Selection summary
Overview
440C is the high-carbon member of the 440 martensitic stainless family and is used where high hardness, wear resistance, and dimensional control are required together with moderate corrosion resistance. Its carbide population, heat-treatment response, retained austenite, grinding practice, and final passivation strongly influence performance, so condition-specific procurement is essential.
This page separates standard-oriented limits from typical reference data. Purchase acceptance comes from the ordered specification and certified material test report.
Names and systems
Identity & standards
Similar designations across ASTM, EN, JIS, and other systems are not automatically interchangeable. Product form and ordered standard control chemistry, properties, dimensions, condition, and testing.
Reference chemistry
Composition
| Element | Reference range | Why it matters |
|---|---|---|
| Carbon | 0.95–1.20% | High hardness and carbide volume |
| Chromium | 16.0–18.0% | Corrosion resistance and carbide formation |
| Molybdenum | ≤ 0.75% | Hardenability and corrosion support |
Concise grade-family reference only. Confirm every element limit against the current standard for the exact product ordered.
Condition matters
Reference properties
Typical optimized hardened-and-tempered reference, not a universal guaranteed range
High-hardness brittle behavior makes generic tensile values poor design substitutes
Typical room-temperature engineering reference
Environment first
Corrosion behavior
Can provide useful corrosion resistance when properly hardened, finished, passivated, and maintained.
Carbides and very high carbon reduce corrosion margin relative to low-carbon high-chromium grades; salt water and crevice exposure require caution.
Temperature, concentration, deposits, crevices, stress, surface finish, cleaning, and fabrication quality can change service performance.
Service limits
Temperature & service
Service temperature must remain below levels that overtemper the selected condition; grinding heat and thermal excursions can locally change hardness.
Delivery condition
Heat treatment & condition
440C is machined in the annealed condition, then austenitized, quenched, optionally cryogenically treated, tempered, and finish ground under a qualified high-hardness cycle.
Retained austenite, carbide distribution, decarburization, grinding burn, and tempering temperature must be controlled alongside final hardness and dimensions.
Process route
Fabrication
Machine in the annealed condition and control austenitizing, quench, cryogenic treatment where used, tempering, grinding heat, and retained austenite.
Welding is generally avoided because of high cracking risk and difficult restoration of properties.
Magnetic response: Ferromagnetic.
Decision boundaries
Comparisons & substitution
440C provides higher hardness and wear resistance than 410, 420, or 431, but lower toughness and a narrower fabrication window.
Bearing or cutting performance is not proven by the grade and hardness alone; cleanliness, carbide condition, heat treatment, surface integrity, lubrication, and load spectrum also control life.
Where it is used
Applications
Ordering scope
Product forms & standards
Bar and shapes ordered with the exact annealed or hardened-and-tempered condition, section, straightness, and test requirements.
Plate, sheet, strip, wire, forgings, or machined components under the form-specific standard with heat identity preserved through final treatment.
Decision support
Selection guidance
Choose this grade when
- Very high hardness and wear resistance are primary and impact loading is controlled.
- A qualified heat treater can demonstrate hardness, microstructure, dimensional stability, and surface integrity.
Review another grade when
- Welding, high toughness, or aggressive chloride resistance is required.
- The design assumes bearing life or corrosion performance from hardness alone without cleanliness and surface controls.
Before ordering
Procurement checklist
Name the governing product specification and edition, exact UNS designation, dimensions, tolerances, finish, and delivery or heat-treatment condition.
Require a traceable material test report and verify chemistry, mechanical tests, heat treatment, marking, and any supplementary examination against the purchase order.
State the service environment, design temperature, fabrication route, inspection plan, certification, packaging, and any regulatory or end-user approval before order release.
Traceable evidence