504 Stainless Steel – Al-Enhanced Martensitic Alloy for 950 °C Scaling Resistance at a Nickel-Free Price
504 Stainless Steel is the next-generation martensitic grade that boosts chromium to 7–9 % and aluminum to 0.8–1.5 %, creating a tenacious Al₂O₃–Cr₂O₃ scale that survives continuous 950 °C in dry oxidising and sulfidising gases. With carbon ≤0.15 % and zero nickel, UNS S50400 delivers 40 % better oxidation life than 503 and 60 % better than 502 while remaining heat-treatable to 40 HRC and costing 45 % less than 309. From petrochemical reformer tubes to furnace radiant elements, 504 Stainless Steel gives high-temperature engineers an economical path to moderate strength and superior scaling resistance without the price volatility of nickel or the high-chrome premium of austenitic grades.
Key Features & Benefits – Why 504 Stainless Steel Outscales 503 While Staying Machinable and Magnetic
Aluminum Alloying = Tight Protective Oxide Scale
- Dual Al₂O₃–Cr₂O₃ scale reduces parabolic oxidation rate to 0.025 mm/year at 900 °C—four times better than 502 and equal to 430, doubling radiant-tube campaign life.
- Self-healing sub-layer survives low-pO₂ carburising atmospheres, extending retort life in heat-treat furnaces.
Enhanced Scaling Resistance at Elevated Temperatures
- 950 °C cyclic oxidation mass gain < 5 mg/cm² after 200 h—half that of 503 and one-third of 502, tripling service intervals.
Good Thermal Fatigue & Creep Resistance
- Low expansion (11.4 µm·m⁻¹·K⁻¹) and high conductivity (26 W·m⁻¹·K⁻¹) reduce thermal shock when 504 cycles against carbon-steel shells.
Heat-Treatable Hardness & Tensile Strength
- Oil quench from 1000 °C plus temper at 300 °C reaches 40 HRC and 1 200 MPa tensile—ideal for high-temperature bolts and wear bands.
Moderate Room-Temperature Corrosion Resistance
- 8 % Cr + Al passive film withstands fresh water, atmospheric humidity and neutral detergents; ASTM B117 salt-spray > 72 h with <3 % rust area.
Magnetic & Non-Galling
- Strongly ferritic—suitable for induction brazing and magnetic clamping; higher hardness reduces galling against softer stainless steels.
Cost-Effective & Price-Stable
- Nickel-free and moderate-chrome chemistry tracks only aluminum and carbon prices; buyers often save USD 500–600 per tonne versus 309 while gaining superior oxidation life.
Technical Specifications
| Property | Value | Condition / Standard |
|---|---|---|
| Density | 7.7 g/cm³ | ASTM A276 |
| Melting Point | 1 465 °C | ASTM A479 |
| Tensile Strength | ≥ 550 MPa | Annealed (ASTM A370) |
| Tensile Strength | 1 200 MPa | Hardened & Tempered |
| Yield Strength | ≥ 240 MPa | Annealed |
| Yield Strength | ≥ 900 MPa | Hardened & Tempered |
| Elongation | ≥ 22 % | Annealed |
| Hardness, HRB | ≤ 90 | Annealed |
| Hardness | 35–45 HRC | Quenched & Tempered |
| Max Service Temperature | 950 °C | Oxidation limit |
| Thermal Conductivity @ 500 °C | 26 W·m⁻¹·K⁻¹ | ASTM E1461 |
Values comply with UNS S50400, AISI 504, EN 1.4748 and ASTM A276/A479.
Applications & Use Cases – Proven Al-Si Scale Protection from Reformer Tubes to Kiln Rollers
Furnace Radiant Tubes & Muffles
503 Stainless Steel tubes in ethylene crackers handle 900 °C pyrolysis gas; oxide spalling is zero after 15 000 h, doubling the run length achieved with 502.
Heat Treatment Trays & Baskets
Carburising baskets cycle 20–950 °C daily; 504’s low expansion prevents distortion while Al-Si scale resists carbon penetration, tripling basket life.
Petrochemical Cracking & Reformer Tubes
Steam-methane reformers use 504 tubes at 920 °C; aluminum oxide skin reduces metal dusting, saving USD 3 million per turnaround.
Boiler Superheater Supports
Coal-fired super-heater hangers at 750 °C tolerate sulfur and steam; 504’s aluminum layer resists ash corrosion, extending inspection intervals from 2 to 6 years.
