Ferritic SS 446

Ferritic SS 446

Ferritic SS 446 is a high-chromium, ferritic stainless steel alloy that is widely recognized for its outstanding resistance to high-temperature corrosion and oxidation. SS 446 is not hardenable like many other stainless steels, but its exceptional ability to withstand sulfidation, oxidation, and other forms of hot corrosion at elevated temperatures makes it an ideal choice for applications where heat resistance is paramount. The high chromium content in grade SS 446, typically between 23% and 27%, is what gives this alloy its excellent corrosion-resistant properties, particularly in high-temperature environments.

Chemical Composition

[#corrosion-resistance]Corrosion Resistance[#corrosion-resistance]

Ferritic SS 446 is a high-chromium alloy known for its exceptional resistance to high-temperature corrosion, making it ideal for use in harsh industrial environments. While grade SS 446 is non-hardenable, its resistance to oxidation, sulfidation, and other types of hot corrosion sets it apart from many other stainless steels.

This grade’s composition, featuring a high chromium content (typically 23-27%), grants it remarkable heat resistance and protection against the corrosive effects of extreme temperatures.

Due to its superior heat and corrosion resistance, Ferritic SS 446 is widely utilized in demanding applications such as recuperators, spouts for conveying molten copper alloys, neutral salt pot electrodes, oil burner parts, and combustion chambers.

These applications require materials that can endure high temperatures without significant degradation, and grade SS 446 excels in these areas, providing long-lasting durability and performance.

The properties of grade stainless steel 446 make it especially well-suited for environments that are exposed to hot gases, molten metals, and aggressive chemicals. While Ferritic SS 446 may not have the same hardness as other alloys, its outstanding resistance to high-temperature oxidation and sulfidation is a critical advantage in industries like power generation, petrochemical processing, and metal production.

In addition to its corrosion resistance, Ferritic SS 446 is also known for its excellent weldability and formability, which adds to its versatility across various applications. With its combination of high chromium content and robust resistance to hot corrosion, grade SS 446 remains a top choice for high-performance, high-temperature environments.

 Grade stainless steel 446 remains an indispensable material for high-heat environments where corrosion resistance is the critical performance factor.

Specifications of SS 446

GRADE UNS EN JIS ASTM
SS 446 S46600 1.4762 SUS 446 A 268, A 276, A 314, A 176

Ferritic SS 446 is well-regarded for its weldability using traditional methods such as TIG, MIG, and Stick welding, but it is not suitable for oxyacetylene welding due to its heat sensitivity.

The high chromium content in grade SS 446 makes it more prone to thermal distortion, so welding should be performed with the lowest possible heat input to minimize the risk of cracking and distortion. It is recommended to use thin electrode diameters, low current intensity, and stringer bead welding to ensure proper fusion without overheating. 

While Type 308 welding material can be used, it does not match the scaling resistance of the base metal, and care should be taken to account for the differences in the coefficient of thermal expansion between the base and weld metals.

The ductility loss can be recovered in SS 446 by a little temperature hike at the range of temperatures of 700°C to 800°C. In the temperature range of 600°C to 900°C, 1.4762 has the affinity to sigma phase embrittlement, thus, after longer application within this range of temperature range, the ductile values are strongly reduced particularly at the range of 800ºC-900ºC.The steel should not be used in this temperature range if mechanical stress is in position.

[#fabrication-and-heat-treatment]Heat Treatment[#fabrication-and-heat-treatment]

An interesting fact about SS 446 is that it is the only alloy with heat resistance that can tolerate molten copper and brass. AISI 446 composition enables it to create an impact on high ductile-to-brittle transition temperature. Whenever necessary, annealing should be performed at 1550-1650°F followed by rapid cool.

Physical Properties

Grade Density (g/cm3) Elastic Modulus (GPa) Coeff of Thermal Expansion (μm/m/°C) Thermal Conductivity (W/m.K)
SS 446 7.8 200 0-100°C 21.6
10.4

[#weldability]Weldability[#weldability]

446 stainless steel data sheet suggests it can be easily welded using traditional methods except oxyacetylene welding. Chrome steels with ferritic properties are heat sensitive. Therefore, the 446 stainless steel should be welded with the heat with the lowest possible input by using thin electrode diameter, low current intensity and stringer bead welding.

Ferritic SS 446 is commonly used in applications requiring excellent resistance to high-temperature corrosion. Its composition and properties make it ideal for demanding environments such as recuperators, oil burner parts, and neutral salt pot electrodes. 

Other popular applications for grade stainless steel 446 include spouts for conveying molten copper alloys, combustion chambers, furnace and kiln linings, stack dampers, boiler baffles, glass molds, and soot blowers.

Type 308 Welding Material can be used while welding SS 446, however, it does not resemble any resistance to scaling equivalent to the base metal. While welding, AISI 446 composition has to be taken care of regarding the difference in coefficient of thermal expansion of the base and weld metal too.

[#applications]Applications of SS 446[#applications]

In industries such as petrochemical, power generation, and metal processing, Ferritic SS 446 is crucial due to its resistance to sulfidation, oxidation, and other forms of hot corrosion. 

However, it should be noted that SS 446 becomes severely embrittled in the temperature range of 700°F-1000°F, which limits its use in some applications. Despite this, the grade's ability to withstand high temperatures and corrosive environments makes it an invaluable material in many industrial sectors.

Some of the popular applications of SS 446 are:

  • Neutral salt pot electrodes
  • Recuperators
  • Spouts for conveying molten copper alloys
  • Oil burner parts
  • Combustion chambers
  • Furnace and kiln linings
  • Stack dampers
  • Boiler baffles
  • Glass molds
  • Soot blowers
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