Project Description
654SMO (UNS S32654), also designated as 1.4652, X1CrNiMoCuN25-25-7, and 015Cr24Ni22Mo7Mn3CuN, represents the highest alloy content commercially available in the super-austenitic stainless steel family. With 7.0–8.0% molybdenum, 24.0–25.0% chromium, and 0.45–0.55% nitrogen, 654SMO achieves a calculated pitting resistance equivalent number (PREN) exceeding 55 — among the highest of any wrought stainless steel grade — making it suitable for the most aggressive chloride-containing environments where even 254SMO (PREN ~43) reaches its performance limits. SHUNFU METAL, certified to ISO 9001:2015 and API Q1, produces 654SMO bars through controlled electric arc furnace (EAF) melting with AOD refining, utilizing a deliberate manganese addition (2.0–4.0%) to maintain the exceptionally high nitrogen solubility required for this grade’s unique combination of strength and corrosion resistance.
654SMO Stainless Steel Bar — Overview
Developed by Outokumpu as an evolutionary step beyond 254SMO, 654SMO extends the super-austenitic concept to its metallurgical limits — higher chromium, nickel, molybdenum, and nitrogen than any other single-phase austenitic stainless steel — delivering near-immunity to pitting corrosion in ambient-temperature seawater and exceptional resistance to crevice corrosion in gasketed joints and under-deposit conditions. The alloy’s yield strength (430 MPa minimum) is approximately 40% higher than 254SMO and 2.5 times that of 316L, attributed to powerful solid solution strengthening from the ultra-high nitrogen content. In oil and gas operations, 654SMO has become the definitive material for critical seawater handling components, plate heat exchangers, flue gas desulfurization scrubbers on offshore platforms, ultra-deepwater subsea instrumentation, and sour service equipment exposed simultaneously to high chlorides and hydrogen sulfide. SHUNFU METAL supplies 654SMO bars in the solution-annealed condition (1180–1220°C, water quenched), with every production lot verified by in-house optical emission spectrometry (OES), tensile and hardness testing, and full MTC documentation per EN 10204 Type 3.1.
654SMO Equivalent Grades — International Standards
| Standard | Designation |
|---|---|
| ASTM A479 / A276 / A240 | UNS S32654 |
| EN 10088-3 / DIN | 1.4652 / X1CrNiMoCuN25-25-7 |
| GB/T 1220 | 015Cr24Ni22Mo7Mn3CuN |
No direct JIS or GOST equivalents exist for 654SMO. SHUNFU METAL supplies bars certified to ASTM A479 UNS S32654 and EN 10088-3 Grade 1.4652, with full heat traceability and API Q1 documentation provided as standard.
SHUNFU METAL
654SMO Applications — Oil & Gas Industry
Where 254SMO reaches its corrosion limits, 654SMO becomes the preferred upgrade path — providing PREN > 55 for environments that challenge even high-molybdenum nickel alloys at a substantially lower cost than nickel-based alternatives such as C-276. SHUNFU METAL supplies 654SMO bars to manufacturers of the following critical oil and gas components, with every production lot verified against ASTM A479 UNS S32654 requirements:
Supply Range — 654SMO Bar Dimensions
SHUNFU METAL maintains dedicated production capability for 654SMO bars across hot-rolled, cold-finished, and forged product forms, processed through ISO 9001:2015 controlled workflows. The ultra-high alloy content of 654SMO demands exceptionally precise hot working and heat treatment parameters — final solution annealing at 1180–1220°C followed by rapid water quenching is critical to dissolve all chromium-rich sigma and chi intermetallic phases and achieve a fully austenitic microstructure. SHUNFU METAL’s metallurgical team verifies the absence of deleterious secondary phases through microstructural examination before release. The following dimensional ranges are offered as standard:
| Product Form | Diameter / Thickness Range | Width Range | Length (Standard) | Surface Finish |
|---|---|---|---|---|
| Hot Rolled Round | 10 mm – 250 mm | — | 3000 – 6000 mm | Black / Pickled |
| Cold Finished / Peeled Round | 5 mm – 80 mm | — | 2000 – 6000 mm | Peeled / Polished |
| Hot Rolled Flat | 10 mm – 100 mm | 50 mm – 350 mm | 2000 – 6000 mm | Pickled |
| Forged Round | 100 mm – 600 mm | — | 1000 – 5000 mm | Rough Machined / Black |
| Forged Flat / Block | 50 mm – 300 mm | 100 mm – 600 mm | 1000 – 4000 mm | Rough Machined / Black |
All bars are supplied with EN 10204 Type 3.1 Mill Test Certificates documenting heat number, full chemical analysis (including nitrogen, manganese, and copper), mechanical test results, solution annealing temperature verification, and dimensional compliance. Intergranular corrosion testing per ASTM A262 Practice C (Huey test) and critical pitting temperature (CPT) testing per ASTM G48 Method C are available upon request for extreme-service qualification requirements.
