Therma 309S/4833
EN 1.4833, ASTM TYPE 309S / UNS S30908

General characteristics

Austenitic grade with improved oxidation resistance. Commonly used for furnace equipment, annealing boxes, thermo wells, baffle plates and salt pots.

A common feature of Outokumpu high temperature steels is that they are designed primarily for use at temperatures exceeding ~550 °C, i.e. in the temperature range where creep strength as a rule is the dimensioning factor and where HT corrosion occurs. Optimising steels for high temperatures has meant that their resistance to aqueous corrosion has been limited. All steels are austenitic, resulting in relatively high creep strength values.

Typical applications

Outokumpu high temperature steels can be and have been used in a number of applications where the temperature exceeds 550°C, e.g. for equipment and components within:

  • Furnace equipment
  • Annealing boxes
  • Thermo wells
  • Baffle plates and salt pots
  • Iron, steel, and non-ferrous industries
  • Engineering industry
  • Energy conversion plants
  • Cement industry


Product forms, available sizes and finishes


Product typeFinishesThicknessWidth
Cold rolled coil2B, 2BB, 2C, 2D, 2E, 2G, 2H, 2J, 2R0,05-6,353-2040
Cold rolled sheet2B, 2BB, 2C, 2D, 2E, 2G, 2J, 2R0,50-6,35300-2040
Hot rolled coil, pickled1C, 1D, 1G, 1U2,00-12,7050-2040
Precision strip2R0,05-1,503-649
Quarto plate1D6,00-50,00400-3000


Product typeFinishesThicknessWidth
Cast billet127,00-180,00127-180
Wire rod (Rod coil) hex9,00-27,009-27
Wire rod (Rod coil) round5,00-27,005-27
Wire rod (Rod coil) square9,00-24,009-24
Chemical composition

Typical chemical composition is given in the table below. The chemical composition is given as % by weight.

Typical 0.0622.312.3
ASME II A SA-240 ≤0.08≤2.0022.0-24.012.0-15.0
ASTM A240 0.04-0.10≤2.0022.0-24.012.0-15.0
ASTM A240 ≤0.08≤2.0022.0-24.012.0-15.0
EN 10095 ≤0.15≤2.0022.00-24.0012.00-14.00≤0.11
IS 6911 ≤0.20≤2.0022.0-25.011.0-15.0≤0.70
IS 6911 ≤0.08≤2.0022.0-24.012.0-15.0≤0.70
Mechanical properties

Whilst Outokumpu high temperature steels are mainly optimised for oxidation and high temperature corrosion resistance, they also have good mechanical properties, partly due to their austenitic structure and partly due to certain alloying elements. Design values are usually based on minimum proof strength values for constructions used at temperatures up to around 550°C. For higher temperatures, mean creep strength values are used.


StandardRp0.2Rp1.0RmElongationImpact strengthRockwellHBHV
Product type: Cold rolled coil and sheet
Typical (thickness 1 mm)280320600
ASME II A SA-240 ≥ 205 ≥ 515 ≤ 217
ASTM A240 ≥ 205 ≥ 515 ≤ 217
ASTM A240 ≥ 205 ≥ 515 ≤ 95HRB ≤ 217
EN 10095 ≥ 210 ≥ 250500-700 ≥ 35
IS 6911 ≥ 210 ≥ 490 ≤ 95HRB ≤ 217
IS 6911 ≥ 205 ≥ 515 ≤ 95HRB ≤ 217
Product type: Hot rolled coil and sheet
Typical (thickness 4 mm)3303806104885
ASME II A SA-240 ≥ 205 ≥ 515 ≤ 217
ASTM A240 ≥ 205 ≥ 515 ≤ 217
ASTM A240 ≥ 205 ≥ 515 ≤ 217
EN 10095 ≥ 210 ≥ 250500-700 ≥ 35
IS 6911 ≥ 210 ≥ 490 ≤ 95HRB ≤ 217
IS 6911 ≥ 205 ≥ 515 ≤ 95HRB ≤ 217
Product type: Hot rolled quarto plate
Typical (thickness 15 mm)30034062050
ASME II A SA-240 ≥ 205 ≥ 515 ≤ 95HRB ≤ 217
ASTM A240 ≥ 205 ≥ 515 ≤ 95HRB ≤ 217
ASTM A240 ≥ 205 ≥ 515 ≤ 95HRB ≤ 217
EN 10095 ≥ 210 ≥ 250500-700 ≥ 35
IS 6911 ≥ 210 ≥ 490 ≤ 95HRB ≤ 217
IS 6911 ≥ 205 ≥ 515 ≤ 95HRB ≤ 217
Product type: Wire rod

