Grade dossier
440B Stainless Steel
440B stainless steel is a high-carbon, high-chromium martensitic grade identified as UNS S44003. It is commonly compared with EN 1.4112 / X90CrMoV18, but the published chemistries are not identical, so equivalence must be verified against the governing purchase specification. Its strongest procurement case is a hardened wear component—such as cutlery, hardened balls and precision mechanical parts—where approximately 58–59 HRC hardness is required together with moderate stainless corrosion resistance.
Identity before substitution
Specify 440B with the required condition and hardness
The grade name alone is not a complete purchase specification. 440B 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.
440B stainless composition
Producer chemistry reference for UNS S44003
440B sits between 440A and 440C in carbon level
Carpenter publishes 0.75–0.95% carbon and 16.0–18.0% chromium for UNS S44003, with molybdenum up to 0.75%. That carbon range supports higher hardness than 440A while remaining below the common 440C carbon range. Use the ordered product specification and heat-specific MTC for acceptance. EN 1.4112 is a common comparison, but its published chemistry is not identical to S44003.
| C | 0.75–0.95% |
|---|---|
| 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 |
440B stainless properties
Mechanical properties depend on the heat-treatment route
Carpenter heat-treatment condition references
| Full anneal | 843–871°C · very slow furnace cool |
|---|---|
| Full-anneal hardness | about 223 HB |
| Process anneal | 732–760°C · air cool |
| Process-anneal hardness | about 241 HB |
| Hardening | 1010–1066°C · warm-oil quench or air cool |
| Low-temperature temper | 149–177°C for at least 1 hour |
Selection indicators
| Hardened hardness capability | about 58–59 HRC |
|---|---|
| Density | about 7.65 g/cm³ |
| Elevated-temperature limit | not normally recommended above about 427°C when corrosion performance matters |
| Magnetic response | Magnetic in all normal conditions |
| Corrosion context | similar to 410 in many mild environments; salt spray rated restricted by Carpenter |
The values above are producer-published condition references, not universal acceptance minimums. Section size, hardening temperature, quench severity, retained austenite and tempering temperature can materially change the final result. Release the order against the specified condition, hardness target and actual test/MTC results.
Selection boundary
Use 440B when a 58–59 HRC-class martensitic stainless is the right balance
440B is strongest when the design needs a hard, wear-resistant stainless component but does not require the highest hardness ceiling of 440C. Its high carbon content narrows the welding, forming and toughness window, so corrosion environment, impact loading, section size and heat-treatment route should be reviewed before substitution.
Good reasons to evaluate it
Hardened balls, cutlery and precision wear parts requiring approximately 58–59 HRC
Precision mechanical components where high hardness and moderate stainless corrosion resistance are both needed
Cutting or instrument components where the approved heat treatment and final hardness are defined
Applications where 440A is not hard enough but 440C is not necessary
Reasons to stop and review
Seawater, salt-spray or aggressive chloride service without dedicated corrosion data
Impact-critical or toughness-dominated parts where a high-carbon martensitic grade may be too brittle
Extensive welding, cold forming or heading without a qualified fabrication route
Orders that state only “440B” but omit the final hardness, delivered 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.
Carpenter reports approximately 58–59 HRC after hardening and a low-temperature temper at about 149–177°C for at least one hour. The specified process should control retained austenite, distortion and final hardness.
440B 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.
440B stainless supplier checklist
Buy by form, specification, size and delivered condition
A 440B 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. Carpenter confirms multiple manufactured forms, but exact live-stock sizes should be quoted from current inventory rather than assumed from a generic web range.
Carpenter: bar-rounds, billet, strip, wire and wire-rod
Applicable examples: ASTM A276, A314, A473, A580 and ASTM F899
Legacy federal reference: QQ-S-763 · verify current contract requirements
EN comparison: 1.4112 · X90CrMoV18 · chemistry verification required
MTC / test-report checkpoint
Verify heat number and traceability, 440B / UNS S44003 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 test results, surface/straightness requirements and any supplementary inspection. If EN 1.4112 is proposed as an equivalent, compare chemistry and properties line-by-line before approval.
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Interactive selection check
Test 440B against the controlling design question
Procurement FAQ
Questions to close before ordering 440B stainless steel
What is 440B stainless steel?
440B is a high-carbon, high-chromium martensitic stainless steel, UNS S44003. Carpenter reports approximately 58–59 HRC after suitable hardening and low-temperature tempering. EN 1.4112 / X90CrMoV18 is a common comparison, but its published chemistry is not identical and should be verified before substitution.
How hard can 440B stainless steel become?
Carpenter publishes approximately 58–59 HRC after hardening at about 1010–1066°C followed by a low-temperature temper around 149–177°C. Actual hardness depends on section size, quench, retained austenite and tempering, so the target condition should be specified and tested.
Is 440B stainless steel highly corrosion resistant?
It has moderate stainless corrosion resistance and Carpenter describes its corrosion behavior as generally similar to Type 410 in many mild environments. Salt-spray resistance is rated restricted, so 440B should not be treated like a 316-type chloride-resistant grade.
Is 440B 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 440B RFQ include?
State product form, ASTM/EN requirement, UNS S44003, dimensions and tolerances, delivered condition, required final hardness, heat-treatment responsibility, surface finish, quantity, service environment, MTC and supplementary inspection requirements. If EN 1.4112 is proposed, verify the chemistry and mechanical-property requirements before approving it as an equivalent.
Sources, scope and RFQ
Trace the 440B data, then certify the actual heat and condition
UNS S44003 identity, 0.75–0.95% carbon and 16–18% chromium chemistry, approximately 58–59 HRC hardness capability, annealing/hardening/tempering guidance, machining notes, weldability guidance, forms and applicable specifications.
440-series family positioning: 440A, 440B and 440C use progressively higher carbon to increase hardness capability, helping place 440B between the lower-carbon 440A and higher-carbon 440C options.
1.4112 is identified as an AISI 440B comparison in Swiss Steel data, but its published chemistry differs from Carpenter UNS S44003 data. Treat the EN mapping as a comparison that requires purchase-specification verification.
The current ASTM or EN product specification and the heat-specific MTC/test report control acceptance. State condition, hardness, dimensions, heat-treatment responsibility and supplementary inspection explicitly.