Stainless steels for high service temperatures

Therma

Therma range contains heat-resistant stainless steels for use in applications with high service temperatures. This product has excellent oxidation and creep resistance. 

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Outokumpu Therma grades

Therma 253 MA®

Therma 253 MA is a stainless steel with excellent oxidation and creep resistance in cyclic conditions that is best employed in temperatures up to 1150 °C/2100 °F. There is a slight susceptibility to embrittlement during continuous operation at 600–850 °C/1110–1560 °F.

  • EN: 1.4835
  • ASTM type: - / S30815
  • Microstructure: Austenitic
Typical applications
  • Oil industry equipment
  • Conveyor belts
  • Refractory anchors
  • Expansion bellows
  • Radiant tubes, tube shields, and valves and flanges
  • Rotary kilns
  • Exhaust manifolds
  • Power generation applications
  • Cyclone dip tubes
  • Impact separators
  • Bell furnaces and muffle furnaces
  • Automotive components
  • Heat treatment trays
  • Dampers
  • Recuperator tubes for the steel industry
  • Large-scale bakery ovens
Product forms
Chemical composition
  • C: 0.09
  • Cr: 21
  • Ni: 11
  • Mo:
  • N: 0.17
  • Other: Ce:0.05 Si:1.60

Therma 310S/4845

Austenitic heat resisting 4845 grade with very good oxidation resistance. This grade 4845 belongs to austenitic chromium-nickel stainless steel grades. A specific feature for 4845 grade is high chromium and high nickel contents, which make this grade suitable for use in high temperatures. 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.

Characteristic properties
• Good resistance to oxidation
• Good resistance to high-temperature corrosion
• Good mechanical strength at elevated temperatures

  • EN: 1.4845, 1.4951
  • ASTM type: 310S / S31008
  • Microstructure: Austenitic
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:

  • Industrial furnace equipment
  • Oil industry equipment
  • Heat treatment baskets
  • Heat exchanges
  • Steam boilers and thermowells
  • Iron, steel, and non-ferrous industries
  • Engineering industry
  • Energy conversion plants
  • Cement industry
Product forms
Chemical composition
  • C: 0.05
  • Cr: 25.5
  • Ni: 19.1
  • Mo:
  • N:
  • Other:

Therma Alloy 800

The Therma range contains heat-resisting stainless steels and alloys for use in applications with high service temperatures normally > 550 °C/1020 °F. Outokumpu Therma Alloy 800 is a high temperature alloy design for high creep strength, resistance to carburization, oxidation, and other types of high-temperature corrosion.

Therma Alloy 800 (EN 1.4876, UNS N08800) is stabilized austenitic alloys with high Nickel and Chromium content as well as controlled additions of Carbon, Titanium and Aluminum. Additionally, grain size is controlled for improved creep strength properties.

  • EN: 1.4876
  • ASTM type: - / N08800
  • Microstructure: Austenitic
Typical applications
  • Heating element tubing
  • General high-temperature service in carburizing conditions
  • Steam/hydrocarbon reformers
  • Heat exchangers
  • High temperature process equipment
Product forms
Chemical composition
  • C: 0.03
  • Cr: 20
  • Ni: 30.5
  • Mo:
  • N:
  • Other: Al:0.15 Ti:0.15

Therma Alloy 800/800H

The Therma range contains heat-resisting stainless steels and alloys for use in applications with high service temperatures normally > 550 °C/1020 °F. Outokumpu Therma Alloy 800/800H & 800T is a series of high temperature alloys design for high creep strength, resistance to carburization, oxidation, and other types of high-temperature corrosion.

Therma Alloy 800 series (EN 1.4876/1.4958/1.4959, UNS N08800/N08810/N08811) are stabilized austenitic alloys with high Nickel and Chromium content as well as controlled additions of Carbon, Titanium and Aluminum. Additionally, grain size is controlled for improved creep strength properties.

  • EN: 1.4876, 1.4958
  • ASTM type: - / N08810, N08800
  • Microstructure: Austenitic
Typical applications

  • Heating element tubing

  • General high-temperature service in carburizing conditions

  • Steam/hydrocarbon reformers

  • Heat exchangers

  • High temperature process equipment

Product forms
Chemical composition
  • C: 0.07
  • Cr: 20.5
  • Ni: 30.5
  • Mo:
  • N:
  • Other: Al:0.30 Ti:0.30

Therma Alloy 800T

The Therma range contains heat-resisting stainless steels and alloys for use in applications with high service temperatures normally > 550 °C/1020 °F. Outokumpu Therma Alloy 800/800H/800T is a series of high temperature alloys design for high creep strength, resistance to carburization, oxidation, and other types of high-temperature corrosion.

Therma Alloy 800 series (EN 1.4876/1.4958/1.4959, UNS N08800/N08810/N08811) are stabilized austenitic alloys with high Nickel and Chromium content as well as controlled additions of Carbon, Titanium and Aluminum. Additionally, grain size is controlled for improved creep strength properties.

