Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175 / ISO 15156-2
- NORSOK M-650 Qualified
- API 6A Certified
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
ASTM A479: Super Duplex 2507 Bar (UNS S32750)
ASTM A479 is the standard specification for stainless and heat-resisting steel bars and shapes for use in pressure vessels and general service. Within A479, super duplex 2507 is registered as UNS S32750 and is the canonical bar specification for the alloy. The European equivalent is Werkstoff 1.4410 / X2CrNiMoN25-7-4 per EN 10088-3.
TorqBolt supplies A479 UNS S32750 round bar, hex bar, square bar, and flat bar across diameters 6 mm to 250 mm with mill test certificates that record chemistry, mechanical properties, ferrite content, and heat treatment history.
ASTM A479 Scope
A479 covers stainless and heat-resisting steel bars and shapes intended for general use in pressure vessels and other applications, including high-temperature service. The standard governs chemistry, mechanical properties, heat treatment, dimensions, surface condition, marking, and traceability for hot-finished and cold-finished bars and shapes. UNS S32750 falls under the duplex / super duplex grades within A479.
ASTM A479 Chemistry for UNS S32750
| Element | Min % | Max % |
|---|---|---|
| Carbon (C) | (no min) | 0.030 |
| Chromium (Cr) | 24.0 | 26.0 |
| Nickel (Ni) | 6.0 | 8.0 |
| Molybdenum (Mo) | 3.0 | 5.0 |
| Nitrogen (N) | 0.24 | 0.32 |
| Manganese (Mn) | (no min) | 1.20 |
| Silicon (Si) | (no min) | 0.80 |
| Phosphorus (P) | (no min) | 0.035 |
| Sulfur (S) | (no min) | 0.020 |
| Copper (Cu) | (no min) | 0.50 max, residual, not intentional |
The 0.50 max copper window is residual rather than intentional. This distinguishes UNS S32750 from S32760 (Zeron 100, 0.5 to 1.0 percent intentional Cu) and S32550 (Ferralium 255, 1.5 to 2.5 percent intentional Cu).
ASTM A479 Mechanical Requirements for UNS S32750
| Property | Minimum |
|---|---|
| Tensile strength | 795 MPa (116 ksi) |
| Yield strength (0.2 percent offset) | 550 MPa (80 ksi) |
| Elongation in 50 mm (2 in) | 15 percent |
| Hardness | 32 HRC max (or 310 HBW max) |
For sour service per NACE MR0175 / ISO 15156, hardness is restricted to 28 HRC max, which overrides the A479 32 HRC limit when both apply.
Heat Treatment
Solution annealing at 1040 to 1100 degrees Celsius followed by rapid water quench. The quench must drive the bar through the 600 to 1000 degrees Celsius critical band rapidly to suppress sigma-phase precipitation. Heavy section bars (above 100 mm) require careful quench design. There is no precipitation hardening, no aging, no temper.
Ferrite Content
A479 references ferrite content control through Supplementary Requirement S2. NORSOK M-630 D55 supplements A479 with 35 to 55 percent parent metal ferrite measured per ASTM E562. Mill heats outside this window are downgraded out of super duplex qualification.
Required Tests
| Test | Method |
|---|---|
| Chemistry | ASTM E1086 / E353 / E1019 / E2465 |
| Tensile | ASTM A370 / E8 |
| Hardness | ASTM E10 (HBW) / E18 (HRC) |
| Ferrite (when invoked) | ASTM E562 point count |
| Intermetallic (when invoked) | ASTM A923 Method A or C |
| Pitting (when invoked) | ASTM G48 Method A |
Bar Shapes Supplied
- Round bar 6 mm to 250 mm diameter
- Hex bar across-flats sizes for fastener manufacture
- Square bar for machined components
- Flat bar for structural and machined parts
- Bright drawn bar (cold-finished) for tighter dimensional tolerance
- Forged round bar for sections above 250 mm
Related Standards
- ASTM A276: alternate bar / shape spec for general service
- ASTM A182 F53: forging / flange / forged-fitting spec
- ASTM A789: tube spec
- ASTM A790: pipe spec
- ASTM A815: wrought fittings (WP-S32750)
- EN 10088-3: European bar / wire spec (Werkstoff 1.4410)
- NORSOK M-630: Norwegian MDS D55
- NACE MR0175 / ISO 15156-3: sour-service requirements
ASTM A479 Frequently Asked Questions
What does ASTM A479 cover for UNS S32750?
A479 specifies super duplex 2507 round, hex, square, and flat bar in solution-annealed and water-quenched condition. The grade is UNS S32750 with chemistry 24-26 Cr, 6-8 Ni, 3-5 Mo, 0.24-0.32 N, and 0.50 max copper as residual.
What is the heat treatment for A479 UNS S32750?
Solution annealing at 1040 to 1100 degrees Celsius followed by rapid water quench. No precipitation hardening, no aging, no temper. The quench must drive the bar through the 600 to 1000 degrees Celsius band fast enough to suppress sigma-phase precipitation.
What yield strength does A479 require for 2507?
550 MPa (80 ksi) minimum yield, 795 MPa (116 ksi) minimum tensile, 15 percent minimum elongation in 50 mm. Hardness 32 HRC maximum (or 310 HBW), tightened to 28 HRC maximum when NACE MR0175 / ISO 15156 sour service applies.
How does A479 differ from EN 10088-3 for the same alloy?
A479 specifies yield 550 MPa min and tensile 795 MPa min; EN 10088-3 specifies yield 530 MPa min and tensile 730-930 MPa. Mill heats routinely meet both windows simultaneously. Cross-certification on both standards is normal practice.
What ferrite range applies to A479 UNS S32750?
A479 references ferrite control under Supplementary Requirement S2. NORSOK M-630 D55 supplements with 35 to 55 percent parent ferrite per ASTM E562. NACE MR0175 widens the window to 35 to 65 percent for sour service, accounting for weld metal as well as parent.
Is A479 the right standard for super duplex 2507 fasteners?
A479 covers the bar from which fasteners are machined or hot-headed. The fastener spec itself is typically ASTM A1082 (which references A479 chemistry). Mill bar comes to A479; finished fasteners ship to A1082 with A479 chemistry on the certificate.
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