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What is SS 446 Stainless Steel?
Quick answer
- Definition
- SS 446 is a 23–27% chromium ferritic stainless steel with excellent oxidation and sulphidation resistance at high temperatures, up to about 1,100 °C.
- Family
- Ferritic stainless steel
- Key strength
- 23–27% chromium for scaling resistance
- Main forms
- Tubes, Plates, Sheets, Bars
- Typical uses
- Furnace parts and annealing boxes; Burner nozzles and combustion chambers; Glass-mould parts
Grade 446 has the highest chromium of the common ferritic stainless steels. It forms a tenacious oxide in air and resists sulphur-bearing atmospheres better than nickel-rich austenitic grades, which can suffer nickel-sulphide attack.
It's used for furnace parts, burner nozzles, glass-mould parts, thermocouple sheaths and recuperators. SS 446 has limited toughness at room temperature and can embrittle after long exposure around 475 °C, so it suits hot, low-stress parts.
Key characteristics
- 23–27% chromium for scaling resistance
- Excellent in sulphurous hot atmospheres
- Nickel-free
- Limited room-temperature toughness
What are the specifications and equivalents of SS 446?
| Product form | Specification / designation | Product page |
|---|---|---|
| Tubes | ASTM A268 TP446 | SS 446 tubes → |
| Plates | ASTM A240 / ASME SA240 446 | SS 446 plates → |
| Sheets | ASTM A240 / ASME SA240 446 | SS 446 sheets → |
| Bars | ASTM A276 / A479 446 | SS 446 bars → |
UNS S44600 · EN 1.4762 (related) (cross-reference; limits are similar but not identical)
What is the chemical composition of SS 446?
| Element | Limit (%) |
|---|---|
| C | 0.20 max |
| Mn | 1.50 max |
| P | 0.040 max |
| S | 0.030 max |
| Si | 1.00 max |
| Cr | 23.0 – 27.0 |
| N | 0.25 max |
What are the mechanical properties of SS 446?
| Property | Value |
|---|---|
| Tensile strength | 515 MPa (75 ksi) |
| Yield strength (0.2% offset) | 275 MPa (40 ksi) |
| Elongation | 20% |
| Hardness | ≈ 200 HBW |
Physical properties and service temperature
| Property | Value |
|---|---|
| Density (typical) | 7.5 g/cm³ (7500 kg/m³) |
| Magnetism | Magnetic. |
| Heat treatment | Annealed; it can't be hardened by heat treatment. |
| Service temperature | Oxidation resistance to about 1,100 °C (indicative). |
How is SS 446 welded and fabricated?
Weldable in thin sections; grain growth in the heat-affected zone can reduce toughness in heavier sections.
Always follow a qualified welding procedure (for example ASME Section IX) and the filler-metal recommendations for SS 446. Verify incoming material by PMI and check the mill test certificate against the specification.
Which SS 446 products do we supply?
SS 446 Stainless Steel is available in 4 product forms, from ready stock or mill-sourced to your specification, with EN 10204 3.1 mill test certificates (3.2 with third-party inspection on request).
SS 446 TubesASTM A268 TP446Specification & sizes
How it's madeSeamless tubes are hot-extruded or pierced and then cold-drawn or pilgered to size. Welded tubes are formed from strip, welded (TIG/laser/HF), bead-worked and drawn or sized. Heat-exchanger and boiler tubes are annealed after final forming, and U-tubes are bent and stress-relieved as required.
- Specification
- ASTM A268 TP446
- Size range
- OD 3 mm to about 127 mm (¼" to 5") typical, wall 0.5 mm to 12 mm; BWG or mm; straight lengths up to about 30 m, U-bent to drawing
- Finish
- Annealed & pickled, bright annealed (BA), polished (sanitary), cold-drawn
- Ends
- Plain square-cut, deburred; U-bends with stress-relieved bends on request
Testing & documents
- Eddy-current and/or ultrasonic testing on each tube
- Hydrostatic or pneumatic test
- Flattening, flaring and flange tests
- Grain size (H grades), IGC and hardness when specified
- Surface roughness (Ra) for sanitary and instrumentation tube
- EN 10204 3.1 certificate; 3.2 with third-party inspection
SS 446 PlatesASTM A240 446Specification & sizes
How it's madeSlabs are hot-rolled on a reversing plate mill (or a Steckel/hot-strip mill for thinner plate), then heat treated (annealed, normalised, or quenched and tempered, depending on material), descaled and pickled or shot-blasted. Plates are cut to size by plasma, oxy-fuel, waterjet or shearing.
