AISI 440C Forgings: UNS S44004 / EN 1.4125 / SUS440C
AISI 440C is a high-carbon, high-chromium martensitic stainless steel (0.95 to 1.20 % C, 16.0 to 18.0 % Cr, up to 0.75 % Mo) that hardens to about 58 to 60 HRC, the highest hardness of any stainless steel, with strong wear and rolling-contact performance and moderate corrosion resistance. It is used hardened and tempered for bearing balls and races, valve seats and needle valves, cutlery, gauge blocks, pump parts and bushings. Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory in Jiangyin, Jiangsu, China, supplies 440C as forged round bar, rings, seamless rolled rings, discs, blocks, sleeves and hollow bars. Enquiries: sales@steelforgepieces.com, +86-189-2135-9659.
- TypeMartensitic stainless
- UNSS44004
- EN number1.4125 / X105CrMo17
- JISSUS440C
- Hardness58 to 60 HRC
- Supply conditionAnnealed or H+T
Forged product forms in AISI 440C
We produce 440C by open-die forging and ring rolling. This route suits the grade because 440C behaves like a high-carbon tool steel in the press, and the hot work has to be controlled closely to avoid cracking and carbide segregation. Every piece leaves with a mill test certificate covering heat number, chemical analysis and delivered condition. Sizes depend on the geometry, so send a drawing or your dimensions and we will confirm what we can forge.
| Form | Typical use in 440C | Sizes |
|---|---|---|
| Forged round bar and rod | Bearing races, pins, valve stems, shafts | On request |
| Square, rectangular, flat and hex bar | Blade and cutter blanks, gauge stock | On request |
| Forged rings and seamless rolled rings | Bearing races, valve seat rings, wear rings | On request |
| Discs, blocks, plates | Die blanks, gauge blocks, valve bodies | On request |
| Hollow bar, sleeves, bushes, cylinders, hubs, housings | Bushings, wear sleeves, nozzle bodies | On request |
| Near-net forgings to drawing | Pump parts, pivot pins, nozzles, valve components | To customer drawing |
Normal practice is to deliver annealed for machining, then harden and temper to the contract hardness. Machining allowance, ultrasonic testing class and certification level are agreed per order.
Chemical composition
| Element | Limit (%) | Note |
|---|---|---|
| Carbon (C) | 0.95 to 1.20 | Highest carbon of the 400-series stainless steels |
| Chromium (Cr) | 16.00 to 18.00 | Forms chromium-rich carbides plus the passive film |
| Molybdenum (Mo) | 0.75 max | EN 1.4125 is often quoted as 0.40 to 0.80 |
| Manganese (Mn) | 1.00 max | |
| Silicon (Si) | 1.00 max | |
| Phosphorus (P) | 0.040 max | |
| Sulfur (S) | 0.030 max | 440F is the free-machining variant |
| Iron (Fe) | Balance, about 78 to 80 | Carpenter states 77.98 to 80.23 |
Sources: Carpenter Stainless Type 440C type analysis; Atlas specification limits; Steelinox 1.4125 datasheet.
Mechanical properties by condition
A single strength figure for 440C means very little. It is a heat-treatable grade and the numbers move by nearly a factor of three between annealed and hardened, so always state the condition when you specify it.
