Quick answer: under ASTM B446, Inconel 625 Grade 1 is supplied in the annealed condition and is normally used at service temperatures up to 1100°F (593°C). Grade 2 is supplied in the solution-annealed condition and is normally used above 1100°F (593°C) when creep and rupture resistance are required. The grade number describes the heat-treated condition—not a different UNS alloy chemistry.
What Do Grade 1 and Grade 2 Mean in ASTM B446?
ASTM B446 covers nickel-chromium-molybdenum-niobium alloy UNS N06625 and certain other nickel alloys in hot-worked and cold-worked rod and bar forms. For UNS N06625, the standard separates products by heat-treated condition. This is why a purchase order that states only “Inconel 625 bar” may still be incomplete.
Both grades remain Alloy 625 / UNS N06625. Grade 1 is annealed. Grade 2 is solution annealed. The different thermal processing produces different property priorities and intended service ranges, so the grade should be selected from the project requirements rather than assumed by the supplier.
| ASTM B446 condition | Grade 1 | Grade 2 |
|---|---|---|
| Heat-treated condition | Annealed | Solution annealed |
| Normal service guidance | Up to 1100°F (593°C) | Above 1100°F (593°C) when creep and rupture resistance are required |
| Main selection focus | General corrosion service and room-/moderate-temperature property requirements | Long-duration elevated-temperature loading |
| Alloy designation | UNS N06625 | UNS N06625 |
Why Heat Treatment Changes the Selection
Alloy 625 obtains high strength from solid-solution strengthening by molybdenum and niobium rather than from a precipitation-hardening treatment. Even so, its annealing history affects grain structure and the balance between room-temperature strength, ductility and long-duration elevated-temperature behavior.
Special Metals publishes typical data for both annealed and solution-treated Alloy 625. Its technical bulletin notes that solution-treated material is recommended when optimum creep or rupture resistance is required at elevated temperature. It also shows that typical room-temperature strength and hardness may be lower in the solution-treated condition. This is an important procurement point: “solution annealed” does not automatically mean “stronger in every test.”
When Grade 1 Is Usually the Starting Point
Grade 1 is normally considered when the service temperature does not exceed the ASTM B446 guidance limit and the design does not require Grade 2 creep-rupture performance. Typical engineering priorities can include corrosion resistance, fabrication, dimensional processing and mechanical properties at room or moderate temperature.
That does not mean every component below 1100°F must use Grade 1. A project specification may still call for Grade 2 because of its load duration, thermal cycle, downstream heat treatment or qualification basis. The final requirement must come from the design documents.
When Grade 2 Becomes Important
Grade 2 is normally used above 1100°F (593°C) when resistance to creep and rupture is required. Creep is time-dependent deformation under sustained stress at elevated temperature. Rupture performance concerns the time and stress at which the material eventually fails under those conditions.
This makes Grade 2 particularly relevant when a bar will become a component exposed to sustained high-temperature loading. However, the purchaser should not convert the general temperature statement into an unsupported service guarantee. Actual suitability depends on stress, exposure time, environment, geometry, fabrication history and the applicable design code.
Five Questions to Answer Before Issuing the RFQ
1. What is the controlling product specification?
ASTM B446 applies to rod and bar. Plate, sheet, pipe, tube, forgings and fittings are controlled by other product-form standards. Do not copy the Grade 1 or Grade 2 designation to another product form without checking its applicable specification.
2. What temperature, stress and exposure time will the part experience?
State the maximum continuous and transient temperatures, sustained load, expected service duration and thermal cycling. Grade 2 is associated with elevated-temperature creep and rupture requirements, not simply with the highest short-duration temperature.
3. Will the bar be hot-worked, welded or re-annealed?
ASTM notes that hot working or re-annealing may significantly change properties depending on processing history and temperature. Describe downstream operations so the material condition is not selected in isolation from the manufacturing route.
4. Which mechanical and elevated-temperature tests are required?
Do not request “full testing” without defining the requirement. State the controlling standard revision, test type, temperature, sampling basis, acceptance criteria and whether additional inspection or third-party witnessing is required.
5. What must appear on the material documentation?
The purchase order and material report should clearly identify UNS N06625, ASTM B446 revision, Grade 1 or Grade 2, heat/lot identity, product dimensions, heat-treated condition and required test results. Any project-specific documentation should be listed before quotation.
A Procurement Decision Gate for Inconel 625 Bar
Choose the specification first: confirm ASTM B446 is the correct product-form standard.
Then choose the condition: Grade 1 annealed or Grade 2 solution annealed, based on the design requirement.
Then define the bar: diameter or section, length, quantity, tolerance, straightness and surface finish.
Then define acceptance: mechanical tests, any elevated-temperature tests, NDT, identification and documentation.
Finally define delivery: destination, Incoterm, required date and packaging restrictions.
Copyable Inconel 625 Bar RFQ Description
Inconel 625 / UNS N06625 round bar, ASTM B446-[required revision], Grade [1 or 2], [diameter] × [length], [quantity], [surface finish and dimensional tolerance], heat/lot traceability required, [test and certificate requirements], delivery to [destination] under [Incoterm]. Supplier to confirm compliance and identify any deviation before order acceptance.
Common Specification Mistakes
- Writing only “Inconel 625 bar” without the standard, revision and grade.
- Assuming Grade 2 is universally superior because it is solution annealed.
- Using ASTM B446 for a pipe, tube, plate or forging without checking the correct product standard.
- Selecting solely from maximum temperature while ignoring sustained stress and service duration.
- Adding creep, rupture or third-party testing only after the quotation has been issued.
Request an Inconel 625 Bar Review
Send SASAALLOY the required ASTM revision, Grade 1 or Grade 2 condition, bar dimensions, quantity, surface requirement, inspection scope and destination. The team can review the RFQ and confirm which requirements can be quoted for the specific order. Material availability, testing and delivery must be confirmed against the final purchase specification.
Frequently Asked Questions
Are Inconel 625 Grade 1 and Grade 2 different alloys?
No. Both use UNS N06625 chemistry. Under ASTM B446, the grade distinction identifies different heat-treated conditions and intended service guidance.
Is Grade 2 always stronger than Grade 1?
No. Grade 2 is selected for solution-annealed condition and elevated-temperature creep or rupture requirements. Typical room-temperature strength and hardness do not automatically increase simply because the bar is solution annealed.
Can Grade 1 be used above 1100°F?
ASTM B446 states that Grade 2 is normally employed above 1100°F when creep and rupture resistance are required. Any departure should be determined by the responsible designer using the controlling code, loads, exposure time and qualification requirements.
Can the grade be identified from the bar’s appearance?
No. The conditions cannot be reliably distinguished by visual appearance. Verify the product marking, heat number, purchase order and batch-specific material documentation.