  • EN: 1.4876, 1.4959
  • ASTM type: - / N08810, N08811
  • Microstructure: Austenitic
Typical applications

  • Heating element tubing

  • General high-temperature service in carburizing conditions

  • Steam/hydrocarbon reformers

  • Heat exchangers

  • High temperature process equipment

Product forms
Chemical composition
  • C: 0.07
  • Cr: 20.5
  • Ni: 30.5
  • Mo:
  • N:
  • Other: Al:0.35 Ti:0.50

Therma 4910

Austenitic creep resisting grade with good resistance to stress relaxation cracking. Therma 4910 belongs to the austenitic chromium-nickel-molybdenum stainless steel grades. A specific feature for Therma 4910 grade is high creep resistance as a result of nitrogen and boron alloying, which makes this grade suitable for use in high temperatures. The low carbon content is unusual in creep resisting steels and together with absence of strong carbide forming elements such as titanium and niobium, carbide precipitation leading to stress relaxation cracking is minimized.

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. Therma 4910 is intended for use up to about 800°C. 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.

Characteristic properties:

  • Good resistance to oxidation, suitable for use up to about 800 °C
  • Good resistance to high-temperature corrosion
  • Excellent mechanical strength at elevated temperatures
  • Resistance to stress relaxation cracking, useful especially in the heat affected zone of weldments
  • Although not intended for wet corrosion applications,  the presence of molybdenum and nitrogen is beneficial for pitting  corrosion resistance in chloride environments

  • EN: 1.4910, 1.4429
  • ASTM type: 316LN / S31653
  • Microstructure: Austenitic
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:

  • Industrial furnace equipment
  • Oil industry equipment
  • Heat treatment baskets
  • Heat exchanges
  • Steam boilers and thermowells
  • Iron, steel, and non-ferrous industries
  • Engineering industry
  • Energy conversion plants
  • Cement industry
  • Thermal Energy Storage
  • Molten nitrate salt handling
Product forms
Chemical composition
  • C: 0.025
  • Cr: 17
  • Ni: 12
  • Mo: 2.5
  • N: 0.15
  • Other: B:0.00 P:0.04

Therma 4713

A ferritic low-alloyed stainless steel best employed at 550–800°C/1020–1470°F when you need higher mechanical loading compared to other ferritic grades.

Offers good resistance against sulfur attack compared to austenitic stainless grades.

  • EN: 1.4713
  • ASTM type: - / -
  • Microstructure: Ferritic
Typical applications

Typical applications:

  • Furnace equipment
  • Air heaters
  • Annealing boxes
  • Conveyor belts
  • Thermowells
Product forms
Chemical composition
  • C: 0.06
  • Cr: 6.5
  • Ni:
  • Mo:
  • N:
  • Other: Al:0.80 Si:0.80

Therma 4724

Low-alloyed ferritic heat resisting grade with improved scaling resistance. Uncritical regarding embrittlement at service temperatures. Applied for e.g. furnace equipment, thermal boiler components, grids, burner nozzles, conveying parts, thermowells.

The high temperature (HT) ferritic stainless steels complement Outokumpu austenitic heat and creep portfolio. The main alloying element in the ferritic grades is chromium. Its positive effect on the scaling resistance is enhanced by silicon and aluminium. The characteristic properties are excellent resistance to oxidising and reducing sulphur containing atmospheres, good resistance to oxidation and high thermal conductivity with low thermal expansion.

Therma 4713 does not form brittle phases but should only be exposed to moderately corrosive atmospheres owing to its low chromium content.

Therma 4724 is a truly stainless high temperature grade with 13% chromium. It is not critical in terms of embrittlement. 4742 shows better scaling resistance than 4724 and can be subjected to reducing sulphur environments without risk. It is subject to 475°C embrittlement and grain coarsening at temperatures above 950°C. σ-phase may form after long time exposures to temperatures around 650°C.

1.4762 - with the highest chromium content- is the most resistant to reducing sulphurous gases. It is susceptible to the same embrittlement phenomena as 4742 whilst σ-phase forms during long exposures in the range 600°C to 800°C.

  • EN: 1.4724
  • ASTM type: - / -
  • Microstructure: Ferritic
Typical applications

Outokumpu Stainless ferritic high temperature steels are mostly used in high temperature applications with sulphurous atmospheres and/or low tensile loads such as for installations within:

  • Furnace equipment
  • Thermal boiler components
  • Grids
  • Burner nozzles
  • Conveying parts
  • Thermowells
  • Chemical industry (drums)
  • Power industry (coal burners)
  • Metalworking industry (heat treatment boxes)
Product forms
Chemical composition
  • C: 0.07
  • Cr: 12.5
  • Ni:
  • Mo:
  • N:
  • Other: Al:0.90 Si:1.00

Therma 304H/4948

Stainless steel grade with wet corrosion resistance and improved high-temperature strength (creep resisting steel). Good formability and weldability. Commonly used for tubes and pressure vessels.

