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UNS NUMBER
N06625
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ALLOY FAMILY
Ni-Cr-Mo-Nb
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HARDENING
Solid Solution
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UTS (ANNEALED)
≥827 MPa
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MAX TEMP
~1050°C
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DENSITY
8.44 g/cm³
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Inconel 625 (UNS N06625) is a nickel-chromium-molybdenum alloy with outstanding corrosion resistance and high strength (827–1034 MPa UTS in the annealed condition). The addition of molybdenum (8–10%) and niobium (3.15–4.15%) provides solid-solution strengthening and remarkable resistance to pitting, crevice corrosion, and intergranular attack. Inconel 625 is non-magnetic, retains toughness from cryogenic to 1050°C, and is the workhorse alloy for seawater, flue-gas desulfurization, and chemical processing.
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Ni (Min)
≥58%
Base element
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Cr
20-23%
Oxidation / pitting
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★ Mo
8-10%
Pitting / crevice resistance
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★ Nb+Ta
3.15-4.15%
Solid-solution strengthener
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UTS (ANNEALED)
827-1034 MPa
Typical range
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YS (0.2% ANN.)
414-621 MPa
Yield strength
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ELONGATION
≥30%
Annealed, min
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SERVICE TEMP
-196~1050°C
Cryogenic to high-temp
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What is Inconel 625?
Inconel 625 is a nickel-chromium-molybdenum alloy distinguished by the addition of niobium (columbium) which, together with molybdenum, allows the alloy to be strengthened by the precipitation of face-centered-cubic gamma-double-prime (γ″) without heat treatment. In practice, Inconel 625 is used in the solution-annealed (mill-annealed) condition — the strengthening is inherent from the solid-solution effect of Mo and Nb, with no need for age hardening.
First introduced in the 1960s, Inconel 625 was originally developed for high-temperature seawater applications in the aerospace and marine sectors. Its combination of exceptional corrosion resistance (especially pitting and crevice corrosion, with a PREN of ~48) and high strength (UTS 827–1034 MPa as-annealed) has made it the most widely used corrosion-resistant nickel alloy after the Monel series.
Chemical Composition (Weight %)
| Element |
Min (%) |
Max (%) |
Role in Alloy |
| Nickel (Ni) |
≥58.0 |
— |
Base element; matrix former |
| Chromium (Cr) |
20.0 |
23.0 |
Oxidation resistance; PREN contributor |
| Molybdenum (Mo) |
8.0 |
10.0 |
Pitting/crevice resistance; solid-solution strength |
| Niobium+Ta (Nb+Ta) |
3.15 |
4.15 |
Solid-solution strengthening (γ″ precursor) |
| ★ Iron (Fe) |
— |
5.0 |
Impurity control; limited Fe tolerance |
| Carbon (C) |
— |
0.10 |
Kept low to avoid carbide precipitation |
| Manganese (Mn) |
— |
0.50 |
Deoxidizer; hot-work aid |
| Silicon (Si) |
— |
0.50 |
Deoxidizer |
| Phosphorus (P) |
— |
0.015 |
Impurity; keep very low |
| Sulfur (S) |
— |
0.015 |
Impurity; keep very low |
| Aluminum (Al) |
— |
0.40 |
Minor; controls minor phases |
| Titanium (Ti) |
— |
0.40 |
Minor; PINs grain boundaries |
| Cobalt (Co) |
— |
1.0 |
Occasionally present as impurity |
★ Nb (niobium, formerly columbium) is the defining strengthening element. Fe is limited to 5% max to avoid embrittlement at high temperatures.
Mechanical Properties
Inconel 625 achieves high strength through solid-solution strengthening by molybdenum and niobium, without requiring age hardening. The properties below are for the mill-annealed (solution-annealed) condition per ASTM B443.
| Condition / Form |
UTS (MPa) |
YS 0.2% (MPa) |
Elong. % (min) |
Hardness (HB) |
| Annealed Plate/Sheet |
827–1034 |
414–621 |
30 |
145–220 |
| Annealed Bar/Rod |
827–1034 |
414–621 |
30 |
145–220 |
| Cold-Worked (20%) |
~1000–1200 |
~800–1000 |
15–25 |
250–320 |
Elastic Constants — Modulus of Elasticity: 207 GPa (at 21°C); Shear Modulus: 79 GPa; Poisson's Ratio: 0.31. These values are stable from cryogenic temperatures up to 800°C.
