Grade dossier
444 Stainless Steel
444 stainless steel is a low-carbon, molybdenum-alloyed ferritic grade, UNS S44400, stabilized with titanium and niobium/columbium. Its strongest procurement case is welded equipment exposed to chlorides or hot water—such as heat-exchanger tubing, hot-water tanks and drinking-water systems—where better localized-corrosion resistance than basic ferritic grades and high resistance to chloride stress-corrosion cracking are required.
Identity before substitution
Specify 444 by UNS identity, product form and stabilization chemistry
Type 444 should be ordered as UNS S44400 to the product-specific standard and edition, not as a generic “18Cr-2Mo ferritic” description. ATI lists S44400 in ASTM A240, A268 and A276, while Outokumpu and Aperam use EN 1.4521 as the common European cross-reference. Product form matters: ATI notes that plate may use modified nitrogen chemistry to achieve ASTM A240 mechanical requirements. Put the exact form, dimensions, finish, stabilization requirement, certification and service environment on the purchase order.
444 stainless composition
ASTM A240 sheet/strip chemistry limits for UNS S44400
Product form changes the nitrogen requirement
ATI’s current sheet and strip listing uses N 0.035% max, while its plate listing uses 0.040–0.070% N because commercial 444 chemistry may not meet ASTM A240 plate mechanical requirements. Use the ordered product form and certificate chemistry for acceptance.
| C | 0.025 max |
|---|---|
| Mn | 1.00 max |
| P | 0.040 max |
| S | 0.030 max |
| Si | 1.00 max |
| Cr | 17.5–19.5 |
| Mo | 1.75–2.50 |
| Ni | 1.00 max |
| N | 0.035 max · sheet/strip |
| Ti + Nb/Cb | 0.20 + 4(C+N) min · 0.80 max |
444 stainless properties
Separate current ASTM flat-product minimums from manufacturer-typical indicators
ATI current A240 sheet/strip minimums
| Tensile strength | 415 MPa min |
|---|---|
| 0.2% yield strength | 275 MPa min |
| Elongation | 20% min |
| Rockwell hardness | 96 HRB max |
ATI technical-sheet typical indicators
| Tensile strength | about 517 MPa |
|---|---|
| 0.2% yield strength | about 345 MPa |
| Elongation | about 30% |
| Rockwell hardness | about 80 HRB |
The first panel reflects ATI’s current published ASTM A240 sheet/strip minimums. The second panel is manufacturer-typical data from ATI’s technical sheet and is not an acceptance limit. 444 is ferritic and cannot be hardened by heat treatment; delivered properties depend on product form, thickness, cold work and annealing condition.
Selection boundary
Use 444 when chloride SCC resistance and 2% molybdenum solve the requirement
444 combines ferritic chloride stress-corrosion-cracking resistance with molybdenum-enhanced pitting and crevice-corrosion resistance. That makes it a strong candidate for hot-water and heat-transfer equipment, but it is not a universal replacement for 316 or higher-alloy grades in every chemical environment.
Good reasons to evaluate 444
Hot-water tanks and drinking-water systems where chloride SCC resistance is a controlling concern
Heat-exchanger tubing and welded heat-transfer equipment requiring stabilized ferritic corrosion performance
Food-processing equipment after cleaning chemistry, temperature and crevice geometry are reviewed
Automotive exhaust or hot-corrosion components where ferritic thermal behavior and creep resistance are useful
Stop and review before release
Strong reducing-acid service without corrosion data; ATI boiling-test data show severe attack in 10% sulfuric and sulfamic acid
Treating practical chloride-SCC immunity as immunity to pitting or crevice corrosion in every chloride concentration and temperature
Using the ASME Section VIII listing temperature as a universal service-temperature guarantee for every product and atmosphere
Ordering plate with sheet/strip chemistry assumptions; ATI specifically notes a modified nitrogen route for ASTM A240 plate mechanical compliance
Fabrication route
Protect stabilization and corrosion performance through forming and welding
444 has good cold formability, but ferritic forming behavior differs from austenitic grades. Confirm bend radius, draw severity, grain direction, gauge and surface finish on the actual product.
