UNS S44003 (AISI 440B) Forgings: Bars, Rings, Discs and Hollow Bars
High carbon martensitic stainless steel, 0.75 to 0.95 % C and 16 to 18 % Cr, hardenable to about 58 HRC. Forged to order in Jiangyin, China.
Key facts
UNS S44003 is the Unified Numbering System number for AISI Type 440B, a high carbon martensitic stainless steel with 0.75 to 0.95 % carbon and 16.00 to 18.00 % chromium. It hardens by heat treatment to about 58 HRC. It is specified for parts that must stay hard and resist wear in mildly corrosive service: bearing races, valve seats and stems, cutlery, gauge blocks, moulds and dies.
The 440 series runs 440A (UNS S44002), 440B (UNS S44003) and 440C (UNS S44004). All three carry 16 to 18 % chromium and differ in carbon content. 440B is harder than 440A and more machinable than 440C.
Jiangyin Jiangnan Metal Co., Ltd. forges UNS S44003 to order as round, square, flat and hex bar, seamless rolled rings, discs, blocks, hollow bar and sleeves. The works is at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Enquiries go to sales@steelforgepieces.com or +86-189-2135-9659.
- UNS number
- S44003
- AISI / SAE
- 440B
- EN / W.-Nr.
- 1.4112, X90CrMoV18
- JIS
- SUS 440B
- Family
- Martensitic stainless
- Carbon
- 0.75 to 0.95 %
- Chromium
- 16.00 to 18.00 %
- Max hardness
- About 58 HRC
- Magnetic
- Yes, ferromagnetic
- Weldable
- Not normally
What is UNS S44003?
UNS S44003 is a hardenable chromium stainless steel of the martensitic class. Its AISI designation is 440B. The S4 prefix in the UNS number marks a martensitic or ferritic stainless steel; the remaining digits map to the AISI 440 series, where the final letter separates carbon levels rather than a change of alloy system.
Carbon is what separates this grade from general purpose stainless steels. At 0.75 to 0.95 %, UNS S44003 holds several times the carbon of Type 304 or Type 316. On quenching, that carbon forms a martensitic matrix with chromium carbides dispersed through it. The carbides give the grade its abrasion resistance. They also consume chromium that would otherwise strengthen the passive film, so corrosion resistance is moderate and closer to Type 410 than to an austenitic grade.
This governs how the grade is bought and used. UNS S44003 is supplied annealed, machined soft, then hardened and tempered to the required hardness. It is not welded into fabrications, and it is not used in seawater or acid service.
Check the designation before ordering. UNS S44003 is Type 440B. Type 440C is UNS S44004, at 0.95 to 1.20 % carbon. A drawing that calls out "UNS S44003 / 440C" contradicts itself. Resolve it before the melt is ordered, because the two grades harden to different values and are not interchangeable.
Chemical composition of UNS S44003
The limits below are those of ASTM A276 for Type 440B. This is the chemistry Jiangyin Jiangnan Metal melts and certifies to unless a customer specification narrows the range.
| Element | Symbol | Minimum | Maximum | Function in the grade |
|---|---|---|---|---|
| Carbon | C | 0.75 | 0.95 | Sets attainable hardness; forms chromium carbides for wear resistance |
| Chromium | Cr | 16.00 | 18.00 | Provides the passive film; forms carbides |
| Molybdenum | Mo | – | 0.75 | Improves hardenability and pitting resistance |
| Manganese | Mn | – | 1.00 | Deoxidiser; ties up residual sulphur |
| Silicon | Si | – | 1.00 | Deoxidiser |
| Phosphorus | P | – | 0.040 | Residual, restricted for toughness |
| Sulphur | S | – | 0.030 | Residual, restricted for transverse ductility |
| Iron | Fe | Balance | Matrix | |
Source: ASTM A276/A276M, Type 440B (UNS S44003). Mill certificates report ladle analysis against these limits. Product analysis to the ASTM permitted variations is available on request.