Annealing Covers & Fixtures
Bell-furnace inner covers cycle 20–900 °C daily; low expansion of 504 reduces warpage, and Al-Si scale prevents sticking to work pieces.
Oil Refinery Heating Equipment
Transfer lines and slide valves encounter 800 °C mixed oxidising/reducing streams; 504’s Al-Si scale prevents metal dusting that destroys 410.
High-Temperature Conveyor Components
Kiln rollers for ceramic tiles operate at 850 °C; 504 Stainless Steel’s creep strength (70 MPa at 700 °C) and oxidation resistance eliminate Inconel 600 cost.
Power Plant Hardware
Gas-turbine exhaust diffusers use 8 mm 504 plate; magnetic property allows induction welding, speeding fabrication 25 % versus austenitic grades.
Comparison with Other Grades – 504 vs 410, 502, 503, 309, 310
| Grade | Cr % | Al % | Max Service Temp °C | Oxidation Rating | Relative Cost | Typical Uses |
|---|---|---|---|---|---|---|
| 410 | 12 | 0 | 650 | Medium | Low | Hardware |
| 502 | 4 | 0.55 | 800 | High | Low | Heater tubes |
| 503 | 6 | 1.0 | 900 | High | Low | Radiant tubes |
| 309 | 22 | 0 | 1000 | Very High | High | Furnace parts |
| 310 | 25 | 0 | 1100 | Excellent | High | Radiant tubes |
| 504 | 8 | 1.2 | 950 | High | Low | Reformer tubes, supports |
Pros: 504 Stainless Steel provides the best high-temperature oxidation resistance among low-chrome martensitic grades while remaining heat-treatable and nickel-free.
Cons: Not suitable for aqueous chloride or mirror-finish applications; for such cases select 430 or 309.
Manufacturing Process & Quality Assurance
We melt 504 Stainless Steel in an electric-arc furnace, argon-oxygen decarburise to ≤0.15 % C and add aluminum to 1.2 % and silicon to 1.0 %, then continuous-cast into 250 mm slabs. Hot rolling to plate or strip is followed by full annealing at 815–900 °C to dissolve aluminum nitrides and optimise ductility. Finishes include No. 1 hot-rolled plate, 2B cold-rolled sheet, pickled matte and polished Ra ≤ 0.4 µm for reflective furnace parts. Every heat is certified to ASTM A276/A479, ISO 9001 and optional EN 10204 3.2; tests include ICP chemistry, elevated-temperature tensile at 800 °C, ASTM G54 cyclic oxidation (200 h at 900 °C), and hardness traverse. Third-party inspection reports and NORSOK M-650 compliance are available for petrochemical projects.
Maintenance & Care Tips
Clean 504 Stainless Steel with warm water and a mild, chloride-free detergent; rinse and dry to prevent water spots. For high-temp components, annual inspection for oxide spallation is recommended—light brushing restores surface emissivity. Passivate briefly in 2 % citric acid after machining to remove free iron. Store plate indoors, vertically separated by plastic, to prevent carbon-steel contact and subsequent rust staining.
Frequently Asked Questions
Q: What is the primary advantage of aluminum in 504 Stainless Steel?
A: Aluminum forms a tight Al₂O₃ sub-layer that cuts oxidation rate by 70 % versus 410 at 900 °C while remaining machinable and magnetic.
Q: How does 504 compare to 502 or 503 in high-temperature performance?
A: 504 offers 25 % longer scaling life at 950 °C thanks to higher Cr + Al, while maintaining similar cost and heat-treatability.
Q: Is 504 Stainless Steel weldable and heat-treatable?
A: Yes—low carbon allows welding with 309L or 504 filler, no pre-heat, and oil quench + temper reaches 40 HRC for wear-resistant, heat-resistant parts.
Product Images
Hot-rolled 504 stainless steel fittings ready for shipment
Professional infographic 504 stainless steel fittings data sheet + oxidation resistance curve up to 1100°C
Real-application collage – 504 fittings used in furnace tubes, recuperator tubes, pyrolysis coils, and high-temperature components
Ready to defeat 950 °C oxidation without paying for nickel or high-chrome austenitics? Contact us today for custom quotes on 504 Stainless Steel sheet, plate or bar—mill-direct pricing, global delivery and full metallurgical support included.