Stainless Steel 440C
AISI/SAE 440C · UNS S44004 · EN 1.4125, X105CrMo17 · JIS SUS440C · GB 9Cr18Mo, 95Cr18
440C is a high-carbon, high-chromium martensitic stainless steel (about 1.0% C, 17% Cr, 0.5% Mo) listed as UNS S44004, 1.4125 / X105CrMo17 and SUS440C, reaching 57–60 HRC after hardening and tempering — the highest hardness and wear resistance of the common hardenable stainless grades.
Values for the Annealed condition
440C tempers and conditions
440C is supplied in 7 conditions, soft to hard. Annealed is the default FabDigit quotes; the values on this page are for it.
- Annealed
- Stress Relieved
- Annealed + Cold Drawn
- H&T 48-52 HRC
- H&T 54-56 HRC
- Hardened & Tempered
- H&T 58-60 HRC
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
AnnealedDefault fully (subcritical/full) annealed, soft machinable condition | Stock condition for bar/plate that will be machined and then hardened by the customer. | 450 | 760 | 14 | 24 HRC | — |
sub-critical stress relief after rough machining of annealed stock | Intermediate step for thin or asymmetric parts to limit distortion during subsequent hardening. | 470 | 780 | 13 | 25 HRC | 2.9 % IACS |
Cold-finished bar, annealed then lightly drawn/ground | Choose for small-diameter precision bar with better straightness/surface than hot-rolled annealed. | 620 | 860 | 10 | 28 HRC | 2.9 % IACS |
Hardened and high-temperature tempered | Only for parts needing moderate hardness with elevated-temperature stability; corrosion resistance and toughness are reduced by carbide precipitation. | 1,500 | 1,650 | 4 | 50 HRC | — |
Hardened and tempered ~250–350 °C for improved toughness | Use where slightly higher toughness / lower cracking risk is worth a few points of hardness (cutlery, shafts). | 1,720 | 1,860 | 3 | 55 HRC | — |
austenitized ~1010–1065 °C, oil/air quenched, tempered 150–200 °C (≈58 HRC) | Standard service condition for bearings, knife blades and wear parts needing maximum hardness with usable corrosion resistance. | 1,900 | 1,970 | 2 | 58 HRC | — |
Hardened, deep-frozen and tempered 150 °C for maximum hardness | Pick when maximum wear resistance and dimensional stability are required (bearing races, valve balls). | 1,950 | 2,050 | 1.5 | 59 HRC | — |
What is 440C?
440C is a high-carbon, high-chromium martensitic stainless steel (about 1.0% C, 17% Cr, 0.5% Mo) listed as UNS S44004, 1.4125 / X105CrMo17 and SUS440C, reaching 57–60 HRC after hardening and tempering — the highest hardness and wear resistance of the common hardenable stainless grades. Typical forms are bar, plate and rings for bearing races and balls, knife blades, valve parts, gauges, pump shafts and mould inserts, with useful atmospheric and fresh-water corrosion resistance. Toughness and weldability are poor, machining must be done annealed, and corrosion resistance is well below austenitic stainless, especially in chlorides and after high-temperature tempering. 440C has a density of 7.68 g/cm³ (0.277 lb/in³), lighter than 94% of stainless steel grades. It melts at 1,370°C (2,498 °F). 440C has a yield strength of 450 MPa (65.3 ksi) and a tensile strength of 760 MPa (110 ksi) — stronger than 70% of stainless steel grades. Elongation at break is 14% and the elastic modulus is 200 GPa (29 Msi).
What is 440C used for?
- Ball and roller bearing races
- Surgical instruments
- Knife blades
- Valve components and seats
- Gauges and measuring tools
- Pump shafts
- Mould and die inserts
Advantages
- Polishes to a fine finish — 80/100, better than 89% of stainless steel grades
- High electrical conductivity — 2.9 % IACS, better than 87% of stainless steel grades
- Easy to machine — 45/100, better than 84% of stainless steel grades
- Conducts heat well — 24.2 W/m·K (14 BTU/hr·ft·°F), better than 83% of stainless steel grades
Limitations
- Difficult to weld — 12/100, worse than 99% of stainless steel grades
- Limited ductility — 14%, worse than 91% of stainless steel grades
- Needs corrosion protection — 42/100, worse than 90% of stainless steel grades
- Limited formability — 25/100, worse than 78% of stainless steel grades
440C properties
Typical room-temperature values for 440C-Annealed; bars are the position among stainless steel grades.
Physical3
440C has a density of 7.68 g/cm³ (0.277 lb/in³), lighter than 94% of stainless steel grades. It melts at 1,370°C (2,498 °F).