654SMO Chemical Composition per ASTM A479
654SMO pushes the metallurgical limits of single-phase austenitic stainless steel: 7.0–8.0% molybdenum, 24.0–25.0% chromium, and 0.45–0.55% nitrogen collectively yield a PREN exceeding 55. The deliberate 2.0–4.0% manganese addition is not a residual but a critical alloying element that increases nitrogen solubility in the melt, enabling the exceptionally high nitrogen content that delivers both superior corrosion resistance and elevated yield strength. At SHUNFU METAL, every heat is verified by in-house optical emission spectrometry (OES) against ASTM A479 UNS S32654 limits, with nitrogen content confirmed by inert gas fusion analysis prior to release for processing:
| Element | C | Mn | Si | P | S | Cr | Ni | Mo | N | Cu |
|---|---|---|---|---|---|---|---|---|---|---|
| Wt % | 0.020 max | 2.00–4.00 | 0.50 max | 0.030 max | 0.005 max | 24.00–25.00 | 21.00–23.00 | 7.00–8.00 | 0.45–0.55 | 0.30–0.60 |
Composition conforms to ASTM A479 UNS S32654 and EN 10088-3 Grade 1.4652. The PREN value calculated as %Cr + 3.3(%Mo) + 16(%N) = 24.5 + 3.3(7.5) + 16(0.50) ≈ 57.3, representing near-immunity to pitting corrosion in ambient seawater and a critical pitting temperature (CPT) typically exceeding 90°C in neutral chloride solutions. The manganese range (2.0–4.0%) is critical to the alloy’s manufacturing feasibility, as it increases nitrogen solubility in the liquid melt to accommodate the 0.45–0.55% nitrogen content that defines this grade. SHUNFU METAL’s API Q1 certified traceability links every finished bar to its original heat analysis.
654SMO Mechanical Properties — Solution Annealed Condition
654SMO achieves its exceptional mechanical properties through intense solid solution strengthening from the ultra-high nitrogen content (0.45–0.55%), delivering yield strength approximately 2.5 times that of 316L and 40% higher than 254SMO. The alloy is supplied exclusively in the solution-annealed condition (1180–1220°C followed by rapid water quenching) to ensure complete dissolution of all secondary phases. SHUNFU METAL performs in-house tensile testing (ASTM E8) and hardness testing (ASTM E18) on every production lot, with full results documented on the MTC:
| Property | 654SMO (S32654) | 254SMO (S31254) | 316L (S31603) | Test Method |
|---|---|---|---|---|
| Tensile Strength (MPa / ksi) | 750 min / 109 | 650 min / 94 | 485 min / 70 | ASTM E8 |
| Yield Strength 0.2% (MPa / ksi) | 430 min / 62 | 300 min / 44 | 170 min / 25 | ASTM E8 |
| Elongation in 4D (%) | 35 min | 35 min | 30 min | ASTM E8 |
| Hardness (HB) | HB 250 max | HB 210 max | HB 217 max | ASTM E10 |
Values per ASTM A479 for bar products in the solution-annealed condition. The 430 MPa minimum yield strength of 654SMO is the highest of any single-phase austenitic stainless steel, achieved without cold working — a direct result of the interstitial nitrogen content providing powerful solid solution strengthening while simultaneously enhancing pitting resistance. This strength advantage permits thinner-walled component designs with attendant weight savings in offshore platform and subsea applications.
Key properties at service temperature: 654SMO retains excellent toughness at cryogenic temperatures and resists sigma phase embrittlement up to approximately 350°C in continuous service. Its CPT in neutral chloride solutions typically exceeds 90°C, making it suitable for hot seawater and high-chloride brine applications where lower-alloyed stainless steels undergo rapid localized attack. SHUNFU METAL’s ISO 9001:2015 accredited laboratory validates all mechanical properties on representative test specimens from each heat treatment batch, with API Q1 ensuring full material traceability from melt to end user. Charpy V-notch impact testing per ASTM A370 is available for subsea and cryogenic qualification.