Mechanical and physical properties
UNS S44003 is supplied annealed and develops its service properties only after hardening and tempering. Values for the two conditions are far apart, so they are listed separately.
| Property | Annealed | Hardened and tempered at 148 C |
|---|---|---|
| Hardness | 269 HB max, hot finished 285 HB max, annealed and cold drawn | 57 to 59 HRC (about 58 HRC max) |
| Tensile strength | 740 to 760 MPa | 1850 to 1950 MPa |
| 0.2 % proof stress | 420 to 450 MPa | 1800 to 1900 MPa |
| Elongation in 50 mm | About 14 % | 2 to 4 % |
| Elastic modulus | 200 GPa | 200 GPa |
| Magnetic response | Ferromagnetic | Ferromagnetic |
Annealed hardness limits are per ASTM A276 for hot finished and cold drawn 440 series bar. Strength values are typical for bar stock and are indicative, not guaranteed minima. Properties on a forging depend on section size, forging ratio and quench route, and are agreed on the order.
| Property | Value | Unit and condition |
|---|---|---|
| Density | 7650 | kg/m3 |
| Elastic modulus | 200 | GPa |
| Thermal expansion | 10.1 | µm/m·C, 0 to 100 C |
| Thermal expansion | 10.3 | µm/m·C, 0 to 200 C |
| Thermal conductivity | 24.2 | W/m·K at 100 C |
| Specific heat | 460 | J/kg·K, 0 to 100 C |
| Electrical resistivity | 600 | nΩ·m |
These values are common to 440A, 440B and 440C and are quoted for the annealed condition.
Equivalent grades and cross-reference
UNS S44003 is 440B in AISI and SAE, 1.4112 (X90CrMoV18) in EN, SUS 440B in JIS and STS440B in KS. Chinese and Russian counterparts are close in purpose but differ in composition.
| Standard system | Designation | Match |
|---|---|---|
| UNS, USA | S44003 | Exact |
| AISI / SAE, USA | 440B | Exact |
| ASTM, USA | A276 / A479 / A580, Type 440B | Exact |
| EN / W.-Nr., EU | 1.4112, X90CrMoV18 | Near equivalent. 1.4112 adds vanadium and runs a higher Mo range. |
| DIN, Germany, superseded | X90CrMoV18, X91CrMoV18 | Near equivalent |
| JIS, Japan | SUS 440B, JIS G4303 | Exact |
| KS, Korea | STS440B | Exact |
| GB, China | 9Cr18MoV, 90Cr18MoV, 8Cr17 | Approximate |
| GOST, Russia | 95Kh18 | Approximate |
| BS / UNI / UNE | X90CrMoV18 | Near equivalent |
Cross-references are functional guidance, not certified interchangeability. Where a code or customer specification names one system, order to that system. Jiangyin Jiangnan Metal certifies to the standard stated on the purchase order.
440A, 440B and 440C compared
The three grades are one alloy at three carbon levels. Raising carbon raises attainable hardness and wear resistance, and lowers toughness, machinability and corrosion resistance. 440B is the middle grade, specified when 440A will not hold hardness and 440C is too brittle or too slow to machine.
| Grade | UNS | Carbon % | Typical max hardness | Specified when |
|---|---|---|---|---|
| 440A | S44002 | 0.60 to 0.75 | About 56 HRC | Corrosion resistance and toughness lead, hardness is secondary |
| 440B | S44003 | 0.75 to 0.95 | About 58 HRC | Balanced hardness, toughness and machinability |
| 440C | S44004 | 0.95 to 1.20 | About 60 HRC | Maximum hardness and wear resistance, bearings and heavily abraded parts |
| 440F | S44020 | 0.95 to 1.20 | About 58 HRC | Free machining version of 440C for high volume turned parts |
Hardness figures are typical maxima after hardening and low temperature tempering. Jiangyin Jiangnan Metal forges all four grades. Send the drawing and service conditions if the selection is open.
Where no 440 grade will serve, because the part has to be welded or has to resist chlorides, the usual alternatives are the precipitation hardening stainless steels. 17-4PH (UNS S17400) reaches about 44 HRC, welds readily and resists corrosion far better. PH13-8Mo gives higher toughness at similar strength.
Heat treatment of UNS S44003
UNS S44003 air hardens, so every thermal step affects the delivered condition. The schedule below is standard practice for Type 440B and is the route Jiangyin Jiangnan Metal follows on these forgings.
| Operation | Temperature | Cooling and hold | Notes |
|---|---|---|---|
| Forging, hot working | 1038 to 1204 C (1900 to 2200 F) | Cool slowly after forging, then anneal fully | Pre-heat to 760 C (1400 F) first. Do not work below 927 C (1700 F), the grade cracks. |
| Annealing | 843 to 871 C (1550 to 1600 F) | Very slow furnace cool | Delivery condition for machining. Gives 269 HB max. |
| Hardening, pre-heat | 760 C (1400 F) | Equalise | Limits thermal shock in a high carbon section. |
| Hardening, austenitise | 1010 C (1850 F) | Soak to through-heat | Dissolves carbides into the matrix. |
| Quench | – | Air or oil | Oil for heavy sections, air is adequate for thin ones. |
| Tempering | 148 C (300 F) | Soak, then air cool | For maximum hardness, about 58 HRC. |
| Stress relief after grinding | 150 to 175 C | 2 to 4 h | Recommended on precision parts. |
Standard mill practice for Type 440B, consistent with published producer datasheets. Soak times depend on section size and are confirmed per order.
