For general-purpose stainless-steel applications where corrosion resistance, formability, and longevity are priorities, 304 (UNS S30400) is the stronger choice; for cost-sensitive, heat-exposed applications—most notably automotive exhaust systems—409 (UNS S40900) provides an economical, weldable ferritic option with adequate oxidation resistance. Choose 304 when corrosion performance and non-magnetic behavior matter; choose 409 when budget, thermal expansion compatibility with carbon steel, and low cost are paramount.
304 vs 409 Stainless Steel comparison table
| Property / Topic | 304 (Austenitic) | 409 (Ferritic, Ti-stabilized) |
|---|---|---|
| UNS / Common names | UNS S30400 / AISI 304 | UNS S40900 / AISI 409 |
| Main alloying elements | Cr ~18–20%, Ni ~8–10% | Cr ~10.5–11.5%, Ni ~0–0.5%, Ti stabilized |
| Microstructure | Austenitic (FCC) — non-magnetic (annealed) | Ferritic (BCC) — magnetic |
| Corrosion resistance | High (general corrosion, pitting) | Moderate — much lower than 304 |
| High-temperature oxidation | Good to ~870–900°C intermittent | Good for exhaust service; oxidation resistant vs carbon steel |
| Weldability | Excellent; no post-weld anneal usually needed | Good for spot/arc welds, beware grain growth and sensitization |
| Typical uses | Food, pharma, chemical, architectural, equipment | Automotive exhaust, mufflers, heat shields, low-cost exterior parts |
| Relative cost | Higher (Ni content) | Lower (low Ni) |
| Formability | Excellent | Good, but less ductile than 304 |
| Magnetic? | Typically non-magnetic | Magnetic |
Chemical composition
304 is a classic 18/8 stainless alloy: roughly 18–20% chromium and 8–10% nickel with low carbon (~0.08% max). 409 typically contains ~10.5–11.5% chromium, very low nickel (often ≤0.5%), and is titanium-stabilized to prevent chromium carbide precipitation during welding and elevated-temperature exposure. The much higher nickel and chromium in 304 explains its superior corrosion resistance and austenitic structure; the lower alloy content of 409 is the reason for its lower cost and ferritic structure.
Microstructure and metallurgical implications
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304 (Austenitic): Face-centered cubic (FCC) crystal structure that remains stable from cryogenic through high service temperatures. This gives high ductility, excellent toughness even at low temperature, and good work-hardening response. Austenitic steels do not become strongly magnetic in the annealed condition.
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409 (Ferritic, Ti-stabilized): Body-centered cubic (BCC) ferritic matrix. Titanium ties up carbon and prevents sensitization during welding by forming stable TiC/TiN, improving intergranular corrosion resistance in welded sections. Ferritic steels have lower thermal expansion than austenitics, improving dimensional compatibility with carbon steels (one reason they’re used in exhaust systems).
Practical effect: 304 is more forgiving for deep drawing and complex forming; 409 provides dimensional stability in thermal cycles and is cheaper for high-temperature service where heavy corrosion resistance is not required.
