Sandvik SAF 2507 (Bar)

Chemical composition (nominal) %

Forms of supply

Finishes and dimensions
SAF 2507 bar steel is stocked in a large number of sizes. The standard size range for stock comprises 20-250 mm, see pocket card S-02909. Round bar is supplied in solution annealed and water quenched condition. The surface is peeled turned and polished.
Lengths
Bars are delivered in random lengths of 3-7 m, depending on diameter.
Straightness

Tolerances, mm-sizes

Surface conditions

Surface conditions	Ra, µm Typical value	Size, mm dia
Peeled and burnished	1	20-250

Machining

Being a two-phase material (austenitic-feritic) SAF 2507 will present a different wear picture from that of single-phase steels of type AISI 304L. The cutting speed must therefore be lower than that recommended for AISI 304L. It is recommended that a tougher insert grade is used than when machining austenitic stainless steels, e.g. AISI 304L. Also in comparison with SANMAC SAF 2205 lower speed and tougher insert grade is recommended. Machining recommendations available on request. More cutting data information for SANMAC SAF 2205 is available in the product handbook S-02909-ENG, these recommendations could act as guidelines in choice of appropriate cutting data.

Physical properties

Density: 7.8 g/cm³, 0.28 lb/in³
Specific heat capacity
Metric units Imperial units

Thermal conductivity
Metric units, W/(m °C)

Imperial units, Btu/(ft h °F)

Thermal expansion
Sandvik SAF 2507 has a coefficient of thermal expansion close to that of carbon steel. This gives Sandvik SAF 2507 definite design advantages over austenitic stainless steels in equipment comprising of both carbon steel and stainless steel. The values given below are average values in the temperature ranges.
Metricunits, x10^-6/°C

Imperial units, x10^-6/°F

Figure 3. Thermal expansion, per °C (30-100°C, 86-210°F).

Resistivity

Modulus of elasticity, (x10³)
Metric units Imperial units

Corrosion resistance

General corrosion

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 hours 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.

Heat Treatment

Bars are normally delivered in solution annealed and quenched condition. Billets are supplied in hot-worked condition. If additional heat treatment is needed after further processing the following is recommended.

Solution annealing

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 ^oF) for 5h followed by air cooling

Mechanical properties

Bar steel is tested in delivery condition.

The following figures apply to material in the solution annealed and quenched condition.

For small sections the proof strength values are higher than those listed below at 20 °C (68 °F).

More detailed information can be supplied on request.

At 20°C (68°F)

1 MPa = 1 N/mm²
a) R_p0.2 corresponds to 0.2% offset yield strength.
b) Based on L₀ = 5.65√S₀ , where L₀ is the original gauge length and S₀the original cross-section area.
c) For sizes below 50 mm/2" R_m min. 800 MPa.

At higher temperatures

If SAF 2507 is exposed for prolonged periods to temperatures exceeding 250°C (480°F), the microstructure
changes which results in a reduction in impact strength. This effect does not necessarily affect the behaviour
of the material at the operating temperature.

More detailed information can be supplied on request.

Impact strength

SAF 2507 possesses good impact strength. Figure 2 shows typical impact energy values for SAF 2507 in
different sizes at -20°C (-4°F), using standard Charpy V specimens. Samples taken in the longitudinal direction.

The impact energy (Charpy V) at 20°C (68°F) is min 100 J (74 ft-lb).

Welding

The weldability of SAF 2507 is good. Suitable welding methods are manual metal-arc welding with covered electrodes or gas-shielded arc welding. Welding should be undertaken within the heat input range of 0.2-1.5 kJ/mm and with an interpass temperature of maximum 150°C (300°F). Preheating or post-weld heat treatment is not necessary.

Matching filler metals are recommended in order to obtain a weld metal with optimum corrosion resistance and mechanical properties. For gas-shielded arc welding use Sandvik 25.10.4.L, and for manual metal-arc welding the covered electrode Sandvik 25.10.4.LR.

Applications

SAF 2507 is a duplex stainless steel especially 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