Grade dossier
409 Stainless Steel
409 stainless steel is an economical, titanium-stabilized ferritic stainless family built around roughly 11% chromium. Its strongest procurement case is automotive and industrial exhaust fabrication where carbon steel needs better oxidation and corrosion resistance, but a higher-alloy stainless grade would add cost or performance that the service does not require.
Identity before substitution
Specify 409 by stabilized UNS variant, product form and service
The label “409” is not enough for a controlled purchase. ATI notes that ASTM A240 orders for UNS S40900 may be supplied as one of the stabilized 409 variants unless the purchaser states additional requirements. State the required UNS or accepted stabilization route, product form, standard edition, dimensions, finish, service temperature, welding route, certification and any surface-appearance requirement.
409 stainless composition
ASTM A240 stabilized 409 chemistry — producer example UNS S40920
Do not order “409” without checking the stabilization route
ATI explains that an ASTM A240 order written only as S40900 may be fulfilled with one of the stabilized 409 variants unless additional requirements are stated. The limits below follow Cleveland-Cliffs’ Type 409 / UNS S40920 product data. If another UNS variant is required, put it on the purchase order.
| C | 0.03 max |
|---|---|
| Mn | 1.00 max |
| P | 0.040 max |
| S | 0.020 max |
| Si | 1.00 max |
| Cr | 10.50–11.70 |
| Ni | 0.50 max |
| N | 0.030 max |
| Ti | 8(C+N) min · 0.15–0.50 |
409 stainless properties
Separate ASTM A240 minimums from Type 409 mill typical values
ASTM A240 / UNS S40920 minimums
| Tensile strength | 379 MPa min |
|---|---|
| 0.2% yield strength | 172 MPa min |
| Elongation | 20% min |
| Hardness | 88 HRB max |
Published Type 409 annealed typical values
| Typical UTS | 414 MPa |
|---|---|
| Typical 0.2% YS | 234 MPa |
| Typical elongation | 32% |
| Typical hardness | 66 HRB |
Cleveland-Cliffs also publishes 409 ULTRA FORM typical values of about 427 MPa UTS, 241 MPa yield strength, 35% elongation and 67 HRB. These are manufacturer examples, not acceptance values. Cold work can raise strength sharply while reducing elongation, so the delivered condition belongs on the RFQ and MTC review.
Selection boundary
Where 409 belongs—and where the service should escalate
409 is selected for economical ferritic exhaust service, good formability and better oxidation/corrosion resistance than carbon steel. It is not a decorative stainless grade and it is not the default for severe chlorides, aggressive acids or the hottest exhaust positions.
Good reasons to evaluate 409
Automotive and truck exhaust systems, mufflers, tailpipes, catalytic-converter shells and tubular manifolds.
Industrial exhaust equipment, gas-turbine exhaust silencers and other hot-gas sheet or tube components after temperature review.
Heat exchangers, fuel filters, agricultural equipment and formed parts where Type 409 corrosion resistance is sufficient.
Complex sheet or tube forming where stabilized ferritic behavior and economical alloy content are valuable.
Stop and review these constraints
Appearance-critical service: titanium-stabilized 409 can show cosmetic streaking or localized red rust around surface inclusions.
Aggressive chloride, acid or crevice service: higher-chromium or molybdenum-bearing stainless grades can provide substantially better pitting and general corrosion resistance.
Continuous oxidation service near or above about 789°C in air: atmosphere, load and duty cycle can make a higher-temperature ferritic grade more appropriate.
Heavy welded sections: Cleveland-Cliffs specifically recommends reviewing 409 Ni for welded applications over about 3.05 mm where improved toughness and weldability are needed.
Fabrication route
Form and weld 409 around stabilized ferritic behavior
Type 409 can be cut, blanked and formed without unusual difficulty; Cleveland-Cliffs notes that brake presses normally used on carbon steel can also be used.
