Key Feature

The Economical Titanium-Stabilized Ferritic Stainless. Lower chromium content and titanium stabilization provide cost-effective corrosion resistance for automotive and moderate temperature applications.

The most economical stainless steel for automotive exhaust systems and similar applications.

Common Designations

UNS S40900
AISI 409
EN 1.4512, X6CrTi12
JIS SUS409
BS 409S19

Originally developed for automotive exhaust systems; now used in various cost-sensitive applications.

Chemical Composition (Typical wt.%)

C: ≤ 0.08
Cr: 10.5 - 11.7Ti: ≥ 6×C (min 0.15%)Mn: ≤ 1.00
Si: ≤ 1.00
P: ≤ 0.045
S: ≤ 0.030

Lower chromium than 430/304; titanium stabilization prevents sensitization.

Mechanical Properties (Annealed)

Tensile Strength (Rm): ≥ 380 - 550 MPa
Yield Strength (Rp0.2): ≥ 205 - 275 MPa
Elongation (A): ≥ 20-25%
Hardness (HB): ≤ 183

Adequate strength for most automotive and industrial applications.

Physical Properties

Density: 7.70 g/cm³
Melting Range: 1425 - 1510 °C
Thermal Expansion: 10.8 × 10⁻⁶/K (20-400°C)
Thermal Conductivity: 25.0 W/m·K (100°C)
Strongly magnetic

Low thermal expansion similar to carbon steel; beneficial for exhaust systems.

Heat Treatment

Annealing: 790-850°C, air cool
Not hardenable by heat treatmentStress Relief: 650-760°C
Maximum Service Temperature: 650-700°C

Can only be strengthened by cold working; titanium stabilization provides thermal stability.

Corrosion Resistance

Moderate resistance to atmospheric corrosion, exhaust gases, and mild chemicals. Not suitable for marine or severe chemical environments.

Adequate for automotive exhaust and many industrial applications; inferior to 304/430.

Weldability

Good weldability with proper techniques
No post-weld heat treatment requiredTitanium prevents sensitization

Suitable for most welding methods; maintains corrosion resistance in weld zone.

Key Standards (Coil)

ASTM A240 (Plate, Sheet, and Strip)
ASTM A480 (General Requirements)
EN 10088-2
JIS G4305
SAE J409

Specifically referenced in automotive industry standards.

Common Applications (from Coil)

• Automotive Exhaust Systems: Mufflers, catalytic converter housings, tailpipes
• Industrial Exhaust: Chimney liners, exhaust stacks, pollution control equipment
• Heat Exchangers: Low-cost heat exchanger plates, automotive radiators
• Agricultural Equipment: Structural components, trim, exhaust parts
• Construction: Roofing, siding, architectural trim (non-coastal)
• Containers: Chemical tanks (mild service), storage containers
• Furniture: Outdoor furniture frames, structural components

Specifically designed for cost-sensitive applications requiring better corrosion resistance than carbon steel.