Alloy 625
Nickel-alloy 625 selection by designation, product form, heat treatment and exposure conditions.
Tags: materials, nickel-alloys, specialty-metals
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Identity and producer names
Haynes reports 491 MPa 0.2% yield for cold-rolled Alloy 625 sheet and 417 MPa for hot-rolled plate, both tested at room temperature after mill annealing at 1,052°C. These are producer characterization results. ASTM B443-19 separately distinguishes annealed Grade 1 and solution-annealed Grade 2 for rolled flat products. Haynes 625 tensile tables, ASTM rolled-product scope
Alloy 625 commonly denotes the nickel-chromium-molybdenum-niobium alloy associated with UNS N06625 and material number 2.4856. INCONEL is a producer trade name, not the generic designation of every supplier's 625 material. Special Metals identifies its INCONEL alloy 625 with those designations; other producers supply their own named products and documentation. Preserve the actual manufacturer and product identity when ordering. Special Metals: INCONEL alloy 625
Special Metals' limiting-composition table includes nickel 58% minimum, chromium 20–23%, molybdenum 8–10%, and niobium plus tantalum 3.15–4.15% by mass. This abbreviated table does not include all controlled elements or replace the governing purchase specification. The bulletin attributes strength primarily to molybdenum and niobium solid-solution strengthening rather than a required precipitation-hardening treatment. Special Metals: composition and strengthening
Product form and heat-treated condition
ASTM B443-19 covers rolled N06625 plate, sheet and strip and distinguishes Grade 1, annealed, from Grade 2, solution annealed. Its scope is for those flat products, not a universal specification for bar, tubing, forgings, powder or weld overlay. Select the product specification and edition appropriate to the purchased form. ASTM: B443-19 scope and conditions
Record the annealing condition and verify the ordered grade before applying a property table.
VDM's sheet 4118, revision 06 has a March 2022 cover and June 2022 internal page headings. It separately describes soft-annealed Grade 1 and solution-annealed Grade 2. Report that document identity accurately rather than converting its upload date into a new edition. VDM: Alloy 625 datasheet
Bounded mechanical example
Haynes publishes these room-temperature results for its HAYNES 625 product:
| Product and condition | 0.2% yield strength | Ultimate tensile strength | Elongation |
|---|---|---|---|
| Cold-rolled sheet, mill annealed at 1,052 °C | 491 MPa | 923 MPa | 47.5% |
| Hot-rolled plate, mill annealed at 1,052 °C | 417 MPa | 894 MPa | 48% |
Source: Haynes: 625 tensile tables.
Haynes cautions that long-term exposure above 593 °C can significantly embrittle its 625 alloy. Its higher short-term-temperature descriptions are not blanket continuous-service ratings. Haynes: thermal-exposure caution
Assess time, temperature, environment, stress and the applicable design rules together. Room-temperature tensile strength, short-term elevated-temperature strength, creep rupture and post-exposure ductility answer different questions. For a heated assembly, include startup, shutdown and maintenance cycles in the material assessment.
Corrosion: preserve condition and exposure
VDM states that optimum corrosion performance requires the correct metallurgical condition and a clean structure. It discusses chloride-containing media for soft-annealed Grade 1 separately from corrosive hot-gas environments for solution-annealed Grade 2. These claims support condition-specific selection rather than immunity to every chemical environment. VDM: corrosion resistance by condition
For a proposed vessel, bellows or seawater component, specify fluid composition, concentration, impurities, temperature, pressure, velocity, deposits and crevice geometry. Include cleaning chemicals and shutdown conditions. Assess base metal, weld and heat-affected material together, and distinguish loss of mass from localized attack or cracking. A laboratory critical-pitting temperature, if used, must retain its solution and test method; it is not a maximum operating temperature for an unrelated fluid.
Obtain the applicable material/code requirements for pressure service, sour service or other regulated duty. A producer's application list is a discovery aid and does not qualify an individual heat or fabricated assembly.
Forming, machining and welding
VDM describes Alloy 625 as work hardening faster than austenitic stainless steels, requiring appropriate tool and equipment selection and potentially intermediate annealing during substantial cold deformation. It recommends heat treatment after hot working to restore the desired microstructure and corrosion performance. Use the procedure for the exact product and required final condition rather than applying a generic nickel-alloy furnace cycle. VDM: fabrication guidance
Plan machining around actual stock condition, tool, operation, rigidity and cooling. A material's high strength does not supply a cutting-speed recipe, and a nominal alloy match does not ensure equivalent tool life. Check surface integrity and dimensions after the intended sequence of machining and thermal operations.
Haynes' welding/fabrication guide includes 625 among its solid-solution alloys and emphasizes removing grease, cutting fluids, markings, scale and other contamination from weld areas. It warns that lead, sulfur, phosphorus and other low-melting-point contamination can cause embrittlement or cracking. It also calls for oxide removal between passes to avoid inclusions and incomplete fusion. Haynes: welding and fabrication guidance
Qualify the joint, filler, shielding, heat input, interpass control, cleaning and inspection for the application. Distinguish wrought N06625 from a deposited “625” overlay: filler classification, dilution, layer count and actual deposited chemistry require their own acceptance criteria. Neither a matching name nor an acceptable-looking bead establishes equivalent bulk-alloy corrosion performance.
Purchase and qualification record
Retain:
- UNS/material designation, actual producer, product form and specification edition.
- Required annealed or solution-annealed condition and subsequent process history.
- Certificate, heat analysis, mechanical tests and dimensional requirements.
- Design temperature, load duration, environment and governing code basis.
- Forming, machining, welding and cleaning procedures and acceptance results.
- Representative aging or corrosion tests where the intended duty needs them.
The VDM document's internal date discrepancy is stated above, and ASTM B443-19 is cited specifically for its published scope. The accessible Special Metals and Haynes sources do not establish clear technical revision dates in the reviewed text; URL upload paths and website copyright dates do not establish editions. Obtain current controlled documents for contractual use.