In an industrial landscape that constantly demands strength, corrosion resistance, and affordability, ferritic stainless steels have found a robust niche. Among these, 446 stainless steel stands out for its high chromium content and unmatched oxidation resistance at elevated temperatures. Known by its UNS number S44600, SS 446 is used extensively in furnace parts, boiler components, and combustion systems.
Equally important is the role this material plays in the recycled stainless steel economy, offering a sustainable and cost-efficient path for high-heat resistant steel products. This article explores every aspect of ferritic stainless steel 446, including its material science, application industries, and how it fits into the growing market for scrap and recycled steel.
2. Overview of 446 Ferritic Stainless Steel
SS 446 belongs to the ferritic family of stainless steels, which means its microstructure is primarily composed of ferrite (a body-centered cubic structure). This differs from the austenitic grades (like 304 or 316), which are non-magnetic and have higher nickel content. The ferritic structure makes SS 446 magnetic, cheaper (due to low nickel), and less prone to stress corrosion cracking.
Key characteristics of 446:
- High chromium content (up to 27%)
- Excellent resistance to scaling and oxidation
- Good corrosion resistance in many atmospheres
- Magnetic
- Relatively low cost
- Limited formability and weldability
3. Chemical Composition of SS 446
Here is the typical chemical makeup:
The high chromium levels are what give SS 446 its exceptional heat and oxidation resistance—well above many 300-series stainless steels.
4. Mechanical and Physical Properties
These values indicate moderate mechanical strength but excellent stability at elevated temperatures, making SS 446 ideal for cyclical heat environments.
5. High-Temperature and Corrosion Resistance
SS 446 is designed to resist:
- Oxidation up to 1100 °C
- Sulfidation
- High-temperature scaling
- Carburization
While it isn’t the best performer in aqueous corrosion resistance compared to 316L or duplex stainless, it remains suitable for:
- Combustion gas environments
- Exhaust systems
- Oil and gas burners
- Industrial kilns
The alloy's weakness lies in pitting corrosion under stagnant chloride-rich conditions, so it’s not recommended for marine or submerged applications unless protected.
6. Fabrication, Welding, and Heat Treatment
6.1 Machinability
Machining is possible but challenging due to its hard oxide-forming nature. Use:
- Sharp carbide tools
- Slow speeds
- High feed rates
- Rigid tooling setups
6.2 Welding
Weldable with care. Use low heat input, short arc lengths, and proper filler materials such as 308L or 309L. Avoid interpass temperatures over 150°C to reduce grain growth or sigma-phase formation.
6.3 Heat Treatment
- Annealing: 760–830°C, then rapid air or water quench
- Avoid long exposure at 475–550°C to prevent embrittlement due to sigma phase
7. Industrial Applications of SS 446
SS 446 excels in high-temperature service and is widely used in:
- Furnace Parts: Recuperators, retorts, furnace liners
- Boiler Systems: Superheaters, baffle plates, economizer tubing
- Glass & Ceramic Plants: Kiln components, support hardware
- Chemical Plants: Heat exchangers, oxidation chambers
- Automotive: Exhaust manifolds, turbocharger casings
- Oil Burners & Incinerators: Burner nozzles, flue components
Its affordability, heat resistance, and reliability make it indispensable in extreme environments.
8. Recycled Steel and Stainless Scrap Economy
8.1 Role in Recycling
SS 446 plays a growing role in recyclable steel markets:
- Magnetic, so easy to separate during processing
- Retains valuable chromium content
- Often mixed with other stainless scraps to make low-alloy ferritics
8.2 Sources of Scrap
- Industrial waste: Decommissioned furnace parts, exhaust systems
- Consumer goods: Burners, chimneys, high-temp grills
- Foundries: Off-cuts and trimming from new SS 446 fabrications
8.3 Benefits of Recycled SS 446
- Lower energy footprint compared to virgin production
- Cheaper raw material for foundries
- Preserves strategic chromium resources
9. Low-Cost Stainless Steel Alternatives
SS 446 is cost-effective, but in some applications, even lower-cost grades may suffice. Below is a comparison table:
In projects where appearance and aqueous corrosion are not critical, 409 and 430 may offer acceptable performance at a lower cost.
10. Conclusion
Ferritic stainless steel 446 offers a unique blend of cost-efficiency, oxidation resistance, and high-temperature stability, especially valuable in environments where nickel-rich alloys like 310 or Inconel are too expensive. Its magnetic, ferritic nature, and easy recyclability further enhance its utility in a world moving toward sustainable, circular economies.
In applications such as heat exchangers, incinerators, and combustion systems, 446 is often the best material in terms of price-to-performance ratio. As recycling practices improve and chromium demand continues to grow, SS 446 scrap will also become a valuable asset in the stainless steel market.
