High-carbon martensitic stainless steel · open-die forgings
AISI 440B Forgings (UNS S44003, SUS 440B, DIN 1.4112)
- AISI 440B
- UNS S44003
- SUS 440B
- DIN 1.4112
- X90CrMoV18
- 9Cr18MoV
- SAE 51440B
- ASTM A276
- ASTM A473
- 58 HRC max
Short answer: what is AISI 440B?
AISI 440B is a high-carbon martensitic stainless steel containing 0.75–0.95% carbon and 16.0–18.0% chromium, catalogued as UNS S44003, SUS 440B in Japan and closely matched by DIN/EN 1.4112 (X90CrMoV18) in Europe. It is the middle member of the 440 family: harder than 440A, more corrosion resistant and slightly tougher than 440C. Hardened at 1010–1066 °C and tempered at about 150 °C it reaches a maximum hardness of 58 HRC, and it is always used in the hardened-and-tempered condition, never as-annealed.
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, forges AISI 440B / UNS S44003 to customer drawings as seamless rolled rings, shafts, discs, hubs, flanges, sleeves, bushings, blocks, valve components and round bar. Forgings are supplied annealed for machining at roughly 223 HB, or hardened and tempered to a stated HRC band, and certified to ASTM A276, ASTM A473, JIS G4303 or GB/T 1220 with EN 10204 3.1 as standard and 3.2 third-party witness on request. Written quotations are issued within 24 hours from sales@steelforgepieces.com or 0086-189-2135-9659.
- UNS
- S44003SUS 440B · SAE 51440B
- Carbon
- 0.75–0.95%Cr 16.0–18.0%, Mo 0.75% max
- Max hardness
- 58 HRCtempered at ≈148 °C
- Annealed hardness
- ≈223 HBmachining condition
- Density
- 7.74 g/cm³0.280 lb/in³
- Melting point
- 1482 °C2700 °F
- Forge from
- 1038–1150 °Cstop above 927 °C
- Harden
- 1010–1066 °Cwarm oil or air quench
- Full anneal
- 843–871 °Cfurnace cool, very slow
- Magnetic
- Yesferromagnetic in all conditions
Values on this page are published typical figures for screening and specification writing. Certified results for your order come from the mill certificate for the actual heat.
What AISI 440B forged products can you buy?
Jiangyin Jiangnan Metal produces UNS S44003 by two routes. Open-die forging covers shafts, blocks, discs, hubs and near-net blanks. Seamless ring rolling produces rings and races, which is the usual route for bearing and valve-seat hardware. 440B is a carbide-rich steel, so the forging route is chosen to keep reduction uniform and to avoid the centre bursts that this grade is prone to.
Rings and races
Seamless rolled rings, bearing races, valve seat rings, wear rings and spacer rings in 440B.
Shafts and stems
Forged shafts, pump shafts, spindles, valve stems, pivot pins and plungers, rough or finish machined.
Discs, hubs, blocks
Forged discs, disks, hubs, flanges, blanks, blocks, gauge-block stock and die blocks.
Bar and hollow forms
Forged round, square, flat and hexagonal bar; trepanned hollow bar; forged sleeves, bushings and nozzles.
| Forged product | Typical size range in 440B | Where it is used |
|---|---|---|
| 440B forged rings and rolled rings | 200–1,500 mm OD, 25 mm minimum wall | Bearing races, valve seat rings, wear rings |
| 440B forged shafts and spindles | To 3,000 mm length, Ø60–500 mm | Pump shafts, valve stems, plungers, pivot pins |
| 440B forged discs, disks and hubs | To 1,000 mm diameter | Blanks for cutlery dies, gauge blocks, wear plates |
| 440B forged flanges and flange blanks | To 900 mm OD | Valve bonnets and bodies in mild-corrosion service |
| 440B forged round bars, square, flat and hex bar | Ø40–400 mm; flats and squares to drawing | Machined instrument parts, cutlery stock, fasteners |
| 440B forged sleeves and bushings | To 800 mm OD, bored or trepanned | Wear bushings, guide sleeves, nozzle bodies |
| 440B hollow bars, forged tubes and cylinders | Trepanned hollows machined from forged bar | Pump casings, barrels, cases and shells |
| 440B forged valve parts: seats, stems, bodies, bonnets, seat rings | To drawing | Valve trim where hardness and wear govern |
| 440B forged blocks, blanks and dies | To 2,000 kg single piece | Mould and die blanks, gauge blocks, tooling |
Every form is supplied either fully annealed for machining, or hardened and tempered to an agreed HRC band, with the heat-treatment chart record attached to the certificate. Send the finished drawing rather than a billet size: on a crack-sensitive grade like 440B, the forging route and the post-forge anneal matter more to the delivered cost than the machining rate does.
