SUS 310S vs. AISI 314 Stainless Steel

1. Introduction

In the realm of high-temperature engineering, selecting the right stainless steel alloy is critical to ensuring durability, safety, and efficiency.

Two prominent contenders in this space are SUS 310S and AISI 314 stainless steel, celebrated for their resistance to extreme heat and corrosive environments.

This article delivers a detailed, data-driven comparison of these alloys, exploring their chemical composition, mechanical properties, and real-world applications.

By dissecting their strengths, limitations, and technical nuances, engineers and material scientists can make informed decisions to optimize performance in industries ranging from petrochemicals to power generation.

2. Designation and Nomenclature

Origins and Standards

• SUS 310S follows the Japanese Industrial Standard (JIS G4303), where “SUS” denotes stainless steel for structural use.
  It aligns with ASTM 310S (UNS S31008), a low-carbon variant of the 310 series, with a maximum carbon content of 0.08% to enhance weldability.
• AISI 314 adheres to ASTM A240/A276 (UNS S31400), an American specification designed for severe high-temperature service.
  Its name stems from the American Iron and Steel Institute (AISI), emphasizing its silicon-rich composition (1.5–2.5%) for superior oxidation resistance.

Global Equivalents

3. Chemical Composition and Alloying Philosophy

Key Differences and Philosophical Implications:

• SUS 310S emphasizes lower carbon content, targeting applications where weldability and resistance to intergranular corrosion are priorities.
  It offers balanced performance for structural components in thermal systems.
• AISI 314 shifts focus toward enhanced oxidation and scaling resistance, leveraging higher silicon and moderate carbon,
  making it more suitable for cyclic thermal loads and carburizing environments.

4. Physical and Thermal Properties of SUS 310S vs AISI 314 Stainless Steel

Both alloys share nearly identical density and melting ranges, reflecting their similar base chemistry.

However, AISI 314’s slight edge in creep rupture strength and thermal cycling owes to its elevated silicon content, which forms a more protective silica-rich oxide scale.

Conversely, SUS 310S offers marginally higher thermal conductivity, aiding heat dissipation in furnace fixtures.

5. Mechanical Properties of SUS 310S vs. AISI 314 Stainless Steel

SUS 310S and AISI 314 stainless steel are both high-temperature austenitic stainless steels designed to maintain mechanical integrity under thermal stress.

While their baseline room-temperature properties are similar, key differences emerge under prolonged exposure to elevated temperatures due to compositional factors such as silicon and carbon content.

Table: Comparative Mechanical Properties at Room and Elevated Temperatures

6. Corrosion and Oxidation Resistance

Oxidation Behavior

• 310S resists continuous oxidation up to 1150°C in air, forming a thin Cr₂O₃ scale. It excels in dry, non-sulfurous environments like heat treatment ovens.
• 314 pushes the limit to 1200°C, with its SiO₂-Cr₂O₃ scale resisting spalling and thickening in cyclic heating (e.g., cement kiln preheaters).

Aggressive Environments

• Carburization: 314’s silicon inhibits carbon diffusion, making it 30% more resistant than 310S in CO-rich atmospheres (e.g., petrochemical reformers).
• Sulfidation: In H₂S-containing gases, 314’s SiO₂ layer acts as a barrier, extending service life by 25% compared to 310S in refinery furnaces.
• Nitridation: Both alloys perform well, but 314’s higher nickel content offers marginal superiority in ammonia synthesis reactors.

Surface Treatments

• Passivation: Both benefit from nitric acid passivation to remove free iron and enhance corrosion resistance.
• Coatings: 314 may undergo aluminizing for extra protection in sulfidic environments, while 310S often relies on its inherent oxide layer for moderate conditions.

7. Weldability and Fabrication of SUS 310S vs. AISI 314 Stainless Steel

The weldability and fabrication characteristics of SUS 310S and AISI 314 stainless steel play a pivotal role in their industrial adoption, as high-temperature applications often require complex shaping, joining, and machining.

Weldability: Challenges and Best Practices

Both alloys belong to the austenitic stainless steel family, which generally offers good weldability due to their single-phase microstructure.

However, their distinct chemical compositions—especially carbon (C) and silicon (Si)—create notable disparities in welding behavior.

SUS 310S: The Weldability Champion

• Low Carbon Advantage:
  With a maximum carbon content of 0.08% (vs. 0.25% in AISI 314), SUS 310S minimizes the formation of chromium carbides (M₂₃C₆) in the heat-affected zone (HAZ).
  This reduces the risk of sensitization, a phenomenon where grain boundaries lose corrosion resistance due to chromium depletion.

