Grade dossier
440C Stainless Steel
440C stainless steel is a high-carbon, high-chromium martensitic grade identified as UNS S44004 and commonly cross-referenced to EN 1.4125 / X105CrMo17. Its strongest procurement case is a hardened wear component—such as bearing balls and races, valve parts, cutting components or precision mechanical parts—where very high hardness and abrasion resistance are required together with moderate stainless corrosion resistance.
Identity before substitution
Specify 440C with the required condition and hardness
The grade name alone is not a complete purchase specification. 440C is normally selected for its response to hardening and tempering; in the annealed condition it is easier to machine, while the final hardened condition provides the high hardness and wear resistance that distinguish the grade. Product form, governing standard, dimensions, annealed or hardened condition, heat-treatment responsibility, final hardness target and certification should therefore be stated together.
440C stainless composition
Producer chemistry reference for UNS S44004
High carbon is the defining difference
Carpenter Technology and ATI publish 0.95–1.20% carbon and 16.0–18.0% chromium for 440C. The high carbon level enables very high hardness after heat treatment but also reduces toughness, formability and weldability compared with lower-carbon martensitic grades. Use the ordered product specification and MTC for acceptance.
| C | 0.95–1.20% |
|---|---|
| Cr | 16.00–18.00% |
| Mo | 0.75% max |
| Mn | 1.00% max |
| Si | 1.00% max |
| P | 0.040% max |
| S | 0.030% max |
| Fe | Balance |
440C stainless properties
Mechanical properties depend on the heat-treatment route
Carpenter typical hardened + tempered example
| Heat treatment | 1038°C harden, oil quench, 316°C temper |
|---|---|
| 0.2% yield strength | 1896 MPa |
| Ultimate tensile strength | 1965 MPa |
| Elongation in 50.8 mm | 2% |
| Reduction of area | 10% |
| Brinell hardness | 580 HB |
Selection indicators
| Maximum hardness capability | about 60 HRC |
|---|---|
| Annealed hardness reference | about 223 HB |
| Density | about 7.6–7.7 g/cm³ |
| Magnetic response | Magnetic in all normal conditions |
| Primary strength | Wear resistance after hardening |
The hardened values above are producer-published typical data, not universal minimums. Section size, austenitizing temperature, quench severity, retained austenite, sub-zero treatment and tempering temperature can materially change hardness, strength and dimensional response. Release the order against the specified condition and actual test/MTC results.
Selection boundary
Use 440C for hardness and wear—not as a universal corrosion grade
440C is strongest when the design genuinely needs a hard, wear-resistant stainless component. The high carbon content that delivers hardness also narrows the fabrication and toughness window, so corrosion environment, impact loading, section size and heat-treatment route should be reviewed before substitution.
Good reasons to evaluate it
Bearing balls, races and rolling-contact parts requiring very high hardness
Valve, pump and precision mechanical wear components
Cutting, cutlery or instrument components where approved material and heat treatment are defined
Parts that need high abrasion resistance plus moderate stainless corrosion resistance
Reasons to stop and review
Seawater, aggressive chloride or highly corrosive service without dedicated corrosion data
Impact-critical or toughness-dominated parts where a very hard high-carbon martensitic grade may be too brittle
Extensive welding, cold forming or heading without a qualified fabrication route
Orders that state only “440C” but omit final hardness, condition and heat-treatment responsibility
Fabrication and heat treatment
Machine soft, harden under control and treat welding as an exception
Carpenter recommends most machining in the dead-soft annealed condition; the high carbon content makes machining behavior more tool-steel-like than low-carbon stainless grades.
A published hardening route is about 1010–1066°C followed by warm-oil quenching or air cooling. Avoid overheating because excessive temperature can reduce the attainable final hardness.
For maximum hardness, Carpenter gives a low-temperature temper reference of about 149–177°C for at least one hour. The specified process should control retained austenite, distortion and final hardness.
440C is seldom welded. If welding is unavoidable, Carpenter recommends about 260°C preheat and an immediate 732–760°C anneal with slow furnace cooling; use a qualified WPS for the actual joint.
440C stainless supplier checklist
Buy by form, specification, size and delivered condition
A 440C stainless supplier should identify the exact mill form, governing standard, dimensions, annealed or heat-treated condition, surface condition, heat-treatment responsibility, final hardness requirement and inspection package. Producer pages confirm multiple product forms, but exact live-stock sizes should be quoted rather than assumed from a generic web range.
Carpenter: bar, rounds, billet, wire, fine wire and rod
Applicable examples: ASTM A276, A314, A473, A493, A580 and A756
AMS examples: 5618, 5630 and 5880
EN cross-reference: 1.4125 · X105CrMo17
MTC / test-report checkpoint
Verify heat number and traceability, 440C / UNS S44004 identity, governing specification and edition, chemistry, ordered form and dimensions, annealed or hardened-and-tempered condition, heat-treatment route where supplier-controlled, final hardness or mechanical-test results, surface/straightness requirements and any supplementary inspection. Do not treat a catalog grade name as proof of the delivered condition.
Interactive selection check
Test 440C against the controlling design question
Procurement FAQ
Questions to close before ordering 440C stainless steel
What is 440C stainless steel?
440C is a high-carbon, high-chromium martensitic stainless steel, UNS S44004, commonly cross-referenced to EN 1.4125 / X105CrMo17. It is primarily selected for very high hardness and wear resistance after hardening and tempering.
Can 440C stainless steel reach 60 HRC?
Yes. Carpenter publishes an approximate maximum hardness of about Rockwell C 60 after suitable heat treatment. Actual hardness depends on austenitizing temperature, quench, section size, retained austenite and tempering, so the target condition should be specified and tested.
Is 440C stainless steel highly corrosion resistant?
It has moderate stainless corrosion resistance, but it should not be treated like a 316-type corrosion grade. Swiss Steel comparison data specifically shows 1.4125 / 440C as unsuitable for seawater in the referenced comparison. Review the actual chloride, temperature, deposits and cleaning conditions before selection.
Is 440C easy to machine or weld?
It is best machined in the dead-soft annealed condition. Welding is uncommon because of the grade's high-hardness capability; if unavoidable, preheat and immediate post-weld heat treatment are required by published Carpenter guidance.
What should a 440C RFQ include?
State product form, ASTM/AMS/EN requirement, UNS S44004 or EN 1.4125 designation, dimensions and tolerances, delivered condition, required final hardness, heat-treatment responsibility, surface finish, quantity, service environment, MTC and supplementary inspection requirements.
Sources, scope and RFQ
Trace the 440C data, then certify the actual heat and condition
UNS S44004 identity, chemistry, approximately 60 HRC hardness capability, typical hardened mechanical properties, annealing/hardening/tempering guidance, machining notes, weldability guidance, forms and applicable specifications.
440C chemistry reference and the broader hardening, tempering, fabrication and martensitic-grade context used to check the producer values.
EN identity for 440C, martensitic classification and comparative hardness/corrosion evidence including the seawater limitation.
The current ASTM, AMS or EN product specification and the heat-specific MTC/test report control acceptance. State condition, hardness, dimensions, heat-treatment responsibility and supplementary inspection explicitly.