Grade 409 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.
Grade 409 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.
The properties given below relate to annealed tubing of ASTM A268. The specified properties may not be similar to other products such as bar and coil.
The typical chemical compositional ranges of grade 409 stainless steels are given below:
Mechanical Properties
The table below provides the mechanical properties of grade 409 stainless steels:
Table 2 - Mechanical properties of grade 409 stainless steels
| 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 |
| 409 | 450 | 240 | 25 | 75 | 131 |
Physical Properties
The physical properties of annealed grade 409 stainless steels are tabulated below:
Table 3 - Physical properties of annealed grade 409 stainless steels
| 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 |
| 409 | 7800 | 200 | 11.0 | 11.7 | 12.4 | 25.8 | 27.5 | 460 | 600 |
Grade Specification Comparison
Table 4 provides approximate grade comparisons of 409 stainless steels:
Table 4 - Grade specifications for 409 grade stainless steel
| Grade | UNS No | Old British | Euronorm | Swedish SS | Japanese JIS |
| BS | En | No | Name |
| 409 | S40900 | 409S19 | - | 1.4512 | X6CrTi12 | - | SUH 409 |
Possible Alternative Grades
The following table gives possible alternative grades of 409 stainless steels:
Table 5 - Possible alternative grades of 409 stainless steels
| Grade | Properties |
| 3CR12 | Easy to weld and good corrosion resistance. Heavy sections are more easily available when compared to 409. |
| 304 | High heat resistance and corrosion resistance. Grade 304 is expensive. |
| 321 | 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 410 martensitic grades with 12% chromium and 3CR12. However, the corrosion resistance is lower than that of grade 430 steels containing 17% chromium. The surface of grade 409 steels is liable to mild corrosion, which limits the usage of steels for decorative purposes.
Heat Resistance
Grade 409 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.
Heat Treatment
Annealing of grade 409 steels is carried out at temperatures ranging from 790 to 900°C, followed by air-cooling. Thermal treatment does not harden grade 409 steels.
Welding
Grade 409 steels must be pre-heated to temperatures of 150 to 260°C before welding. Although grade 430 and 409 filler rods or electrodes can be used during welding of grade 409 steels, grade 309 electrodes or filler rods are strongly recommended by AS 1554.6. Care should be taken to weld grade 409 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 grade 409 stainless steels are listed below:
- Automotive exhaust tubing
- Catalytic converter systems
- Mufflers
