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Super Austenitic 6% Mo UNS N08925 / N08926 Plate and Sheet
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The super austenitic 6% molybdenum grades UNS N08925 and UNS N08926 occupy the practical space between standard austenitic stainless steels and nickel alloys. Both carry 6.0–7.0 % molybdenum with 24.00–26.00 % nickel and 19.00–21.00 % chromium, which delivers chloride resistance far beyond 316L while retaining the fabrication characteristics buyers expect from austenitic material. Hefei Tailan Metal supplies these grades as plate, sheet and strip to ASME SB-625, and as bar and wire to ASME SB-649.
Material Specifications and Grade Comparison
The table below sets out the governing material specification and the grade comparison for Super Austenitic 6% Molybdenum UNS N08925 / N08926 Plate and Sheet. All composition and mechanical values are taken directly from the ASME BPVC Section II specifications named in each row.
| Grade | UNS | Cr, % | Ni, % | Mo, % | Cu, % | N, % | C max, % |
|---|---|---|---|---|---|---|---|
| 254 SMO | N08925 | 19.00–21.00 | 24.00–26.00 | 6.0–7.0 | 0.8–1.5 | 0.10–0.20 | 0.020 |
| 654 SMO | N08926 | 19.00–21.00 | 24.00–26.00 | 6.0–7.0 | 0.5–1.5 | 0.15–0.25 | 0.020 |
| Alloy 31 | N08031 | 26.0–28.0 | 30.0–32.0 | 6.0–7.0 | 1.0–1.4 | 0.15–0.25 | 0.015 |
| Alloy 33 | R20033 | 31.0–35.0 | 30.0–33.0 | 0.50–2.0 | 0.30–1.20 | 0.35–0.60 | 0.015 |
Product Forms, Sizes and Material Route
Product forms and size range
We supply N08925 and N08926 as plate, sheet and strip to ASME SB-625, and as bar and wire to ASME SB-649. The super austenitic grades are supplied in a solution-annealed condition with a bright or pickled finish as ordered. Because the sheet market for these grades is concentrated in a small number of European mills, we confirm current size and thickness availability against stock before quoting rather than publish a range we cannot hold. Corresponding fittings to ASME SB-366 are available as CR1925 / WP1925 and CR1925N / WP1925N.
Material route and heat treatment
SB-625 covers the plate, sheet and strip, and SB-649 covers bar and wire. Heat treatment is solution annealing; the fitting specification SB-366 Table 3 gives the reference temperatures of 1800–1900 °F [983–1038 °C] for N08925 and 2150 °F [1177 °C] for N08926, with rapid air or water quench. These two grades are close in composition but differ in heat treatment and nitrogen content, which is why they are not interchangeable in every service condition.
Choosing between N08925 and N08926
Both grades carry 6.0–7.0 % molybdenum, and both outperform standard austenitic grades in chloride service. N08926 carries nitrogen at 0.15–0.25 % against 0.10–0.20 % for N08925 and is the usual choice where crevice corrosion and chloride pitting in stagnant or low-flow conditions dominate the risk. N08925 is widely used where general seawater and process chloride exposure applies. N08926 also carries a higher tensile requirement — 94 ksi [650 MPa] against 87 ksi [600 MPa] — with elongation of 35 % against 40 %. Where seawater splash zones or chlorinated seawater are involved, confirm the grade with our technical department against the specific chloride concentration and temperature.
