Views: 3 Author: Shirley Publish Time: 2026-05-11 Origin: Site
The 0.2% offset yield strength of Inconel 625 (UNS N06625) at 700°C (1292°F) is approximately 414–448 MPa (60–65 ksi), depending on product form and heat-treatment condition. This exceeds the yield strength of 316L stainless steel at the same temperature by more than 300% and outperforms most commercially available austenitic alloys, making Inconel 625 the go-to material for high-temperature pressure vessels, heat exchangers, and aerospace combustion hardware.
Among the materials evaluated for these roles, Inconel 625 is one of the most comprehensively characterized nickel-chromium-molybdenum superalloys in service today. Its strength at 700°C is often cited in technical datasheets and specifications but rarely explained in context. This blog post fills that gap: we define the measurement, compare Inconel 625 against relevant competitor alloys at 700°C, explain the metallurgical reasons for its superiority, and provide sourced data in a ready-to-use reference table.
Defining Yield Strength
Yield strength is defined as the stress (force per unit area) at which a material transitions from elastic (recoverable) deformation to plastic (permanent) deformation. Engineers most commonly use the 0.2% offset method: the stress corresponding to a strain of 0.002 (0.2%) on the engineering stress–strain curve. This value is reported in megapascals (MPa) in SI units, or in ksi (kilopounds per square inch) in imperial systems.
The Effect of Elevated Temperature
As temperature rises, atomic thermal vibrations weaken metallic bonds, and thermally activated dislocation glide becomes easier. The net result is a progressive reduction in yield strength. For most ferritic and austenitic stainless steels, yield strength at 700°C can be as little as 20–30% of the room-temperature value. [2] For nickel superalloys such as Inconel 625, solid-solution strengthening by molybdenum and niobium, combined with the formation of metastable δ (delta) and γ′′ (gamma double-prime) precipitates, dramatically slows this drop.
Inconel 625 is a nickel-based superalloy with the following nominal chemistry, per ASTM B443 and AMS 5599: [3,4]
Element | Ni | Cr | Mo | Nb+Ta | Fe (max) | C (max) |
Wt. % | Balance (~58%) | 20.0–23.0 | 8.0–10.0 | 3.15–4.15 | 5.0 | 0.10 |
Table 1. Nominal chemical composition of Inconel 625 per ASTM B443 / UNS N06625. [3]
Four overlapping mechanisms contribute:
• Solid-solution strengthening by Mo and Nb: Both elements have large atomic radii relative to nickel, creating lattice strain that impedes dislocation movement at elevated temperatures. [5]
• Precipitation of γ′′ (Ni₃Nb): On prolonged exposure above 650°C, metastable gamma-double-prime precipitates form and further pin dislocation glide planes. [5]
• Cr₂O₃ surface oxide: Although a surface phenomenon rather than a bulk strengthening mechanism, the self-healing chromia layer prevents oxidation-assisted crack growth at 700°C, maintaining effective cross-section and load-bearing capacity. [6]
• Austenitic FCC matrix: The face-centred cubic crystal structure provides more slip systems than ferritic BCC steels, enabling better hot ductility alongside high strength. [2]
Published Values by Product Form
The yield strength of Inconel 625 at 700°C varies slightly with product form (sheet, plate, bar, seamless tube) and heat-treatment condition (annealed vs. solution-treated). The following values are drawn from the Special Metals Corporation Inconel Alloy 625 Technical Data Sheet, ASTM B443/B444 minimum requirements, and the ASM Handbook: [3,4,7]
Alloy / Grade | 0.2% YS at 700°C (MPa) | 0.2% YS at 700°C (ksi) | UTS at 700°C (MPa) | Elongation at 700°C (%) | Standard / Source |
Inconel 625 (annealed) | 448 | 65 | 760 | 45 | [3,7] |
Inconel 625 (sol. treated) | 414 | 60 | 724 | 48 | [3] |
Inconel 718 (aged) | 862 | 125 | 1000 | 18 | [8] |
Hastelloy C-276 | 310 | 45 | 620 | 50 | [9] |
316L SS (annealed) | 110 | 16 | 300 | 35 | [2] |
310S SS (annealed) | 140 | 20 | 320 | 38 | [2] |
Alloy 800H | 170 | 25 | 380 | 40 | [10] |
Inconel 601 (annealed) | 220 | 32 | 450 | 42 | [11] |
Incoloy 825 (annealed) | 170 | 25 | 370 | 45 | [12] |
Table 2. Comparative 0.2% offset yield strength and tensile properties at 700°C (1292°F). Data from Special Metals, ASM Handbook, and ASTM standards. Values represent annealed condition unless stated. [2,3,7–12]
Key Insight: Inconel 718 outperforms Inconel 625 at 700°C because of its gamma-prime / gamma-double-prime precipitation hardening. However, Inconel 718 is significantly more expensive, more difficult to weld, and susceptible to strain-age cracking. For weldability-critical applications such as clad piping, exhaust ducts, and heat exchanger tubing, Inconel 625 offers the superior balance of yield strength, corrosion resistance, and fabricability at 700°C.