Physical Properties
| Property |
Value |
Note |
| Density |
8.44 g/cm³ |
Slightly denser than 304 SS (7.9) |
| Melting Range |
1290–1350°C |
Solidus ~1290°C, Liquidus ~1350°C |
| Thermal Cond. (21°C) |
9.8 W/m·K |
Lower than carbon steel |
| Thermal Exp. (21–93°C) |
12.8 ×10⁻⁶ /K |
Comparable to austenitic SS |
| Specific Heat |
410 J/kg·K |
At 21°C |
| Electrical Resistivity |
1.28 µΩ·m |
At 21°C |
| Magnetic Property |
Non-magnetic |
Annealed condition; non-magnetic even when cold worked |
| PREN (Pitting Resistance) |
~48 |
PREN = %Cr + 3.3×%Mo + 16×%N |
Corrosion Resistance
Seawater & Marine Environments
Inconel 625 has exceptional resistance to flowing seawater, with no recorded failures from chloride stress-corrosion cracking (SCC) — the failure mode that causes 316L stainless steel to crack within months. Its PREN (~48) far exceeds that of 316L (PREN ~24) and even 904L (PREN ~35). Inconel 625 is essentially immune to pitting and crevice corrosion in natural seawater, making it the standard material for propeller shafts, seawater pump bodies, and subsea hardware.
Pitting & Crevice Corrosion
The high molybdenum content (8–10%) is the primary driver of Inconel 625's resistance to localized corrosion. In chloride-containing environments (including brackish water, produced water, and sour gas with chlorides), Inconel 625 reliably resists pit initiation. In ASTM G48 testing, the Critical Pitting Temperature (CPT) exceeds 100°C for alloy 625, compared to ~25°C for 316L.
Acid Environments
Inconel 625 is resistant to non-oxidizing acids (hydrochloric, phosphoric) at moderate concentrations and temperatures. It is also resistant to oxidizing acids (nitric) but not as outstanding as Inconel 600. Sulfuric acid resistance is good up to ~50% concentration at room temperature. In flue-gas desulfurization (FGD) scrubbers, Inconel 625 cladding is widely used to resist the acidic condensate (pH 1–3) created by SO₂ absorption.
High-Temperature Oxidation
Chromium (20–23%) forms a tenacious Cr₂O₃ scale that protects the alloy up to ~1050°C in air. Above 1050°C, the scale breaks down and internal oxidation accelerates. Inconel 625 is also resistant to carburizing and nitriding atmospheres at elevated temperatures, making it suitable for furnace components and heat-treatment equipment.
Inconel 625 vs. Similar Alloys — Selection Guide
| If you need... |
Choose... |
Why |
| Maximum corrosion resistance in seawater |
Inconel 625 |
Highest PREN (~48); immune to Cl⁻ SCC |
| High strength + age hardening |
Inconel 718 or Monel K500 |
625 is solid-solution only; does not age-harden |
| Lower cost, seawater OK |
Monel 400 / 316L Duplex |
625 is over-specified for mild seawater |
| High-temp oxidation above 1050°C |
Inconel 600 or 601 |
Higher Cr (up to 23–25%) for extreme oxidation |
| Sour gas (NACE) with high strength |
Incoloy 925 or 718 |
Age-hardenable; 625 is acceptable but not optimized for sour |
Applicable Standards
| Standard |
Product Form |
| ASTM B443 |
Plate, Sheet, Strip |
| ASTM B444 |
Seamless Pipe and Tube |
| ASTM B446 |
Bar, Rod, Forging Stock |
| ASTM B564 |
Forged Fittings, Flanges |
| ASME SB-443 / SB-444 / SB-446 |
Corresponding ASME Boiler & Pressure Vessel Code editions |
| NACE MR0175 / ISO 15156 |
Sour service qualification (hardness control required) |
HT PIPE Supply — Inconel 625 Product Forms
| Product Form |
Specifications |
HT PIPE Supply |
| Seamless Pipe |
ASTM B444 / ASME SB-444 |
✅ Available |
| Welded Pipe |
ASTM B705 / ASME SB-705 |
✅ Available |
| Forged Fittings |
ASTM B564 / ASME B16.11 |
✅ Available |
| Butt-Weld Fittings |
ASME B16.9 / MSS SP-43 |
✅ Available |
| Flanges |
ASME B16.5 / B16.47 / ASTM B564 |
✅ Available |
| Plate / Sheet |
ASTM B443 / ASME SB-443 |
✅ Available |
| Bar / Rod |
ASTM B446 / ASME SB-446 |
✅ Available |
All Inconel 625 products from HT PIPE are supplied in the mill-annealed (solution-annealed) condition. Material test reports (MTRs) per EN 10204 3.1 or 3.2 are provided as standard. NACE MR0175 compliance certification is available on request for sour-service applications.