• • Welding Processes: Gas tungsten arc welding (GTAW/TIG) and gas metal arc welding (GMAW/MIG) are preferred,
    with 310L filler metal (UNS S31003, ≤0.03% C) used to match corrosion resistance and prevent carbide precipitation.
  • Post-Weld Treatment: No mandatory post-weld heat treatment (PWHT) is required for most applications, even for thick sections (≥10 mm),
    making it ideal for on-site repairs and complex assemblies like furnace tube networks.

• Weld Joint Performance:
  Welded joints in 310S retain ≥90% of the base metal’s tensile strength at room temperature and 80% at 800°C, with elongation values matching the parent material (≥40%).
  This reliability supports its use in welded heat exchangers for petrochemical reformers.

AISI 314: Managing Carbide Formation and Hot Cracking

• Higher Carbon and Silicon Challenges:
  The 0.25% maximum carbon and 1.5–2.5% silicon in 314 increase the likelihood of HAZ carbide formation and hot cracking during welding.
  Silicon, while critical for high-temperature scale formation, also lowers the alloy’s liquidus temperature, creating microsegregation risks in the weld pool.

• • Preheating Requirements: Preheat to 200–300°C before welding to reduce thermal stress and slow cooling rates, minimizing sigma phase (Fe-Cr) precipitation in the HAZ.
  • Filler Metal Selection: Use 314-specific filler metal (e.g., ER314) or 310-type filler (ER310) to match the base metal’s chromium and nickel content, ensuring consistent high-temperature strength.
  • Post-Weld Heat Treatment (PWHT): Essential for thick sections (>15 mm),
    involving solution annealing at 1050–1100°C followed by rapid cooling to redissolve carbides and restore ductility.
    This adds 20–30% to fabrication time compared to 310S.

• Weld Joint Performance:
  Properly heat-treated welds in 314 achieve 95% of the base metal’s creep strength at 900°C, but neglecting PWHT can reduce this to 70%,
  increasing the risk of long-term failure in load-bearing components like kiln support beams.

Fabrication: Forming, Machining, and Heat Treatment

Cold Forming: Ductility Dictates Usability

• SUS 310S:
  With an elongation of ≥40% in the annealed state, 310S excels in cold forming processes like deep drawing, stamping, and roll bending.
  It readily forms intricate shapes such as furnace fan blades or heat exchanger fins without intermediate annealing, even for thicknesses up to 5 mm.

• • Example: A 310S furnace baffle with a 90° bend radius of 1.5x thickness maintains 95% of its as-formed ductility, critical for vibration-resistant applications.

• AISI 314:
  Slightly lower elongation (≥35%) and higher silicon-induced solid solution hardening make cold forming more challenging.
  It requires 10–15% higher forming forces, and severe cold working (e.g., >20% reduction) may necessitate post-forming annealing at 1050°C to restore ductility, adding complexity to part production.

Hot Working: Temperature and Tooling Considerations

• Forging and Hot Rolling:

• • 310S: Forge at 1100–1200°C, with a narrow working range to avoid sigma phase formation (above 950°C).
    Hot-rolled products like bars and plates exhibit uniform grain size (ASTM No. 6–7), ideal for subsequent machining.
  • 314: Requires higher forging temperatures (1150–1250°C) due to silicon-enhanced hot hardness, increasing energy consumption by 15% and tool wear by 20%.
    Post-forging, rapid cooling (water or air) is critical to prevent sigma phase precipitation.

• Machinability:
  Both alloys are prone to work-hardening during machining, but 314’s higher silicon content exacerbates tool wear.
  Use cobalt-based carbide tools with high rake angles (15–20°) and abundant coolant to manage heat:

• • 310S: Machining speed of 50–70 m/min for turning operations, with a surface finish of Ra 1.6–3.2 μm achievable with proper lubrication.
  • 314: Reduced to 40–60 m/min to minimize tool flaking, increasing machining time by 25% for equivalent features.

Heat Treatment: Annealing and Stress Relief

• Solution Annealing:

• • Both alloys require heating to 1050–1150°C followed by quenching to dissolve carbides and homogenize the microstructure.
    310S achieves full softening (≤187 HB) with this process, while 314 reaches ≤201 HB, balancing hardness and ductility.

• Stress Relief:
  For welded components, stress relief at 850–900°C for 1–2 hours reduces residual stresses without promoting carbide precipitation, a common practice in 310S boiler headers and 314 kiln brackets.