ATI reports satisfactory TIG and MIG welding. Use procedures that minimize oxygen, carbon and nitrogen pickup; gas-shielded processes are preferred and argon shielding is recommended.
The Ti + Nb/Cb stabilization is designed to maintain resistance to intergranular corrosion in the as-welded condition, so post-weld heat treatment is not required simply to restore that corrosion resistance.
For dissimilar joints or demanding service, qualify filler metal, heat input, restraint, purge/shielding practice and post-weld cleaning against the real environment and code requirements.
444 stainless supplier evidence
Buy the actual 444 sheet, strip, plate or tube route—not just the grade name
ATI currently lists 444 in plate, sheet and strip and identifies ASTM A240, A268 and A276 coverage in its technical data. Outokumpu lists Supra 444/4521 in hot-rolled coil, cold-rolled coil and precision strip, while Aperam publishes source-specific coil, sheet, precision-strip and tube dimensions. Treat these as attributable producer evidence, not as a claim that every 444 stainless supplier stocks the same range.
Aperam K44M coil evidence: 0.40–3.0 mm thick · up to 1524 mm wide
Aperam K44M sheet/blanks evidence: 0.50–5.0 mm thick · up to 1250 mm wide
Aperam K44X tube evidence: 0.80–2.0 mm wall · 8–168 mm diameter
ATI form evidence: plate, sheet and strip · ASTM A240; technical sheet also cites A268 and A276
MTC and purchase-order checkpoint
Match the heat number to the ordered form and standard. Verify Cr, Mo, C, N and Ti + Nb/Cb stabilization, then check tensile/yield/elongation/hardness requirements, dimensions, finish and inspection. Example MTC acceptance fields should show heat identity, actual chemistry, mechanical results and the exact ASTM/ASME/EN designation used for the shipment.
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Interactive selection check
Test 444 against the controlling procurement question
Procurement FAQ
Questions to close before ordering 444 stainless steel
What is 444 stainless steel?
444 is a low-carbon, molybdenum-alloyed ferritic stainless steel, UNS S44400. ATI describes it as roughly 18% chromium and 2% molybdenum with titanium plus niobium/columbium stabilization for intergranular-corrosion resistance.
What is the EN equivalent of 444 stainless steel?
EN 1.4521 / X2CrMoTi18-2 is the common European cross-reference used by Outokumpu and Aperam for Type 444 / UNS S44400. Final substitution still requires the ordered standard, chemistry and MTC to match.
Can 444 stainless steel be hardened by heat treatment?
No. ATI states that 444 remains single-phase ferritic up to its melting range and cannot be hardened by heat treatment. Strength is instead influenced by product form, thickness, cold work and annealing condition.
What are two important 444 application constraints?
First, excellent resistance to chloride stress-corrosion cracking does not mean immunity to all pitting, crevice or chemical attack. Second, ATI uses different nitrogen control for plate than for sheet/strip, so the product form and standard must be locked down before chemistry is approved.
What should a 444 RFQ include?
State UNS S44400 or EN 1.4521, product standard and edition, sheet/strip/plate/tube form, dimensions and tolerances, finish, welding/forming route, chloride or process chemistry, temperature, pressure/code requirements, MTC fields and any supplementary testing.
Sources, scope and RFQ
Trace the 444 chemistry, product form and actual supply evidence before release
UNS S44400 identity, current ASTM A240 plate/sheet/strip chemistry, density and minimum mechanical requirements. It also documents the higher-nitrogen chemistry used for plate to meet ASTM A240 mechanical properties.
Ferritic structure, ASTM A240/A268/A276 and ASME SA-240/SA-268 references, corrosion and SCC test data, as-welded intergranular-corrosion guidance, typical mechanical data, welding practice and ATI product forms.
Current producer evidence for EN 1.4521 / UNS S44400 as a 2% Mo ferritic grade for hot-water tanks and drinking-water pipes, with hot-rolled coil, cold-rolled coil and precision-strip supply routes.
Current mill-source dimensional evidence for 1.4521 / ASTM 444, including K44M coil and sheet ranges and K44X tube, precision strip and precision sheet ranges.