409 stainless steel is a heat-resisting ferritic stainless steel providing good oxidation and corrosion resistance compared to carbon steel. This titanium stabilized grade is suitable for automotive exhaust systems, due to its good formability, weldability, and corrosion resistance, 409 stainless steel has been successfully used in other industrial applications as well.
Type 409 grade is ferritic stainless steel with less chromium (10.5 – 11.75%) and very little nickel (0.5% max). It combines good elevated temperature corrosion resistance with medium strength, good formability, and overall cost. It is less expensive to produce than 304.
409 Stainless Steel Composition
| Grade | C | Si | Mn | P | S | Cr | Ni | Ti | Fe |
|---|---|---|---|---|---|---|---|---|---|
| 409 | 0.08 | 1.00 | 1.00 | 0.045 | 0.045 | 10.5 – 11.75 | 0.5 | 6xC | Bal |
| TP409 | 0.08 | 1.00 | 1.00 | 0.045 | 0.030 | 10.5 – 11.7 | 0.5 | 6xC Min, 0.75 Max | Bal |
409 Stainless Steel 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 |
| TP409 | 380 | 170 | 20 | 207 | 95 |
409 Stainless Steel Physical Properties
- Density: 7.7g/Cm3
- Melting Point: 1480 – 1530 ℃
- Specific Gravity: 7.68
- Modulus Of Elasticity In Tension: 190 GPa
409 Stainless Steel Equivalent
- UNS S40900
- EN X2CrTi12
- DIN 1.4512
- JIS SUS409L
Forms
- Sheet
- Coil
- Pipe
- Plate
- Bar
409 Stainless Steel Advantages
- Ferritic stainless steel with magnetic
- Cost-effective choice compared to 300 series stainless steel
- Excellent oxidation and corrosion resistance
- Good mechanical properties
- Typical applications in automotive exhaust systems and heat exchanger tube
Corrosion Resistance
Grade 409 stainless steel has 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 steel is liable to mild corrosion, which limits the usage of steel for decorative purposes.
The corrosion resistance of 409 stainless steel is better than coated carbon steel, similar to that of Type 410 stainless steel, and less than that of Type 304/304L stainless steel. Type 409 is not suggested for cosmetic or surface-critical applications as light surface rusting can form during exposure to atmospheric conditions.
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 the 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, to mitigate grain growth.
The 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.
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.
Typical Applications
- Automotive exhaust systems
- Catalytic converters
- Mufflers
- Tailpipes
- Farm equipment
- Structural support and hangers
- Transformer cases
- Furnace components
- Heat exchanger tube
409 Stainless Steel Exhaust Pipe
Advantages: 409 stainless steel has good corrosion resistance, especially in high temperature and high humidity environments with good durability. It also has high wear and thermal fatigue resistance and can withstand high temperatures and pressures in exhaust systems. In addition, 409 stainless steel is relatively affordable and suitable for general automotive exhaust systems.
Cons: Compared to 304 stainless steel, 409 stainless steel has lower corrosion and oxidation resistance. It is less resistant to acidic environments and chlorides, so rust and corrosion may occur in certain harsh environments.
But now it is gradually replaced by 301 and 304 stainless steel. With a combination of performance and price, 304 stainless steel has become the new favorite in the stainless steel exhaust market due to its moderate price and ease of operation. While 409L stainless steel, with its excellent resistance to corrosion, high temperature and fatigue, occupies more than 90% of the market share, not only enhances the life of the exhaust system components but also achieves a lightweight design, which improves engine efficiency and reduces exhaust emissions. Despite its outstanding performance, 316 stainless steel is not commonly used in automotive exhaust applications due to its high price.
304 vs 409 Stainless Steel
The main differences between 304 stainless steel and 409 stainless steel are composition, properties and application scenarios. 304 stainless steel contains more nickel and chromium, with better corrosion resistance and oxidation resistance, while 409 stainless steel contains less chromium, lower cost, commonly used in less demanding application scenarios.
304 stainless steel is a general-purpose stainless steel material with stronger rust resistance than 200 series stainless steel materials, and better high-temperature resistance, able to withstand temperatures as high as 1,000-1,200 degrees Celsius.304 stainless steel has excellent stainless steel corrosion resistance and better resistance to intergranular corrosion.2 Additionally, 304 stainless steel has a density of 7.93g/ cm³, has a high coefficient of thermal expansion and thermal conductivity, but in a high-temperature environment due to thermal expansion and contraction of the stress generated by the material may lead to deformation or even rupture.
Stainless steel 409 is the stainless steel with the lowest chromium content and is widely used in non-structural applications such as automotive exhaust systems. It has low carbon and titanium stability, which improves weldability, but low toughness at low temperatures limits its use in structural applications. 409 stainless steel has better oxidation resistance, making it suitable for extending the life of automobiles and lightweighting of automobiles, and as a recyclable and reusable environmental material.