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. The relatively low Ni and Mo content of Forta DX 2304 and Forta EDX 2304 makes these grades more price stable compared to common standard stainless steel grades.

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

The chemical composition is given as % by mass.

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.

¹⁾Elongation according to EN standard:
A₈₀ for thickness below 3 mm.
A for thickness = 3 mm.
Elongation according to ASTM standard A_2” or A₅₀.

Uniform corrosion

The resistance to uniform corrosion increases with high chromium content and the duplex stainless steels generally have a high chromium content. Forta DX 2304/Forta EDX 2304 is no exception. In strongly oxidising acids like nitric acid non-molybdenum alloyed steels are often more resistant than the molybdenum alloyed steels. Forta DX2304/Forta EDX 2304 is an excellent alternative due to high chromium content and low molybdenum content. More information about the resistance in different acids can be found in Outokumpu Corrosion Handbook. The corrosion tables can also be found from the here: Corrosion tables.

Pitting and crevice corrosion

The resistance to pitting and crevice corrosion increases with the content of chromium, molybdenum and nitrogen.

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

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

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.

Machining

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.

Welding

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.

Forta DX 2304 can be welded with high productivity methods (kg/h). For heavy gauge thickness, the use of heat input up to 3 KJ/mm can often be used without impairing weld metal properties. Suitable filler for welding Forta DX 2304 is ISO 23 7 NL or 22 9 3 NL.

More detailed information concerning welding procedures can be obtained from the Outokumpu Welding Handbook, available from our sales offices.

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.