440A vs 440B vs 440C Stainless Steel Sheet and Plate Selection
440A, 440B and 440C are hardenable martensitic stainless steels, not interchangeable versions of ordinary corrosion-resistant sheet. Their increasing carbon content changes the balance between attainable hardness, wear resistance and toughness. For a flat blade, wear plate or precision blank, the delivery condition and subsequent hardening route are as important as the grade.
Start with the required performance of the finished component: cutting-edge retention, abrasive wear, impact loading, corrosion exposure and dimensional accuracy. Then select the grade and define whether the purchase is annealed machining stock or material in a specified hardened-and-tempered condition.
Carbon Content: The Main Difference
| Grade / UNS | Carbon, mass % | Chromium, mass % |
|---|---|---|
| 440A / S44002 | 0.60–0.75 | 16.00–18.00 |
| 440B / S44003 | 0.75–0.95 | 16.00–18.00 |
| 440C / S44004 | 0.95–1.20 | 16.00–18.00 |
Reference composition ranges above follow Carpenter Technology’s published grade information. For these grade references, manganese and silicon are each 1.00% maximum, phosphorus 0.040% maximum, sulfur 0.030% maximum and molybdenum 0.75% maximum. These are reference chemistry limits, not measured values from SAKYSTEEL inventory; the order standard and heat certificate govern acceptance.
Specify the complete grade and standard. “440 stainless” does not distinguish 440A from 440B or 440C. JIS, EN and other designations must be checked against the actual chemical, dimensional and testing requirements before substitution; similar names are not proof of full equivalence.
Choose the Balance, Not Just the Highest Hardness
| Grade | Reason to consider it | Question to resolve |
|---|---|---|
| 440A | Lower-carbon option where the hardness–toughness balance is important | Does its achievable condition meet the required edge or wear performance? |
| 440B | Intermediate carbon and hardening response | Is the specified condition justified by testing rather than a generic grade comparison? |
| 440C | High hardness and wear resistance for demanding contact surfaces | Can the component tolerate the toughness, machining and corrosion trade-offs? |
Published hardness figures are condition-dependent. A hardness near 60 HRC is associated with suitably hardened 440C, not every annealed sheet carrying the designation. Thickness, thermal cycle, retained austenite and tempering affect the final result. Do not write one catalogue hardness into a purchase order without defining condition, measurement method and acceptance range.
These grades are used in cutting and wear applications; 440C also appears in bearing and valve components. That does not make flat stock suitable for every bearing or every medical instrument. Product form, cleanliness, fatigue loading and application-specific qualification must match the finished part.
Sheet and Plate: Plan the Complete Manufacturing Route
Annealed stock for preparation and machining
Annealed material is often considered when blanks require profiling, drilling or substantial machining before final hardening. State thickness, width, length, edge condition and surface quality. Clarify whether the dimensions refer to the supplied plate or the finished component, and identify allowances for later grinding or cleanup.
Hardening and distortion control
A thin flat part and a thick plate do not respond identically during thermal processing. Uneven sections, asymmetric machining and unsupported geometry can contribute to distortion. Agree the heat-treatment responsibility, process qualification and inspection stage before placing the order. Final flatness may need to be checked after hardening and finishing, not only on the incoming blank.
Grinding, joining and elevated-temperature service
Grinding must control local heating and surface damage. Welding high-carbon martensitic grades is not a routine substitute for a qualified joining procedure. Do not infer elevated-temperature strength or creep suitability from high room-temperature hardness: a component exposed to heat requires a separate assessment of the grade, temper and service conditions.
Retained Product Photographs
Photographs show product appearance, not proof of grade, hardness or batch compliance. Use identification and inspection records to verify the actual supplied material.
Inspection Points for a Comparable Quotation
- Grade, UNS designation, governing product standard and required delivery condition.
- Plate or sheet dimensions, thickness tolerance, flatness and usable edge requirements.
- Final hardness range and whether it applies before or after customer heat treatment.
- Machining and grinding allowances, surface finish and any defect limits.
- Heat traceability and required chemical, mechanical or additional inspection records.
- Quantity, cut-blank arrangement and destination; separate mandatory requirements from preferences.
Review the stainless steel sheet and plate range when preparing the material specification. Availability of an exact 440-series grade, thickness and condition must be confirmed for the inquiry; a broad product range is not a statement that every combination is stocked.
Technical reference: Carpenter Technology guide to specialty alloys. Reference information is not a test certificate for a supplied batch.
Review a 440-Series Flat-Product Requirement
Send the drawing, grade, dimensions, quantity, delivery condition and intended hardening or finishing route. Include the final hardness and flatness requirements so the quotation can address the finished-part needs.