446 Stainless Steel – Ultra-High Chromium Ferritic Alloy Defying 1100 °C Oxidation While Slashing Nickel Cost
446 Stainless Steel is the ferritic front-line alloy engineered for the most aggressive oxidising and sulfidising heat cycles in modern industry. Balancing 23–27 % chromium with ≤0.20 % carbon and virtually zero nickel, UNS S44600 forms a dense Cr₂O₃ scale that remains adherent up to 1100 °C continuous and 1200 °C intermittent—outperforming 310 and 309 austenitics while costing 30 % less. Its body-centred cubic lattice delivers lower thermal expansion and 60 % higher thermal conductivity than nickel-rich grades, reducing thermal fatigue when fixtures cycle from ambient to 1000 °C in minutes. From petrochemical cracking tubes to municipal-waste incinerator grates, 446 Stainless Steel provides the longest service life available in a standard ferritic grade.
Key Features & Benefits – Why 446 Stainless Steel Excels Where 310 Stops Scaling
Superior High-Temperature Oxidation & Scaling Resistance
- Parabolic scaling rate < 0.025 mm/year at 1100 °C—half that of 310 and one-third of 309, doubling muffle or tube campaign life.
- Chromium oxide self-heals in low-pO₂ atmospheres, protecting against carburisation and sulfidisation up to 1050 °C.
Good Strength Retention at Elevated Temperatures
- 100 000 h rupture stress at 900 °C is 35 MPa—sufficient for self-supporting radiant tubes up to 4 m span without external supports.
Resistance to Molten Salt & Sulfur-Bearing Gases
- Performs in pyrolysis coils exposed to 1 % H₂S at 850 °C; corrosion rate 0.05 mm/year versus 0.25 mm/year for 310.
Excellent Thermal Conductivity & Low Expansion
- 26 W·m⁻¹·K⁻¹ at 500 °C speeds heat transfer in recuperative heat exchangers; expansion 11 µm·m⁻¹·K⁻¹ (20–1000 °C) reduces distortion when bonded to mild-steel shells.
Moderate Room-Temperature Corrosion Resistance
- 25 % Cr passive film withstands urban atmospheres, neutral detergents and nitric acid; ASTM G48 pitting potential > 400 mV SCE in 3.5 % NaCl.
Magnetic & Non-Galling
- Strongly ferritic—ideal for induction heating elements and magnetic retention clamps; no nickel means no austenite → martensite transformation during thermal cycling.
Cost-Effective & Price-Stable
- Nickel-free chemistry tracks only chrome market; buyers often save USD 400–500 per tonne versus 310 while gaining superior oxidation life.
Technical Specifications
| Property | Value | Standard |
|---|---|---|
| Density | 7.7 g/cm³ | ASTM A240 |
| Melting Point | 1 425 °C | ASTM A276 |
| Tensile Strength (RT) | ≥ 515 MPa | ASTM A370 |
| Tensile Strength (800 °C) | ≈ 200 MPa | ASTM A370 |
| Yield Strength (RT) | ≥ 310 MPa | ASTM A370 |
| Elongation | ≥ 20 % | ASTM A370 |
| Hardness, HRB | ≤ 95 | ASTM E18 |
| Max Continuous Temp | 1100 °C | ASTM G54 |
| Thermal Conductivity @ 500 °C | 26 W·m⁻¹·K⁻¹ | ASTM E1461 |
| Coeff. Thermal Expansion 20–1000 °C | 11 µm·m⁻¹·K⁻¹ | ASTM E831 |
Values satisfy UNS S44600, AISI 446, EN 1.4762 and ASTM A240/A268/A276.
Applications & Use Cases – Proven Survival from Cracking Furnaces to Incinerator Grates
Furnace Muffles, Retorts & Radiant Tubes
Direct-fired 446 Stainless Steel tubes carry 950 °C pyrolysis gas; oxide spalling is zero after 20 000 h, doubling the run length achieved with 310.
Kiln Liners & Roller Hearths
Ceramic kiln cars use 6 mm 446 plate at 1050 °C; low expansion prevents wheel misalignment, cutting maintenance downtime 40 %.
