In the field of high-performance engineering, selecting the right alloy for specific temperature and corrosion conditions is crucial. Whether in oil and gas, chemical processing, or power generation, the balance between strength, corrosion resistance, and temperature capability determines long-term reliability.
One of the rising stars in this category is Alloy N09935, a nickel-iron-chromium alloy known for its excellent corrosion resistance and mechanical stability. But how high can it go in terms of temperature?
This article from SASAALLOY explores in detail the maximum service temperature of Alloy N09935, how it compares to other nickel-based alloys like 718 and 625, and the factors that affect its thermal performance in real-world applications.
1. Introduction to Alloy N09935
Alloy N09935 is a nickel-iron-chromium alloy containing additions of molybdenum, copper, titanium, and niobium, designed to combine high strength with excellent resistance to pitting, crevice, and stress corrosion cracking, especially in H₂S- and CO₂-containing environments.
The alloy is precipitation-hardenable, allowing it to maintain strong mechanical properties after aging treatment. It complies with ASTM B649 and is approved by NACE MR0175 / ISO 15156 for sour-gas service.
Key features include:
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Exceptional resistance to chloride and sulfide corrosion
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High yield and tensile strength after aging
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Good weldability and fabricability
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Stable performance at elevated temperatures
2. Maximum Service Temperature – The Basic Definition
The maximum service temperature of an alloy refers to the highest temperature at which it can operate continuously and safely without significant loss of mechanical strength, oxidation resistance, or corrosion protection.
For nickel-based alloys like N09935, this value depends on:
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Microstructural stability
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Phase transformations
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Precipitate coarsening during service
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Oxidation and scaling resistance
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Long-term exposure conditions (pressure, atmosphere, environment)
3. Alloy N09935 Maximum Service Temperature
Laboratory testing and field performance data show that:
The maximum continuous service temperature for Alloy N09935 is approximately 650°C (1200°F).
At this temperature range, Alloy N09935 maintains good mechanical strength, corrosion resistance, and structural stability. Beyond 650°C, there is a gradual decline in strength due to overaging and grain coarsening of the precipitation-hardened microstructure.
3.1 Safe Service Range
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Continuous service: up to 650°C (1200°F)
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Intermittent exposure: short periods up to 700°C (1290°F) may be tolerated without critical degradation
However, for components requiring high stress retention or fatigue resistance, the recommended upper limit should remain below 650°C.
4. Comparison with Other Nickel Alloys
| Alloy | Type | Maximum Service Temperature | Typical Application |
|---|---|---|---|
| N09935 | Ni-Fe-Cr-Mo-Cu | 650°C | Oilfield equipment, chemical processing, sour gas service |
| Inconel 718 (UNS N07718) | Ni-Cr-Fe | 700°C | Aerospace turbines, bolts, high-temp fasteners |
| Alloy 625 (UNS N06625) | Ni-Cr-Mo | 980°C | Heat exchangers, furnace components |
| Alloy 925 (UNS N09925) | Ni-Fe-Cr-Mo-Cu | 600°C | Downhole tools, marine fasteners |
| Alloy 945 (UNS N09945) | Ni-Fe-Cr-Mo-Nb | 650–680°C | Wellhead and completion equipment |
From this comparison, Alloy N09935’s 650°C limit places it between Alloy 925 and Alloy 718 — offering better high-temperature strength than 925 and similar corrosion protection, but at a lower cost and with easier fabricability than 718.
5. Why Alloy N09935 Performs Well at Elevated Temperatures
Several metallurgical factors contribute to the alloy’s temperature stability:
5.1 Precipitation Hardening Mechanism
Alloy N09935 derives strength through precipitation of Ni₃(Ti,Nb) phases during aging. These precipitates remain stable up to about 650°C before coarsening begins, ensuring a long life under cyclic loading and stress.
5.2 Solid Solution Strengthening
The combination of molybdenum and chromium strengthens the nickel-iron matrix, reducing dislocation mobility at high temperature. This enhances creep resistance and prevents deformation under pressure.
5.3 Protective Oxide Film
At elevated temperatures, the alloy forms a thin, adherent Cr₂O₃ oxide film that protects against further oxidation and scaling. This layer remains stable up to about 700°C in air or oxidizing gas mixtures.
5.4 Controlled Grain Structure
Through appropriate heat treatment (solution + aging), Alloy N09935 develops a fine-grained, uniform microstructure that improves toughness and resists grain growth during thermal exposure.
6. Effects of Overheating
Operating above the recommended 650°C may cause:
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Overaging of precipitates, reducing yield strength
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Grain coarsening, decreasing toughness
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Oxidation scale thickening, reducing corrosion protection
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Microstructural instability, especially near weld heat-affected zones
Therefore, components like tubing, shafts, and connectors used in long-term high-temperature service should maintain continuous exposure below 650°C for optimal performance.