Specification and Inspection Requirements
| Item | Requirement |
|---|---|
| Material specification | ASME SB-625 (plate, sheet and strip), SB-649 (bar and wire) |
| Grades | UNS N08925 and UNS N08926 — low carbon Cr-Ni-Fe-Mo-Cu and Cr-Ni-Fe-Mo-Cu-N |
| Heat treatment | Supplied in the annealed temper per SB-625 §1.1. SB-366 Table 3 lists the fitting heat treatment as 1800–1900 °F [983–1038 °C] for N08925 and 2150 °F [1177 °C] for N08926, both with rapid air or water quench |
| Corrosion resistance | Chloride and halide environments including seawater; the higher nitrogen content of N08926 further assists resistance to pitting in crevices |
| Product forms | Plate, sheet, strip, rolled bar and wire |
| Related fitting specification | ASME SB-366 covers N08925 and N08926 as CR1925 / WP1925 and CR1925N / WP1925N fittings |
Chemical Composition
Chemical composition shall conform to the applicable ASME specification. The table below reproduces the composition limits for the grades covered by Super Austenitic 6% Molybdenum UNS N08925 / N08926 Plate and Sheet.
| Element | UNS N08925 (SB-625 Table 1) | UNS N08926 (SB-625 Table 1) |
|---|---|---|
| Chromium, % | 19.00–21.00 | 19.00–21.00 |
| Nickel, % | 24.00–26.00 | 24.00–26.00 |
| Molybdenum, % | 6.0–7.0 | 6.0–7.0 |
| Copper, % | 0.8–1.5 | 0.5–1.5 |
| Nitrogen, % | 0.10–0.20 | 0.15–0.25 |
| Carbon, max, % | 0.020 | 0.020 |
| Manganese, max, % | 1.00 | 2.00 |
| Phosphorus, max, % | 0.045 | 0.03 |
| Sulfur, max, % | 0.030 | 0.01 |
| Silicon, max, % | 0.50 | 0.5 |
| Iron | Balance | Balance |
Mechanical Property Requirements
| Alloy (SB-625 Table 2) | Form | Tensile min, ksi (MPa) | Yield min, psi (MPa) | Elongation min, % |
|---|---|---|---|---|
| UNS N08925 | sheet / strip / plate | 87 (600) | 43 000 (295) | 40 |
| UNS N08926 | sheet / strip / plate | 94 (650) | 43 000 (295) | 35 |
| UNS N08031 | sheet / strip / plate | 94 (650) | 40 000 (276) | 40 |
| UNS R20033 | sheet / strip / plate | 109 (750) | 55 000 (380) | 40 |
Applications and Service Environments
Seawater and desalination
Desalination plant brine and seawater piping, heat exchangers and flash tanks where chloride concentration can exceed the limits of 316L and standard duplex. The super austenitic grades handle seawater and bromide-containing cooling water.
Chemical process equipment
Sulphuric and hydrochloric acid handling in pulp and paper, chemical and pharmaceutical plant, where austenitic formability is wanted alongside chloride resistance.
Scrubber and pollution control
FGD scrubbers, wet scrubbers and absorption columns where the process condenses hydrochloric acid from flue gas. These duties combine chloride with oxidising conditions that defeat many alloys.
Food, beverage and pharmaceutical
Hygienic sheet and tube for washdown and processing environments where chloride sanitising chemicals and high hygiene standards both apply.
Certification, Testing and Inspection
Chemical composition
Full analysis to ASME SB-625 for the applicable grade, with product check analysis tolerances available on order.
Mechanical properties
Tensile and yield properties and elongation per the applicable material specification, with SB-649 Table 2 values applying to bar and wire.
Heat treatment
Solution annealed, with the heat treatment recorded on the mill test report.
Intergranular corrosion
Material supplied shall be capable of passing the intergranular corrosion test; the test need not be performed on any given lot unless specified on the purchase order.
Surface condition
Free of scale and surface defects; pickled finish supplied as standard with bright finish on request.
Documentation
Mill test report with heat number traceability, EN 10204 3.1 or 3.2 certification available on order.
Ordering Information
Specify the grade (N08925 or N08926), product form (plate, sheet, strip, bar or wire), dimensions with the tolerance basis, surface finish, quantity, and the service environment including chloride concentration, temperature and whether the material will be field welded. We will confirm availability, supply route and lead time, and issue a quotation on request. If you need intergranular corrosion testing, specific surface condition or third-party inspection, please state this with the enquiry.
