AISI 310S Stainless Steel

1. Introduction

310S is the low‑carbon modification of 310™, developed to comply with ASTM requirements for high‑temperature austenitic stainless steels. Its chemistry—characterised by high chromium (24–26%) and high nickel (19–22%)—gives this alloy exceptional resistance to oxidation, thermal cycling, and high‑temperature corrosion. The reduced carbon level of the 310S grade (≤0.08 wt%) minimises carbide precipitation, improving stability and resistance to sensitisation during prolonged operation in the 650–900 °C temperature range.

310S is widely used in applications demanding continuous service temperatures up to ~1100 °C (2010 °F), including furnaces, heating equipment, thermal processing systems, and components exposed to cyclic or sustained high temperature atmospheres. Its excellent structural stability and scale resistance make it a well trusted material for elevated temperature engineering across multiple industries.

2. Chemical Composition

310S™’s chemistry ensures superior oxidation resistance and mechanical stability at high temperatures.

Chemical Composition

3. Mechanical and Physical Properties

310S (EN 1.4845 / UNS S31008) retains strength and structural stability at temperatures far above those tolerated by standard austenitic stainless steels. Its high chromium and nickel levels provide consistent mechanical performance across a wide temperature range, while also supporting excellent resistance to oxidation, carburisation, and thermal cycling.

All values below reflect the alloy’s behaviour in the annealed condition and demonstrate the characteristic high‑temperature capability of the 310 family.

3.1 Tensile Properties at Temperature

310S maintains significant tensile and yield strength at elevated temperatures, supporting continuous service in furnace atmospheres and other severe thermal environments. The alloy exhibits increasing ductility as temperatures rise above ~900 °C, a feature typical of fully austenitic materials.

Tensile Properties of 310S at Elevated Temperature

These values illustrate the alloy’s continuing strength through to ~1100 °C, alongside a predictable increase in ductility at very high temperatures. This combination allows 310S to withstand thermal shock and dimensional stresses in cyclic heating operations.

3.2 Physical Properties

The physical behaviour of 310S reflects its fully austenitic microstructure and high chromium–nickel matrix, resulting in low thermal conductivity, a relatively high coefficient of expansion, and inherent non‑magnetic characteristics in the annealed state.

Density
8.03 g/cm³ (0.29 lb/in³)

Coefficient of Thermal Expansion

4. Applications

310S (EN 1.4845 / UNS S31008) is selected for service environments where components must withstand continuous or cyclic exposure to extremely high temperatures, aggressive combustion products, and thermal shock. Its combination of high chromium and nickel content provides excellent resistance to oxidation, carburisation, nitriding, and sulphidation under a wide range of process conditions.

The applications below reflect the alloy’s established use across thermal‑processing industries, chemical plants, and high‑temperature equipment manufacturing.

4.1 Industrial Heat‑Processing Equipment

310S is extensively used for components operating in oxidising furnace atmospheres up to ~1100 °C. Its superior scale adhesion, high‑temperature strength retention, and resistance to metal dusting or carbon ingress make it a preferred grade for thermal‑processing plants.

Typical furnace and heating‑system applications include:

• Radiant tubes, burners, and burner nozzles
• Furnace linings, muffle sections, and internal baffles
• Conveyor belts, rollers, and walking‑beam components
• Heat treatment baskets, fixtures, retorts, and trays used for supporting small parts
• Tube hangers, supports, and structural elements exposed to cyclic heating

4.2 Chemical Processing Environments

310S demonstrates strong resistance to hot corrosive gases and many process chemicals, particularly where oxidation or sulphur contamination is a concern. It tolerates environments that contain:

• Hot concentrated acids (e.g., nitric acid in oxidising conditions)
• Ammonia‑bearing atmospheres, including cracked ammonia in high‑temperature furnaces
• Sulphur dioxide and other sulphur‑containing combustion gases
• Carburising and mixed gas atmospheres, where high Ni assists resistance to carbon ingress

4.3 High‑Temperature Oxidation and Thermal Cycling

310S provides excellent resistance to oxidation, supported by the formation of a compact, adherent chromia (Cr₂O₃) scale that withstands repeated thermal cycling. This behaviour allows continuous use in oxidising atmospheres approaching 1100 °C, with the alloy outperforming lower‑chromium austenitic steels in both scale integrity and structural stability.

4.4 Summary of Key Application Advantages

310S is typically selected where the following properties are required:

• High‑temperature strength retention
• Excellent oxidation resistance in air and combustion atmospheres
• Resistance to carburisation, metal dusting, nitriding, and sulphidation
• Dimensional stability under repeated heating and cooling cycles
• Long‑term performance in furnace or heater environments nearing 1100 °C

5. Welding

310S (EN 1.4845) is an austenitic stainless steel with good weldability, suitable for all standard fusion welding methods. Its high chromium and nickel content, together with its low carbon level, supports stable performance in welded structures used in high temperature service. However, several metallurgical characteristics of the alloy require specific consideration during fabrication to ensure optimal joint integrity and corrosion resistance.

5.1 General Weldability

310S can be welded using all common processes, including:

• Gas Tungsten Arc Welding (GTAW/TIG)
• Gas Metal Arc Welding (GMAW/MIG/MAG)
• Shielded Metal Arc Welding (SMAW)
• Submerged Arc Welding (SAW)

5.2 Carbon Control and “L‑Grade” Fillers

Although 310S has a low carbon content, situations requiring even stricter control against carbide precipitation may justify the use of “L‑grade” filler metals such as ER309L.

This maintains low carbon in the weld deposit and minimises chromium‑carbide formation during exposure to high‑temperature sensitisation ranges.

5.3 Post‑Weld Cleaning and Scale Removal

To restore corrosion and oxidation resistance, all weld heat tint and oxidised scale must be removed from the weld and adjacent heat‑affected zones.

Acceptable cleaning methods include:

• Stainless‑only wire brushing
• Grinding

Chemical cleaning:

• Pickling pastes or solutions containing nitric acid + hydrofluoric acid
• Thorough water rinsing afterwards is essential

5.4 Weld Defects and Metallurgical Considerations

Because of its fully austenitic solidification pattern, 310S weld metal typically contains little to no ferrite, which:

• increases susceptibility to hot cracking
• can make the weld pool sluggish
• benefits from silicon‑bearing filler metal additions to improve fluidity

5.5 Summary

When welded using appropriate filler metals and proper post‑weld cleaning, 310S provides:

• Reliable high‑temperature joint stability
• Strong resistance to oxidation and carburisation
• Good weld mechanical integrity
• Excellent service life in furnace atmospheres

Best results are achieved using matching or silicon‑enhanced fillers, controlling heat input, and ensuring thorough removal of weld scale.

6. Heat Treatment / Annealing

310S is a fully austenitic stainless steel and cannot be strengthened through heat treatment. Instead, heat treatment is used to restore a uniform microstructure, dissolve chromium carbides formed during intermediate‑temperature exposure, and re‑establish optimum corrosion and oxidation resistance. The alloy responds predictably to solution annealing and exhibits stable grain structure after proper heat treatment.

6.1 Solution Annealing

Solution annealing is the primary heat‑treatment process for 310S.

Recommended conditions

• Temperature: 2050–2150 °F (1120–1175 °C)
• Holding time: Approximately 30 minutes per inch of section thickness
• Cooling: Rapid cooling (air or water quench) to maintain a fully austenitic, carbide‑free microstructure

6.2 Scale Formation During Annealing

Annealing in air results in the formation of a thin, adherent chromium‑rich oxide layer. This oxide must be removed prior to service or further fabrication operations, as residual scale can compromise corrosion resistance and adversely affect surface finish.

