Grade dossier
439 Stainless Steel
439 stainless steel is a titanium-stabilized, 17–19% chromium ferritic grade identified as UNS S43035 and historically listed as ASTM XM-8. Its strongest procurement case is welded or formed heat-transfer and automotive-exhaust hardware that needs better oxidation and general corrosion resistance than 409 while retaining ferritic resistance to chloride stress-corrosion cracking.
Identity before substitution
Specify 439 by UNS/EN identity, stabilization and product form
Type 439 is not simply a generic “17% chromium ferritic” grade. ATI identifies it as titanium-stabilized UNS S43035 / ASTM XM-8, while worldstainless maps the common European counterpart to EN 1.4510 / X3CrTi17. The purchase order should state the governing standard, product form, dimensions, annealed condition, stabilization chemistry, finish, fabrication route and service environment.
439 stainless composition
ASTM chemistry limits for UNS S43035 / Type 439
Use the ordered standard, not a generic alloy label
ATI’s technical data sheet lists the following ASTM A240 / A268 / A479 chemistry limits for UNS S43035. ATI 439 HP is a lower-carbon enhanced-formability implementation that still meets the grade requirements. EN 1.4510 is a close cross-reference, but its published chemistry limits are not identical; verify the heat-specific MTC.
| C | 0.07 max |
|---|---|
| Mn | 1.00 max |
| P | 0.040 max |
| S | 0.030 max |
| Si | 1.00 max |
| Cr | 17.00–19.00 |
| Ni | 0.50 max |
| Ti | 0.20 + 4(C+N) min · 1.10 max |
| N | 0.040 max |
439 stainless properties
Separate specification minimums from manufacturer-typical annealed values
ATI 439 HP sheet/strip published minimums
| Tensile strength | 415 MPa min |
|---|---|
| 0.2% yield strength | 205 MPa min |
| Elongation | 22% min |
| Rockwell hardness | 89 HRB max |
ATI 439 HP typical annealed indicators
| Tensile strength | about 455 MPa |
|---|---|
| 0.2% yield strength | about 290 MPa |
| Elongation in 2 in | about 34% |
| Rockwell hardness | about 78 HRB |
The first panel reflects ATI’s currently published sheet/strip minimums for ATI 439 HP; the second is manufacturer-typical annealed data from the technical sheet. Product form, thickness, cold work, annealing route and the governing specification can change the required values. Acceptance should be based on the purchase order and heat-specific MTC.
Selection boundary
Use 439 when stabilization, weldability and ferritic thermal behavior solve the requirement
439 is strongest where a stabilized ferritic structure, good weldability, low thermal expansion and resistance to chloride stress-corrosion cracking matter. It should not be treated as a universal substitute for 304/316, or for higher-molybdenum ferritic grades where localized chloride corrosion is the controlling failure mode.
Good reasons to evaluate 439
Automotive exhaust manifolds, mufflers and other hot exhaust components where 409 oxidation/corrosion margin is insufficient
Heat-exchanger tubing where ferritic thermal expansion and chloride stress-corrosion-cracking resistance are useful
Residential furnace primary heat exchangers and welded hot-water equipment in reviewed oxidizing service
Formed and welded ferritic components that benefit from titanium stabilization and as-welded intergranular-corrosion resistance
Stop and review before release
Severe pitting or crevice-corrosion service where a molybdenum-bearing grade such as 444 may be required
Long dwell exposure around 371–537°C without evaluating 475°C embrittlement and impact-property loss
Heavy or low-temperature sections without checking the ferritic ductile-to-brittle transition for the actual thickness and thermal history
Automatic substitution between S43035, S43036 / 430Ti and EN 1.4510 without reconciling chemistry, standard and certification
Fabrication route
Control tube forming, welding, annealing and thermal exposure together
ATI 439 HP is the enhanced-formability version of 439 and is specifically positioned for severe tube bending such as automotive exhaust manifolds. Confirm bend radius, wall thinning, tooling and surface condition on the actual ordered gauge.