| Condition | Tensile (MPa) | Yield Rp0.2 (MPa) | Elongation | Hardness |
|---|---|---|---|---|
| Annealed | 758 | 448 | 14 % | 269 HB max |
| Hardened, tempered 204 °C (400 °F) | 2030 | 1900 | 4 % | 59 HRC |
| Hardened, tempered 316 °C (600 °F) | 1860 | 1740 | 4 % | 56 HRC |
| Property | Metric | Imperial |
|---|---|---|
| Modulus of elasticity | 200 GPa | 29.0 x 10³ ksi |
| Shear modulus | 83.9 GPa | 12 200 ksi |
| Bulk modulus | 166 GPa | 24 100 ksi |
| Poisson's ratio | 0.27 to 0.30 | 0.27 to 0.30 |
| Density | 7.62 to 7.80 g/cm³ | 0.275 to 0.282 lb/in³ |
| Melting point | about 1483 °C | 2500 to 2700 °F |
| Thermal conductivity at 100 °C | 24.2 W/m·K | 168 BTU·in/hr·ft²·°F |
| Mean thermal expansion, 0 to 100 °C | 10.2 µm/m·°C | 5.6 to 5.67 µin/in·°F |
| Magnetic response | Magnetic in all conditions | |
Sources: Carpenter Technology Stainless Type 440C; AZoM, Stainless Steel Grade 440C (UNS S44004); Rolled Alloys 440C data sheet; Atlas Steels. Density is given as 7.62 g/cm³ by Carpenter and 7.80 g/cm³ by AZoM, so use the certificate value for critical mass calculations.
Forging, heat treatment and fabrication
Forging and hot working
Treat 440C like a high-speed tool steel. Preheat to 760 to 816 °C (1400 to 1500 °F), then heat slowly and evenly to 1038 to 1149 °C (1900 to 2100 °F). Carpenter specifies no forging below 927 °C (1700 °F); Rolled Alloys sets the floor at 954 °C (1750 °F), so work to whichever your specification calls out. Reheat as often as needed, cool slowly in a furnace or in warm dry lime or ashes, then anneal. Forging outside this window is the usual cause of cracked 440C.
Annealing
Full anneal for maximum softness: heat evenly to 843 to 871 °C (1550 to 1600 °F), soak, then cool very slowly in the furnace. Process anneal: 732 to 760 °C (1350 to 1400 °F), then air cool.
Hardening and tempering
Austenitise at 1010 to 1066 °C (1850 to 1950 °F), soak, then quench in warm oil or cool in air. Do not overheat, because full hardness cannot be recovered afterwards. A low-temperature temper follows the quench, and the tempering temperature sets the final hardness: 204 °C gives about 59 HRC, 316 °C about 56 HRC. Keep the temper below roughly 427 °C (800 °F), since corrosion resistance and toughness both fall away above that.
Machining and grinding
Machine in the dead-soft annealed condition. The high carbon content makes it cut much like high-speed steel, chips are tough and stringy, so chip curlers and breakers matter and carbide or ceramic tooling is preferred. Size hardened parts by grinding. On cutlery and blade work, avoid overheating during grinding and polishing, which costs you both hardness and corrosion resistance.
Welding
440C is seldom welded, because it air hardens. Where welding cannot be avoided, preheat and hold at about 260 °C (500 °F), weld with high heat input, then immediately anneal 6 to 8 hours at 732 to 760 °C (1350 to 1400 °F) with a slow furnace cool. The part must not drop below 260 °C between welding and annealing. Matching-composition consumables are preferred; AWS E/ER309 is also used.
Corrosion resistance
440C holds up in normal domestic and mild industrial conditions, including many petroleum products and organic materials. It is not a replacement for an austenitic or duplex grade. Resistance is moderate in nitric acid and sodium hydroxide, good against humidity, and restricted in salt spray, sulfuric acid, acetic acid and phosphoric acid. For chloride-rich or seawater service, specify duplex or super-austenitic instead. 440C is also not normally used hot, because corrosion resistance drops when the material is annealed or tempered above about 427 °C. Keep surfaces free of scale and lubricant, and consider specifying passivation after machining.
If chloride pitting is the governing risk, we can quote the same geometry in A182 F51 duplex, F53 super duplex or 904L.
Equivalent grades and specifications
| System | Designation |
|---|---|
| AISI / SAE | 440C, SAE 51440C, SAE J405 (51440C) |
| UNS | S44004 |
| EN / DIN | 1.4125, X105CrMo17 |
| JIS (Japan) | SUS440C |
| AFNOR (France) | Z100CD17 |
| GB (China) | 102Cr17Mo, 9Cr18Mo (GB/T 1220) |
| ASTM | A276, A314, A473, A493, A580 |
| Aerospace and military | AMS 5618, AMS 5630, AMS 5880, QQ-S-763, MIL-S-862 |
Sources: AZoM other designations list; Carpenter applicable specifications; Steelinox 1.4125; GB/T 1220 grade tables. Note that 9Cr18 without molybdenum is a related but different Chinese grade, so confirm which one your drawing calls for.