- Specification
- ASTM A240 / ASME SA240 446
- Size range
- Thickness about 3 – 150 mm (and heavier on request), widths 1,000 – 3,000 mm, lengths 2,000 – 12,000 mm; cut-to-size and profile-cut parts
- Finish
- No.1 (hot-rolled, annealed and pickled) for stainless; shot-blasted, mill scale or primed for carbon steel
- Ends
- Mill edge, sheared, plasma or waterjet cut, profile cut to drawing
Testing & documents
- Chemical analysis and tensile tests (per plate or heat)
- Impact tests for low-temperature and pressure-vessel plates
- Ultrasonic testing (e.g. ASTM A435 / A578) when specified
- IGC, HIC and simulated PWHT tests as required
- Flatness and dimensional inspection
- EN 10204 3.1 certificate; 3.2 with third-party inspection
SS 446 SheetsASTM A240 446Specification & sizes
How it's madeHot-rolled coil is cold-rolled to final thickness, then annealed and pickled (2B/2D) or bright annealed (BA), temper-passed, and polished or textured as needed. Coils are then levelled and cut into sheets.
- Specification
- ASTM A240 / ASME SA240 446
- Size range
- Thickness about 0.3 – 6 mm, standard sizes 1,000 × 2,000, 1,219 × 2,438 (4 × 8 ft), 1,250 × 2,500 and 1,500 × 3,000 mm; custom cut lengths
- Finish
- 2B, 2D, BA, No.4 (brushed), HL (hairline), No.8 (mirror), embossed, PVC or laser-film protected
- Ends
- Sheared or slit edges; laser-cut blanks on request
Testing & documents
- Chemical and mechanical tests
- Surface and finish inspection
- Thickness and flatness checks
- Hardness and bend tests as specified
- EN 10204 3.1 certificate; 3.2 with third-party inspection
SS 446 BarsASTM A276 / A479 446Specification & sizes
How it's madeBillets are hot-rolled or forged to size, then heat treated (annealed, solution treated, or quenched and tempered) and finished by descaling, peeling, turning, cold-drawing or centreless grinding for bright bar with tight tolerance.
- Specification
- ASTM A276 / A479 446
- Size range
- Round bars about 3 – 500 mm diameter; hex 6 – 100 mm A/F; square and flat sections to order; lengths 3 – 6 m random or cut to size
- Finish
- Black (hot-rolled), peeled, bright drawn, centreless ground and polished (h9 / h11 tolerance)
- Ends
- Saw-cut, chamfered on request
Testing & documents
- Chemical and mechanical tests
- Ultrasonic testing for internal soundness
- Hardness, IGC and impact tests as specified
- Straightness and tolerance checks
- EN 10204 3.1 certificate; 3.2 with third-party inspection
Where is SS 446 used?
Typical applications
- Furnace parts and annealing boxes
- Burner nozzles and combustion chambers
- Glass-mould parts
- Thermocouple protection tubes
- Recuperators and heat exchangers for flue gas
Industries
What should you specify when buying SS 446?
- Grade and specification, e.g. ASTM A268 TP446
- Product form, size and tolerance
- Heat treatment / condition and surface finish
- Quantity, delivery location and required date
- Tests: PMI, hydro/NDT, IGC, impact or hardness as required
- Certificate type (EN 10204 3.1 / 3.2) and third-party inspection
See our RFQ checklist guide and what drives metal prices.
Explore more on SS 446
SS 446 products
Guides
Comparisons & articles
Frequently asked questions
Why use SS 446 instead of SS 310S?
In sulphur-bearing hot gases, nickel-rich grades like SS 310S can suffer sulphidation. The nickel-free SS 446 resists this, although it's less tough at room temperature.
What is SS 446 used for?
Furnace parts and annealing boxes, Burner nozzles and combustion chambers, Glass-mould parts, Thermocouple protection tubes. It's used across Cement, Heavy Engineering, Power Generation.
What is the UNS number of SS 446?
SS 446 is designated UNS S44600; the closest EN cross-reference is 1.4762 (related).
Which product forms is SS 446 available in?
Tubes, Plates, Sheets, Bars, to ASTM A268 TP446, ASTM A240 446, ASTM A240 446 and related specifications.
What is the density of SS 446?
About 7.5 g/cm³ (7500 kg/m³), used for weight calculations.
Is SS 446 magnetic?
Magnetic.
What temperature can SS 446 withstand?
Oxidation resistance to about 1,100 °C (indicative).