Complete properties comparison table
| Property category | 304 Stainless Steel (bar / plate / pipe) | 409 Stainless Steel (bar / plate / pipe) |
|---|---|---|
| UNS / common names | UNS S30400; AISI 304; “18-8” austenitic stainless | UNS S40900; AISI 409; titanium-stabilized ferritic stainless |
| Typical chemical composition (wt%) | C ≤0.08; Cr 17.5–19.5; Ni 8.0–10.5; Mn ≤2.0; Si ≤0.75; P ≤0.045; S ≤0.03; N ≤0.10. (per ASTM A240 ranges for 304/304L variants). | C ≤0.03; Cr 10.5–11.7; Ni ≤0.5; Ti ≈ (6×C) up to ~0.75%; Mn ≤1.0; Si ≤1.0; P ≤0.04; S ≤0.02. Titanium added to stabilize carbon and avoid carbide precipitation. |
| Microstructure | Austenitic (FCC) — non-magnetic when annealed; work-hardening possible. | Ferritic (BCC), Ti-stabilized — magnetic, stable up to elevated temperatures without transforming. |
| Density | ~7.9–8.03 g/cm³ (≈0.285 lb/in³) | ~7.65–7.8 g/cm³ (slightly lower due to lower Ni) |
| Elastic modulus (E) | ≈193–200 GPa (28–29 ×10^6 psi) typical for austenitic stainless | ≈200–210 GPa (slightly higher typical for ferritic structures) |
| Thermal expansion (20–300°C) | ≈16–17 ×10^−6 /°C (higher than ferritic). Example: 9.4 ×10^−6 /°F noted in some datasheets — convert as needed. | ≈10–12 ×10^−6 /°C (lower than austenitic; better match with carbon steel) |
| Thermal conductivity (room temp) | ≈16 W/m·K (moderate) | ≈18–24 W/m·K (ferritics usually higher thermal conductivity than austenitics) |
| Electrical resistivity (20°C) | ~0.72–0.74 μΩ·m (≈28.3 ×10^−6 Ω·in at 68°F reported) | Slightly lower resistivity than 304 (ferritic family) — typical values vary by exact chemistry |
| Typical tensile strength — annealed (bars/plates/pipes) | UTS: ≈515–720 MPa (varies by cold work & product form). Yield (0.2%): ≈205–310 MPa. Elongation: ≥40% in many sheet/plate specs. | UTS: ≈350–480 MPa (typical); Yield: ≈170–300 MPa depending on form; Elongation: ≈20–30% (lower ductility vs 304). ASTM/UNS datasheets list minimums (e.g., tensile ~380 MPa, yield ~170 MPa as minimums in some mill specs). |
| Hardness (HB / HRB) | Annealed: Brinell ≤ ~200 BHN (Rockwell B ≤ ~92 typical per plate datasheets). Cold-worked forms higher. | Annealed: BHN typically ≤ ~180; cold forming increases hardness. 409 is not a high-hardness alloy in annealed condition. |
| Corrosion resistance (general) | Excellent general corrosion resistance (atmospheric, many chemicals, food contact). Susceptible to pitting in warm chloride environments; consider 304L/316 for improved resistance. | Moderate corrosion resistance — better than plain carbon steel and protected by Ti stabilization in welded HAZs, but inferior to 304 in wet chloride or marine conditions. Designed for oxidation resistance at elevated temperature (exhaust service). |
| High-temperature behaviour | Good scale resistance and strength to moderate temperatures; risk of carbide precipitation (sensitization) in 425–870°C zone unless low-C (304L) or stabilized. | Good oxidation resistance in cyclic exhaust temperatures; designed for elevated temperature stability. Not suitable for continuous service at extreme high temperatures where specialty alloys are required. |
| Magnetic properties | Non-magnetic when annealed; some magnetism after heavy cold work. | Magnetic (ferritic) |
| Forming & cold work | Excellent formability and deep-drawing for plate and thin sections; bars readily cold-drawn; pipes easily formed in austenitic grades. | Good formability for stamping and bending (commonly used for exhaust parts). Less ductile than 304 for deep drawing operations. Ti stabilisation helps during welding. |
| Weldability & filler | Welds readily with standard stainless fillers (ER308/308L etc.); typically no post-weld anneal required for common fabrications; watch HAZ sensitization for high temp exposures. | Good weldability for automotive fabrication; titanium stabilization reduces risk of intergranular corrosion in HAZ; use appropriate filler metal and control interpass temps in critical applications. |
