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What is SS 409 Stainless Steel?
Quick answer
- Definition
- SS 409 is an 11% chromium, titanium-stabilised ferritic stainless steel designed for automotive exhausts and other mildly corrosive, high-temperature applications.
- Family
- Ferritic stainless steel
- Key strength
- About 11% chromium: lowest-cost stainless
- Main forms
- Pipes, Tubes, Plates, Sheets, Coils
- Typical uses
- Automotive exhaust systems and mufflers; Catalytic converter shells; Heat-exchanger fins and tubes
Grade 409 is the most economical stainless steel in common use. With about 10.5–11.7% chromium and titanium stabilisation, it resists oxidation and exhaust-gas corrosion far better than carbon or aluminised steel, while remaining weldable in thin gauges.
ASTM A240 now lists several SS 409 variants (S40910, S40920, S40930) with different stabilisation requirements. Surface rusting (light staining) is acceptable in its intended uses, so SS 409 isn't chosen for appearance.
Key characteristics
- About 11% chromium: lowest-cost stainless
- Titanium-stabilised for weldability
- Magnetic ferritic structure
- Resistant to chloride stress corrosion cracking
What are the specifications and equivalents of SS 409?
| Product form | Specification / designation | Product page |
|---|---|---|
| Pipes | ASTM A268 / A554 (welded) | SS 409 pipes → |
| Tubes | ASTM A268 TP409 | SS 409 tubes → |
| Plates | ASTM A240 / ASME SA240 409 | SS 409 plates → |
| Sheets | ASTM A240 / ASME SA240 409 | SS 409 sheets → |
| Coils | ASTM A240 / ASME SA240 409 | SS 409 coils → |
UNS S40900 · EN 1.4512 (cross-reference; limits are similar but not identical)
What is the chemical composition of SS 409?
| Element | Limit (%) |
|---|---|
| C | 0.030 max |
| Mn | 1.00 max |
| P | 0.040 max |
| S | 0.020 max |
| Si | 1.00 max |
| Cr | 10.5 – 11.7 |
| Ni | 0.50 max |
| Ti | 6×(C+N) – 0.50 |
| N | 0.030 max |
What are the mechanical properties of SS 409?
| Property | Value |
|---|---|
| Tensile strength | 380 MPa (55 ksi) |
| Yield strength (0.2% offset) | 170 MPa (25 ksi) |
| Elongation | 20% |
| Hardness | 179 HBW / 88 HRB |
Physical properties and service temperature
| Property | Value |
|---|---|
| Density (typical) | 7.7 g/cm³ (7700 kg/m³) |
| Magnetism | Magnetic. |
| Heat treatment | Annealed; it can't be hardened by heat treatment. |
| Service temperature | Good oxidation resistance; highly resistant to chloride stress corrosion cracking. |
How is SS 409 welded and fabricated?
Weldable in thin sections; grain growth in the heat-affected zone can reduce toughness in heavier sections.
Always follow a qualified welding procedure (for example ASME Section IX) and the filler-metal recommendations for SS 409. Verify incoming material by PMI and check the mill test certificate against the specification.
Which SS 409 products do we supply?
SS 409 Stainless Steel is available in 5 product forms, from ready stock or mill-sourced to your specification, with EN 10204 3.1 mill test certificates (3.2 with third-party inspection on request).
SS 409 PipesASTM A268 / A554Specification & sizes
How it's madeSeamless pipe is pierced from a solid billet and hot-finished or cold-drawn. Welded pipe is formed from strip or plate and welded longitudinally (ERW/HFW, TIG/plasma, EFW, LSAW) or spirally (SAWH). Stainless and nickel-alloy pipe is then solution annealed and pickled. Carbon and alloy steel pipe is supplied as-rolled, normalised, or normalised and tempered according to the specification.
- Specification
- ASTM A268 / A554 (welded)
- Size range
- NPS ⅛" to 48" and larger (DN 6 – DN 1200+), schedules 5S to XXS, single random, double random and cut lengths
- Finish
- Annealed & pickled, bright annealed, mill finish, black, varnished, galvanised or 3LPE / FBE coated (by material)
- Ends
- Plain end (PE), bevelled end (BE, ASME B16.25), threaded (NPT / BSP), grooved
Testing & documents
- Chemical and mechanical (tension, flattening, flare/bend) tests
- Hydrostatic test or non-destructive electric test (UT/ET) on each length
- Dimensional and visual inspection
- Intergranular corrosion (stainless), impact (low-temperature), hardness (sour service) when specified
- PMI and third-party inspection on request
- EN 10204 3.1 certificate; 3.2 with third-party inspection
SS 409 TubesASTM A268 TP409Specification & sizes
How it's madeSeamless tubes are hot-extruded or pierced and then cold-drawn or pilgered to size. Welded tubes are formed from strip, welded (TIG/laser/HF), bead-worked and drawn or sized. Heat-exchanger and boiler tubes are annealed after final forming, and U-tubes are bent and stress-relieved as required.
