Inconel 625 Round Bar: UNS N06625 Properties and Buyer's Guide
Quick Summary
Inconel 625 (UNS N06625 / W.Nr. 2.4856) is a nickel-based superalloy that keeps its strength and corrosion resistance from cryogenic temperatures up to about 980 °C, making it the default choice for aerospace engine components, chemical-processing equipment and offshore sour-service hardware.
Inconel 625 Round Bar: UNS N06625 Properties and Buyer's Guide
Inconel 625 (UNS N06625 / W.Nr. 2.4856) is a nickel-based superalloy that keeps its strength and corrosion resistance from cryogenic temperatures up to about 980 °C, making it the default choice for aerospace engine components, chemical-processing equipment and offshore sour-service hardware. When buying 625 round bar, verify ASTM B446 compliance on the certificate, solution-annealed condition (typically 1,090–1,200 °C), and full heat chemistry — nickel minimum 58%, chromium 20–23%, molybdenum 8–10%, niobium+tantalum 3.15–4.15%.
No other commonly stocked alloy combines this breadth: 625 resists pitting and crevice corrosion in seawater and sour gas, holds useful strength at temperatures where stainless steels have lost most of theirs, and welds without the post-weld cracking problems of many high-strength nickel alloys. That combination explains its premium price — and why verifying the certificate matters more here than on almost any other bar stock.
What Inconel 625 Is
Alloy 625 is a solid-solution-strengthened nickel-chromium-molybdenum-niobium alloy. The nominal chemistry per UNS N06625:
| Element | Range |
|---|---|
| Nickel (Ni) | 58.0% min (balance) |
| Chromium (Cr) | 20.0–23.0% |
| Molybdenum (Mo) | 8.0–10.0% |
| Niobium + Tantalum (Nb+Ta) | 3.15–4.15% |
| Iron (Fe) | 5.0% max |
| Carbon (C) | 0.10% max |
| Manganese (Mn) | 0.50% max |
| Silicon (Si) | 0.50% max |
| Phosphorus / Sulfur | 0.015% / 0.015% max |
The molybdenum and niobium do the strength work: molybdenum strengthens the nickel matrix directly, and niobium combines with nickel to form the intermetallic phase that gives the alloy much of its high-temperature strength — without the heat treatment dependence of precipitation-hardened alloys. That is why 625 is solution-annealed, not aged: its strength comes from chemistry, not from a separate aging step.
Key Properties
- Temperature capability: useful strength from cryogenic levels to ~980 °C; oxidation resistance in air to about the same range.
- Corrosion resistance: outstanding in seawater (essentially immune to pitting and crevice attack in quiet and flowing seawater), resistant to sour gas (H₂S + CO₂ + chloride) environments that define offshore and subsea service, and broadly resistant to organic and inorganic process media.
- Weldability: readily weldable without preheat, and notably resistant to strain-age cracking — a significant practical advantage over some other nickel superalloys.
- Strength: in solution-annealed bar to ASTM B446, typical room-temperature tensile strength exceeds 830 MPa with yield above 415 MPa, retaining useful values at several hundred degrees Celsius.
Equivalents and Standards
| System | Designation |
|---|---|
| UNS | N06625 |
| W.Nr. / EN (Europe) | 2.4856 / NiCr22Mo9Nb |
| ASTM | B446 (bar and rod) |
| ISO | NiCr22Mo9Nb |
ASTM B446 is the bar specification buyers will see on certificates: it defines the chemistry, mechanical minimums and condition (Grade 1 = annealed at 1,090 °C min; Grade 2 = annealed at higher temperature ranges for specific stress-relief applications). When a purchase order says "625 round bar," the certificate line to insist on is compliance with ASTM B446 Grade 1 unless the application specifies otherwise.
Applications
- Aerospace: engine exhaust components, turbine shrouds, bellows and ducting — where 625's strength retention and oxidation resistance run to ~980 °C (Yuze Metal supplies 625 round bar 6–250 mm serving this segment).
- Offshore and subsea: fasteners, valve trim, instrument hardware in seawater and sour service.
- Chemical processing: vessels, heat-exchanger internals and hardware for chloride-bearing media and mixed-acid service.
- Nuclear and power: components where water chemistry and temperature both attack stainless alternatives.
The common thread in all four: environments where 316L or duplex stainless would pit, crack under stress corrosion, or lose strength well below the operating temperature.
What to Verify on an Export Order
Nickel superalloy pricing invites substitution and partial-certificate games; the checks below close the main gaps:
- ASTM B446 certificate with full heat chemistry. Every element in the table above, heat-numbered, EN 10204 3.1 equivalent. The niobium content is a particularly useful authenticity marker — below-spec niobium signals off-spec or diluted melts.
- Condition: solution annealed. Standard practice is 1,090–1,200 °C followed by rapid cooling. Certificate should state it; a mill-annealed bar with no annealing temperature line is a red flag.
- Ultrasonic testing on bar above roughly 50 mm to ASTM A388 or equivalent, since internal soundness matters for machined aerospace and pressure-retaining parts.
- Surface and diameter tolerance — peeled/ground bar for machined components; as-rolled for less demanding hardware.
- Traceability paperwork — heat number linking certificate to bar ends, retained by the mill.
Pricing Reality
625 round bar prices move with the LME nickel price and with molybdenum/niobium raw-material costs, and legitimate quotes sit well above stainless grades — often by a factor of eight to fifteen depending on size and quantity. Quotes materially below that band deserve skepticism: off-spec chemistry (iron-heavy dilution) is the most common way lowball 625 offers exist. Comparing certificates, not just prices, is the buyer's protection — the same principle covered in the guide to choosing a metals supplier from China.
Talk to Yuze Metal About Inconel 625
Yuze Metal Limited supplies Inconel 625 round bar 6–250 mm in solution-annealed condition, every heat with a full ASTM B446 certificate — chemistry, annealing temperature and traceability — and ultrasonic testing on request for aerospace and pressure-retaining parts. Nickel alloy pricing moves; our quotes move with it, and the certificates that back them stay complete.
Write to us at info@yuzemetal.com or message us on WhatsApp; we reply fast.