| Surface finishes (common) | 2B, No.1, No.4 (brushed), BA, mirror — widely available; finish affects corrosion resistance and cleanability. | Typically supplied in No.1, 2B and brushed finishes for exhaust/trim applications; surface coating or aluminized options common for cost/oxidation control. |
| Typical standard specifications (forms) | Plates/Sheets: ASTM A240 / ASME SA240; Bars: ASTM A276; Seamless Pipe/Tubes: ASTM A312 (when appropriate); Welding filler codes: AWS A5.9/5.11 recommendations for filler. | Sheets/Plates: often supplied per ASTM A240 or OEM automotive specs; Pipe: welded exhaust tubing per OEM or API where applicable; UNS S40900 listed in many mill datasheets and ISO/DIN equivalents exist (e.g., ISO 4954 X6CrNb12). |
| Typical commercial sizes / tolerances | Plates: thicknesses from 0.5 mm to 200 mm+; Bars: round up to large diameters and flats/hex; Pipes: welded and seamless OD 1/8" up to large diameters with standard wall thickness schedules. Tolerances per ASTM/EN product standards and mill drawing. | Common in thin gauge coils/sheets for exhaust (0.4–2.0 mm typical for mufflers); plates and bars available but less common in large structural uses compared to 304; pipe commonly used as welded exhaust tube. |
| Typical applications by form | Bar: fasteners, shafts, fittings. Plate: tanks, food equipment, architectural panels. Pipe: process piping, hygienic tubing, structural. | Bar: limited use (non-critical). Plate/sheet: exhaust headers, heat shields. Pipe: automotive exhaust tubing, mufflers, low-cost ducting. |
| Recycling and scrap value | Higher scrap value due to Ni content; recycling stream well established. | Lower scrap value vs 304 because of low Ni content; still recyclable within stainless stream but lower unit value. |
| Typical cost drivers | Nickel and chromium commodity prices; forming/finishing premiums. | Lower alloy content makes 409 significantly less expensive in raw material cost; processing and coatings may add cost. |
Practical notes for engineers & buyers
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Bar form: cold-drawn 304 bar will show higher yield/tensile and reduced elongation vs annealed plate; specify temper (annealed/ cold-drawn) when ordering.
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Plate form: 304 plate is preferred for pressure/vessel and hygienic applications; 409 plate typically used for stamped parts or where oxidation resistance (not aqueous corrosion) is the priority.
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Pipe/tube: for process piping and potable water, specify 304 and the correct piping standard (ASTM A312/A358 or EN equivalents). For automotive exhaust tubing, 409 is the common economy choice; consider aluminized or coated options for improved life in salted roads.
Corrosion resistance: environments, thresholds, and failure modes
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304: Strong general corrosion resistance to atmospheric, potable water, food environments, moderate organic acids, and many chemical process conditions. It is susceptible to chloride-induced pitting and crevice corrosion in warm chloride environments but outperforms ferritic grades dramatically in marine and aggressive chloride conditions.
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409: Engineered for oxidation resistance and cost efficiency rather than outstanding resistance to aqueous corrosion. It resists oxidation at elevated temperatures encountered in exhaust service and performs better than uncoated carbon steel in outdoors use, but it will corrode faster than 304 in wet chloride environments or where sustained moisture and salts occur.
Authoritative manufacturer data and material databases show this relative ranking; treat 409 as “industrial-grade” stainless for combustion/oxidation exposure, and 304 for contact, hygienic, and chloride-bearing environments.
