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Compare 304 and 409 stainless steel by alloy chemistry, microstructure, corrosion resistance, mechanical properties, magnetism, thermal behavior, fabrication, product form, application and procurement cost drivers.
The structural difference behind the selection decision
Typical chemistry and physical-property comparison: Outokumpu Core 304/4301 and Moda 409/4512 datasheets. *Annealed 304 is normally regarded as non-magnetizable in the datasheet; cold work or welding can create measurable magnetic response.
304 and 409 solve different engineering problems. 304 is a general-purpose austenitic grade designed around corrosion resistance and fabrication versatility. 409 is a lower-alloy ferritic grade commonly selected when exhaust-temperature behavior, low thermal expansion and material economy are more important than cosmetic corrosion resistance.
| Decision factor | 304 stainless steel | 409 stainless steel |
|---|---|---|
| General corrosion resistance |
Better general-purpose corrosion resistance for indoor,
mild outdoor, food and process applications.
Preferred |
Designed for mildly corrosive service. Surface discoloration or rust staining can occur where appearance is important. |
| Automotive exhaust | Can tolerate elevated temperature, but usually carries unnecessary nickel cost for many exhaust components. |
Commonly selected for automotive and industrial exhaust systems.
Preferred |
| Magnetism | Austenitic and normally non-magnetizable in annealed condition, although cold work can produce magnetic response. | Ferritic and magnetizable. |
| Thermal expansion | Higher thermal expansion: approximately 16.0 ×10⁻⁶/K from 20–100°C. |
Lower thermal expansion: approximately 10.5 ×10⁻⁶/K
from 20–100°C.
Lower expansion |
| Thermal conductivity | Approximately 15 W/m·K at 20°C. |
Approximately 25 W/m·K at 20°C.
Higher conductivity |
| Machining | Work-hardens and generally requires stainless-specific cutting practice. |
Relatively easy to machine, with behavior closer to
low-alloyed carbon steel.
Easier machining |
| Material cost | Higher alloy cost because of its substantial nickel content. |
Lower-nickel ferritic chemistry generally supports a lower
alloy-cost position.
Cost advantage |
Selection rule: 409 should not be treated as a lower-cost direct substitute for 304. Use it only when the environment and design allow the lower corrosion resistance of a low-chromium ferritic grade.
304 and 409 belong to different stainless steel families, so comparisons should always state the source, product condition and standard. The values below separate manufacturer typical chemistry from standardized mechanical-property data.
Typical manufacturer chemistry from Outokumpu Core 304/4301 and Moda 409/4512 datasheets. These are typical values rather than purchase-order chemistry limits.
| Element / structure | 304 / 1.4301 | 409 / 1.4512 | Selection significance | Source / condition |
|---|---|---|---|---|
| Carbon, C | 0.04% | 0.02% | Low interstitial content supports fabrication and weld behavior; exact limits depend on grade standard. | Outokumpu typical composition |
| Chromium, Cr | 18.1% | 11.5% | The substantially higher chromium level is a major reason 304 offers stronger general corrosion resistance. | Outokumpu typical composition |
| Nickel, Ni | 8.1% | 0.2% | Nickel stabilizes the austenitic structure of 304. 409's low nickel content helps reduce alloy cost. | Outokumpu typical composition |
| Titanium, Ti | Not a normal alloy addition | Approx. 0.30% | Titanium stabilization improves resistance to sensitization and supports weldability in 409. | Outokumpu typical composition |
| Microstructure | Austenitic | Ferritic | Explains major differences in magnetism, thermal expansion, toughness and stress-corrosion behavior. | Outokumpu grade-family classification |
Values below use EN 10088-2 cold-rolled coil and sheet data so the two grades are compared under the same product-form basis.