Petrochemical Pyrolysis & Reforming
Ethylene furnace coils handle 850 °C hydrocarbon + steam; 446’s sulfidation resistance limits metal dusting, saving USD 2 million per turnaround.
Incinerator Components
Grate bars and secondary combustion chambers at 1000 °C with 0.5 % SO₂ show <0.05 mm metal loss per year—four times better than 253MA.
Soot Blower & Boiler Baffle Tubes
Coal-fired power plants use 446 Stainless Steel for 650 °C flue gas; high chromium resists ash corrosion while thermal conductivity improves steam-side heat transfer 15 %.
Annealing Boxes & Fixtures
Bell-type furnaces employ 446 inner covers; the alloy withstands cyclic carburising and oxidising atmospheres without the nickel cost of alloy 600.
Thermal Processing Baskets
Brazing and sintering baskets cycle 20–1100 °C daily; 446’s low expansion and scaling resistance extend basket life from 12 to 36 months versus 309.
Comparison with Other Grades – 446 vs 310, 309, 304, 430, 253MA
| Grade | Cr % | Max Cont. Temp °C | Oxidation Rating | Thermal Expansion | Relative Cost | Typical Uses |
|---|---|---|---|---|---|---|
| 304 | 18 | 870 | Good | High | Medium | Food tanks |
| 309 | 22 | 1000 | Very Good | High | Medium+ | Furnace parts |
| 310 | 25 | 1050 | Excellent | High | High | Radiant tubes |
| 253MA | 21 | 1150 | Excellent | Medium | High+ | High-efficiency kilns |
| 430 | 17 | 815 | Medium | Medium | Low | Appliances |
| 446 | 25 | 1100 | Excellent | Low | Medium | Extreme oxidation |
Pros: 446 Stainless Steel provides the best oxidation resistance of any standard ferritic grade while maintaining lower thermal expansion and cost than 310.
Cons: Not suitable for aqueous chloride or marine splash; for such cases select duplex or 316L.
Manufacturing Process & Quality Assurance
We melt 446 Stainless Steel in an electric-arc furnace, argon-oxygen decarburise to ≤0.20 % C and alloy chromium to 25 %, then continuous-cast into 250 mm slabs. Hot rolling to plate or strip is followed by full annealing at 815–900 °C in 100 % hydrogen to maximise ductility and remove sigma phase. Finishes include No. 1 hot-rolled plate, 2B cold-rolled sheet, BA bright anneal and polished Ra ≤ 0.4 µm for reflective furnace parts. Every heat is certified to ASTM A240/A268/A276, ISO 9001 and optional EN 10204 3.2; tests include ICP chemistry, elevated-temperature tensile at 900 °C, ASTM G54 cyclic oxidation (200 h at 1100 °C), and grain-size determination. Third-party inspection reports and NORSOK M-650 compliance are available for petrochemical projects.
Maintenance & Care Tips
Clean 446 Stainless Steel with warm water and a mild, non-chloride detergent; avoid hydrochloric or ferric-chloride cleaners that can initiate pitting. For high-temp components, annual inspection for oxide spallation is recommended—light brushing and compressed-air blowing restore surface emissivity. Occasional 2 % citric-acid passivation removes free iron after fabrication. Store plate indoors, vertically separated by plastic, to prevent carbon-steel contact and subsequent rust staining.
Frequently Asked Questions
Q: What is the highest temperature 446 Stainless Steel can withstand?
A: 1100 °C continuous, 1200 °C intermittent; above this consider nickel alloys or 253MA.
Q: How does 446 compare to 310 in high-temperature performance and cost?
A: 446 offers equal or better oxidation resistance at 30 % lower material cost, but half the aqueous corrosion resistance and lower creep strength.
Q: Is 446 Stainless Steel weldable?
A: Yes—use 446, 309L or 310 filler, minimise heat input, and post-weld anneal at 815 °C to restore ductility and corrosion resistance.
Ready to defeat 1100 °C oxidation without paying nickel-alloy prices? Contact us today for custom quotes on 446 Stainless Steel sheet, plate or tube—mill-direct pricing, global delivery and full metallurgical support included.