Effect of Exposure Duration on Yield Strength
Long-term isothermal exposure at 700°C promotes δ-phase precipitation along grain boundaries, which can reduce ductility while modestly increasing yield strength. ASTM STP 1049 reports that after 1,000 hours at 700°C, Inconel 625 yield strength may increase to approximately 480–510 MPa due to precipitation strengthening, but elongation can drop to below 20%. [13] This trade-off must be factored into long-service-life design, particularly for components operating under creep-fatigue interaction.
International pressure vessel and piping codes establish minimum guaranteed yield strength values that are lower than typical test results, providing a safety margin for statistical variation. For Inconel 625: [14,15]
• ASME Section II, Part D (2023 Edition): minimum allowable stress at 700°C ≈ 119 MPa for Inconel 625 bar (ASME SB-446). Note: ASME allowable stress is derived from the lesser of YS/1.5 or UTS/3.5, not the full yield strength. [14]
• EN 10302:2008 (European creep-resistant steel & alloy standard): minimum 0.2% proof strength (Rp0.2) at 700°C for alloy NiCr22Mo9Nb (equivalent to 625) = 250 MPa minimum (design minimum; actual test values exceed 414 MPa). [15]
• NACE MR0175 / ISO 15156: confirms Inconel 625 in the annealed condition meets sulphide stress cracking resistance requirements in sour service environments, even at elevated temperatures. [16]
Aerospace & Gas Turbine
Inconel 625 is used in exhaust systems, thrust-reverser structures, and combustion-liner splash plates where temperatures routinely reach 650–750°C. Its 448 MPa yield strength at 700°C—combined with excellent fatigue resistance—makes it a primary choice specified in aerospace material standards such as AMS 5599 (sheet/strip/plate) and AMS 5666 (bar/rod). [4]
Chemical Processing & Hydrocarbon Refining
Catalytic reforming reactors, hydrotreating vessels, and acid regeneration systems operate in the 600–750°C range in the presence of chlorides, sulphur compounds, and strong acids. Inconel 625 tubing (ASTM B444 Grade 1 and Grade 2) maintains structural margins and resists pitting and crevice corrosion simultaneously, eliminating the need for additional corrosion allowance. [3,6]
Nuclear & Energy
In pressurised water reactors (PWR), Inconel 625 weld overlay cladding is applied to reactor pressure vessel nozzles. The yield strength retention at design-basis accident temperatures (up to 700°C in certain transient scenarios) is a critical qualification parameter reviewed under 10 CFR 50 Appendix A. [17]
Subsea & Offshore
Although subsea temperatures are low, Inconel 625 is widely used in wellhead equipment and flexible risers because its high room- and elevated-temperature yield strength allows thin-wall designs that reduce weight and buoyancy penalties—critical in deepwater installations. [16]
Selection Criterion | Inconel 625 | Key Alternatives | Recommendation |
Yield strength at 700°C | ⭐⭐⭐⭐ (448 MPa) | SS 316L: ⭐ (110 MPa) Alloy 718: ⭐⭐⭐⭐⭐ (862 MPa) | 625 best for weldable mid-range strength |
Weldability | ⭐⭐⭐⭐⭐ (Excellent) | SS 316L: ⭐⭐⭐⭐⭐ Alloy 718: ⭐⭐ (Crack-sensitive) | 625 preferred in clad/ERW applications |
Corrosion resistance | ⭐⭐⭐⭐⭐ (Outstanding) | Hastelloy C-276: ⭐⭐⭐⭐⭐ SS 316L: ⭐⭐⭐ | Similar to C-276 in oxidising media |
Relative cost (raw material) | Moderate-High | SS 316L: Low Alloy 718: High Hastelloy C-276: High | 625 best cost-performance for 600–800°C |
Creep life at 700°C | ⭐⭐⭐⭐ | SS 316L: ⭐⭐ Alloy 800H: ⭐⭐⭐ | 625 superior for <30,000 hour targets |
Table 3. Engineering selection matrix for high-temperature applications at approximately 700°C.
Q: Is the yield strength of Inconel 625 listed in ASTM standards?
Yes. ASTM B443 (plate and sheet) and ASTM B446 (bar) specify minimum room-temperature mechanical properties. Elevated-temperature data is published in ASTM STP 1049 and ASME Section II, Part D. The typical annealed 0.2% YS at 700°C is ≈ 448 MPa per Special Metals’ published data. [3,7,14]
Q: Does welding reduce Inconel 625 yield strength at 700°C?
The weld heat-affected zone (HAZ) of Inconel 625 may experience slight grain growth, reducing local yield strength by approximately 5–10%. Post-weld annealing at 980°C (30 min) restores uniform properties. ENiCrMo-3 filler metal (AWS A5.14) is typically specified to maintain compositional integrity. [4,7]
Q: How does 700°C compare to Inconel 625’s maximum service temperature?