| Property | 304 / 1.4301 | 409 / 1.4512 | Procurement interpretation | Source / condition |
|---|---|---|---|---|
| 0.2% proof strength | 230 MPa | 220 MPa | Yield values are relatively close in this condition; strength alone does not define the grade choice. | EN 10088-2, cold-rolled coil/sheet |
| Tensile strength | 540–750 MPa | 380–560 MPa | 304 has the higher specified tensile range in the compared cold-rolled condition. | EN 10088-2, cold-rolled coil/sheet |
| Elongation | 45% | 25% | 304 provides substantially greater tensile ductility, while 409 remains suitable for many forming operations. | EN 10088-2, cold-rolled coil/sheet |
Metric values from Outokumpu technical datasheets.
| Property | 304 | 409 | Why it matters | Condition / source |
|---|---|---|---|---|
| Density | 7.9 kg/dm³ | 7.7 kg/dm³ | 409 is slightly less dense. | Typical physical property |
| Elastic modulus | 200 GPa | 220 GPa | 409 has a somewhat higher elastic modulus. | 20°C |
| Thermal expansion | 16.0 ×10⁻⁶/K | 10.5 ×10⁻⁶/K | Lower expansion can reduce thermal movement and welding distortion in 409 components. | 20–100°C |
| Thermal conductivity | 15 W/m·K | 25 W/m·K | 409 conducts heat more readily than 304. | 20°C |
| Specific heat | 500 J/kg·K | 460 J/kg·K | Relevant to thermal-cycle and heating calculations. | 20°C |
| Electrical resistivity | 0.73 Ω·mm²/m | 0.60 Ω·mm²/m | 409 has lower electrical resistivity. | 20°C |
| Magnetizable | No | Yes | Magnetic response can be a decisive functional requirement. | Outokumpu physical-property classification |
304 has a much broader general-purpose product range. 409 is most commonly procured as sheet and coil for formed and welded exhaust or industrial components.
| Product form / finish | 304 | 409 | Procurement note |
|---|---|---|---|
| Cold-rolled coil & sheet | Common | Common | A primary commercial form for both grades. |
| Hot-rolled coil & sheet | Common | Common | Common for fabricated and industrial components. |
| Quarto plate | Common | Verify source | 304 has broader plate availability; verify 409 supply before designing around heavy plate. |
| Precision strip | Available | Verify source | Mill program and dimensional range vary. |
| Pipe & tube | Widely available | Application-specific | 409 tube is strongly associated with exhaust applications; confirm applicable tube specification. |
| 2B / 2D | Common | Available | Specify required visual appearance and surface condition. |
| BA / 2R | Available | Available | Availability depends on mill and dimensional range. |
| Polished decorative finish | Common | Less typical | 304 is normally favored where decorative appearance and corrosion resistance are key design requirements. |
Check the conditions that matter for your component. The result provides a preliminary material direction before the product form, dimensions, process and exact service environment are reviewed.
Preliminary result
For general stainless service where appearance and corrosion resistance matter, 304 is normally the safer starting point. It provides a wider application envelope than low-chromium 409.
Send Conditions to an EngineerWater, salts, cleaning chemistry, atmospheric exposure and appearance.
Exhaust gas, thermal cycling, expansion and dry oxidation requirements.
Stamping, deep drawing, welding, machining and surface-finish needs.
Grade, product form, thickness, finish, test certificate and inspection.
The two grades should not be ranked simply as “better” and “worse.” 304 is the broader corrosion-resistant grade, while 409 is an application-specific ferritic material with strong value in exhaust and thermally cycled components.