- Specification
- ASTM A268 TP409
- Size range
- OD 3 mm to about 127 mm (¼" to 5") typical, wall 0.5 mm to 12 mm; BWG or mm; straight lengths up to about 30 m, U-bent to drawing
- Finish
- Annealed & pickled, bright annealed (BA), polished (sanitary), cold-drawn
- Ends
- Plain square-cut, deburred; U-bends with stress-relieved bends on request
Testing & documents
- Eddy-current and/or ultrasonic testing on each tube
- Hydrostatic or pneumatic test
- Flattening, flaring and flange tests
- Grain size (H grades), IGC and hardness when specified
- Surface roughness (Ra) for sanitary and instrumentation tube
- EN 10204 3.1 certificate; 3.2 with third-party inspection
SS 409 PlatesASTM A240 409Specification & sizes
How it's madeSlabs are hot-rolled on a reversing plate mill (or a Steckel/hot-strip mill for thinner plate), then heat treated (annealed, normalised, or quenched and tempered, depending on material), descaled and pickled or shot-blasted. Plates are cut to size by plasma, oxy-fuel, waterjet or shearing.
- Specification
- ASTM A240 / ASME SA240 409
- Size range
- Thickness about 3 – 150 mm (and heavier on request), widths 1,000 – 3,000 mm, lengths 2,000 – 12,000 mm; cut-to-size and profile-cut parts
- Finish
- No.1 (hot-rolled, annealed and pickled) for stainless; shot-blasted, mill scale or primed for carbon steel
- Ends
- Mill edge, sheared, plasma or waterjet cut, profile cut to drawing
Testing & documents
- Chemical analysis and tensile tests (per plate or heat)
- Impact tests for low-temperature and pressure-vessel plates
- Ultrasonic testing (e.g. ASTM A435 / A578) when specified
- IGC, HIC and simulated PWHT tests as required
- Flatness and dimensional inspection
- EN 10204 3.1 certificate; 3.2 with third-party inspection
SS 409 SheetsASTM A240 409Specification & sizes
How it's madeHot-rolled coil is cold-rolled to final thickness, then annealed and pickled (2B/2D) or bright annealed (BA), temper-passed, and polished or textured as needed. Coils are then levelled and cut into sheets.
- Specification
- ASTM A240 / ASME SA240 409
- Size range
- Thickness about 0.3 – 6 mm, standard sizes 1,000 × 2,000, 1,219 × 2,438 (4 × 8 ft), 1,250 × 2,500 and 1,500 × 3,000 mm; custom cut lengths
- Finish
- 2B, 2D, BA, No.4 (brushed), HL (hairline), No.8 (mirror), embossed, PVC or laser-film protected
- Ends
- Sheared or slit edges; laser-cut blanks on request
Testing & documents
- Chemical and mechanical tests
- Surface and finish inspection
- Thickness and flatness checks
- Hardness and bend tests as specified
- EN 10204 3.1 certificate; 3.2 with third-party inspection
SS 409 CoilsASTM A240 409Specification & sizes
How it's madeHot-rolled coil (HRC) comes from the hot-strip mill. Cold-rolled coil (CRC) is further reduced on a cold mill, then annealed and pickled or bright annealed, and skin-passed. Slitting lines cut master coils into narrow strips to the width you order.
- Specification
- ASTM A240 / ASME SA240 409
- Size range
- Thickness about 0.3 – 12 mm; widths from narrow slit strip (about 10 mm) to 1,250 / 1,500 / 2,000 mm; coil ID 508 / 610 mm; coil weights to order
- Finish
- No.1 (hot-rolled, annealed, pickled), 2B, 2D, BA, No.4 for stainless; HR black, pickled & oiled, CR for carbon steel
- Ends
- Mill edge or slit edge
Testing & documents
- Chemical and mechanical tests
- Thickness profile and surface inspection
- Hardness and bend tests
- EN 10204 3.1 certificate; 3.2 with third-party inspection
Where is SS 409 used?
Typical applications
- Automotive exhaust systems and mufflers
- Catalytic converter shells
- Heat-exchanger fins and tubes
- Agricultural equipment
- Transformer and electrical cases
What should you specify when buying SS 409?
- Grade and specification, e.g. ASTM A268 / A554
- Product form, size and tolerance
- Heat treatment / condition and surface finish
- Quantity, delivery location and required date
- Tests: PMI, hydro/NDT, IGC, impact or hardness as required
- Certificate type (EN 10204 3.1 / 3.2) and third-party inspection
See our RFQ checklist guide and what drives metal prices.
Explore more on SS 409
Guides
Comparisons & articles
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Frequently asked questions
Does SS 409 stainless steel rust?
It can develop light surface rust in wet conditions, but it resists perforation and exhaust-gas corrosion much better than carbon steel. It's chosen for function, not appearance.
What is SS 409 used for?
Automotive exhaust systems and mufflers, Catalytic converter shells, Heat-exchanger fins and tubes, Agricultural equipment. It's used across Automotive & Transport, Heavy Engineering, Sugar.
What is the UNS number of SS 409?
SS 409 is designated UNS S40900; the closest EN cross-reference is 1.4512.
Which product forms is SS 409 available in?
Pipes, Tubes, Plates, Sheets, Coils, to ASTM A268 / A554, ASTM A268 TP409, ASTM A240 409 and related specifications.
What is the density of SS 409?
About 7.7 g/cm³ (7700 kg/m³), used for weight calculations.
Is SS 409 magnetic?
Magnetic.
What temperature can SS 409 withstand?
Good oxidation resistance; highly resistant to chloride stress corrosion cracking.