Inconel Alloy 625 Fasteners

Nickel-Chromium-Molybdenum-Niobium Alloy – Outstanding Corrosion & Fatigue Resistance

Buy Inconel 625 (UNS N06625 / Werkstoff 2.4856 / ASTM B446 / AMS 5666) bolts, stud bolts, heavy hex nuts, and custom fasteners from Exotic Alloy. Alloy 625 is a solid-solution-strengthened nickel-chromium-molybdenum alloy with niobium additions that suppress precipitation during heat treatment, providing outstanding fatigue strength and excellent corrosion resistance from cryogenic to 980°C (1800°F).

Exotic Alloy manufactures Inconel 625 fasteners conforming to ASTM B446, AMS 5666, NACE MR0175, and ASME SB-446. Available in metric M6–M100 and imperial ¼"–4" with full EN 10204 3.1 mill test certificates for marine, subsea, and chemical processing service.

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Technical Data

Alloy 625 Specifications

Chemical Composition — Inconel Alloy 625 (wt. %)

Element	Ni	Cr	Mo	Nb+Ta	Fe	Co	Al	Ti	Mn	Si	C
Min %	58.00	20.00	8.00	3.15	–	–	–	–	–	–	–
Max %	Balance	23.00	10.00	4.15	5.00	1.00	0.40	0.40	0.50	0.50	0.10

Mechanical Properties — Inconel Alloy 625

Condition	UTS (MPa)	YS 0.2% (MPa)	Elongation (%)	Hardness
Annealed Bar (Grade 1)	827	414	30	≤ 99 HRB
Annealed Bar (Grade 2)	965	517	30	–
Cold Worked / Aged	1241	827	12	–

Physical Properties

Density	8.44 g/cm³
Melting Range	1290–1350°C (2350–2460°F)
Specific Heat Capacity	410 J/kg·K at 21°C
Thermal Conductivity	9.8 W/m·K at 24°C
Thermal Expansion	12.8 µm/m·°C (21–538°C)
Electrical Resistivity	1.29 µΩ·m

Equivalent Grades & Standards

UNS	Werkstoff / DIN	EN / BS	AFNOR
N06625	2.4856	NiCr22Mo9Nb	NC22DNb

Key Specifications: ASTM B446 / B443 / B444 / AMS 5666 / ASME SB-446

Machinability: Inconel 625 work-hardens rapidly. Use carbide tooling with positive rake angles, low cutting speeds (20–40 SFM turning), high feed rates, rigid setup, and continuous flood cooling with soluble or sulfurized oil. Avoid re-cuts over already hardened surface.

Welding: Weld with GTAW using ERNiCrMo-3 filler (matching composition). Inconel 625 is used as a cladding/overlay weld material itself. No post-weld heat treatment required. Inter-pass temperature must remain below 150°C (300°F).

Forging: Hot forge at 1066–1177°C (1950–2150°F). Do not forge below 982°C (1800°F) as the alloy embrittles. Post-forge anneal at 1150°C (2100°F) with rapid quench.

Heat Treatment: Anneal at 1093–1204°C (2000–2200°F), rapid air cool or water quench. For elevated-temperature service (Grade 2), stabilize at 870°C (1600°F) for 1 hour to precipitate M₆C carbides on grain boundaries.

Inconel 625 achieves PREN ≈ 51, providing exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking (SCC) in chloride-bearing seawater to 60°C. Resistant to mineral acids (HCl, H₂SO₄, HNO₃) and alkalis. Widely qualified per NACE MR0175 for sour service.

Key Characteristics

Outstanding high-temperature strength and oxidation resistance.
Excellent resistance to pitting, crevice corrosion, and intergranular attack.
High fatigue and thermal-fatigue strength in cyclic temperature service.
Superb resistance to chloride-ion stress-corrosion cracking.
Maintains structural integrity from cryogenic to extreme high-temperature service.

Typical Applications

Aerospace engineering: jet engine turbine blades, discs, and casings.
Chemical processing: reactor vessels, pressure containment bolting.
Marine and subsea: offshore wellhead, Christmas tree, HPHT connectors.
Nuclear power: reactor core hardware, primary coolant system fasteners.
Power generation: steam turbine bolting, ultra-supercritical boiler components.

Alloy 625