6.3 Scale Removal and Surface Cleaning

A combination of mechanical and chemical cleaning methods is recommended for complete removal of annealing scale.

Mechanical cleaning options:

• Silica sand or glass bead blasting
• Grinding with stainless‑only abrasive tools

Chemical pickling

A typical descaling bath consists of:

• 5–25% nitric acid (HNO₃)
• 0.5–3% hydrofluoric acid (HF)
• Temperature: ambient to ~140 °F (50 °C)

After pickling:

• Thorough rinsing with clean water is essential
• Final drying prevents spotting or acid residues

6.4 Sensitisation and Phase Stability

Although 310S contains low carbon, prolonged exposure to temperatures between ~800–1650 °F (427–899 °C) can still cause carbide or sigma‑phase precipitation. These metallurgical changes may reduce ductility and corrosion resistance if components are not properly annealed before service or after extensive thermal cycling.

A full solution anneal is the recommended corrective treatment for such microstructural embrittlement.

6.5 Hardenability

Because 310S remains fully austenitic across temperatures encountered in industrial service, it cannot be hardened by heat treatment. Any increases in strength must be obtained through:

• Cold work
• Warm work

However, these strengthening effects are not stable at high temperature. Cold‑worked material used in furnace or heater environments will lose its elevated strength during service and may experience reduced creep resistance if not properly annealed prior to long‑term high‑temperature exposure.

6.6 Summary

Proper heat treatment ensures that 310S maintains:

• A fully austenitic microstructure
• Maximum corrosion and oxidation resistance
• High ductility in thermal cycling
• Long‑term dimensional stability

Solution annealing, followed by correct surface cleaning, is essential for components intended for severe high‑temperature duty.

7. Fabrication Characteristics

310S is readily fabricated into complex furnace and high‑temperature assemblies, offering the advantageous forming behaviour typical of fully austenitic stainless steels. Its toughness, work‑hardening characteristics, and thermal properties must be considered when selecting forming, machining, or cutting techniques, particularly for precision components that will experience sustained or cyclic high‑temperature exposure.

7.1 Cutting and Machining

Like other high‑alloy austenitic grades, 310S is tougher than carbon steel and exhibits a strong tendency to work harden. During machining, cutting forces increase steadily as deformation progresses, and incorrect cutting parameters can quickly produce hardened surface layers.

Key machining considerations

• Tools must be sharp, rigidly supported, and designed for continuous cutting rather than rubbing.
• Deeper cuts at slower speeds are preferred to cut beneath work‑hardened zones.
• Generated chips are stringy and ductile, requiring controlled chip‑breaking.
• The alloy’s low thermal conductivity (compared with ferritic grades) leads to localised heat retention, requiring attention to coolant application and dimensional tolerance control.

7.2 Cold Forming

310S can be cold‑formed using the same methods applied to other austenitic stainless steels, including bending, roll‑forming, drawing, spinning, stretching, flanging, and hydroforming. Its higher nickel and chromium content provides excellent ductility, but the alloy work‑hardens rapidly.

Cold forming behaviour

• Work hardening increases the required forming force as deformation progresses.
• Excessive deformation without intermediate annealing may lead to cracking.
• Components intended for high temperature use should be fully solution annealed after heavy forming to restore ductility and metallurgical stability.

7.3 Hot Working

Hot working of 310S can be carried out within a relatively narrow temperature range governed by metallurgical stability and oxidation behaviour.

Recommended hot‑working parameters

• Start temperature: 1800–2145 °F (980–1120 °C)
• Finish temperature: Not below 1800 °F (980 °C)

Working at temperatures above this range can reduce hot ductility due to ferrite formation. Working below this range increases the risk of carbide or sigma‑phase precipitation and associated brittleness. After forging, parts should be cooled rapidly to a black heat to minimise time spent in the sensitisation temperature band.

