Forta FDX 27
ASTM FDX 27 / UNS S82031

General characteristics

Ferritic-austenitic stainless steels also referred to as duplex stainless steels, combine many of the beneficial properties of ferritic and austenitic steels. Due to the relatively high content of chromium and nitrogen, these steels offer good resistance to localized and uniform corrosion.
The new FDX product family exhibits a unique combination of high strength and substantially improved formability utilizing Transformation Induced Plasticity (TRIP). Characteristic properties are:

• Increased formability compared to other duplex grades
• High mechanical strength
• Good resistance to uniform corrosion
• Good resistance to pitting and crevice corrosion
• High resistance to stress corrosion cracking and corrosion fatigue
• Good abrasion and erosion resistance
• Good fatigue resistance
• High energy absorption
• Low thermal expansion
• Good weldability

Typical applications

The FDX family provides a totally new stainless steel solution for applications where the formability of other duplex grades is not sufficient or limits the design efficiency. Examples of potential applications are given below:

• Plate heat exchangers
• Flexible pipes
• Pump components
• Components for automotive industry
• Components for structural design
• Domestic heater piping
• Central heating piping

 

Product forms, available sizes and finishes

Flat

Product typeFinishesThicknessWidth
Cold rolled coil2E, 2H0,40-5,0036-1500
Cold rolled sheet2E0,40-5,0036-1500
Chemical composition

 

 

CMnCrNiMoNOther
Typical 
ASME II A SA-240 ≤0.05≤2.5019.0-22.02.0-4.00.60-1.400.14-0.24
ASTM A240 ≤0.05≤2.5019.0-22.02.0-4.00.60-1.400.14-0.24
EN 10088-3 0.015-0.0301.05-1.3019.90-20.302.65-3.001.15-1.300.180-0.210Si:0.30-0.50 Cu:0.30-0.50
Mechanical properties

 

 

StandardRp0.2Rp1.0RmElongationImpact strengthRockwellHBHV
 MPaMPaMPa%J
Product type: Cold rolled coil and sheet
Typical (thickness 1 mm)650850
ASME II A SA-240 ≥ 400 ≥ 650 ≤ 31HRC ≤ 290
ASTM A240 ≥ 500 ≥ 650 ≤ 31HRC ≤ 290

1)Elongation according to EN standard:
A80 for thickness below 3 mm.
A for thickness = 3 mm.
Elongation according to ASTM standard A2” or A50.

Corrosion resistance

The duplex grades provide in general a wide range of corrosion resistance in various environments. However, as the increased formability of FDX 27™ is based on the TRIP-effect (Transformation Induced Plasticity), where the metastable austenite transforms partly into martensite during cold-forming or mechanical treatments like grinding or shot blasting, there is a risk that the corrosion resistance decreases somewhat in those affected areas. All investigations and data presented in this data sheet are from un-deformed flat specimens.

Pitting corrosion resistanceCrevice corrosion resistance
PRECPTCCT
027±3

PRE Pitting Resistant Equivalent calculated using the formula: PRE = %Cr + 3.3 x %Mo + 16 x %N
CPT Corrosion Pitting Temperature as measured in the Avesta Cell (ASTM G 150), in a 1M NaCl solution (35,000 ppm or mg/l chloride ions).
CCT Critical Crevice Corrosion Temperature is the critical crevice corrosion temperature which is obtained by laboratory tests according to ASTM G 48 Method F

 

 

Physical properties

 

 

DensityModulus of elasticityThermal exp. at 100 °CThermal conductivityThermal capacityElectrical resistanceMagnetizable
kg/dm3GPa10-6/°CW/m°CJ/kg°CµΩm
7,720512,514,55000,8Yes
Fabrication


Cold forming
The high proof strength of duplex stainless steel compared to austenitic and ferritic stainless steel can impose some differences in forming behavior depending on chosen forming technique. The impact of the high strength varies for different forming techniques. Common for all is that the estimated forming forces will be higher than for the corresponding austenitic and ferritic stainless steel grades. This effect will usually be lower than expected from just the increase in strength since the choice of duplex stainless steel is often associated with down gauging.
FDX 27™ have excellent formability properties in comparison to other duplex stainless steels such as LDX 2101® and 2304 and close to standard austenitic stainless steels such as 4307 and 4404. The TRIP effect offers a balanced work hardening rate resulting in an enhanced uniform elongation and higher work hardening ratio at large (plastic) deformations in comparison to other duplex grades. These remarkable mechanical properties make the FDX grades more suitable for manufacturing of components with stretch forming as the primary forming operation. As for most of the duplex stainless steels, the Lankford values (r-values) are less than 1.0 in all directions but always larger than 0.4.
Figure 1 shows the elongation versus the proof strength for different types of stainless steels, illustrating that the FDX grades form a type of group with a new and unique combination of properties.



Figure 1

The key advantage of FDX 27™ compared to other duplex grades is that they are more adaptable to various forming processes since they have far better formability. For example, components to be formed predominantly by deep drawing can almost be designed as those made in standard austenitic stainless steels with good results. Moreover, physical try-outs verify that the FDX grades are suitable for forming intensive component such as heat exchanger plates. Outokumpu, Avesta Research Centre can support customers in detailed computer analyses of the impact on the forming process of the FDX grades.


Welding

Duplex steels including FDX 27™ generally have good weldability and can be welded using most of the welding methods used for austenitic stainless steels.

Standards & approvals

 

 

StandardDesignation
ASME SA-240M Code Sect. II. Part AUNS S82031
ASTM A240/A240MUNS S82031
EN 10088-31.4637