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409 Stainless Steel

Penn Stainless inventory now includes Alloy 409 (UNS S40900) in sheet, sheet coil, plate, round bar, processed flat bar and tubular products.


General Properties

Alloy 409 is a general purpose, chromium, titanium stabilized, ferritic stainless steel whose primary application is automotive exhaust systems. It contains 11% chromium which is the minimum amount for the formation of the passive surface film which gives stainless steels their corrosion resistance. It combines good elevated temperature corrosion resistance with medium strength, good formability, and overall cost. Alloy 409 resists corrosion strongly compared to carbon steel and is used as an alternative to carbon steel in mildly challenging environments where its high resistance to corrosion and high temperature oxidation gives an advantage. It is commonly used in applications where appearance is a secondary quality to mechanical properties and corrosion resistance.


Although Alloy 409 is designed principally for the automotive exhaust industry, it has been successfully used in other industrial applications as well. Some examples of applications that call for Alloy 409 include:

  • Automotive exhaust systems
  • Catalytic converters
  • Mufflers
  • Tailpipes
  • Farm equipment
  • Structural support and hangers
  • Transformer cases
  • Furnace components
  • Heat exchanger tubing


  • ASTM/ASME: UNS S40900
  • EURONORM: FeMi35Cr20Cu4Mo2
  • DIN: 2.4660

Corrosion Resistance:

  • Resists atmospheric and exhaust gas corrosion
  • In most atmospheres a light surface rust will form which inhibits further corrosion but makes the surface less appealing

 Heat Resistance

  • Generally classified as resistant to scaling in intermittent service up to 1499oF (815oC ) and up to 1247oF (675oC) in continuous service


  • Readily weldable
  • Pre-heat of 302 to 500oF (150 to 260oC) is recommended
  • Post-weld annealing at 1400 to 1499oF improved weld ductility
  • Post-weld annealing is not required when welding thin sections
  • Automotive exhaust tubing is typically welded without filler metal

Chemical Properties:

C Mn Si P S Cr Ni Ti
409 max:0.08 max:1.0 max:1.0 max:0.045 max:0.045 min: 10.5 max: 11.75 max: 0.5 min: 0.48 max: 0.75

Mechanical Properties:

Grade Tensile Strength MPa (min) Yield Strength 0.2% MPa(min) Elongation % Hardness (Brinell) MAX Hardness (Rockwell B) MAX
409 380 207 20 207 95

Physical Properties:

Thermal Conductivity
(BTU/h ft. °F)
(in x 10^-6)
Modulus of
(psi x 10^6)
Coefficient of
Thermal Expansion
°F x 10^-6
Specific Heat
at 68°F: 0.280 9.4 at 212°F 28.3 at 68°F 29 5.84 at 32 – 212°F 0.114 at 68°F to 212°F 2500 to 2590
12.4 at 932 °F 39.4 at 752°F 6.60 at 32 – 1000°F
49.6 at 1652 °F 6.86 at 32 – 1500°F

Alloy 409 PDF