Do not temper between 425 and 565 C. Tempering UNS S44003 in this range precipitates carbides at the grain boundaries and lowers both toughness and corrosion resistance. Where a lower hardness is wanted, select 440A or a different alloy system rather than over-tempering 440B.
Machining, welding and cold working
Machinability
Machine UNS S44003 annealed, before hardening. Chips are tough and stringy and need chip breaker geometry to control. Carbide or ceramic tooling is recommended, with rigid setups, positive rake and ample coolant. At 58 HRC the material is ground rather than turned, so the working sequence is rough machine, harden and temper, then finish grind.
Welding
UNS S44003 is not normally welded. The carbon content makes it air hardening and an unmanaged weld will crack. Where welding cannot be avoided: pre-heat to 260 C (500 F) and hold above that temperature throughout, weld with matching filler and high heat input, then anneal at once at 732 to 760 C (1350 to 1400 F) for 6 to 8 hours with a slow furnace cool. The part must not drop below 260 C between welding and annealing. For a hardenable stainless steel that welds readily, specify 17-4PH.
Cold working
Only slight cold work is practical by conventional methods, and only in the annealed condition. The grade is not suitable for deep drawing or severe forming.
Corrosion resistance
Hardened and tempered, UNS S44003 resists mild atmospheres, fresh water, steam, ammonia, many petroleum products and organic materials. Performance is close to Type 410. It is not suitable for seawater, halide bearing media or acids. Corrosion resistance drops further if the grade is used annealed, or tempered above about 425 C. Polished surfaces perform better than as-ground surfaces, and overheating during grinding degrades the passive layer.
UNS S44003 forged products
Jiangyin Jiangnan Metal Co., Ltd. produces UNS S44003 by open-die forging and ring rolling, to customer drawing or as standard stock shapes. Parts are normally delivered annealed and rough machined with an agreed machining allowance, so the buyer can finish machine before hardening.
Forged round, square, flat and hex bar
Forged rather than rolled, for a worked structure through the full section. Diameter and section to enquiry.
Seamless rolled rings
Circumferential grain flow, for bearing races and valve seat rings.
Discs, plates and blocks
Upset forged discs and rectangular blocks for gauge blocks, moulds and die inserts.
Hollow bar, sleeves and bushes
Trepanned or mandrel forged hollows for bushings, cylinders, housings and hubs.
Shafts and stepped forgings
Stepped and flanged shafts, pivot pins, valve stems and spindles.
Near net custom forgings
To drawing. Send the shape, finished weight and quantity for a size and weight check.
Process route and quality control
- Melting. EAF with LF refining. ESR remelt where a customer specification calls for it.
- Forging. Open-die press with controlled forging ratio. Pre-heat to 760 C, forge at 1038 to 1204 C, finish above 927 C.
- Heat treatment. Full anneal after forging. Hardening and tempering to a specified hardness on request.
- Testing. Chemical analysis, hardness, tensile and impact as ordered. Ultrasonic examination to ASTM A388 or EN 10228-3. Grain size to ASTM E112.
- Documentation. EN 10204 3.1 mill test certificate as standard. 3.2 third party inspection on request.
- Quality system. ISO 9001 certified.
Applications for UNS S44003
UNS S44003 is specified where a part has to stay hard and hold a working surface in a mildly corrosive environment.
Bearings
Ball bearings, roller bearings and bearing races needing stainless behaviour with rolling contact hardness.
Valve components
Valve seats, seat rings, stems, bodies and bonnets in petroleum and general process service.
Cutlery and blades
Knife blades, industrial blades and detergent resistant cutlery requiring edge retention.
Moulds and dies
Plastic moulding inserts and die components exposed to corrosive resins.
Measuring equipment
Gauge blocks and measuring instruments needing dimensional stability and wear resistance.
Medical and pump parts
Surgical instruments, nozzles, pivot pins and wear critical pump internals.
Frequently asked questions about UNS S44003
What is UNS S44003?
UNS S44003 is the Unified Numbering System number for AISI Type 440B, a high carbon martensitic stainless steel with 0.75 to 0.95 % carbon, 16.00 to 18.00 % chromium and up to 0.75 % molybdenum. It hardens by heat treatment to about 58 HRC and is used where high hardness and wear resistance are needed together with moderate corrosion resistance.