409 is readily welded by arc, resistance spot and seam processes. Filler selection depends on temperature and joint service; published examples include ER309/ER308L for many non-high-temperature joints.
409 tubing is commonly produced by high-frequency or GTAW processes. A short post-weld anneal around 871–899°C can improve tube formability when the manufacturing route requires it.
For thicker welded applications, low-temperature toughness and joint geometry deserve special review. Do not assume a thin-gauge exhaust welding practice transfers directly to heavy section.
409 stainless supplier checklist
Use attributable mill ranges, then verify the exact 409 variant on the MTC
A 409 stainless supplier should identify the exact stabilized UNS variant, product form, thickness, width, finish, condition and governing standard. Cleveland-Cliffs publishes Type 409 coils and cut lengths from 0.015–0.250 in. (0.381–6.350 mm) thick and widths up to 48 in. (1219 mm). Outokumpu lists 409/4512 in hot- and cold-rolled coil. Treat these as attributable mill references, not a claim of this website’s live stock.
Cleveland-Cliffs: coils and cut lengths · 0.381–6.350 mm thick
Cleveland-Cliffs: widths up to 1219 mm
Outokumpu Moda 409/4512: hot-rolled and cold-rolled coil
Common flat-product basis: ASTM A240 · EN cross-reference 1.4512
MTC / test-report checkpoint
Verify heat number and traceability, the actual UNS designation supplied, governing specification and edition, chemical analysis including stabilization elements, mechanical results, ordered thickness/width/length, finish, annealed condition, weld or tube-processing requirements and any supplementary inspection. If S40910, S40920 or S40930 is specifically required, state it rather than relying on a generic 409 description.
Interactive procurement check
Test 409 against the controlling design question
Procurement FAQ
Questions to close before ordering 409 stainless steel
What is 409 stainless steel?
409 is a stabilized ferritic stainless family with nominally about 11% chromium. It is widely used in automotive and industrial exhaust systems because it combines economical alloy content, useful oxidation/corrosion resistance and good formability.
Which UNS number should be specified for 409?
Do not assume that every 409 order is chemically identical. ATI notes that ASTM A240 orders written as S40900 may be fulfilled by stabilized 409 variants such as S40910, S40920 or S40930 unless the purchaser states additional requirements. Put the required UNS or accepted stabilization route on the purchase order.
What ASTM A240 mechanical values should be checked?
Cleveland-Cliffs lists ASTM A240 / UNS S40920 minimums of 379 MPa tensile strength, 172 MPa 0.2% yield strength, 20% elongation and 88 HRB maximum hardness. The applicable product specification and heat-specific MTC control acceptance.
Can 409 stainless steel be used at high temperature?
Yes, especially in exhaust service, but the limit depends on atmosphere, load and thermal cycling. Cleveland-Cliffs gives about 789°C as a practical upper continuous oxidation-service reference in air and notes that more demanding hot-end service can require higher-chromium ferritic grades.
What should a 409 RFQ include?
State the exact 409 UNS variant or accepted equivalent, ASTM or EN standard and edition, product form, thickness/width/length, finish, quantity, operating temperature and atmosphere, corrosion environment, forming and welding route, MTC requirement and supplementary inspection.
Sources, scope and RFQ
Trace the 409 data, then certify the actual stabilized heat
Ferritic classification, S40900 family identity, ASTM A240 stabilized-variant procurement note, composition ranges, typical room-temperature properties, corrosion limits and automotive exhaust applications.
UNS S40920 chemistry and ASTM A240 minimums, typical annealed properties, coil and cut-length size range, oxidation-service guidance, forming, weldability and heavy-gauge welding note.
Ferritic classification, EN 1.4512 / X2CrTi12 cross-reference, S40910 reference, hot- and cold-rolled coil forms and exhaust-system application guidance.
Use the current ASTM A240 or applicable EN product standard plus the heat-specific MTC/test report for acceptance. State the exact stabilized variant whenever the application or customer specification requires one.