Duplex Stainless Steel

Duplex stainless steel is a kind of stainless steel composed of ferrite and austenite

What is duplex stainless steel ?

Duplex stainless steel is a kind of stainless steel composed of ferrite and austenite. The ferrite content is about 50%, and the austenite content is about 50%. This kind of steel has the characteristics of both austenitic stainless steel and ferritic stainless steel. Compared with ferritic stainless steel, duplex stainless steel has higher plasticity and toughness and better intergranular corrosion resistance, while maintaining the brittleness and high thermal conductivity of ferritic stainless steel at 475 ℃.

Compared with austenitic stainless steel, it has higher strength, corrosion resistance, and stress resistance. Duplex stainless steel has excellent corrosion resistance, high strength, and easy to manufacture.

Their physical properties are between austenitic stainless steel and ferritic stainless steel, but closer to ferritic stainless steel and carbon steel. The corrosion resistance of duplex stainless steel is related to the content of Cr, Mo, and Ni.

DSS
Duplex Stainless Steel

Duplex stainless steel grades & types

The first type is a low alloy type, representing UNS S32304.

The steel contains no molybdenum, PREN: 24-25, and can be used instead of AISI 304 or 316 in stress corrosion resistance.

Our Steel Grades

SAF 2304 duplex stainless steel

The second type is medium alloy type, which represents UNS S31803. PREN: 32-33. 

It has corrosion resistance between 316L and 6% Mo + n austenitic stainless steel.

Our steel grades

saf 2205 duplex stainless steel

The third type is the high alloy type, which generally contains 25% Cr, Mo, and N, and some also contain copper and tungsten.

The standard grade is UNS S32550.

PREN: 38-39.

It has better corrosion resistance than 22% Cr duplex stainless steel.

Our steel grades

AISI 329 duplex stainless steel round bar

The fourth type is super duplex steel, containing high molybdenum and nitrogen.

The standard grade is UNS S32750, some also contain tungsten and copper.PREN > 40.

It can be used in a harsh environment and has good corrosion resistance and mechanical properties.

It is equivalent to super austenitic stainless steel.

Our steel grades

Equivalent of commonly used duplex stainless steel

 ChinaUSSwedenGermanyFranceJapan
Low alloy type00Cr23Ni4NUN23(SAF2304)SS23(SAF2304)W.Nr.1.4362UR35NDP11
Medium alloy type

00Cr18Ni5Mo3Si2

00Cr22Ni5Mo3N

UNS S31500

UNS S31803

SS2376(3RE60)

SS2377(SAF2205)

W.Nr.1.4417

W.Nr.1.4462

UR45N

DP1

DP8

High alloy type

0Cr25Ni5Mo2

00Cr25Ni7Mo3WCuN

UNS S32900

UNS S31260

SS2324(10RE51)

W.Nr.1.4460

W.Nr.1.4501

 

329J1

329J2L

Super Duplex Steel

00Cr25Ni7Mo4N

00Cr25Ni6Mo3CuN

UNS S32750

UNS S32550

SS2328(SAF2507)

W.Nr.1.4410

W.Nr.1.4507

 

UR47N+

UR52N+

Duplex stainless steel properties

Corrosion resistance

The corrosion resistance of duplex stainless steel is equal to that of CA6NM stainless steel and higher than that of marine stainless steel, such as 6% Mo austenitic stainless steel. All duplex stainless steels have better stress and corrosion resistance than 300 series austenitic stainless steel. Their strength is much higher than that of austenitic stainless steel, and they have good plasticity and toughness. It has excellent corrosion resistance and is also a nickel saving stainless steel.

Mechanical property

Duplex steel has excellent mechanical properties. It has high strength and fatigue strength, and its yield strength is twice that of 18-8 austenitic stainless steel. The elongation of the solid solution is 25%, and the toughness value (AK) is above 100J.

Weldability

It can be welded with austenitic stainless steel or carbon steel without preheating before welding and heat treatment after welding.

Thermal conductivity

Compared with austenitic stainless steel, it has higher thermal conductivity, smaller linear expansion coefficient, and higher heat transfer efficiency

Brittleness

This alloy steel still has the brittleness tendency of high chromium ferritic stainless steel, so it is not suitable to be used in working conditions above 300 ° C.

Chemical composition

The main alloying elements of dual-phase steel are Cr, Ni, Mo, and n.

Cr and Mo are ferrite elements, while Ni and N are austenite elements.

Some steels also contain elements such as Mn, Cu, and W.

Cr, Ni, and Mo can improve the corrosion resistance.

 CCrNiMoNPS
SAF 23040.03023.04.50.10.0400.040
SAF 22050.03021.0-23.04.5-6.52.5-3.50.08-0.20.0300.030
SAF 25070.03024.0-26.06.0-8.03.0-5.00.320.0350.020
3RE600.03018.0-19.04.25-5.252.0-2.50.05-0.10.0300.030
AISI 3290.08023.0-28.02.0-5.01.2-2.00.0400.030

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