Inconel 625 (UNS N06625): Weld-Overlay & Seawater-Resistant Nickel Superalloy
ASTM B443 / ASTM B446 / AMS 5599 / AMS 5666 · Published: 2026-05-31 · Updated: 2026-05-31
Inconel 625 is a solid-solution-strengthened nickel-chromium-molybdenum-niobium alloy that achieves its strength primarily from molybdenum and niobium solid-solution hardening rather than precipitation hardening (unlike Inconel 718). This gives...
Inconel 625 is a solid-solution-strengthened nickel-chromium-molybdenum-niobium alloy that achieves its strength primarily from molybdenum and niobium solid-solution hardening rather than precipitation hardening (unlike Inconel 718). This gives 625 excellent weldability — it is the standard filler metal (ERNiCrMo-3 / AWS A5.14) for dissimilar metal welding of nickel alloys and for corrosion-resistant weld overlays on carbon steel substrates in oil-and-gas and chemical processing equipment. Its outstanding resistance to chloride pitting and crevice corrosion (PREN ~50) makes it the preferred material for seawater-handling components (navy submarine seawater piping, offshore platform riser cladding, desalination brine heaters) where 316L and duplex stainless are inadequate.
Quick Facts
| Category | Nickel Alloy |
| Standard | ASTM B443 / ASTM B446 / AMS 5599 / AMS 5666 |
| Density | 8.44 g/cm³ |
| Yield Strength | 414-517 MPa (60-75 ksi) annealed; up to 1103 MPa (160 ksi) Grade 1 solution-treated |
| Tensile Strength | 827-965 MPa (120-140 ksi) annealed; up to 1241 MPa (180 ksi) Grade 1 |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| EN NiCr22Mo9Nb | Compare |
| DIN 2.4856 | Compare |
| JIS NCF625 | Compare |
| GB GH3625 | Compare |
| UNS N06625 | Compare |
Related Materials
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Frequently Asked Questions
Why is Inconel 625 preferred as a weld overlay vs solid alloy construction?
Economic and engineering reasons: (1) A carbon steel pressure vessel with 3-5 mm Inconel 625 weld overlay on the internal surface costs 30-50% less than a solid Inconel 625 vessel while providing identical internal corrosion resistance; (2) the carbon steel backing provides strength at operating temperature — solid 625 loses strength above 650°C; (3) thermal expansion mismatch between C- steel and 625 is manageable (carbon steel ~12 × 10⁻⁶/K vs 625 ~13 × 10⁻⁶/K — only 8% difference) — thermal cycling does not delaminate properly applied weld overlay; (4) Code qualification — ASME Section VIII Div 1 and 2 permit weld overlay for corrosion allowance in pressure vessel design (UG-26 and UCS-56). The minimum overlay thickness is typically specified as 3 mm (1/8 inch) after final machining, confirmed by ultrasonic testing (UT) for bond integrity and chemical analysis (PMI) for alloy verification.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu