Forta SDX 100
EN 1.4501, ASTM UNS S32760

General characteristics

Austenitic-ferritic stainless steel also referred to as duplex stainless steels, combine many of the beneficial properties of ferritic and austenitic steels. Due to the high content of chromium and nitrogen, and often also molybdenum, these steels offer good resistance to localised and uniform corrosion. The duplex microstructure contributes to the high strength and high resistance to stress corrosion racking. Duplex steels have good weldability. All duplex grades have the maximum service temperature restricted to 250 or 325°C according to EN10028-7 or ASME II-D 2007 respectively. Outokumpu produces a range of duplex grades, LDX 2101®, 2304, LDX 2404®, 2205, 4501 and 2507. The properties of 4501 is in general terms very similar to those of 2507. Grade 4501 is delivered if specified.

Typical applications

• Pulp and paper industry
• Desalination plants
• Flue-gas cleaning
• Cargo tanks and pipe systems in chemical tankers
• Seawater systems
• Firewalls and blast walls on offshore platforms
• Components for structural design
• Storage tanks
• Pressure vessels
• Heat exchangers
• Water heaters
• Rotors, impellers and shafts


Product forms, available sizes and finishes


Product typeFinishesThicknessWidth
Quarto plateHot rolled white5,00-60,00≤ 3200
Chemical composition

The typical chemical composition for this grade is given in the table below, together with composition limits given for this grade according to different standards. The required standard will be fully met as specified on the order.


TypicalForta SDX 1000.0225. W:0.70
ASTM A240/A240MUNS S32760<0.030<124.0-26.06.0-8.03.0-4.00.20-0.30Si:<1 P:<0.030 S:<0.010 Cu:0.50-1 W:0.50-1
EN 10088-21.4501<0.030<217.5-19.58.5-11.53.0-4.00.12-0.22Si:<1 P:<0.045 S:<0.015 Cu:0.50-1 W:0.50-1
Mechanical properties

The duplex stainless steels have much higher mechanical strength compared to standard stainless steels. If the high strength of the duplex grades can be utilised, down gauging can be done in many applications leading to cost efficient solutions. The allowable design values may vary between product forms. The appropriate values are given in the relevant specifications.

The product types P= hot rolled plate, H=hot rolled strip and C=cold rolled coil and strip.


StandardGradeRp0.2Rp1.0RmImpact strengthRockwellHBHV
Product type: Hot rolled quarto plate
Typical (thickness 15 mm)Forta SDX 100580830260

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

Uniform corrosion Uniform corrosion occurs when all, or at least a large section, of the passive layer is destroyed. This typically occurs in acids or in hot alkaline solutions. The influence of the alloy composition on the resistance to uniform corrosion may vary significantly between different environments; chromium is essential for ensuring the passivity of stainless steels, nickel helps reduce the corrosion rate of depassivated steel, molybdenum enhances passivity (except for strongly oxidising environments, such as warm concentrated nitric acid) and copper has a positive effect in the presence of reducing acids such as dilute sulphuric acid. In an environment with constant temperature and chemical composition, uniform corrosion occurs at a steady rate. This rate is often expressed as a loss of thickness per unit time, e.g. mm/y. Stainless steels are normally considered to be resistant to uniform corrosion in environments in which the corrosion rate does not exceed 0.1 mm/y. Impurities may drastically affect the corrosivity of acid solutions. For guidance on materials selection in a large number of environments capable of causing uniform corrosion, the tables and iso-corrosion diagrams in Outokumpu Corrosion Handbook may be consulted. Pitting and Crevice corrosionChloride ions in a neutral or acidic environment facilitate local breakdown of the passive layer. As a result, pitting and crevice corrosion can propagate at a high rate, causing corrosion failure in a short time. Since the attack is small and may be covered by corrosion products or hidden in a crevice, it often remains undiscovered until perforation or leakage occurs. Resistance to pitting corrosion is determined mainly by the content of chromium, molybdenum and nitrogen in the stainless steel. This is often illustrated using the pitting resistance equivalent (PRE) for the material, which can be calculated using the formula: PRE = %Cr + 3.3 x %Mo + 16 x %N. The PRE value can be used for rough comparisons of different materials. A more reliable means, however, is to rank the steel according to the critical pitting temperature (CPT) of the material. There are several different methods available, for example ASTM G 150 that uses the Avesta Cell with a 1M NaCl solution (35 000 ppm or mg/l chloride ions). The CPT-values are shown in the table below. Higher contents of chromium, molybdenum and nitrogen also enhance the crevice corrosion resistance of the stainless steel. Typical values of the critical crevice corrosion temperature (CCT) in 6% FeCl3 + 1% HCl according to ASTM G48 Method F are included in the table below. The CPT and CCT values vary with product form and surface finish, the values given are for ground surfaces. Both ASTM G150 and G48 are methods for ranking the relative pitting or crevice corrosion resistance for the different stainless steels but they do not give the maximum temperature for using these alloys in real service environments.