The microstructure difference can be as important as the corrosion difference.
| Requirement | 304 | 409 | Selection effect |
|---|---|---|---|
| Deep drawing | Excellent general formability and high ductility. | Stabilized 409 is particularly suitable for deep drawing. | Both can be formed, but tooling and springback behavior differ. |
| Machining | More difficult because of toughness and work hardening. | Relatively easy; behavior is closer to low-alloy carbon steel. | 409 can reduce machining difficulty where its corrosion level is adequate. |
| Welding distortion | Higher thermal expansion and lower conductivity can increase distortion and shrinkage stress. | Lower thermal expansion and higher conductivity generally reduce distortion. | Joint design and welding procedure remain important. |
| Chloride SCC | Austenitic stainless steels can be susceptible under the required combination of chloride, tensile stress and temperature. | Ferritic structure provides very high resistance to chloride-induced stress corrosion cracking. | SCC resistance does not mean 409 has better overall chloride corrosion resistance. |
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409-family naming varies more between standards and producers than the familiar 304 designation. The purchase order should therefore define the exact UNS or EN grade together with the applicable product standard.
| System | 304 | 409 family | Procurement note |
|---|---|---|---|
| Common grade name | 304 | 409 | Common commercial shorthand should not replace the exact standard designation. |
| UNS / ASTM identity | S30400 | 409-family designation varies by product; Moda 409/4512 is associated with S40910 | State the exact UNS requested instead of writing only “409”. |
| EN material number | 1.4301 | 1.4512 | Common Outokumpu comparison grades used on this page. |
| EN designation | X5CrNi18-10 | X2CrTi12 | 409-family EN grade is a low-carbon titanium-stabilized ferritic stainless. |
| Microstructure | Austenitic | Ferritic | Not interchangeable based only on nominal strength. |
| Related low-carbon option | 304L / 1.4307 | 409L variants are available | Confirm the actual grade and chemistry required by the fabrication standard. |
“Equivalent” grades are not automatically interchangeable. Chemistry, stabilization, mechanical requirements, thickness range, testing, heat treatment and product form must all be checked before substitution.
Direct answers to the material-selection questions that most often determine whether 304 or 409 is the better fit.
304 is an austenitic chromium-nickel stainless steel with significantly greater general corrosion resistance. 409 is a lower-chromium, low-nickel, titanium-stabilized ferritic stainless steel commonly used for exhaust applications.
409 generally has a lower alloy-cost position because it contains far less nickel than 304. Actual purchase price still depends on product form, thickness, quantity, processing, mill source and current alloy surcharges.
409 is stainless steel, but its corrosion resistance is intentionally lower than 304. In wet, salty or more aggressive atmospheric service, surface discoloration or rust staining can occur even while the component remains structurally serviceable.
409 combines useful dry oxidation resistance, low thermal expansion, high thermal conductivity, good formability, weldability and a lower-alloy cost structure. This combination is well suited to many automotive and industrial exhaust components.
Yes. 409 has a ferritic microstructure and is magnetizable. Annealed 304 is generally regarded as non-magnetizable, although cold forming and welding can create some magnetic response.
304 has substantially better general corrosion resistance because of its higher chromium content and austenitic Cr-Ni chemistry. 409 is intended mainly for mildly corrosive environments where its application-specific thermal and cost advantages are useful.
409 is generally easier to machine. Ferritic 409 machining behavior is closer to low-alloy carbon steel, while 304 is tougher, work-hardens readily and normally requires more controlled stainless-steel machining practice.
Yes. 304 has excellent weldability using conventional methods. Stabilized 409 is also weldable, but ferritic stainless welding practice should control heat input and filler-metal selection. 409's lower thermal expansion and higher thermal conductivity can reduce welding distortion compared with 304.
Only when the environment, appearance requirement, magnetic behavior, product form and fabrication process permit it. 409 should not be treated as a universal low-cost substitute for 304 because its corrosion resistance and application envelope are different.
Numeric values are identified by source and condition so that typical manufacturer data is not presented as a universal procurement requirement. Final orders should reference the governing standard and material certificate.
Comparison structured around procurement decisions, grade standards and current manufacturer technical data.
Review scope includes chemistry, structure, mechanical data, corrosion logic, physical properties, fabrication and product-form differences.
Current technical comparison prepared using published manufacturer and standard-reference data.
2026-09-23 — Initial T09 page created with grade selector, source-conditioned tables, application matrix, FAQ and procurement CTA routing.
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