Applications for forged 440C
440C is picked where hardness and wear resistance dominate and corrosion exposure is mild. Typical parts: bearing balls and races, cutlery and knives, needle valves, ball check valves, valve seats and seat rings, pump parts, ball studs, bushings, gauge blocks, measuring instruments, moulds and dies, and wear-resistant textile components. Forged and ring-rolled 440C gets specified over bar stock when the part is large, when grain flow has to follow the contour of a race or a seat, or when the section is too big to cut economically from round bar.
Request a quotation
Send a drawing, or just the dimensions, quantity, required condition and hardness, and the certification you need. We will come back with weight, price and lead time.
Jiangyin Jiangnan Metal Co., Ltd., Open-Die Forging Factory
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Phone, WhatsApp, WeChat: +86-189-2135-9659
Email: sales@steelforgepieces.com
Frequently asked questions
What hardness can AISI 440C reach?
About 58 to 60 HRC after hardening and tempering. Carpenter Technology states that when heat treated, Type 440C attains the highest hardness of any stainless steel, around Rockwell C 60. Atlas data gives 59 HRC after a 204 °C temper and 56 HRC after a 316 °C temper. Hardness quoted on the Rockwell B scale, such as 97 HRB, is a converted annealed value and does not apply to hardened 440C.
What is AISI 440C equivalent to?
UNS S44004, EN 1.4125 / X105CrMo17, JIS SUS440C, AFNOR Z100CD17, SAE 51440C, and Chinese GB/T 1220 grade 102Cr17Mo (9Cr18Mo). Product specifications are ASTM A276, A314, A473, A493 and A580, plus AMS 5618, AMS 5630 and AMS 5880.
What is the difference between 440A, 440B and 440C?
Carbon content, and therefore attainable hardness. 440C carries the most carbon at 0.95 to 1.20 % and reaches the highest hardness and wear resistance of the three. 440B (1.4112, X90CrMoV18) sits between 420 and 440C. 440A has the least carbon and is the toughest and most corrosion resistant of the family. 440F is the free-machining version.
At what temperature is 440C forged?
Preheat 760 to 816 °C, forge from 1038 to 1149 °C, and stop before the stock drops below 927 °C (Carpenter) or 954 °C (Rolled Alloys). Reheat as needed, cool slowly in a furnace or in warm dry lime or ashes, then anneal.
Is 440C magnetic?
Yes. As a martensitic stainless steel it is ferromagnetic in both the annealed and hardened conditions, and it hardens by heat treatment.
Can you supply 440C forgings to drawing with certificates?
Yes. We supply 440C forged bars, rings, seamless rolled rings, discs, blocks, sleeves and near-net parts to customer drawing, annealed or hardened and tempered, with mill test certificates. Email sales@steelforgepieces.com or call +86-189-2135-9659.
Data sources
Data above is taken from published mill datasheets and cross-checked: Carpenter Technology Stainless Type 440C; AZoM, Stainless Steel Grade 440C (UNS S44004); Rolled Alloys 440C Stainless data sheet; Atlas Steels 440C data; Steelinox 1.4125 / AISI 440C. Where sources disagree on density and the molybdenum range, both figures are shown. Values are typical or specification limits at room temperature, not a guarantee for a particular delivery. The governing numbers for any order are those on the mill test certificate.
Cite this page: Jiangyin Jiangnan Metal Co., Ltd. (2026). AISI 440C Forgings: UNS S44004 / EN 1.4125 / SUS440C, composition, properties and forging data. steelforgepieces.com/Stainless-Steel/AISI-440C.html