SAF 2507® is a high alloy super duplex (austenitic-ferritic) stainless steel for service in highly corrosive conditions. The grade is characterized by:
- Excellent resistance to stress corrosion cracking in chloride-bearing environments
- Excellent resistance to pitting and crevice corrosion
- High resistance to general corrosion
- Very high mechanical strength
- Physical properties that offer design advantages
- High resistance to erosion corrosion and corrosion fatigue
- Good weldability
: X 2 CrNiMoN 25-7-4
- EN 10216-5
- EN 10297-2
- ASTM A511, A790
- NORSOK MDS D51
- Pressure Equipment Directive (2014/68/EU)
- Approved by the American Society of Mechanical Engineers (ASME) for use in accordance with ASME Boiler and Pressure Vessel Code, Section VIII, div. 1
- ASME B31.3 Chemical Plant and Petroleum Refinery piping
- VdTÜV-Werkstoffblatt 508
- ISO 15156-3/NACE MR 0175 (Sulphide stress cracking resistant material for oil field equipment). Applies to liquid quenched tubes
Status according to EN 10 204/3.1
Chemical composition (nominal) %
SAF 2507® is a duplex stainless steel specially designed for service in aggressive chloride-containing environments. Typical applications are:
- Oil and gas industry
- Seawater cooling
- Salt evaporation industry
- Desalination plants
- Geothermal wells
- Refineries and petrochemical plants
- Mechanical components requiring high strength
- Pulp and paper industry
SAF 2507® is highly resistant to corrosion by organic acids, e.g. formic and acetic acid. It is suitable for use at high concentrations and temperatures, where austenitic stainless steels corrode at a high rate.
Resistance to inorganic acids is comparable to that of high alloy austenitic stainless steels in certain concentration ranges.
Pitting and crevice corrosion
The pitting and crevice corrosion resistance of a stainless steel is primarily determined by the content of chromium, molybdenum and nitrogen. An index for comparing the resistance to pitting and crevice corrosion is the PRE number (Pitting Resistance Equivalent).
The PRE is defined as, in weight-% PRE = %Cr + 3.3 x %Mo + 16 x %N
For duplex stainless steels the pitting corrosion resistance is dependent on the PRE-value in both the ferrite phase and the austenite phase, so that the phase with the lowest PRE-value will be limiting for the actual pitting corrosion resistance. In SAF 2507® the PRE-value is equal in both phases, which has been achieved by a careful balancing of the elements.
The minimum PRE-value for SAF 2507® is 41.
This is significantly higher than e.g. the PRE-values for other duplex stainless steels of the 25Cr type which are not "super-duplex". As an example, UNS S31260 (25Cr3Mo0.2N) has a PRE-value of typically 38.
One of the most severe pitting and crevice corrosion tests applied to stainless steel is ASTM G48, i.e., exposure to 6% FeCl3 with and without crevices (method A and B respectively). When pits are detected following a 24 hour exposure, together with a substantial weight loss (>5 mg), the test is interrupted. Otherwise, the temperature is increased 5°C (9°F) and the test is continued with the same sample. Figure 4 shows critical pitting and crevice temperatures (CPT and CCT) from this test.
Figure 4. Critical pitting and crevice temperatures in 6% FeCl3. 24h (similar to ASTM G48).
Stress corrosion cracking
SAF 2507® has excellent resistance to chloride induced stress corrosion cracking.
Erosion corrosion and corrosion fatigue
The superior mechanical properties combined with the improved corrosion resistance of SAF 2507® result in excellent resistance to both erosion corrosion and corrosion fatigue compared to standard austenitic stainless steels.
Forms of supply
Finishes and dimensions
SAF 2507® hollow bar is produced to order in hot-finished condition in the size range OD 32 – 275 mm, ID as required. Dimensions are given as outside and inside diameter with guaranteed component sizes after machining.
Outside diameter +2 / -0 %, but minimum +1 / -0 mm
Inside diameter +0 / -2 %, but minimum +0 / -1 mm
Closer tolerances can be supplied.