Project Experience — Inconel 625
HT PIPE has supplied Inconel 625 products to offshore and chemical processing projects worldwide. Recent representative cases:
| Project |
Product |
Specification |
| Offshore Platform Seawater Lift Pipe (South China Sea) |
Inconel 625 Clad Plate + Forged Flanges |
ASTM B443 / ASTM B564, NACE MR0175 |
| Flue-Gas Desulfurization Absorber Lining (Jiangsu, China) |
Inconel 625 Strip Lining, Welded Pipe Spools |
ASTM B444, ASME SB-444 |
| Subsea Flowline Jumper (Southeast Asia) |
Inconel 625 Seamless Pipe + BW Fittings |
ASTM B444, API 6A, NACE MR0175 |
Our technical team can provide material selection advice, welding procedure specifications (WPS), and pre-qualification support for Inconel 625 in sour and seawater applications.
| FREQUENTLY ASKED QUESTIONS |
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FAQ — Inconel 625
| Q1: Can Inconel 625 be age-hardened like Inconel 718? |
| No. Inconel 625 is a solid-solution-strengthened alloy — it does not respond to precipitation hardening. Its strength comes from the solid-solution effect of Mo and Nb in the Ni-Cr matrix. If you need age-hardening capability, consider Inconel 718 (precipitation-hardenable, UTS up to 1240 MPa) or Monel K500 (UTS up to 965 MPa). For most corrosion applications, 625's as-annealed strength (827–1034 MPa UTS) is already sufficient. |
| Q2: Is Inconel 625 weldable? |
| Yes — Inconel 625 is readily weldable using GTAW (TIG), SMAW (stick), and GMAW (MIG). The recommended filler metals are ERNiCrMo-3 (for GTAW/GMAW) and ENiCrMo-3 (for SMAW), matching the base alloy composition. Preheat is not required. Interpass temperature should be controlled below 150°C. Post-weld heat treatment is not required for corrosion resistance and is generally not recommended, as it can cause precipitation of deleterious phases (sigma, mu) if held in the 650–980°C range for extended periods. |
| Q3: What is Inconel 625's maximum service temperature? |
| Inconel 625 retains useful strength up to approximately 1050°C (1920°F) in continuous service in air. Above this temperature, the protective Cr₂O₃ scale begins to break down. For intermittent service or short excursions, it can handle up to 1150°C. At cryogenic temperatures down to -196°C, Inconel 625 maintains excellent toughness with no ductile-to-brittle transition, making it suitable for LNG and subzero process applications. |
| Q4: Is Inconel 625 suitable for sour-gas (NACE) service? |
| Yes, with precautions. Inconel 625 is acceptable for NACE MR0175/ISO 15156 service provided the material hardness is controlled. In the annealed condition, 625 typically has a hardness of 145–220 HB, well below the 35 HRC (roughly 350 HB) limit for NACE compliance. However, if cold-worked, the hardness can exceed the NACE limit — material for sour service must be supplied in the annealed condition with hardness test confirmation. 625's resistance to chloride SCC also makes it inherently suitable for the sour-environment cracking mechanisms defined in NACE MR0175. |
| Q5: How does Inconel 625 compare to Hastelloy C276 in corrosion resistance? |
| Both alloys have excellent corrosion resistance, but they target different environments. Inconel 625 (Ni-Cr-Mo-Nb) is stronger at high temperatures and has better oxidation resistance — preferred for seawater, high-temp oxidation, and FGD linings. Hastelloy C276 (Ni-Cr-Mo-W) has higher molybdenum + tungsten and is superior in reducing acid environments (HCl, H₂SO₄) and in severe pitting/crevice scenarios (PREN ~68 for C276 vs. ~48 for 625). For seawater, 625 is typically the more cost-effective choice; for aggressive chemical processing with strong reducing acids, C276 is preferred. |
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Need Inconel 625 for Your Project?
HT PIPE supplies Inconel 625 seamless pipe, fittings, flanges, and plate with full MTR documentation. Contact our technical team for material selection advice and a competitive quotation.
Request a Quote |
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