Stainless Steel 409

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Description

Stainless Steel – Grade 409 (UNS S40900), SUS409

Chemical Formula

Fe, <0.08% C, 10.5-11.75% Cr, <0.5% Ni, <1.0% Mn, <1.0% Si, <0.045% P, <0.03% S, 6x%C-0.75% Ti

Introduction

SUS409 stainless steel is a Ferritic steel that offers good mechanical properties and high-temperature corrosion resistance. It is commonly considered as a chromium stainless steel, with applications in exhaust systems of automobiles and applications that demand weldability.

SUS409 steels are also available in highly stabilized forms, such as grades S40930, S40920 and S40910. The stability of these grades is provided by the presence of niobium, titanium, or both, in the composition of steels.

Composition

Grade C Mn Si P S Cr Ni Ti
SS 409 min.

max.

0.08

1.00

1.00

0.045

0.045

10.5

11.75

0.5

6x C

0.75

Mechanical Properties

Grade Tensile Strength (MPa) min Yield Strength 0.2% Proof (MPa) min Elongation (% in 50mm) min             Hardness
Rockwell B (HR B) max Brinell (HB) max
SS 409 450 240 25 75 131

Physical Properties

Grade Density (kg/m3) Elastic Modulus (GPa) Mean Coefficient of Thermal Expansion (μm/m/°C) Thermal Conductivity (W/m.K) Specific Heat 0-100°C (J/kg.K) Electrical Resistivity (nΩ.m)
0-100°C 0-315°C 0-538°C at 100°C at 500°C
SS409 7800 200 11.0 11.7 12.4 25.8 27.5 460 600


Grade Specification Comparison

Grade UNS No Old British Euronorm Swedish SS Japanese JIS
BS En No Name
SS409 S40900 409S19 1.4512 X6CrTi12 SUH 409

 

Possible Alternative Grades

Grade Properties
3CR12  Easy to weld and good corrosion resistance. Heavy sections are more easily     available when compared to 409.
SUS304  High heat resistance and corrosion resistance. Grade 304 is expensive.
SUS321  Better heat resistance when compared to 304 or 409.
Aluminized steel  Cheaper than grade 409 stainless steel, but less resistant to exhaust gases.

Corrosion Resistance

Grade 409 stainless steels have excellent resistance to exhaust gas and atmospheric corrosion, superior to that of SS410 martensitic grades with 12% chromium and 3CR12. However, the corrosion resistance is lower than that of grade SS430 steels containing 17% chromium. The surface of grade SS 409 steels is liable to mild corrosion, which limits the usage of steels for decorative purposes.

Heat Resistance

Grade 409SS stainless steels offer scaling resistance at temperatures up to 675°C during continuous operation, and up to 815°C under intermittent conditions. These temperatures pertain to specific service environments.

Welding

Grade 409SS steels must be pre-heated to temperatures of 150 to 260°C before welding. Although grade 430SS and 409 filler rods or electrodes can be used during welding of grade 409 steels, grade 309SS electrodes or filler rods are strongly recommended by AS 1554.6. Care should be taken to weld grade 409 stainless steels with minimum heat, in order to mitigate grain growth.

Ductility of the welded products can be improved by annealing post-welding at temperatures of 760 to 815°C. However, this is not required for thin welded products. Welding of exhaust tubing of automobiles is carried out without filler rods.

Applications

The typical applications of 409 stainless steels are listed below:

  • Automotive exhaust tubing
  • Catalytic converter systems
  • Mufflers

 

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