2025 Price Comparison Table — USD / metric ton
| Region | Product form | 304 Stainless (USD / t) | 409 Stainless (USD / t) | Quick notes |
|---|---|---|---|---|
| USA | Plate (hot-rolled / cold-rolled) | 3,200 – 3,800 | 1,500 – 2,200 | 304 plate follows US coil/plate market (higher due to Ni). Tariffs / duties can push import prices higher. |
| USA | Bar (round/flat bar, drawn) | 3,400 – 4,200 | 1,700 – 2,400 | Bar premiums reflect extra processing; 409 bar less common but cheaper. |
| USA | Pipe / Tube (welded & seamless) | 3,000 – 3,800 | 1,300 – 2,000 | Seamless pipe and precision tube are priced at a premium. |
| Europe (North / West) | Plate (delivered EU) | 2,750 – 3,300 (≈€2,350–2,800) | 1,100 – 1,900 (≈€900–1,600) | MEPS / FastMarkets report 304 cold-rolled and plate benchmark levels in this band. |
| Europe | Bar (round/flat) | 2,900 – 3,500 | 1,300 – 2,100 | Bar & specialty sections carry fabrication premiums and alloy surcharges. |
| Europe | Pipe / Tube | 2,700 – 3,200 | 1,000 – 1,800 | Delivery terms, customs, and CE/pressure approvals affect landed price. |
| China (domestic FOB / mill) | Plate (HRC/CRC) | 1,300 – 1,900 | 700 – 1,200 | China domestic coil/sheet prices and supplier listings place 304 significantly lower than EU/US; 409 frequently offered at much lower mill prices. |
| China | Bar (hot-rolled / cold-finished) | 1,500 – 2,200 | 800 – 1,400 | Bar from China mills typically sold FOB with volume discounts; quality grades (tight chemistry / MTR) add premium. |
| China | Pipe / Tube (welded & seamless) | 1,200 – 1,900 | 650 – 1,300 | Welded tube much cheaper than seamless; export price varies with MOQ and coating. |
How these ranges were derived
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Sources used: regional price indexes and market commentary (MEPS / FastMarkets), China supplier listings and market trackers (industry posts and made-in-China supplier pages), and regional news on trade policy that affects landed costs. Representative sources include MEPS/FastMarkets for EU/US plate levels, China market posts for domestic mill and FOB pricing, plus press on tariffs and trade measures that influence US import pricing.
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Units & basis: prices shown are USD per metric ton. Some original market feeds report €/t or USD per lb; values here were converted to USD/t for cross-region comparability.
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Form & spec variation: price depends strongly on: grade variant (304 vs 304L), mill finish (2B, BA, No.1), thickness, tolerance, pipe wall and OD, seamless vs welded, large vs small quantities, certifications (MTR, EN 10204 3.1/3.2), and whether prices are FOB mill, CIF port, or delivered. The table gives typical market ranges — always get an itemized supplier quotation.
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Market drivers & volatility: nickel and chromium raw-material costs, scrap prices, regional demand, and trade policy (tariffs/anti-dumping) drive swings in 2025. For example, higher import tariffs in the US (reported in mid-2025) are a material reason US landed prices can sit above EU/China levels.
Thermal properties and high-temperature performance
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Operating envelope: 409 is optimized for exhaust temperatures and cyclic thermal loads (oxidation resistance to several hundred °C). Its ferritic matrix retains stability during thermal cycling. 304 has good elevated temperature strength and oxidation resistance but can form chromium carbides at temperatures roughly 425–870°C if not low carbon (304L) or stabilized; this may lead to intergranular corrosion in some welded assemblies.
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Thermal expansion: Austenitic 304 expands more with temperature than ferritic 409; designers choose 409 where thermal expansion similar to carbon steel is desirable to avoid differential stresses.
Design note: For continuous high temperature service above ~870–900°C, or when prolonged scaling resistance is needed, consult specialized high-temperature alloys. 409 and 304 differ but neither is a “superalloy.”
Fabrication: forming, welding, and joining
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Forming: 304’s ductility makes it ideal for deep drawing, bending, and spinning. 409 forms well for stamped exhaust components but requires tighter control for complex shapes.
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Welding: 304 welds readily with standard austenitic filler metals (ER308/308L family). 409 is often welded with similar ferritic fillers or with special procedures to avoid grain-growth embrittlement; titanium stabilization helps prevent chromium carbide precipitation during welding in 409, improving intergranular corrosion resistance of weld heat-affected zones. For pressure-bearing applications, follow the manufacturer’s welding procedures.
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Post-weld treatments: 304 usually does not require post-weld anneal for common fabrication. 409 may benefit from controlled post-weld heat treatments in some cases to restore properties, depending on the product form. Always perform stress-relief and inspection that match code/spec requirements.