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.

  • EN: 1.4948
  • ASTM type: 304H / S30409
  • Microstructure: Austenitic
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:

  • Tubes
  • Pressure vessels
  • Iron, steel, and non-ferrous industries
  • Engineering industry
  • Energy conversion plants
  • Cement industry
Product forms
Chemical composition
  • C: 0.05
  • Cr: 18.1
  • Ni: 8.3
  • Mo:
  • N:
  • Other:

Therma 321H/4878

Low alloyed grade. Commonly used for furnace equipment, case hardening boxes.

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.

  • EN: 1.4878
  • ASTM type: 321H / S32109
  • Microstructure: Austenitic
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
  • Case hardening boxes
  • Iron, steel, and non-ferrous industries
  • Engineering industry
  • Energy conversion plants
  • Cement industry
Product forms
Chemical composition
  • C: 0.05
  • Cr: 17.3
  • Ni: 9.1
  • Mo:
  • N:
  • Other: Ti:0.40

Therma 309S/4833

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.

  • EN: 1.4833, 1.4950
  • ASTM type: 309S / S30908, TYPE 309H / UNS S30909
  • Microstructure: Austenitic
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
Chemical composition
  • C: 0.06
  • Cr: 22.3
  • Ni: 12.3
  • Mo:
  • N:
  • Other:

Therma 314/4841

Austenitic heat resisting grade with excellent oxidation resistance. Commonly used for furnace equipment, super heater suspensions, enameling grates etc.

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.

  • EN: 1.4841
  • ASTM type: 314 / S31400
  • Microstructure: Austenitic
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
  • Super heater suspensions
  • Enameling grates
  • Iron, steel, and non-ferrous industries
  • Engineering industry
  • Energy conversion plants
  • Cement industry
Product forms
Chemical composition
  • C: 0.06
  • Cr: 24.3
  • Ni: 19.2
  • Mo:
  • N:
  • Other: Si:1.70

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For High Service Temperatures

Therma

The Therma range contains heat- and creep-resisting stainless steels with excellent oxidation and creep resistance for use in applications with high service temperatures (≥ 550°C/1020°F).

Austenitic heat- and creep-resisting stainless steels have resistance to carburizing and nitriding/low oxygen hot gas and higher creep strength, in general.

Therma 253 MA/4835 (EN 1.4835) is an austenitic heat-resisting stainless steel with excellent oxidation and creep resistance in cyclic conditions and is best employed in high temperatures up to 1100°C/2012°F.

Therma 310S/4845 (EN 1.4951) is an austenitic heat- and creep-resisting stainless steel with excellent oxidation resistance in mildly cyclic conditions and is best employed in high temperatures up to 1050°C/1920°F.

The ferritic heat-resisting stainless steels Therma 4713 (EN 1.4713) and Therma 4724 (EN 1.4724) have good resistance to sulfur-containing hot gases and lower thermal expansion compared to nickel-alloyed grades. Therma 4713 and Therma 4724 are best employed in temperatures up to 800°C/1470°F and 850°C/1560°F, respectively

Outokumpu Whitepaper

Outokumpu has published a white paper on Therma range stainless steels for high temperature applications

High temperature stainless steels are vital for applications exceeding 550 °C, with some grades enduring up to 1150 °C. These materials are crucial in industries such as iron, steel, metallurgy, general engineering, energy plants, and cement. Selecting the optimal grade ensures safety, reliability, and longevity, considering factors like corrosion resistance, mechanical properties, microstructural stability, and physical properties. Visit the landing page and download the white paper to learn more.
Visit the landing page and download the paper

Standards and approvals

EN 10028-7 Flat products for pressure purposes – Stainless steels
EN 10088-1 Stainless steels – Part 1: List of stainless steels
EN 10088-2 Stainless steels – Corrosion resisting sheet/plate/strip for general and construction purposes
EN 10088-3 Stainless steels – Corrosion resisting semi-finished products/bars/rods/wire/sections for general and construction purposes
EN 10088-4 Stainless steel flat products, technical delivery conditions, steels for constructions
EN 10217-7 Welded steel tubes for pressure purposes – Stainless steel tubes
EN 10296-2 Welded circular steel tubes for mechanical and general engineering purposes - Stainless Steel tubes
ASTM A182 / ASME SA-182   Forged or rolled alloy-steel pipe flanges, forged fittings etc. for high temperature service
ASTM A240 / ASME SA-240 Heat-resisting Cr and Cr-Ni stainless steel plate/sheet/strip for pressure purposes
ASTM A276 Stainless and heat-resisting steel bars/shapes
ASTM A479 / ASME SA-479 Stainless steel bars for boilers and other pressure vessels
Eurocode 3 / EN 1993-1-4 Design of steel structures – Part 1-4: General rules – Supplementary rules for stainless steels
ISO 15510 Stainless steels – chemical composition

 

The most commonly used international product standards are given in the table. For a list of standards by product, visit Steel Finder.

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