7. Mechanical Properties Retention with Temperature
| Temperature (°C) | Yield Strength (MPa) | Tensile Strength (MPa) | Elongation (%) |
|---|---|---|---|
| Room Temp | 900 | 1080 | 35 |
| 400°C | 870 | 1020 | 32 |
| 550°C | 820 | 960 | 30 |
| 650°C | 760 | 900 | 28 |
These values illustrate that Alloy N09935 retains over 80% of its room-temperature strength at 650°C, making it a reliable material for continuous elevated-temperature operation.
8. Application Scenarios by Temperature Zone
Below 300°C
Used in chemical process equipment, pump housings, and valve components where corrosion is dominant.
300–500°C
Ideal for downhole tubing, flanges, and wellhead components that experience both thermal stress and sour gas corrosion.
500–650°C
Used in heat-exposed fasteners, pump impellers, and flow control systems where both oxidation and mechanical strength are critical.
Above 650°C, other superalloys like Inconel 625 or Alloy 718 are recommended.
9. Alloy N09935 vs Alloy 718 – Temperature Performance Comparison
| Property | Alloy N09935 | Alloy 718 |
|---|---|---|
| Max Continuous Temperature | 650°C | 700°C |
| Creep Resistance | Good | Excellent |
| Oxidation Resistance | Very Good | Excellent |
| Corrosion Resistance (H₂S/CO₂) | Superior | Limited |
| Fabricability | Easier | Difficult |
| Cost | Moderate | Higher |
While Alloy 718 provides better creep strength at very high temperatures, Alloy N09935 offers a better overall performance in environments combining heat and corrosive media, such as oilfield production systems.
10. Thermal Expansion and Conductivity
| Property | Alloy N09935 | Alloy 718 |
|---|---|---|
| Coefficient of Thermal Expansion (20–600°C) | 13.4 × 10⁻⁶ /°C | 13.0 × 10⁻⁶ /°C |
| Thermal Conductivity (W/m·K) | 11.5 | 11.0 |
Alloy N09935’s thermal expansion and conductivity are similar to 718, ensuring dimensional stability and predictable heat transfer performance during prolonged thermal exposure.
11. Real-World Applications
11.1 Oil and Gas
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Tubing hangers, packers, completion tools
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Downhole shafts and seals exposed to 500–650°C
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Components in high-pressure H₂S/CO₂ environments
11.2 Chemical Processing
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Heat exchanger plates
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Reactor fittings
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Valves and pump housings for chloride solutions
11.3 Power Generation
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High-temperature fasteners and couplings
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Gas turbine auxiliary systems
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Exhaust ducting and support structures
In these fields, Alloy N09935 serves as a cost-effective alternative to Alloy 718 or Alloy 625, providing reliable performance at moderate high temperatures with excellent corrosion protection.
12. Fabrication and Heat Treatment for Temperature Stability
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Solution Annealing: 1000–1100°C, followed by rapid cooling
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Aging Treatment: 720–760°C for several hours, to develop precipitation strength
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Weldability: Good; use matching filler metals or Alloy 625-type filler for corrosion resistance
These treatments produce an optimized microstructure capable of withstanding both thermal cycling and chemical attack up to 650°C.
13. Advantages of Alloy N09935 in Elevated-Temperature Service
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Balanced Strength and Corrosion Resistance – Retains high mechanical strength under thermal stress.
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Stable Microstructure – Precipitates remain fine and coherent up to 650°C.
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Oxidation Protection – Chromium-rich oxide layer prevents scaling.
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Ease of Fabrication – Easier machining and forming compared to 718.
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Cost Efficiency – Lower nickel content reduces raw material cost.
These benefits make it a versatile choice for complex, high-demand components where both heat and chemical attack are present.
14. SASAALLOY Technical Expertise
SASAALLOY supplies Alloy N09935 in multiple product forms — bars, plates, forgings, and tubes — all produced under ASTM, ASME, and NACE MR0175 standards.
With decades of metallurgical experience, our team supports clients in:
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Material selection and design optimization
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Thermal exposure analysis and life prediction
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Customized heat treatment for maximum temperature performance
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Quality assurance with 3.1 / 3.2 certificates and PMI verification
For projects that operate near the limits of performance, SASAALLOY provides the technical confidence and reliability your systems demand.
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15. Conclusion
The maximum service temperature of Alloy N09935 is approximately 650°C (1200°F) for continuous operation. This makes it a robust choice for oilfield and chemical environments where both corrosion and heat are critical concerns.
While alloys like 718 or 625 may handle higher extreme temperatures, Alloy N09935 delivers an exceptional balance of thermal stability, mechanical strength, and corrosion resistance, particularly in sour-gas and chloride-containing conditions.
Engineers selecting materials for modern energy systems, refinery components, or heat-exposed fasteners can rely on Alloy N09935 for long-term stability and cost efficiency.
For technical datasheets, temperature resistance charts, or expert consultation, contact SASAALLOY — your trusted global partner in nickel-based alloy innovation.
Post time: Oct-29-2025