Corrosion Resistance
Grade 409 resists atmospheric and exhaust gas corrosion. A light surface rust will form in most atmospheres; this rust retards further corrosion but makes the surface undesirable for decorative applications. The corrosion resistance is about the same as that of 3CR12 and the 12% chromium martensitic grades such as 410, and inferior to the 17% chromium grade 430.
Heat Resistance
Generally, 409 is classified as resistant to scaling in intermittent service up to 815°C and up to 675°C in continuous service, but these temperatures are dependent upon the exact service environment.
Heat Treatment
Annealing
Heat to 790-900°C and air cool. This grade cannot be hardened by thermal treatment.
Welding
Readily welded but a pre-heat of 150-260°C is recommended. Grade 409 or Grade 430 electrode or filler rods can be used, but AS 1554.6 pre-qualifies welding of 409 with Grade 309 rods or electrodes. These austenitic fillers result in a more ductile weld.
Post-weld annealing at 760-815°C improves weld ductility.
Post-weld annealing is not required when welding thin sections. Automotive exhaust tubing is typically welded without filler metal (autogenously).
All welding must be carried out with minimum heat input to reduce grain growth effects.
Typical Applications
Automotive exhaust systems, including catalytic converters and mufflers.
Stainless Steel 409 Grade Data Sheet
Specified Properties
The properties for Grade 409 are specified for annealed tubing in ASTM A268M. Compositions of other grades are for coil and sheet in ASTM A240M. Similar but not necessarily identical properties are specified for other products in their respective specifications.
Composition Specification (%)
| Grade | C | Mn | Si | P | S | Cr | Ni | N | Ti | Nb | |
| 409
S40900 |
min. | – | – | – | – | – | 10.5 | – | 6x%C | ||
| max. | 0.08 | 1.00 | 1.00 | 0.045 | 0.030 | 11.7 | 0.50 | 0.75 | |||
| S40910 | min. | – | – | – | – | – | 10.5 | – | – | 6x%C | – |
| max. | 0.03 | 1.00 | 1.00 | 0.040 | 0.020 | 11.7 | 0.50 | 0.030 | 0.50 | 0.17 | |
| S40920 | min. | – | – | – | – | – | 10.5 | – | – | 0.15 & 8 x (C+N) | – |
| max. | 0.03 | 1.00 | 1.00 | 0.040 | 0.020 | 11.7 | 0.50 | 0.030 | 0.50 | 0.10 | |
| S40930 | min. | – | – | – | – | – | 10.5 | – | – | Ti + Nb = (0.08+8) x (C+N) | |
| max. | 0.03 | 1.00 | 1.00 | 0.040 | 0.020 | 11.7 | 0.50 | 0.030 | 0.75 | ||
Mechanical Property Specification
| 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 | 380 | 170 | 20 | 95 | 207 |
| These same tensile, yield and elongation limits also apply to the other grades in ASTM A240M. Hardness limits are 88HRB and 179HB maximum for these other grades in flat rolled product. | |||||
Physical Properties (Typical values in the annealed condition)
| Grade | Density (kg/m3) | Elastic Modules (GPa) | Mean Coefficient of Thermal Expansion | Thermal Conductivity | Specific Heat | Electrical Resistivity | |||
| 0-100°C
(µm/m/°C) |
0-315°C
(µm/m/°C) |
0-538°C
(µm/m/°C) |
at 100°C (W/m.K) | at 500°C (W/m.K) | 0-100°C
(J/kg.K) |
(nΩ.m) | |||
| 409 | 7700 | 208 | 11.0 | 11.7 | 12.4 | 25.8 | 27.5 | 460 | 600 |
Grade Specification Comparison
| Grade | UNS
No |
Euronorm | Swedish SS | Japanese JIS | |
| No | Name | ||||
| 409 | S40900 | 1.4512 | X6CrTi12 / X2CrTi12 | – | SUH 409 |
| There no known standardised international alternatives to the ASTM S40910, S40920 and S40930 grades. | |||||
| These comparisons are approximate only. The list is intended as a comparison of functionally similar materials not as a schedule of contractual equivalents. If exact equivalents are needed original specifications must be consulted. | |||||
Stainless Steel 409 Grade Data Sheet
Possible Alternative Grades
| Grade | Why it might be chosen instead of 409 |
| 3CR12 | Similar corrosion resistance, better weldability and more readily available than 409, particularly in heavy sections. (409 may have better drawability than 3CR12.) |
| 304 | Better corrosion resistance and heat resistance but at higher cost. |
| 321 | Higher heat resistance than 409 or 304. |
| Aluminised steel | Lower cost than stainless steel grade 409, but also a lower resistance to exhaust gases. |