What is AISI 440B, and why does it exist?
The 440 family exists to solve one problem: a steel that can be hardened like a tool steel but still calls itself stainless. Chromium at 16–18% gives the passive film. Carbon at 0.75–0.95% gives the martensite its hardness and forms the chromium carbides that provide wear resistance. Those two requirements fight each other, because every carbide that forms locks up chromium that is no longer available to the passive film.
440B is the deliberate middle setting of that trade-off. 440A (0.60–0.75% C) keeps more chromium in solution and corrodes less, but tops out near 56 HRC. 440C (0.95–1.20% C) reaches 60 HRC and carries the most carbide, at the cost of corrosion resistance and toughness. 440B sits between them at 58 HRC, which is why it appears on cutlery, hardened balls, valve trim and instrument parts where a part has to hold an edge or a wear surface and also see fresh water, steam, mild acids or food.
Three consequences follow from the chemistry, and they govern everything else on this page:
- It air-hardens. A 440B forging left to cool on the shop floor will transform to untempered martensite and can crack overnight. Controlled cooling and an immediate post-forge anneal are not optional.
- Corrosion resistance depends on heat treatment as much as on chemistry. 440B is only corrosion resistant in the hardened-and-tempered condition, tempered below about 425 °C. Annealed 440B, or 440B tempered in the 425–565 °C range, has noticeably poorer corrosion resistance.
- It behaves like a tool steel in the shop. Preheating, soak-through times, warm oil quenching and immediate tempering are handled the way a high-speed steel would be handled, not the way 304 or 316 would be.
440B is not a marine or chloride-service steel
Corrosion resistance is broadly comparable with Type 410: adequate in mild atmospheres, fresh water, steam, ammonia, many petroleum products and organic media, and in some mild acids. It is not adequate in seawater, chloride-bearing process streams or acids of any strength. If your part needs both high hardness and real chloride resistance, look at a precipitation-hardening grade such as 17-4PH or a duplex grade instead, and accept the lower hardness.
What are the equivalents of AISI 440B?
Buyers meet this steel under several names. Some are exact chemistry matches; others are near equivalents with different molybdenum and vanadium bands. We accept purchase orders under any of them, and issue a certificate that lists every specification the heat actually satisfies. The designations are not interchangeable, though, and that difference matters on a drawing.
| Region / body | Designation | Match and notes |
|---|---|---|
| USA · AISI / SAE | AISI 440B, SAE 51440B, SAE J405 (51440B) | The original designation. Use with a product-form specification, never alone. |
| USA · UNS | UNS S44003 | Exact. The unambiguous designation for drawings and purchase orders. |
| Japan · JIS | SUS 440B (JIS G4303) | Exact. Same 0.75–0.95 C, 16–18 Cr, 0.75 Mo max chemistry. |
| Germany / EU · Werkstoff | 1.4112 · X90CrMoV18 (EN 10088-3) | Near equivalent, not identical. 1.4112 runs 0.85–0.95 C, 17–19 Cr, 0.9–1.3 Mo and adds 0.07–0.12 V. Higher Mo and the vanadium change temper response. State which specification governs. |
| China · GB | 9Cr18MoV (GB/T 1220), 9Cr18 | Near equivalent. 9Cr18MoV corresponds more closely to 1.4112 than to 440B. Cross-certification is possible; say so on the order. |
| USA · ASTM product forms | ASTM A276 · A314 · A473 · A580 | A276 bars and shapes; A314 billets and bars for forging; A473 stainless forgings, the one to cite for a forged part; A580 wire. |
| USA · federal / military | QQ-S-763, MIL-S-862 | Legacy US government specifications still quoted on older drawings. |
| Family members | 440A (S44002), 440C (S44004), 440F (S44020) | Same 16–18% Cr, different carbon. See the family comparison before substituting. |
1.4112 and 440B are not the same steel
Many cross-reference tables print 440B = 1.4112 without qualification, and that shortcut causes rejected material. X90CrMoV18 carries up to 1.3% molybdenum and a deliberate 0.07–0.12% vanadium addition; 440B caps molybdenum at 0.75% and specifies no vanadium. A heat can satisfy one and fail the other. If your drawing says 1.4112, order 1.4112 and we will buy to the EN band; if it says 440B or S44003, we buy to the AISI band. If the project needs both callouts, ask for a dual-certified heat at enquiry stage, before the melt.