ATI lists spot, TIG, MIG, laser and high-frequency tube welding as applicable processes. When filler is added, consider a stabilized stainless or nickel-base filler to preserve weld-zone corrosion performance.
The stabilized ferritic structure is designed to retain ductility and intergranular-corrosion resistance in the as-welded condition without routine post-weld annealing, but joint qualification and post-fabrication cleaning still control real performance.
For annealing, ATI gives about 790–871°C followed by quick cooling. Long exposure in roughly 371–537°C can cause 475°C embrittlement, so fabrication and service thermal cycles should be reviewed.
439 stainless supplier evidence
Buy the actual sheet, strip, tube route and standard—not just “439”
ATI publishes concrete availability evidence for 439 HP sheet and strip coil and lists the grade under flat-product, pipe/tubing and bar specifications. Use those dimensions and forms as attributable source evidence, not as a claim that every 439 stainless supplier has identical stock. Confirm current mill route, width, thickness, finish and lead time before quotation.
ATI sheet/strip coil thickness: up to 0.125 in · about 3.18 mm
ATI sheet/strip coil width: up to 48 in · about 1219 mm
Tube / pipe: available through tube and pipe manufacturers using 439 feedstock; OD and wall range are supplier-specific
Current Outokumpu 439/4510 product forms: cold rolled coil and hot rolled coil
MTC and purchase-order checkpoint
Match the heat number to UNS S43035 or the explicitly ordered EN 1.4510 chemistry. Verify C, Cr, Ni, N and titanium stabilization, mechanical results required by the ordered form, dimensions, annealed condition, finish, governing standard and edition. Do not accept a generic “439” certificate if the product standard or stabilization route is unclear.
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Interactive selection check
Test 439 against the controlling procurement question
Procurement FAQ
Questions to close before ordering 439 stainless steel
What is 439 stainless steel?
439 is a titanium-stabilized ferritic stainless steel identified as UNS S43035 and historically as ASTM XM-8. ATI describes it as an 18% chromium alloy designed for good weldability, general corrosion resistance, chloride stress-corrosion-cracking resistance and elevated-temperature service in applications such as exhaust and heat exchangers.
What is the EN equivalent of 439 stainless steel?
The common European cross-reference is EN 1.4510 / X3CrTi17. Cross-reference does not remove the need to specify the exact governing standard and verify chemistry and mechanical requirements on the MTC.
Can 439 stainless steel be hardened by heat treatment?
No conventional martensitic quench-hardening route is used. 439 remains ferritic; delivered strength is controlled mainly by annealed condition, thickness and cold work. ATI gives an annealing range of about 790–871°C followed by quick cooling.
What are two important 439 application constraints?
First, strong resistance to chloride stress-corrosion cracking does not make 439 immune to pitting or crevice corrosion in severe chloride service. Second, long exposure around 371–537°C can cause 475°C embrittlement, and heavy or cold sections also require impact-transition review.
What should a 439 RFQ include?
State UNS S43035 or EN 1.4510, product form, governing standard and edition, thickness/width or tube dimensions, annealed condition, finish, forming and welding route, service temperature and chemistry, MTC requirements and any supplementary inspection.
Sources, scope and RFQ
Trace the 439 chemistry, mechanical basis and actual supply route before release
UNS S43035 identity, ASTM A240/A268/A479 chemistry, typical annealed properties, weldability, annealing guidance, corrosion/oxidation behavior, 475°C embrittlement warning, and published sheet/strip availability to 48 in width and 0.125 in thickness.
Current manufacturer listing for UNS S43035 sheet and strip, ASTM A240 / ASME SA240 basis, published minimum mechanical properties and current composition limits for the enhanced-formability 439 HP implementation.
Current mill-source evidence identifying Type 439 / UNS S43035 as EN 1.4510 ferritic stainless steel, with cold rolled coil and hot rolled coil product forms and automotive-exhaust, sugar-industry and appliance applications.
Maps AISI 439 / UNS S43035 to EN 1.4510 / X3CrTi17. Final release should still use the ordered product standard and heat-specific MTC rather than treating cross-reference tables as an automatic substitution approval.