Other forms of supply
SAF 2507® is also available as solid bar and seamless tube and pipe.
Hollow bar is normally delivered in the solution annealed and quenched condition. If additional heat treatment is needed after further processing the following is recommended.
Slow heating up to 1000°C (1830°F). Annealing at 1050-1125°C (1920-2060°F), followed by quenching.
Stress relief heat treatment at 350°C (660°F) for 5h followed by air cooling.
Hollow bar is tested in the delivery condition.
The following figures apply to material in the solution annealed and quenched condition. Hollow bar with wall thickness above 20 mm (0.787 in.) may have slightly lower values. More detailed information can be supplied on request.
At 20°C (68°F)
|Proof strength, MPa||Tensile strength, MPa||Elongation, %||Hardness, HRC|
|Proof strength, ksi||Tensile strength, ksi||Elongation, %||Hardness, HRC|
1 MPa = 1 N/mm2
a) Rp0.2 and Rp1.0 correspond to 0.2% offset and 1.0% offset yield strength, respectively.
b) Based on L0 = 5.65 √S0 where L0 is the original gauge length and S0 the original cross-sectional area.
At higher temperatures
If SAF 2507® hollow bar is exposed for prolonged periods to temperatures exceeding 250°C (480°F), the microstructure will change which will result in a reduction in impact strength. This effect will not necessarily affect the behavior of the material at the operating temperature.
More detailed information can be supplied on request.
SAF 2507® hollow bar possesses good impact strength. Figure 2 shows typical impact strength values for SAF 2507® in various diameters at -46°C (-51°F), using standard Charpy V specimens. Samples taken in the longitudinal direction.
Figure 2. Impact strength (Charpy V) for SAF 2507® hollow bar at -46°C (-51°F).
Density: 7.8 g/cm3, 0.28 lb/in3
Specific heat capacity
Metric units Imperial units
|Temperature, °C||J/(kg °C)||Temperature, °F||Btu/(lb °F)|
Metric units, W/(m °C)
Imperial units, Btu/(ft h °F)
SAF 2507® has a coefficient of thermal expansion close to that of carbon steel. This gives SAF 2507® definite design advantages over austenitic stainless steels in equipment comprising both carbon steel and stainless steel. The values given below are average values in the temperature ranges.
Metric units, x10-6/°C
Imperial units, x10-6/°F
|Temperature, °C||μΩm||Temperature, °F||μΩin.|
Modulus of elasticity, (x103)
Metric units, imperial units
|Temperature, °C||MPa||Temperature, °F||ksi|
Being a two-phase material (austenitic-ferritic) SAF 2507® will present a different wear picture from that of single-phase austenitic steels of type ASTM 304L. The cutting speed must therefore be lower than that recommended for ASTM 304L. It is recommended that a tougher insert grade is used than when machining austenitic stainless steels, e.g. ASTM 304L. Also in comparison with Sanmac® 2205 lower speed and tougher insert grade is recommended. Machining recommendations available on request. More cutting data information for Sanmac® 2205 is available in the product handbook S-02909-ENG, these recommendations could act as guidelines in choice of appropriate cutting data.
The weldability of SAF 2507® is good. Suitable methods of fusion welding are manual metal-arc welding (MMA/SMAW) and gas-shielded arc welding, with the TIG/GTAW method as first choice.
For SAF 2507®, heat input of 0.2-1.5 kJ/mm and interpass temperature of <150°C (300°F) are recommended. Preheating and post-weld heat treatment is normally not necessary.
Recommended filler metals
ISO 14343 S 25 9 4 N L / AWS A5.9 ER2594 (e.g. Exaton 25.10.4.L)
ISO 3581 E 25 9 4 N L R / AWS A5.4 E2594-16 (e.g. Exaton 25.10.4.LR)
ISO 3581 E 25 9 4 N L B / AWS A5.4 E2594-15 (e.g. Exaton 25.10.4.LB)