Tool 1 of 6
Designation lookup
Type any name you have been given (440B, S44003, SUS440B, 1.4112, 9Cr18MoV, 440C, 420) and see what it maps to, and whether the match is exact.
The lookup covers the 440 family and the martensitic and PH stainless grades we forge most often. Matching a name here does not by itself certify equivalence: acceptance requirements differ between product-form specifications.
What is the chemical composition of AISI 440B?
The composition below is the AISI 440B / UNS S44003 requirement, and it is what we buy raw material against unless the drawing calls for a tighter band. Carbon is the element that decides everything: it sets attainable hardness, it forms the chromium carbides that carry wear resistance, and it is the reason the steel cracks if it is cooled quickly after forging.
| Element | Min | Max | What it does |
|---|---|---|---|
| Carbon (C) | 0.75 | 0.95 | Sets the hardness ceiling at 58 HRC and forms the M23C6 chromium carbides that give wear resistance. The single most important row in this table. |
| Chromium (Cr) | 16.0 | 18.0 | Forms the passive film. Part of it is consumed by carbides, which is why 440B corrodes more readily than a low-carbon 410 or 304. |
| Molybdenum (Mo) | - | 0.75 | Improves hardenability, temper resistance and pitting resistance. Optional in 440B; mandatory and higher in EN 1.4112. |
| Manganese (Mn) | - | 1.00 | Deoxidiser, sulphur control, contributes to hardenability. |
| Silicon (Si) | - | 1.00 | Deoxidiser; raises tempering resistance slightly. |
| Phosphorus (P) | - | 0.040 | Residual. Segregates to grain boundaries and embrittles; keep low on heavy sections. |
| Sulphur (S) | - | 0.030 | Residual. Harms hot workability and transverse toughness. 440F raises it deliberately for machinability. |
| Iron (Fe) | - | Balance | Roughly 80%. |
Where we place the chemistry inside the band
Two heats can both satisfy 440B and behave differently. Carbon near 0.78% with chromium near 17.5% anneals softer and machines more easily; carbon near 0.93% reaches the top of the hardness range and wears better but is less forgiving in the forge and in the quench. Tell us at enquiry stage which matters more for your part, machining cost or peak hardness, and we will target the sub-range when the heat is bought. Ladle analysis appears on every certificate; product analysis on the finished forging is available on request.
440A vs 440B vs 440C vs 420: which one does your part need?
All four grades carry 16–18% chromium. Carbon is the only meaningful variable, and it moves hardness one way and corrosion resistance and toughness the other. 440B is chosen when 440A cannot hold the wear surface and 440C is too brittle or too difficult to machine.
| Property | 420 | 440A · S44002 | 440B · S44003 | 440C · S44004 |
|---|---|---|---|---|
| Carbon % | 0.15 min | 0.60–0.75 | 0.75–0.95 | 0.95–1.20 |
| Chromium % | 12–14 | 16–18 | 16–18 | 16–18 |
| Max hardness | ≈50 HRC | ≈56 HRC | ≈58 HRC | ≈60 HRC |
| Wear resistance | Moderate | Good | Very good | Highest |
| Corrosion resistance | Moderate | Best of the 440 family | Between A and C | Lowest of the 440 family |
| Toughness | Best | Good | Moderate | Lowest |
| Machinability, annealed | Best | Good | Moderate | Hardest to machine |
| Forging crack risk | Low | Moderate | High | Highest |
| Commercial availability | Wide | Limited | Limited, usually made to order | Widest of the 440 family |
| Choose it when | Toughness and cost govern; hardness under 50 HRC is enough | Corrosion resistance governs and 56 HRC is enough | An edge or wear face plus mild-media corrosion resistance | Wear and hardness govern and the part can be designed around low toughness |
An availability note worth knowing before you specify
440C is far more widely stocked than 440A or 440B. For a forged part this matters less than it does for bar stock, because we buy the heat against your order anyway. If your drawing allows either grade and you need a short lead time, say so and we will quote both. If your drawing says 440B specifically, we forge 440B; we do not substitute without written approval.
Tool 2 of 6
440A / 440B / 440C grade selector
Tell it what the part does and what matters most. It returns the grade the duty normally points to, and says what you give up.