Special Metals recommends a maximum continuous service temperature of approximately 980°C for non-structural oxidation resistance. For load-bearing applications where yield strength and creep life are primary constraints, 700°C represents a moderate service temperature at which Inconel 625 remains well within safe operating limits with substantial strength margins. [3]
Q: What is the yield strength of Inconel 625 at room temperature for comparison?
In the annealed condition, the room-temperature 0.2% YS of Inconel 625 is typically 414–517 MPa (60–75 ksi), meaning it retains approximately 87–95% of its room-temperature strength at 700°C—an exceptional performance that illustrates the alloy’s outstanding elevated-temperature stability. [3]
Inconel 625’s 0.2% offset yield strength at 700°C of approximately 414–448 MPa makes it one of the strongest weldable nickel alloys at that temperature. Compared with 316L stainless steel (≈110 MPa), Alloy 800H (≈170 MPa), and even Hastelloy C-276 (≈310 MPa) at the same temperature, Inconel 625 provides a decisive structural advantage. Its unique combination of solid-solution strengthening, corrosion resistance, and weldability makes it the preferred material for aerospace exhaust structures, chemical processing reactors, and nuclear cladding applications operating in the 600–750°C regime.
For engineers and procurement specialists specifying alloy products for high-temperature service, this comparative data—sourced from ASTM standards, ASME codes, and Special Metals technical publications—provides a rigorous, citation-backed foundation for material justification documents and engineering calculations.
Need certified Inconel 625 products? Contact our sales team for mill certificates, ASTM-conforming stock, and custom fabrication in sheet, plate, bar, tube, and welding wire forms.
References
[1] ASTM E8/E8M-22, Standard Test Methods for Tension Testing of Metallic Materials. ASTM International, West Conshohocken, PA, 2022.
[2] ASM Handbook, Volume 2: Properties and Selection: Nonferrous Alloys and Special-Purpose Materials. ASM International, 2020. pp. 841–867 (Elevated-temperature mechanical properties of austenitic stainless steels).
[3] Special Metals Corporation. Inconel® Alloy 625 Technical Data Sheet. Publication SMC-063. Huntington Alloys, 2013. Available at: www.specialmetals.com.
[4] SAE International. AMS 5599P: Nickel Alloy, Corrosion and Heat-Resistant, Sheet, Strip, and Plate, 62Ni-21.5Cr-9.0Mo-3.65Cb (Nb). AMS 5599P, 2021.
[5] Floreen, S., Fuchs, G.E., and Yang, W.J. “The Metallurgy of Alloy 625.” Superalloys 718, 625, 706 and Various Derivatives, TMS, Warrendale, PA, 1994, pp. 13–37.
[6] Berthod, P. “High-Temperature Oxidation Behaviour of Ni-Cr-Mo-Nb Alloys.” Oxidation of Metals, vol. 64, no. 3–4, 2005, pp. 235–252.
[7] ASM Handbook, Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys. ASM International, 2018. Table on Elevated-Temperature Tensile Properties of Nickel-Base Alloys.
[8] Special Metals Corporation. Inconel® Alloy 718 Technical Data Sheet. Publication SMC-045. Huntington Alloys, 2014.
[9] Haynes International. Hastelloy® C-276 Alloy Data Sheet. Kokomo, IN: Haynes International, 2021. H-2002D.
[10] Special Metals Corporation. Incoloy® Alloy 800H/800HT Technical Data Sheet. Publication SMC-047. Huntington Alloys, 2016.
[11] Special Metals Corporation. Inconel® Alloy 601 Technical Data Sheet. Publication SMC-027. Huntington Alloys, 2018.
[12] Special Metals Corporation. Incoloy® Alloy 825 Technical Data Sheet. Publication SMC-065. Huntington Alloys, 2016.
[13] Shankar, V., Bhanu Sankara Rao, K., and Mannan, S.L. “Microstructure and Mechanical Properties of Alloy 625 Weldments.” Journal of Nuclear Materials, vol. 288, no. 2–3, 2001, pp. 222–232.
[14] ASME Boiler and Pressure Vessel Code, Section II, Part D: Properties (Customary). ASME International, New York, 2023 Edition. Table 1A – Allowable Stress Values.
[15] EN 10302:2008. Creep Resisting Steels, Nickel and Cobalt Alloys. European Committee for Standardization (CEN), Brussels, 2008.
[16] ANSI/NACE MR0175 / ISO 15156:2020. Petroleum and Natural Gas Industries – Materials for Use in H₂S-Containing Environments in Oil and Gas Production. NACE International, Houston, TX, 2020.
[17] U.S. Nuclear Regulatory Commission. 10 CFR Part 50 Appendix A – General Design Criteria for Nuclear Power Plants. U.S. Government Printing Office, Washington DC, current edition.
Disclaimer: The data presented in this article are compiled from publicly available technical datasheets, industry standards, and peer-reviewed literature for general informational and educational purposes. Actual material properties depend on product form, heat treatment, testing method, and individual heat chemistry. Always obtain certified mill test reports and consult with a qualified materials engineer before finalising alloy selection for safety-critical applications.
