Technical Resources

2507 Duplex Steel is highly resistant to uniform corrosion by organic acids such as formic and acetic acid. It is also highly resistant to inorganic acids, especially if they contain chlorides. Alloy 2507 is highly resistant to carbide-related intergranular corrosion. Due to the ferritic portion of the duplex structure of the alloy it is very resistant to stress corrosion cracking in warm chloride containing environments. Through additions of chromium, molybdenum and nitrogen localized corrosion such as pitting and crevice attack are improved. Alloy 2507 has excellent localized pitting resistance.

The high chromium and molybdenum content of SAF 2507 makes it extremely resistant to uniform corrosion by organic acids like formic acid and acetic acid. SAF 2507 also provides excellent resistance to inorganic acids, especially those containing chlorides.

In dilute sulfuric acid contaminated with chloride ions, SAF 2507 has better corrosion resistance than 904L, which is a highly alloyed austenitic stainless steel pipe grade specially designed to resist pure sulfuric acid.

Stainless steel tube of type 316L (2.5%Mo) cannot be used in hydrochloric acid due to the risk of localized and uniform corrosion. However, SAF 2507 can be used in dilute hydrochloric acid. Pitting need not be a risk in the zone below the borderline in this figure, but crevices must be avoided.

Intergranural Corrosion
SAF 2507’s low carbon content greatly lowers the risk of carbide precipitation at the grain boundaries during heat treatment; therefore, the alloy is highly resistant to carbide-related intergranular corrosion.

Stress Corrosion Cracking
The duplex structure of SAF 2507 provides excellent resistance to chloride stress corrosion cracking (SCC). Because of its higher alloy content, SAF 2507 is superior to 2205 in corrosion resistance and strength. SAF 2507 is especially useful in offshore oil and gas applications and in wells with either naturally high brine levels or where brine has been injected to enhance recovery.

Pitting Corrosion
Different testing methods can be used to establish the pitting resistance of steels in chloride-containing solutions. The data above were measured by an electrochemical technique based on ASTM G 61. The critical pitting temperatures (CPT) of several high-performance steel in a 1M sodium chloride solution were determined. The results illustrate the excellent resistance of SAF 2507 to pitting corrosion. The normal data spread for each grade is indicated by the dark gray portion of the bar.

Crevice Corrosion
The presence of crevices, almost unavoidable in practical constructions and operations, makes stainless steel pipe more susceptable to corrosion in chloride enviroments. SAF 2507 is highly resistant to crevice corrosion. The critical crevice corrosion temperatures of SAF 2507 and several other high-performance stainless steel are shown above.

1. What are the properties of 253MA?
253MA is a high-temperature austenitic stainless steel, often categorized as a super austenitic or heat-resistant grade, designed to perform exceptionally in elevated-temperature environments. One of its key properties is outstanding high-temperature oxidation and corrosion resistance: it forms a dense, adherent oxide scale composed of chromium, manganese, and silicon at temperatures up to 1150°C (2102°F), which effectively prevents further oxidation and makes it resistant to thermal cycling (repeated heating and cooling) as well as corrosion from industrial atmospheres like combustion gases and steam. It also exhibits good mechanical strength at elevated temperatures, maintaining useful tensile and creep strength across the range of 800°C to 1100°C (1472°F to 2102°F)-a performance that surpasses standard austenitic stainless steels such as 304 and 316 in high-heat scenarios. Additionally, 253MA has excellent thermal conductivity and thermal fatigue resistance; its thermal conductivity is higher than that of many nickel-based superalloys, reducing the buildup of thermal stress, and its austenitic structure enhances resistance to cracking caused by repeated heating and cooling cycles. It also offers good formability, allowing it to be processed through methods like rolling, bending, and deep drawing, along with reliable weldability-when using proper procedures (such as matching filler metals like ER 253MA), it retains joint integrity and high-temperature performance without significant embrittlement. Finally, due to its fully austenitic crystal structure, 253MA remains non-magnetic in both annealed and welded conditions, a trait that is valuable in applications where magnetic interference needs to be avoided.
2. What is the chemical composition of 253MA?
The chemical composition of 253MA is tightly regulated to optimize its high-temperature properties, and it complies with standards such as ASTM A240/A240M, EN 1.4835, and ASME SA-240. The typical composition (measured by weight percentage, wt%) includes carbon (C) in the range of 0.05–0.10 wt% (with a maximum of 0.10 wt%), which enhances high-temperature strength and aids in carbide formation. Chromium (Cr) is present at 20.0–22.0 wt% (maximum 22.0 wt%), serving as the primary element for oxidation resistance by forming a protective Cr₂O₃ scale. Nickel (Ni) makes up 10.0–12.0 wt% (maximum 12.0 wt%), stabilizing the austenitic structure and improving toughness. Manganese (Mn) is included at 1.5–2.5 wt% (maximum 2.5 wt%), helping to form protective oxide scales and boosting high-temperature strength. Silicon (Si) ranges from 1.4–2.0 wt% (maximum 2.0 wt%), enhancing oxidation resistance by forming SiO₂ and supporting the adhesion of the oxide scale. Nitrogen (N) is added at 0.14–0.20 wt% (maximum 0.20 wt%), strengthening the austenitic matrix and improving creep resistance. Cerium (Ce) is present in small amounts (0.03–0.08 wt%, maximum 0.10 wt%), refining the grain structure, improving scale adhesion, and reducing the oxidation rate. Phosphorus (P) and sulfur (S) are controlled to low levels, with maximum limits of 0.04 wt% and 0.03 wt% respectively, to minimize embrittlement and maintain weldability. Iron (Fe) acts as the base metal and constitutes the balance of the composition.
3. What is the tensile strength of 253MA?
The tensile strength of 253MA is dependent on its heat treatment condition, and it is typically supplied in the annealed state-this is the standard condition for its intended high-temperature applications. Standards like ASTM A240 and EN 10088-2 specify its tensile strength values. At room temperature, the ultimate tensile strength (UTS) of 253MA has a minimum requirement of 650 MPa (94,300 psi), with a typical range of 650–750 MPa (94,300–108,800 psi). For elevated temperatures, which are critical to its use case, the minimum UTS is approximately 300 MPa (43,500 psi) at 800°C (1472°F), around 120 MPa (17,400 psi) at 1000°C (1832°F), and roughly 60 MPa (8,700 psi) at 1100°C (2012°F). These values demonstrate the alloy’s ability to retain load-bearing capacity in high-heat environments, a key requirement for applications such as furnace components and exhaust systems.
4. What is the yield strength of 253MA?
Similar to tensile strength, the yield strength of 253MA-measured as 0.2% proof stress, which is the stress at which 0.2% permanent deformation occurs-is specified for the annealed material and varies with temperature. At room temperature, the minimum yield strength requirement is 300 MPa (43,500 psi), with a typical range of 300–400 MPa (43,500–58,000 psi). For elevated temperatures, the minimum 0.2% proof stress is approximately 180 MPa (26,100 psi) at 800°C (1472°F), around 70 MPa (10,150 psi) at 1000°C (1832°F), and roughly 35 MPa (5,080 psi) at 1100°C (2012°F). These yield strength values ensure that 253MA can withstand operational stresses without undergoing permanent deformation, even when exposed to the high temperatures it is engineered to handle.