Screening guidance from published grade behaviour, not a design calculation. Final material selection stays with the design authority for the equipment.
What are the mechanical properties of AISI 440B?
440B is bought and sold on hardness, not on tensile strength. Hardness is what the specification states, what the heat-treatment cycle controls and what the certificate reports. Tensile figures for the hardened condition are published typical values and are quoted below for screening only; at 55 HRC and above a tensile test tells you little that a hardness traverse does not.
| Condition | Hardness | Tensile strength | Yield 0.2% | Elongation |
|---|---|---|---|---|
| Annealed 843–871 °C, furnace cooled | ≈223 HB (255 HB / 25 HRC max) | ≈740 MPa · 107 ksi | ≈425 MPa · 62 ksi | ≈18% |
| Process annealed 732–760 °C, air cooled | ≈255 HB | - | - | - |
| Hardened + tempered 150–177 °C | 57–58 HRC | ≈1,900 MPa · 276 ksi | ≈1,860 MPa · 270 ksi | ≈2% |
| Hardened + tempered 205 °C | 56–57 HRC | ≈1,880 MPa · 273 ksi | ≈1,820 MPa · 264 ksi | ≈2–3% |
| Hardened + tempered 315 °C | 54–56 HRC | ≈1,860 MPa · 270 ksi | ≈1,790 MPa · 260 ksi | ≈3% |
| Hardened + tempered 370 °C | 52–54 HRC | ≈1,790 MPa · 260 ksi | ≈1,700 MPa · 247 ksi | ≈4% |
| Over-tempered 600–675 °C | 35–45 HRC | - | - | - |
Toughness is the limiting property, not strength
Published Izod values for this grade run around 20 J annealed and fall to roughly 9 J after hardening and tempering. That is low, and it is the property that decides whether a 440B part survives. Design out sharp internal corners, undercuts and abrupt section changes; specify generous radii; and where a part sees impact rather than pure wear, consider 440A or a PH grade before raising the hardness.
Retained austenite and sub-zero treatment
Quenched 440B retains austenite, typically a few percent up to around 10% depending on austenitising temperature. On dimensionally critical parts such as gauge blocks, bearing races and precision valve seats, that austenite transforms slowly in service and the part grows. A sub-zero treatment at −73 °C between quench and temper, followed by the normal temper, converts most of it and stabilises the dimensions. Ask for it by name on the order if your part needs dimensional stability; it is not part of the default cycle.
Physical and thermal properties of AISI 440B
| Property | Metric | Imperial | Note |
|---|---|---|---|
| Density | 7.74 g/cm³ | 0.280 lb/in³ | Used by the weight calculator on this page |
| Melting point | 1482 °C | 2700 °F | Published single-point figure |
| Modulus of elasticity | 190–210 GPa | 27,557–30,458 ksi | Tension, room temperature |
| Poisson's ratio | 0.27–0.30 | 0.27–0.30 | - |
| Thermal conductivity | ≈24.2 W/m·K | ≈168 BTU·in/hr·ft²·°F | Figure commonly published for the martensitic 410/440 family at 100 °C |
| Coefficient of thermal expansion | ≈10.2 µm/m·°C | ≈5.7 µin/in·°F | 0–100 °C mean |
| Specific heat | ≈460 J/kg·K | ≈0.11 BTU/lb·°F | 0–100 °C |
| Electrical resistivity | ≈0.60 µΩ·m | ≈60 µΩ·cm | Room temperature |
| Magnetic response | Ferromagnetic in every condition | Hardened 440B makes a fair permanent magnet. Do not specify it where a non-magnetic part is required | |
| Structure | Martensite with chromium carbides | Plus retained austenite unless sub-zero treated | |
Service temperature. 440B is not an elevated-temperature grade. Any sustained exposure above the tempering temperature softens the part, and holding above about 425 °C also costs corrosion resistance. Treat roughly 300–400 °C as the practical ceiling for a load-carrying 440B part, and choose a different family for anything hotter.
Corrosion resistance: where 440B works and where it must not go
Corrosion resistance in this grade is a heat-treatment property as much as a chemistry property. The chromium that is tied up in carbides is not protecting anything. The same steel can therefore pass a test in one condition and fail it in another.
