Performance comparison of 409 heat-resistant ferritic stainless steel

409 stainless steel is a heat-resistant ferritic stainless steel, and the automobile exhaust parts made of it have good oxidation resistance and corrosion resistance. This stainless steel alloy can be made into automobile mufflers, pipe manifolds, exhaust pipes, catalytic converters, mufflers and tailpipes. And the excellent formability, weldability and corrosion resistance of 409 stainless steel have made it used in many other applications, such as culverts, household heating furnaces, automotive thermostats, fuel filter transformer housings and farm equipment.
409 ferritic stainless steel is used well in most areas, but intergranular corrosion may occur in the welding heat-affected zone in some industrial applications. The titanium and niobium content of this alloy is carefully proportioned to resist susceptibility and intergranular corrosion that can occur in the heat-affected zone of welds or other heating conditions in the parent metal. A balanced proportion of stabilizing elements can achieve good weldability without the need for annealing to restore ductility after welding. Its formability and toughness will also be enhanced.
409HP stainless steel is a patented chemical composition of stainless steel plates. Like other 409 alloys, the 11% chromium content makes its corrosion resistance significantly enhanced compared to carbon steel. This stainless steel has sufficient resistance to oxidation and corrosion, making it a good choice for automotive emissions system applications. The hot end exhaust may use an alloy with a chromium content of 18%. 409HP alloy has good processability and has room for full application in applications other than automobiles.
In terms of stress fracture, the fracture data of 409 and 439 alloys at 649°C are very close, while the fracture resistance time of alloy 439 under special stress will be slightly longer. Because the chromium content in 439 alloy is relatively high, when the stress is 10.3 MPa or lower at 816°C, the material will resist fracture for a longer time.
In terms of toughness properties, like other ferritic stainless steels, they will undergo a transition from ductility to brittleness when the temperature decreases under impact load. The ductile-to-brittle transition temperature is a function of many factors, including heat treatment, microstructure, stress state, loading rate notch sharpness, thickness, and material uniformity. Generally, the DBTT value of 409 stainless steel plates with a thickness of 4.77mm and above is higher than room temperature, which means that the plate may be difficult to process due to brittleness.
In terms of corrosion resistance, the chromium content of 409 stainless steel alloy is 11%. Compared with carbon steel, the corrosion resistance of this stainless steel material has been greatly improved. However, compared with other high-priced stainless steels with higher chromium content, especially molybdenum content, its corrosion resistance is relatively low. However, despite this, 409 stainless steel can show sufficient corrosion and oxidation resistance in many automotive and non-automotive applications.