Mechanical Properties

The table below provides the mechanical properties of grade 409 stainless steels:

Table 2 - Mechanical properties of grade 409 stainless steels

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 Specification Comparison

Table 4 provides approximate grade comparisons of 409 stainless steels:

Table 4 - Grade specifications for 409 grade stainless steel

Possible Alternative Grades

The following table gives possible alternative grades of 409 stainless steels:

Table 5 - Possible alternative grades of 409 stainless steels

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