Performs adequately in
- Mild atmospheric exposure, indoor and sheltered outdoor
- Fresh water and steam
- Ammonia and many organic media
- Many petroleum products and lubricants
- Food contact and cutlery service, cleaned and dried
- Some mild acid environments, tested case by case
Should not be used for
- Seawater, brine or any chloride-bearing stream: pitting and crevice attack
- Acids at working concentration, and reducing acids in particular
- Parts that must stay corrosion resistant in the annealed condition
- Parts tempered in or above the 425–565 °C range
- Sustained service above roughly 400 °C
- Applications needing a non-magnetic material
Three rules that decide whether a 440B part corrodes in service
1. Use it hardened and tempered. Optimum corrosion resistance is obtained in the hardened-plus-tempered condition with the temper below about 425 °C. Annealed 440B corrodes noticeably more readily.
2. Keep the surface clean. Scale, grinding debris, drawing lubricant, embedded free iron and coatings all break down the passive film. Passivation after final grinding is normal practice for cutlery, instrument and valve parts.
3. Do not overheat during grinding. A grinding burn is a local re-temper. It removes hardness and corrosion resistance in the exact place the part is most highly stressed.
How is AISI 440B forged?
440B is one of the less forgiving stainless grades to forge. It is a high-carbon, carbide-forming steel with a narrow working window, it air-hardens, and it cracks if it is worked cold or cooled quickly. The route below is what we run in the shop, and it is written the way a heat-treatment department would read it.
Preheat, 760–816 °C
Heat slowly and uniformly. Charging a cold 440B billet straight into a hot furnace puts a thermal gradient across a brittle section and is a common cause of cracks that only appear after the first blow.
Heat to forging temperature, 1038–1177 °C
Our normal target is 1050–1120 °C. Soak through the ruling section, roughly 30 minutes per 25 mm, so the core reaches temperature and not only the skin.
Forge with frequent reheats
Moderate, even reductions. Aim for 4:1 or better total reduction to break up the as-cast carbide network, which is what actually controls the delivered toughness. Reheat as often as the shape needs rather than chasing one more pass out of a cooling billet.
Stop above 927 °C
Do not deform 440B below 1700 °F. Below that the carbide-rich structure has very little hot ductility and surface and centre cracking risk climbs sharply.
Controlled cool, never on the shop floor
Cool in the furnace, or bury in warm dry lime or dry ash. 440B hardens in air: a forging left on a rack will transform to untempered martensite and can crack hours later, with nobody watching.
Full anneal immediately after forging
Cool to room temperature, then anneal at 843–871 °C, about one hour per 25 mm, and cool very slowly in the furnace. Expect roughly 223 HB. This is the condition in which the forging is machined, measured and shipped unless the order says otherwise.
Rough machine, then harden and temper
Machine in the annealed condition, leaving grinding stock. Harden, quench and temper to the specified HRC band, then finish grind. See hardening and tempering below.
Test, examine and certify
Hardness survey, tensile where the order calls for it, UT to ASTM A388 or EN 10228-3, PT to ASTM E165, then an EN 10204 3.1 or 3.2 certificate carrying the heat number and the heat-treatment chart record.
The single most expensive mistake on a 440B forging
Skipping or delaying the post-forge anneal. The part looks fine when it leaves the hammer and cracks in storage, during rough machining, or during hardening, which is the worst case because all the machining value has been added by then. If a subcontractor forges your 440B, put "cool in furnace or lime; full anneal at 843–871 °C immediately after forging" on the purchase order in writing.
Tool 3 of 6
440B forge and heat-treatment cycle generator
Enter the ruling section, the greatest thickness heat has to travel through, and get a printable cycle for your forge shop or heat-treatment subcontractor.
Starting cycles based on the standard 30 minutes per 25 mm soak rule and published 440B temperatures. It is not a qualified procedure. Qualify on coupons from the same heat, with thermocouples on the part and a chart record, before releasing production parts.
Hardening, tempering and annealing AISI 440B
Annealing
Full anneal: heat uniformly to 843–871 °C (1550–1600 °F), soak, and cool very slowly in the furnace. Result is roughly 223 HB, the softest and most machinable condition. Process (intermediate) anneal: 732–760 °C (1350–1400 °F), air cool, giving roughly 255 HB. Use the process anneal between machining operations; use the full anneal after forging and before final machining.
Hardening
Austenitise at 1010–1066 °C (1850–1950 °F), soak about 30 minutes per 25 mm of section, then quench in warm oil or cool in air according to section size. Oil is necessary on heavy sections; thin sections can air harden. Do not overheat. Above roughly 1066 °C more carbide dissolves, more austenite is retained, and full hardness is not reached. The part comes out softer than the same steel quenched from a lower temperature.
