How Is Duplex Stainless Steel Processed for Heavy Applications?

In this comprehensive guide, we’ll explore how duplex stainless steel is processed, its grades, physical properties, and applications.

Duplex stainless steel is a high-performance material widely used in demanding environments like oil & gas, chemical processing, marine, and structural engineering. Known for its excellent combination of mechanical strength and corrosion resistance, duplex stainless steel is specially processed and fabricated to meet the rigorous requirements of heavy-duty industrial applications.

What Is Duplex Stainless Steel?

Duplex stainless steel is a family of stainless steels that features a dual-phase microstructure—approximately equal parts austenite and ferrite. This balanced structure gives duplex steel its superior strength, corrosion resistance, and weldability compared to standard austenitic grades like 304 and 316.

Duplex Stainless Steel Composition

The composition of duplex stainless steel is carefully controlled to achieve its desirable properties. Here is the typical chemical composition:

Element	Typical Range (%)
Chromium (Cr)	21–25
Nickel (Ni)	4.5–7
Molybdenum (Mo)	2.5–4
Nitrogen (N)	0.1–0.3
Manganese (Mn)	≤ 2
Carbon (C)	≤ 0.03
Iron (Fe)	Balance

Key Properties of Duplex Stainless Steel

Property	Value
Tensile Strength	600–900 MPa
Yield Strength	450–650 MPa
Elongation	25–30%
Hardness (Brinell)	170–290 HB
Density	~7.8 g/cm³
Pitting Resistance Equivalent (PREN)	>35 (high resistance to pitting)

These values make duplex stainless steel twice as strong as austenitic grades and highly suitable for heavy structural components and pipelines.

How Duplex Stainless Steel Is Processed?

Melting & Casting

Duplex steel begins its life in an electric arc furnace, where it’s melted and refined to the precise composition. Molten duplex is then cast into slabs or billets for further processing.

Hot Working

Billets are hot rolled or forged into duplex stainless steel round bars, sheets, plates, and pipes. Controlled heat and pressure are applied to maintain uniform grain structure and eliminate impurities.

Heat Treatment

Post-rolling, duplex steel is annealed to:

Relieve internal stresses
Optimize its austenite-ferrite balance
Improve corrosion resistance

The standard annealing temperature ranges from 1040–1100°C, followed by rapid water or air cooling.

Cold Working & Finishing

For precision components or structural profiles, cold working (drawing, bending, machining) enhances strength and surface finish. Duplex stainless steel sheets and plates are then polished or surface-treated as needed.

Duplex Stainless Steel Forms & Grades

Product Type	Common Grades	Applications
Duplex Round Bar	UNS S31803 / S32205	Shafts, fasteners and structural supports
Duplex Steel Pipes	UNS S32205, S32750	Offshore platforms, chemical plants
Duplex Sheets & Plates	UNS S32304, S32760	Pressure vessels, tanks and marine components

Popular Grades of Duplex Stainless Steel:

UNS S31803 / S32205 (Standard Duplex)
UNS S32750 (Super Duplex)
UNS S32760 (Super Duplex)
UNS S32101 (Lean Duplex)

Each grade is selected based on its mechanical strength, corrosion resistance, and weldability for a given application.

Applications of Duplex Stainless Steel in Heavy Industries

Industry	Applications
Oil & Gas	Subsea pipelines, valves, pressure vessels
Marine & Shipbuilding	Propeller shafts, hull components, seawater cooling systems
Chemical Processing	Heat exchangers, reactors, caustic solution tanks
Structural Engineering	Load-bearing beams, bridges, heavy frames
Power Generation	Boiler components, cooling tower parts

Due to its resistance to chloride stress corrosion, duplex is often the material of choice for offshore and marine environments.

Duplex vs Austenitic Stainless Steel

Feature	Duplex Stainless Steel	Austenitic (304/316)
Strength	2x stronger	Moderate
Corrosion Resistance	Excellent (especially to pitting & SCC)	Good
Weldability	Requires expertise	Easier to weld
Cost	Slightly higher	Lower initial cost
Density	~7.8 g/cm³	~7.9 g/cm³

Looking for high-quality Duplex Stainless Products?

Steelco Metal is a leading Duplex Stainless Steel supplier in high-quality products, including:

Duplex round bars
Duplex stainless steel pipes
Sheets and plates for structural, industrial, and marine-grade applications.

We supply a wide range of duplex stainless steel grades and provide custom processing and cutting services to suit your project needs.

FAQ

What is duplex material?

Duplex is a stainless steel alloy with both austenitic and ferritic phases, offering superior strength and corrosion resistance, especially in chloride-rich environments.

What is the density of duplex stainless steel?

The typical density of duplex stainless steel is approximately 7.8 g/cm³, slightly lower than that of austenitic grades.

What are the most common duplex stainless steel grades?

The most widely used grades are UNS S31803 (standard duplex) and UNS S32750/S32760 (super duplex).

Is duplex stainless steel good for welding?

Yes, but it requires controlled heat input and expert welders to maintain the correct austenite-ferrite balance in the heat-affected zone.