Type 440C stainless steel

Identity and selection

Carpenter's 25.4 mm 440C round bars, hardened at 1038°C and oil quenched, gave 60 HRC after a one-hour 149°C temper and 56 HRC after a one-hour 316°C temper. The separate tensile table uses a 316°C temper. Keep the two test series separate when assigning hardness or strength to a condition. Carpenter typical data, pp. 3–4

Type 440C, UNS S44004, is a high-carbon chromium stainless steel used hardened and tempered. Carpenter lists carbon 0.95–1.20%, chromium 16–18% and molybdenum at most 0.75%. Its 2024 alloy card describes moderate corrosion resistance, wear resistance and magnetism in all conditions. Carpenter datasheet, p. 1; 440C alloy card

Do not substitute another 440-series designation solely because its name is similar. Carpenter's card identifies 440A, 440B and 440F Se as related alloys, rather than interchangeable material certifications. Likewise, a magnetic response cannot distinguish an acceptable 440C heat from another magnetic steel. Carpenter alloy card

Grade versus bearing-quality product

ASTM A756-17(2022) covers stainless anti-friction bearing steel. Its public scope addresses chemistry, surface imperfections, decarburization and annealed microstructure/hardness; supplementary requirements apply when ordered. This is a product-quality specification, not a prediction of bearing life. Read the ordered edition and selected requirements rather than treating “440C” as shorthand for bearing-quality stock. ASTM A756-17(2022), scope and abstract

Trace the supplied heat and processing lot separately. Specify the finished hardness range, critical surface requirements and inspection method for the component. Agree which properties are certified and at what stage: an incoming-stock certificate cannot establish the final surface condition after machining, hardening and grinding. Conversely, a final hardness reading does not establish chemistry, subsurface defects or dimensional conformance. These are separate acceptance questions.

Read properties with their heat-treatment condition

Carpenter reports the following typical room-temperature values after hardening at 1038°C, oil quenching and tempering at 316°C:

Do not attach the higher hardness result to the tensile-property row. Neither table supplies guaranteed design allowables for a particular section, orientation or finished part. Specify the required condition first, then obtain applicable acceptance data. Where impact, fatigue or rolling contact governs, tensile strength alone does not answer the design question.

Illustrative arithmetic, not a design allowable: suppose a uniform tensile member has a 100 mm² net section and carries 5 kN. Nominal stress is 5000 N / 100 mm² = 50 MPa. Relative to the cited typical yield value, 50 / 1896 = 0.0264, or about 2.6%. That ratio is not a safety factor: the example omits stress concentrations, load variation, residual stress, defects and the suitability of the actual heat-treated material. A low nominal stress cannot by itself qualify a brittle or notched component.

Processing and environmental limits

Carpenter favors machining in the soft annealed condition, warns against grinding overheating, and describes welding as uncommon with special thermal treatment. Its corrosion ratings restrict salt-spray service and recommend testing; tempering above about 427°C reduces corrosion resistance. Carpenter datasheet, pp. 1–2, 5

Use those statements to define a process-development problem, not a universal furnace cycle or maximum service temperature. The final route must reconcile hardness, dimensions, surface condition and the operating environment. Ask the heat treater how section geometry and finishing allowance will be handled. Reserve inspection after the operations that can change the characteristic being accepted; checking dimensions before hardening does not establish finished dimensions.

For welded construction, require a procedure that addresses the final assembly's condition. A local weld repair should not be assumed to retain the original hardened component's properties. Agree whether subsequent thermal processing is feasible before authorizing the repair, and identify the surfaces and dimensions that need reinspection.

For corrosion qualification, reproduce the relevant fluid, temperature, exposure duration, cleaning cycle and crevice geometry. “Stainless” and a supplier's comparative rating are insufficient acceptance criteria. Also distinguish a clean polished test surface from an installed part with deposits, mating contacts and damaged surfaces. The qualification belongs to the actual service condition.

Source versions and related reference

The currently served Carpenter eight-page datasheet prints ©2026, v 10-26 on its final page and labels its data typical or average rather than guaranteed limits. The separate alloy card prints ©2024, v3-24. ASTM's cited public listing is A756-17(2022). These references support material selection; purchase specifications and approved processing instructions establish acceptance. Carpenter datasheet, p. 8; alloy card; ASTM listing

See also grades, tempers and conditions.