8. Typical Applications of SUS 310S vs. AISI 314 Stainless Steel

In high-temperature environments, choosing the right stainless steel alloy can directly influence operational safety, maintenance intervals, and overall system longevity.

SUS 310S and AISI 314 stainless steel, both austenitic stainless steels with excellent heat resistance, are widely used in various industries.

However, each alloy exhibits unique strengths that make it more suitable for specific applications.

Applications of SUS 310S Stainless Steel

Industry Sector: Petrochemical and Refining

Application: SUS 310S is commonly used in reforming furnaces, radiant tubes, and ethylene cracking coils.

Its combination of high-temperature strength and good weldability makes it well-suited for both static and fabricated components operating in oxidizing conditions.

Industry Sector: Power Generation

Application: This alloy is utilized in superheater tubes, heat exchangers, and boiler components,

where its resistance to thermal cycling and creep deformation ensures consistent performance over time.

Industry Sector: Metallurgy and Heat Treatment

Application: SUS 310S is widely applied in furnace muffles, retorts, and burner nozzles.

It maintains structural integrity under continuous heating, and its low carbon content reduces the risk of sensitization during welding or extended service.

Industry Sector: Cement and Ceramics Manufacturing

Application: In rotary kilns and heat shields, SUS 310S offers excellent oxidation resistance, along with sufficient mechanical flexibility to withstand thermal shock and vibration.

Industry Sector: Waste Incineration

Application: Components such as flue gas ducts and ash handling systems benefit from SUS 310S’s ability to resist corrosion from acidic gases and high-temperature combustion residues.

Industry Sector: Fabrication and Welding Tooling

Application: Due to its weldability and resistance to warping, SUS 310S is favored for jigs, welding fixtures, and supporting structures exposed to thermal stress.

Applications of AISI 314 Stainless Steel

Industry Sector: Industrial Furnaces

Application: AISI 314 is used extensively in furnace doors, radiant panels, heating element supports,

and brackets. Its higher silicon content enhances resistance to oxidation and metal dusting at temperatures exceeding 1100 °C.

Industry Sector: Glass and Ceramics Processing

Application: Thermocouple protection tubes and batch oven linings made from AISI 314 withstand prolonged exposure to extreme heat and corrosive off-gases.

Industry Sector: Steel Manufacturing

Application: This alloy performs reliably in high-temperature furnace rails, skid beams, and soaking pit covers, where both scale resistance and mechanical strength are essential.

Industry Sector: Thermal Processing Equipment

Application: In annealing boxes, radiant supports, and carburizing chambers,

AISI 314’s superior resistance to carburization and nitridation provides long service life in chemically aggressive, high-heat environments.

Industry Sector: Exhaust and Emission Control

Application: AISI 314 is employed in catalytic converter shells, flue ducts,

and thermal barriers within diesel and gas turbine exhaust systems due to its ability to withstand hot oxidation and exhaust gas corrosion.

Industry Sector: Chemical and Energy Sector

Application: It is also selected for components in coal gasification systems and syngas reactors, where its oxidation resistance and structural reliability at high temperatures are critical.

9. Advantages and Disadvantages of SUS 310S vs. AISI 314 Stainless Steel

SUS 310S (JIS G4303 / UNS S31008)

Advantages of SUS 310S

• Superior Weldability: Low carbon (≤0.08%) minimizes carbide precipitation, eliminating post-weld heat treatment (PWHT) for most applications.
• Cost-Effective: 10–15% cheaper than 314 due to lower Ni/Si content; ideal for large-scale use in moderate heat (800–1100°C).
• Excellent Cold Formability: High ductility (≥40% elongation) enables complex shapes via stamping/rolling without annealing.
• Oxidation Resistance: Stable Cr₂O₃ scale in dry air/CO₂ up to 1150°C, suitable for heat treatment furnaces and welded structures.

Disadvantages of SUS 310S

• Lower High-Temp Strength: Creep rupture strength ~37.5% lower than 314 at 900°C (25 MPa vs. 40 MPa).
• Vulnerable to Carburization/Sulfidation: Less resistant to carbon/sulfur ingress in aggressive environments (e.g., coal gasifiers, refineries).
• Limited Cyclic Heat Resistance: Prone to scale spalling at upper temp limits, unsuitable for severe thermal cycling.

