ASTM A479 / A479M, "Standard Specification for Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels", is the primary specification for Ferralium 255 (UNS S32550) bar and billet supplied for pressure-boundary service. The spec covers chemistry, mechanical properties, heat treatment, marking, dimensional tolerance, and the inspection / test report requirements that the bar must meet to be classified as A479 grade S32550.
ASTM A479 covers hot-finished and cold-finished bar (rounds, hexagons, squares, flats), forged bar, and shapes in the chemical compositions listed in Table 1 of the spec. UNS S32550 (Ferralium 255) is included in the ferritic / austenitic (duplex) section. The spec applies to bar intended for boilers, pressure vessels, heat exchangers, and high-pressure piping components.
| Element | Min % | Max % |
|---|---|---|
| Carbon (C) | none | 0.04 |
| Manganese (Mn) | none | 1.50 |
| Phosphorus (P) | none | 0.04 |
| Sulphur (S) | none | 0.030 |
| Silicon (Si) | none | 1.00 |
| Chromium (Cr) | 24.0 | 27.0 |
| Nickel (Ni) | 4.50 | 6.50 |
| Molybdenum (Mo) | 2.90 | 3.90 |
| Copper (Cu) | 1.50 | 2.50 |
| Nitrogen (N) | 0.10 | 0.25 |
| Property | Minimum (UNS S32550) |
|---|---|
| Yield strength, 0.2% offset (Rp0.2) | 550 MPa (80 ksi) |
| Ultimate tensile strength (Rm) | 760 MPa (110 ksi) |
| Elongation in 50 mm (A5) | 15% |
| Hardness, max (Brinell) | 302 HBW |
| Hardness, max (Rockwell C) | 32 HRC |
Per ASTM A479: bar shall be solution-annealed at 1040 °C minimum (1900 °F) followed by water quench or rapid cooling to prevent precipitation of intermetallic phases. TorqBolt practice for Ferralium 255 is 1100 °C solution anneal + water quench, which gives more conservative ferrite-balance margin (45–50% ferrite typical) and lower risk of sigma-phase.
TorqBolt supplies Ferralium 255 (UNS S32550) bar to ASTM A479 with per-heat EN 10204 type 3.2 MTC documenting full chemistry, mechanical properties, heat-treatment certificate, ferrite content per ASTM E562, and PREN calculation. Available diameters: 6 mm to 600 mm round bar; hex / square / flat / cold-finished / forged variants. NORSOK M-650 QTR + NACE MR0175 / ISO 15156-3 sour-service compliance documentation available on request. See Ferralium 255 round bar product page.
