| These properties are specified for annealed tubing in ASTM A268. Similar but not necessarily identical properties are specified for other products such as coil and bar in their respective specifications. Composition Typical compositional ranges for grade 409 stainless steels are given in table 1. Table 1. Composition ranges for 409 grade stainless steel | | | 409 | min. max. | - 0.08 | - 1.00 | - 1.00 | - 0.045 | - 0.030 | 10.5 11.75 | - 0.50 | 6x%C 0.75 | | | | | | | | | | | Mechanical Properties Typical mechanical properties for grade 409 stainless steels are given in table 2. Table 2. Mechanical properties of 409 grade stainless steel Physical Properties Typical physical properties for annealed grade 409 stainless steels are given in table 3. Table 3. Physical properties of 409 grade stainless steel in the annealed condition | | | | | | | | | | | 409 | 7600 | 208 | 11.0 | 11.7 | 12.4 | 25.8 | 27.5 | 460 | 600 | Grade Specification Comparison Approximate grade comparisons for 409 stainless steels are given in table 4. Table 4. Grade specifications for 409 grade stainless steel | | | | | | | | | | 409 | S40900 | 409S19 | - | 1.4512 | X6CrTi12 | - | SUH 409 | | 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. | Possible Alternative Grades Possible alternative grades to grade 409 stainless steels are given in table 5. Table 5. Possible alternative grades to 409 grade stainless steel | | | 3CR12 | Similar corrosion resistance, easier welding 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 resistance to exhaust gases, but at lower cost than stainless steel grade 409. | 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. |