Is UNS S44003 the same as 440C?
No. UNS S44003 is Type 440B. Type 440C is UNS S44004 and carries 0.95 to 1.20 % carbon. Type 440A is UNS S44002 at 0.60 to 0.75 % carbon. The three grades share the same 16 to 18 % chromium base and differ mainly in carbon, which is why 440B sits between 440A and 440C in attainable hardness. Ordering 440C against a drawing that calls for UNS S44003 is a common and costly purchasing error.
What hardness can UNS S44003 reach?
Hardened from 1010 C and tempered at 148 C, UNS S44003 reaches about 58 HRC, with 57 to 59 HRC typical in production. In the annealed delivery condition it is supplied at 269 HB maximum when hot finished, or 285 HB maximum when annealed and cold drawn, per ASTM A276.
What are the equivalent grades for UNS S44003?
UNS S44003 corresponds to AISI and SAE 440B, EN material number 1.4112 (X90CrMoV18), JIS SUS 440B, KS STS440B and, approximately, GB 9Cr18MoV and GOST 95Kh18. The European and Chinese equivalents are close but not identical. EN 1.4112 carries a vanadium addition that UNS S44003 does not require, so any substitution should be confirmed against the drawing.
Can UNS S44003 be welded?
Not normally. The carbon content makes the grade air hardening and prone to cracking. Where welding cannot be avoided, pre-heat to 260 C (500 F), hold above that temperature throughout, weld with matching filler and high heat input, then anneal at once at 732 to 760 C (1350 to 1400 F) for 6 to 8 hours with a slow furnace cool. The part must not drop below 260 C between welding and annealing.
Is 440B stainless steel magnetic?
Yes. UNS S44003 is martensitic and therefore ferromagnetic in both the annealed and the hardened condition. It cannot be used where a non-magnetic stainless steel is required. An austenitic grade such as UNS S31600 (Type 316) would be specified instead.
What standards cover UNS S44003?
Bars and shapes are covered by ASTM A276. Bars for boilers and pressure vessels are covered by ASTM A479. Wire is covered by ASTM A580. Bars to Japanese practice are covered by JIS G4303. Forgings are normally ordered to the chemistry of ASTM A276, with mechanical properties, non-destructive testing and heat treatment condition agreed on the purchase order, because no single ASTM specification covers 440 series forgings on its own.
In what forged shapes is UNS S44003 available?
Jiangyin Jiangnan Metal Co., Ltd. supplies UNS S44003 as open-die forged round bar, square, flat and hexagonal bar, seamless rolled rings, discs and plates, blocks, hollow bar, sleeves, bushes and shafts. Parts are normally delivered rough machined in the annealed condition, so the buyer can finish machine before hardening.
How is UNS S44003 machined?
Machine it annealed, before hardening. Chips are tough and stringy and are best controlled with chip breaker geometry. Carbide or ceramic tooling is recommended. Once hardened to 58 HRC the material is finish ground rather than machined, so the normal sequence is rough machine, harden and temper, then grind.
Who supplies UNS S44003 (440B) forgings?
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging works at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, manufactures UNS S44003 (AISI 440B) forgings to order and exports worldwide. Bar, seamless rolled rings, discs, blocks and hollow bar are produced to drawing under an ISO 9001 quality system, with EN 10204 3.1 certification. Enquiries go to sales@steelforgepieces.com or +86-189-2135-9659.
Request a quotation for UNS S44003 forgings
Send a drawing, or the shape, finished weight and quantity. The reply covers price, lead time and the proposed heat treatment and testing scope, normally within one working day.
Jiangyin City, Jiangsu Province, China
References and citation
Composition and property data on this page are referenced to the following standards:
- ASTM A276/A276M, Standard Specification for Stainless Steel Bars and Shapes
- ASTM A479/A479M, Standard Specification for Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels
- ASTM A580/A580M, Standard Specification for Stainless Steel Wire
- JIS G4303, Stainless Steel Bars
- SAE/ASTM Unified Numbering System for Metals and Alloys
Values described as typical are indicative and are not guaranteed minima. Guaranteed properties are those stated on the mill test certificate issued against a specific order. To cite this page:
Jiangyin Jiangnan Metal Co., Ltd. (2026). UNS S44003 (AISI 440B) Forgings: Chemistry, Properties and Heat Treatment. Jiangyin, Jiangsu, China. https://www.steelforgepieces.com/Alloy-Steel/UNS-S44003.html
A plain text version of this datasheet is available at UNS-S44003.md.