CPT according to ASTM G150 Wet ground to 320 grit CPT according to ASTM G48 E Dry ground to 120 grit CCT according to ASTM G48 F Dry ground to 120 grit

Pitting corrosion resistanceCrevice corrosion resistance

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

The physical properties at room temperature are shown in the table below. Data according to EN10088 or EN10095.


DensityModulus of elasticityThermal exp. at 100 °CThermal conductivityThermal capacityElectrical resistanceMagnetizable


Duplex stainless steel is suitable for all forming processes available for stainless steel. The high proof strength compared to austenitic and ferritics stainless steel can impose some differences in forming behaviour depending on chosen forming technique, such as an increased tendency to springback. This point is particularly relevant to forming of any high strength steel. If the forming process is not already decided, it is certainly possible to choose the most suitable one for duplex grades. Moreover, an excellent interplay between high proof strength, work hardening rate and elongation promote the duplex grades for light weight and cost-efficient applications with complex shapes. 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. It is important to consider that duplex stainless steel may also be more demanding for the tool materials and the lubricant. Also in this case attention should be given to the down gauging.
Duplex steels are generally more demanding to machine than conventional austenitic stainless steel such as 4404, due to the higher hardness. The machinability can be illustrated by a machinability index, as illustrated in below figure. This index, which increases with improved machinability, is based on a combination of test data from several different machining operations. It provides a good description of machinability in relation to 4404. More information can be found in the machining guidelines which are available for each duplex grade.

Duplex steels generally have good weldability and can be welded using most of the welding methods used for austenitic stainless steel:

  • Shielded metal arc welding (SMAW)
  • Gas tungsten arc welding  TIG(GTAW)
  • Gas metal arc welding MIG (GMAW)
  • Flux-cored arc welding (FCW)
  • Plasma arc welding (PAW)
  • Submerged arc welding (SAW)
  • Laser welding
  • Resistance welding
  • High frequence welding

Due to the balanced composition, the heat-affected zone obtains a sufficiently high content of austenite to maintain a good resistance to localised corrosion. The individual duplex steels have slightly different welding characteristics. For more detailed information regarding the welding of individual grades, see the Outokumpu Welding Handbook or contact Outokumpu. The following general instructions should be followed:

  • The material should be welded without preheating
  • The material should be allowed to cool between passes, preferably to below 150°C.
  • To obtain good weld metal properties in as welded condition, filler material shall be used.
  • The recommended arc energy should be kept within certain limits to achieve a good balance between ferrite and austenite in the weld. The heat input should be adapted to the steel grade and be adjusted in proportion to the thickness of the material to be welded.
  • Post-weld annealing after welding with filler is not necessary.
  • To ensure optimum pitting resistance when using GTAW and PAW methods, an addition of nitrogen in the shielding/purging gas is recommended.
Outokumpu 2507 is more prone to inter-metallic precipitation in the weld metal. For this reason the heat input should be below 1-1.5 KJ/mm and the interpass temperature should not exceed +100°C. If welding is done from only one side and the root side will be exposed to corrosive media, it is important to make the root thick and following beads thin with low heat input. This minimises the amount of detrimental sigma phase in the root. For SAW, the wire should not exceed Ø2.4 mm to facilitate low heat input welding.

Suitable filler for welding Outokumpu 2507 is ISO 25 9 4 NL.

Suitable filler for welding Outokumpu 4501 is ISO 25 9 4 NL.


Standards & approvals

Outokumpu produce and certify materials to most international and national standards. Work is continuously on-going to get the different grades approved for relevant standards.


ASTM A240/A240MUNS S32760
EN 10088-21.4501