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.
Super Duplex Stainless Steels
Centrifugally cast duplex stainless tubing offers the corrosion resistance of a 300 series 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 Alloys | 1A CD4MCu | 4A CD3MN | CD7MCuN | 1B CD4MCUN | DPX-1B MOD | 5A CE3MN |
|---|---|---|---|---|---|---|
| Similar Alloy | – | 2205 | Ferralium255® | – | – | 2507 |
| Industry Standards | ||||||
|---|---|---|---|---|---|---|
| ASTM Standard | A 890 A 995 | A 890 A 995 | – | A 890 A 995 | – | A 890 A 995 |
| UNS | J93370 | J92500 | S32550 | J93372 | – | J93404 |
| Similar DIN | – | 1.4462 | 1.4507 | – | – | 1.441 |
Chemical Composition
Spuncast centrifugal cast duplex grades are composed of the following chemical specifications:
| Spuncast Alloys | 1A CD4MCu | 4A CD3MN | CD7MCuN | 1B CD4MCUN | DPX-1B MOD | 5A CE3MN |
|---|---|---|---|---|---|---|
| Carbon max | 0.04 | 0.03 | 0.04 | 0.04 | 0.04 | 0.03 |
| Manganese max | 1 | 1.5 | 1.5 | 1 | 1.5 | 1.5 |
| Silicon max | 1 | 1 | 1 | 1 | 1.1 | 1 |
| Phosphorus max | 0.04 | 0.04 | 0.04 | 0.04 | 0.04 | 0.04 |
| Sulfur max | 0.04 | 0.02 | 0.03 | 0.04 | 0.04 | 0.04 |
| Chromium | 24.5-26.5 | 21.0-23.5 | 24.0-27.0 | 24.5-26.5 | 24.5-26.5 | 24.0-26.0 |
| Nickel | 4.75-6.00 | 4.5-6.5 | 4.5-6.5 | 4.7-6.0 | 4.5-6.0 | 6.0-8.0 |
| Molybdenum | 1.75-2.25 | 2.5-3.5 | 2.9-4.0 | 1.7-2.3 | 2.5-4.0 | 4.0-5.0 |
| Other | Cu2.75-3.25 | Cu1.00 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 Alloys | 1A CD4MCu | 4A CD3MN | CD7MCuN | 1B 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 Values | 235 typical | 235 typical | 235 typical | 235 typical | 235 typical | 218 typical |
| Density lbs/in | 0.28 | 0.28 | 0.28 | 0.28 | 0.28 | 0.28 |
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.