7.4 Forming Forces and Tooling

Due to rapid work hardening, 310S requires stronger forming equipment, more robust tooling, and careful control of deformation rates, especially for operations such as deep drawing or heavy bending.

• Tooling materials must withstand higher stresses and heat generated during forming.
• Lubrication must be adequate to prevent galling, which is more likely in high‑nickel steels.
• Where tight tolerances are required, allowance must be made for elastic spring back, typical of high‑strength austenitic alloys.

7.5 Summary

310S offers excellent formability, machinability, and hot working characteristics for a fully austenitic high temperature stainless steel, provided that:

• Work hardening is managed correctly
• Hot working temperatures remain within the recommended range
• Adequate cutting forces and tooling are used
• Annealing steps are incorporated following heavy forming

8. Creep and Stress‑Rupture Behaviour

310S is engineered for long‑term performance in extreme temperature environments where components are subjected to continuous load. Its high chromium and nickel content gives the alloy excellent resistance to time‑dependent deformation, making it suitable for service conditions where conventional austenitic grades may experience unacceptable levels of creep.

8.1 Creep Strength

At elevated temperatures, 310S maintains structural integrity for extended periods under load. The alloy exhibits stable creep behaviour due to its fully austenitic microstructure and balanced alloying additions, allowing it to withstand prolonged exposure in the upper operating ranges of industrial furnace equipment. As temperature increases, the allowable stress levels decrease in a predictable manner, enabling reliable design for long‑duration high‑temperature service.

8.2 Stress‑Rupture Performance

Stress‑rupture resistance is a key requirement for materials used in continuous high‑temperature operation. 310S offers dependable long‑term rupture performance across a wide temperature range, retaining its load‑bearing capacity in applications approaching the top end of its service limits. The alloy demonstrates the characteristic behaviour of high‑chromium, high‑nickel austenitic steels, with gradual reductions in rupture strength as exposure time and temperature increase.

8.3 Metallurgical Stability at High Temperature

310S maintains good metallurgical stability during long‑term exposure. Although microstructural changes such as carbide or sigma‑phase precipitation may occur at certain intermediate temperatures, these effects are reversible through proper solution annealing. The alloy remains ductile at elevated temperatures, supporting dimensional stability during thermal cycling and mechanical loading.

8.4 Suitability for Long‑Term Elevated‑Temperature Service

The combination of creep resistance, rupture strength, and microstructural stability makes 310S well suited for components exposed to sustained stresses in demanding high‑temperature environments. It provides reliable long‑term performance in furnace internals, heat‑treatment fixtures, radiant heating systems, and high‑temperature process equipment where dimensional accuracy and mechanical reliability must be maintained.

8.5 Summary

310S offers a strong balance of high‑temperature creep resistance, stable rupture behaviour, and excellent structural reliability. These characteristics support its widespread use in continuous high‑temperature service where long‑term mechanical performance is critical.

9. Conclusion

310S (EN 1.4845 / UNS S31008) is a robust, fully austenitic stainless steel engineered for long term service in extreme high temperature environments. Its elevated chromium and nickel content delivers excellent resistance to oxidation, carburisation, sulphidation, and thermal degradation, while the low carbon level enhances stability during exposure to sensitising temperature ranges. These characteristics make the alloy highly suited to furnace components, thermal processing equipment, and chemical processing systems where materials must retain structural integrity under continuous or cyclic thermal load.

The alloy maintains dependable strength and ductility across a wide temperature spectrum and provides predictable creep and stress rupture behaviour essential for prolonged high temperature service. Its fabrication characteristics — including good cold and hot formability, stable machining response, and compatibility with standard welding processes — support the production of complex assemblies used throughout industrial heating and heat treatment operations.

With its strong balance of high temperature mechanical stability, surfacescale resistance, corrosion protection, and fabrication versatility, 310S offers a highly reliable solution for demanding applications requiring long service life, dimensional stability, and consistent performance under aggressive thermal cycling.