosion, especially pitting, crevice corrosion and stress corrosion cracking. They also have an improved toughness and ductility when compared to ferritic stainless steel.

When properly heat treated according to the specification, duplex stainless steel castings can have equal or better density than their forged counterparts.

Spuncast centrifugally casts high-quality, easily repeatable duplex grade products that can meet specific industries’ specs. The results stand up to the mechanical properties of forged 2205 and 2507 steels.

Take the Spuncast Challenge

We’re up to the challenge of meeting your specs and beating the competition on overall costs.

Send us the specs and application needs on your next project requiring PH steel. We’ll provide a quote and full metallurgical makeup to show how we can produce a stronger, more cost-effective tube for your part.

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