1)Elongation according to EN standard:
A80 for thickness below 3 mm.
A for thickness = 3 mm.
Elongation according to ASTM standard A2” or A50.

Corrosion resistance

Aqueous corrosion

Since most high-temperature materials are optimised with regard to strength and corrosion resistance at elevated temperatures, their resistance to electrochemical low-temperature corrosion may be less satisfactory. Components made of high-temperature material should therefore be designed and operated so that acid condensates are not formed, or at least so that any such condensates are drained away.

High-temperature corrosion

The resistance of a material to high-temperature corrosion is in many cases dependent on its ability to form a protective oxide layer. In a reducing atmosphere, when such a layer cannot be created (or maintained), the corrosion resistance of the material will be determined by the alloy content of the material.


When a material is exposed to an oxidising environment at elevated temperatures, a more or less protective oxide layer will be formed on its surface. Even if oxidation is seldom the primary cause of high-temperature corrosion failures, the oxidation behaviour is important, because the properties of the oxide layer will determine the resistance to attack by other aggressive elements in the environment.The oxide growth rate increases with increasing temperature until therate of oxidation becomes unacceptably high or until the oxide layer begins to crack and spall off, i.e. the scaling temperature is reached. The alloying elements that are most beneficial for oxidation resistance are chromium, silicon, and aluminium. A positive effect has also been achieved with small additions of so-called (re)active elements, e.g. ttrium, hafnium, rare earth metals (REM, e.g. Ce and La). These affect the oxide growth so that the formed layer will be thinner, tougher, and more adherent and thus more protective.

Sulphur attacks

Various sulphur compounds are often present in flue gases and other process gases. As a rule, they have a very detrimental effect on the useful life of the exposed components. Sulphides can nucleate and grow due to kinetic effects even under conditions where only oxides would form from a thermodynamic point of view. In existing oxide layers, attacks can occur in pores and cracks. It is therefore essential that the material is able to form a thin, tough, and adherent oxide layer. This requires a high chromium content and preferably also additions of silicon, aluminium, and/or reactive elements.

Pitting corrosion resistanceCrevice corrosion resistance

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

For more information see Outokumpu Corrosion Handbook or contact Outokumpu.


Physical properties

Data according to EN 10088


DensityModulus of elasticityThermal exp. at 100 °CThermal conductivityThermal capacityElectrical resistanceMagnetizable

Like other austenitic steels, heat-resistant steels can also be formed in cold condition. However, as a result of their relatively high nitrogen content, the mechanical strength of certain steels is higher and consequently greater deformation forces will be required.


The relatively high hardness of austenitic steels and their ability to strain harden must be taken into consideration in connection with machining. For more detailed data on machining, please contact Outokumpu, Avesta Research Centre.


The steels have good or very good weldability. To ensure weld metal properties (e.g. strength, corrosion resistance) equivalent to those of the parent metal, a filler material with a matching composition should preferably be used. In some cases, however, a differing composition may improve e.g. weldability or structural stability. Gas shielded welding has resulted in the best creep properties for welds.


Standards & approvals

The most commonly used international product standards are given in the table below.


ASME SA-240M Code Sect. II. Part ATYPE 309S / UNS S30908
ASTM A240/A240MTYPE 309S / UNS S30908; TYPE 309S / UNS S30908
EN 100951.4833
IS 6911, AMENDMENT NO. 2ISS 309; ISS 309S