Grade 409 Stainless Steel and The Properties for SUS Grade 409

Grade 409 Stainless Steel and The Properties for SUS Grade 409

Grade 409 is a titanium-stabilised ferritic stainless steel. Although regarded as a general-purpose chromium stainless steel the almost exclusive application for Grade 409 is automotive exhaust systems. Its applications are those where appearance is a secondary consideration to mechanical properties and corrosion resistance, particularly at high temperatures, and where some weldability is required.

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Cielo Front Axle Assembly Car Exhaust System
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The generic grade 409 has now been replaced in some ASTM specifications (notably the flat rolled specification ASTM A240M) by several “sub-grades”, designated S40910, S40920 and S40930. These have various degrees of stabilisation with titanium, niobium or both titanium and niobium. Any of these may be certified as S40900 (Grade 409). By contrast only standard Grade 409 is listed in ASTM

Stainless Steel Grade 409 -  A268M covering tube.

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 AtlasCR12 and the 12% chromium martensitic grades such as 410, and inferior to the 17% chromium grade 430.

Consult Atlas Technical Assistance for specific environmental recommendations. 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.

Stainless Steel Grade 409 - Heat Treatment Annealing

Heat to 790-900°C and air cool. This grade cannot be hardened by thermal treatment.

Stainless Steel Grade 409 -  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.

Stainless Steel Grade 409 - Typical Applications

Automotive exhaust systems, including catalytic converters and mufflers

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.

Grade 409 Stainless Steel and The Properties for SUS Grade 409




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