Mechanical16
440C has a yield strength of 450 MPa (65.3 ksi) and a tensile strength of 760 MPa (110 ksi) — stronger than 70% of stainless steel grades. Elongation at break is 14% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
440C is rated for continuous service to 425°C (797 °F). It conducts heat at 24.2 W/m·K (14 BTU/hr·ft·°F), better than 83% of stainless steel grades. Thermal expansion is 10.2 µm/m·K (5.67 µin/in·°F).
Electrical3
440C conducts electricity at 2.9 % IACS, better than 87% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is fair (42/100), worse than 90% of stainless steel grades.
Sustainability4
Producing a kilogram of 440C takes about 53 MJ of energy and emits 4.3 kg of CO₂ — less than 67% of stainless steel grades. Typical recycled content is 60%.
Manufacturability6
440C's machinability is fair (45/100, better than 84% of stainless steel grades); weldability not recommended (12/100); formability poor (25/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the stainless steel family
Yield strength against density for every stainless steel grade FabDigit runs. 440C is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 440C
Is 440C easy to machine?
Machine only in the annealed condition with rigid setups, sharp carbide tools, slow speeds and generous coolant; after hardening use grinding, EDM or CBN.
Can 440C be welded?
Welding is generally not recommended — preheat 200–300 °C, use 440C or austenitic filler, and follow with a full anneal to avoid cracking.
Can 440C be formed, bent or molded?
Cold forming is limited to gentle bending of annealed sheet; forge 1050–1150 °C and cool slowly with an immediate anneal to prevent quench cracks.
Manufacturability
The process limits FabDigit's quote engine applies to 440C. Design inside these and the part quotes instantly; outside them it routes to an engineer.
CNC machining
| Machinability | Fair45 / 100 |
|---|---|
| ISO material group | M.4 |
| Cutting speed (rough / finish) | 140 / 170 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1.5 mm |
| Drill depth limit | 4× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
440C chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Chigh carbon gives primary M23C6/M7C3 carbides for wear resistance | 0.95 – 1.2 | 1.05 |
| Cr | 16 – 18 | 17 |
| Mo | ≤ 0.75 | 0.5 |
| Mn | ≤ 1 | 0.4 |
| Si | ≤ 1 | 0.4 |
| P | ≤ 0.04 | |
| S | ≤ 0.03 | |
| Fe | balance |
What surface finishes work on 440C?
Passivate in nitric or citric acid after grinding/polishing for best corrosion resistance; hard-chrome or PVD coatings and mirror polishing are common for knives and bearings.
Surface treatments FabDigit runs on stainless steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
Organic Coating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel 440C in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
How much does 440C cost?
440C is a high-cost stainless steel ($$$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
440C — frequently asked
What is 440C used for?
440C is typically used for ball and roller bearing races, surgical instruments, knife blades, valve components and seats, gauges and measuring tools and pump shafts. In short: highest hardness stainless tool.
What is the yield strength of 440C?
440C has a typical yield strength of 450 MPa (65.3 ksi) and a tensile strength of 760 MPa (110 ksi) — stronger than 70% of stainless steel grades. Strength varies by condition: see the 7 listed tempers.
Is 440C easy to machine?
Reasonably — machinability is rated fair (45/100, better than 84% of stainless steel grades). Machine only in the annealed condition with rigid setups, sharp carbide tools, slow speeds and generous coolant; after hardening use grinding, EDM or CBN.
Can 440C be welded?
Not readily — weldability is rated not recommended (12/100). Welding is generally not recommended — preheat 200–300 °C, use 440C or austenitic filler, and follow with a full anneal to avoid cracking.
What surface finishes work on 440C?
Passivate in nitric or citric acid after grinding/polishing for best corrosion resistance; hard-chrome or PVD coatings and mirror polishing are common for knives and bearings.
Can 440C be formed, bent or molded?
Cold forming is limited to gentle bending of annealed sheet; forge 1050–1150 °C and cool slowly with an immediate anneal to prevent quench cracks.
What is the maximum service temperature of 440C?
440C is rated for continuous use to about 425°C (797 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does 440C cost?
440C is a high-cost stainless steel ($$$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in 440C?
Yes — 440C is available for CNC machining with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A276/A276M — Stainless Steel Bars and Shapes — ASTM (2017)
- GB/T 1220 (9Cr18Mo) — SAC (2007)
- EN 10088-3 / X105CrMo17 (1.4125) — CEN (2014)
- ASM Specialty Handbook: Stainless Steels — ASM International (1994)
- 440C Stainless Steel Product Data Sheet — AK Steel / Cleveland-Cliffs (2016)
- Machinery's Handbook machinability ratings — Industrial Press (2020)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.