Typical and specialized applications
304 — typical uses
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Food-processing equipment and kitchenware
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Chemical tanks, piping and fittings where moderate corrosion resistance needed
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Architectural panels, handrails, and interior cladding
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Fasteners where non-magnetic behavior may be required
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Medical devices and pharmaceutical equipment (with proper finishing)
409 — typical uses
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Automotive exhaust systems: manifolds, mufflers, resonators, mid-pipes (primary use historically)
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Low-cost exterior trims and non-critical ducting
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Applications where oxidation resistance at elevated temperature and low cost override the need for long-term aqueous corrosion resistance.
Designers must balance cost, longevity, and environment: 409 is widely used in mass-produced vehicles where replacement intervals and economy dominate; 304 is chosen where long service life, hygiene, and low maintenance are required.
Cost, sourcing, and MWAlloys offering
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Material cost drivers: Nickel and chromium commodity prices are primary cost drivers for stainless steels. 304’s higher nickel content makes it more expensive than 409, which contains minimal nickel.
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Lead times & inventory: If you need quick delivery from a China supplier that stocks both grades, MWAlloys provides 100% factory pricing for direct-from-mill procurement and maintains fast stock dispatch for common sheet, coil, pipe, and tube dimensions. For project buys, MWAlloys can supply certificates (mill test reports), perform cut-to-length services, and arrange expedited shipping where stock exists.
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Quality controls: MWAlloys performs chemical and mechanical testing to customer requirements, supplies MTRs (material test reports) with each batch, and supports pre-shipment inspection on request.
Procurement tip: for long-term projects, lock pricing with a supplier and request sample test certificates to verify composition and tensile data before committing to large orders.
Inspection, testing, and applicable standards
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304 references: Commonly supplied to ASTM A240 / ASME SA240 for plate and sheet; other forms will reference corresponding ASTM/ASME standards for bars, wire, forgings, or pipe.
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409 references: Frequently referenced by material data sheets and standards used by OEMs; 409 often appears with automotive material specs and ISO/DIN/SAE designations (UNS S40900 / ISO 4954 X6CrNb12).
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Recommended tests: Chemical analysis (OES/ICP), tensile, hardness, pitting resistance tests (where applicable), and visual/exfoliation inspection after forming/welding. For exhaust components, oxidation and thermal-cycle testing can be specified.
When specifying material in a purchase order or drawing, reference the exact UNS/AISI number, thickness/temper, surface finish, and acceptance criteria (e.g., MTR level, heat number traceability).
FAQs
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Is 409 stainless steel better than 304 for car exhaust?
For typical OEM mass production, 409 is preferred because it balances oxidation resistance and cost. For high-end or long-life exhaust systems, 304 performs better against corrosion and road salts. -
Will 304 rust if used outdoors near the coast?
304 resists rust better than ferritic grades, but in aggressive marine chloride environments 316 or specially coated 304L/316L are preferable. -
Is 409 magnetic?
Yes. 409 is ferritic and shows magnetic behavior; 304 in annealed condition is usually non-magnetic. Cold working 304 can introduce slight magnetism. -
Can I weld 409 to carbon steel?
Yes, weld practices must control thermal cycles and filler selection. 409’s thermal expansion is closer to carbon steel, which helps when joining thin sections. -
Which grade is more food-safe?
304 is widely used in food processing and is generally considered food-safe with appropriate surface finish and cleaning. -
How do I choose between 304 and 409 for a kitchen hood?
Choose 304 for hygiene and longevity; 409 may darken and corrode faster from cooking condensates and salt. -
Are 409 stainless steel mufflers durable?
They are durable for typical service life and are cost-effective; however, in climates with heavy road salt use, their lifespan will be shorter than 304 mufflers. -
Does 409 need special heat treatment?
409 is normally supplied annealed and ready for forming/welding; special heat treatments are uncommon for standard exhaust use. -
Which is cheaper to buy and recycle?
409 is cheaper to buy due to low Ni content; recycling value may be lower than 304 because nickel adds value. -
Can MWAlloys supply both grades with test certificates?
Yes, MWAlloys supplies both 304 and 409 with mill test reports (MTRs), traceable heat numbers, and can package/custom-cut per order with factory pricing and quick dispatch.
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