Forta DX 2205 is available as S31803 and S32205 according to the UNS designation system. S32205 has higher minimum values for the main alloying elements.

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.

Mechanical properties at room temperature are shown in the table below.

¹⁾Elongation according to EN standard:
A₈₀ for thickness < 3 mm.
A for thickness ≥ 3 mm.
Elongation according to ASTM standard A₂,, or A₅₀.

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. For guidance on material selection in a large number of environments capable of causing uniform corrosion, consult the tables and isocorrosion diagrams in the Outokumpu Corrosion Handbook.

Pitting and crevice corrosion

Chloride 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). 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. 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) 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 ASTM G48 are methods for ranking the relative pitting or crevice corrosion resistance of the different stainless steels, but they do not give the maximum temperature for using these alloys in real service environments.

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 applicable to stainless steel. The high proof strength compared to austenitic and ferritic stainless steel can impose some differences in forming behavior depending on the chosen forming technique, such as an increased tendency to springback. This point is particularly relevant to the forming of any high-strength steel. If the forming process is not already decided, it is possible to choose the most suitable one for duplex grades. Moreover, an excellent interplay between high proof strength, work hardening rate, and elongation mean that the duplex grades are particularly well suited to lightweight and cost-efficient applications with complex shapes. The impact of the high strength varies for different forming techniques. Common to 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 place higher demands on the tool materials and the lubricanta. Downgauging should also be considered in this case.

Welding

The best results can be obtained with the use of designed fillers. Forta DX 2205 can be welded with high-productivity methods (kg/h). For heavy gauge thickness, heat input up to 3 kJ/mm can often be used without impairing weld properties. Duplex steels generally have good weldability and can be welded using most of the common 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

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

Forta DX 2205 corresponds in American standards to two different steel designations: UNS S31803 and UNS S32205. The latter has closer tolerance limits for some alloying elements to further optimize properties such as corrosion resistance and strength – the properties described in this datasheet correspond to UNS S32205.

Outokumpu produces and certifies materials to most international and national standards. Work is continuously ongoing to have the different grades approved for relevant standards.