AISI 314 (ASTM A240 / UNS S31400)

Advantages of AISI 314

• Extreme Heat Resistance: Operates up to 1200°C with SiO₂-Cr₂O₃ scale, 50°C higher than 310S; superior resistance to sulfidation/carburization in H₂S/CO-rich atmospheres.
• Higher Creep Strength: 85 MPa at 800°C (310S: 60 MPa) and 40 MPa at 900°C, critical for load-bearing components (e.g., kiln supports, turbine parts).
• Aggressive Environment Tolerance: Resists alkali/nitridation in cement/ammonia applications via silicon-enhanced scale.

Disadvantages of AISI 314

• Complex Welding: Requires preheating (200–300°C) and PWHT for thick sections, increasing fabrication costs by 20–30%.
• Lower Ductility: Reduced elongation (≥35%) limits cold forming; better suited for hot forging/casting.
• Premium Cost: 10–15% more expensive due to higher Ni/Si content; limited availability for custom shapes.
• Sigma Phase Risk: Prolonged use >950°C may reduce ductility via sigma phase precipitation.

10. Summary Comparison Table: SUS 310S vs. AISI 314 Stainless Steel

11. Conclusion

In high-temperature service, SUS 310S and AISI 314 stainless steel both deliver reliable austenitic performance, yet they cater to different priorities.

Choose 310S when fabrication ease, low-carbon sensitization control, and moderate creep resistance suffice.

Opt for 314 when cyclic oxidation resistance, silicon-enhanced scale strength, and elevated creep endurance dominate your design criteria.

By aligning alloy selection with your operating temperature, atmosphere, and welding strategy, you’ll maximize component life, minimize maintenance, and ensure safe, efficient plant operation.

Choosing DEZE means choosing a long-term and reliable high-temperature solution.

Our customers include many multinational equipment manufacturers and engineering contractors,

who have verified the stable performance of DEZE products under high temperature, corrosion, and thermal cycle conditions in long-term operation.

If you need technical information, samples, or quotations, please feel free to contact the DEZE professional team.

We will provide you with quick response and engineering-level support.

 

FAQs

Which is better, SUS 310S or AISI 314 stainless steel?

The answer depends on the application. SUS 310S is better for applications involving frequent thermal cycling, welding, and fabrication,

due to its low carbon content, which enhances weldability and reduces the risk of intergranular corrosion.

On the other hand, AISI 314 is more suitable for static components exposed to extremely high temperatures (up to 1150 °C), thanks to its higher silicon and carbon content, which provide superior oxidation and creep resistance.

In summary:

• Choose SUS 310S for versatility, weldability, and cyclic thermal conditions.
• Choose AISI 314 for continuous high-temperature environments and enhanced oxidation resistance.

What lasts longer: SUS 310S or AISI 314?

In cyclic thermal conditions or welded systems, SUS 310S typically exhibits longer service life due to its resistance to sensitization and thermal fatigue.

However, in dry, high-temperature static environments, AISI 314 can outperform SUS 310S because its higher silicon content offers superior oxidation resistance and scale adhesion.

Longevity depends on:

• Temperature range
• Environmental conditions (oxidizing, carburizing, etc.)
• Mechanical stress and fabrication methods

Why is SUS 310S preferred over AISI 314 in welded structures?

SUS 310S contains ≤0.08% carbon, significantly reducing the formation of chromium carbides at grain boundaries during welding.

This improves resistance to intergranular corrosion, especially in high-temperature service.

In contrast, AISI 314 has a higher carbon content (up to 0.25%), which can lead to sensitization and hot cracking during welding unless carefully controlled with appropriate post-weld heat treatments.

Thus, SUS 310S is often the alloy of choice for fabricated or field-welded assemblies.

Why is AISI 314 chosen over SUS 310S for extremely high temperatures?

AISI 314 contains 1.5–3.0% silicon, compared to ≤1.5% in SUS 310S.

This elevated silicon enhances oxidation resistance and allows AISI 314 to maintain protective scale adhesion at temperatures up to 1150 °C,

making it ideal for industrial furnaces, heater elements, and high-temp exhausts.

Moreover, its higher carbon content contributes to improved creep strength under prolonged stress.

This makes AISI 314 a strong candidate for static, long-term exposure in oxidizing or dry atmospheres.

Can SUS 310S vs. AISI 314 be used interchangeably?

While they share similar base chemistry and both belong to the austenitic stainless steel family, interchangeability is limited.

In applications requiring welding or thermal cycling, SUS 310S is more reliable.

Conversely, in high-temperature oxidation-critical applications, AISI 314 should be prioritized. Engineers must evaluate:

• Service temperature
• Exposure environment
• Mechanical loading
• Fabrication requirements

Always refer to the relevant engineering standards and safety factors before substituting one grade for the other.