The austenitising temperature is a genuine engineering choice within that band. Nearer 1066 °C dissolves more carbide and gives the highest attainable hardness, with marginally lower corrosion resistance. Nearer 1010 °C leaves more undissolved carbide, giving slightly lower hardness with better corrosion resistance and more hard particles for wear. State which you want when the part is ordered.
Tempering
Temper immediately after the part reaches hand temperature. Never leave quenched 440B overnight. Minimum one hour per 25 mm of section, two hours minimum in all cases. Tempering at 148–177 °C (300–350 °F) relieves quenching stresses while keeping maximum hardness, around 58 HRC.
Never temper 440B between 425 °C and 565 °C
That band produces temper embrittlement and a marked loss of corrosion resistance at the same time. It is the one heat-treatment instruction on this page that has no exceptions. Tempering between 600 °C and 675 °C is a different operation entirely: it drops hardness to roughly 35–45 HRC to make a part machinable again, and the corrosion resistance of that condition is not what the grade was chosen for.
Stress relief and sub-zero treatment
A stress relief below the tempering temperature can be applied after rough grinding on precision parts. A sub-zero treatment at −73 °C between quench and temper converts retained austenite and stabilises dimensions on gauge blocks, bearing races and precision seats; the normal temper follows it. Both are available on request and must be stated on the order.
Tool 4 of 6
Temper temperature vs hardness and corrosion resistance
Move the tempering temperature and see what happens to hardness, toughness and corrosion resistance before you write it on a drawing.
Screening estimate from published 440B tempering behaviour. Actual hardness depends on the heat, the section size, the quench and the retained austenite level. Qualify on your own coupons.
Machining, grinding and welding AISI 440B
Machining
Machine in the fully annealed condition and nowhere else. Even annealed, 440B cuts roughly like a high-speed tool steel: the chips are tough and stringy, so chip breakers matter, and carbide or ceramic tooling outperforms HSS by a wide margin. Rigid setups, sharp edges, steady feed and no dwelling. Once the part is hardened above about 50 HRC, machining is effectively finished and grinding takes over.
- Carbide or ceramic tooling, positive rake, sharp edges changed on schedule
- Chip breakers for the stringy annealed chip
- Generous, well-directed coolant; never let the tool rub
- Leave grinding stock for post-hardening finishing on tolerance features
Grinding
Grinding is where finished 440B parts are most often ruined. Excess wheel pressure or inadequate coolant produces a local re-temper, called a grinding burn, which removes hardness and corrosion resistance exactly where the part is most stressed, and can leave residual tensile stress and fine surface cracks. Use free-cutting wheels, light passes, flood coolant, and etch-inspect finished precision parts if the application justifies it.
Welding
Welding 440B is not recommended. The grade air-hardens, so the heat-affected zone transforms to untempered martensite and cracks. Where a repair or an attachment is unavoidable: preheat to about 260 °C (500 °F), weld with matching or 410-type filler, and follow immediately with a post-weld treatment at 732–760 °C (1350–1400 °F) held about 6 hours, cooled slowly in the furnace. Austenitic 309 or 310 filler gives a softer, more ductile weld where full hardness across the joint is not needed. A welded 440B part must be re-hardened and re-tempered before it can be regarded as meeting the grade's properties.
Cold working
Only light cold work is practical, and only from the fully annealed condition. Anything more than mild forming, heading or upsetting needs an intermediate anneal.
How do AISI 440B parts fail, and how do you prevent it?
Cracking after forging
Cause: air cooling after the hammer, or deforming below 927 °C. Prevention: furnace or lime cooling, immediate full anneal, UT after annealing rather than after machining.
Quench cracks
Cause: sharp internal corners, abrupt section change, over-austenitising, or a delay before tempering. Prevention: radii on the drawing, controlled soak, warm oil, temper the moment the part can be handled.
Low hardness after heat treatment
Cause: austenitising too high, leaving retained austenite, or an under-soaked heavy section. Prevention: hold 1010–1066 °C with a charted cycle, add sub-zero treatment where dimensions are critical.
Rust on a "stainless" part
Cause: supplied annealed, tempered above 425 °C, or a contaminated and unpassivated surface. Prevention: specify hardened and tempered below 425 °C, passivate after final grinding.
Dimensional growth in service
Cause: retained austenite transforming over months on a precision part. Prevention: sub-zero treatment at −73 °C between quench and temper, followed by the normal temper.
Brittle fracture in service
Cause: hardness specified higher than the duty needs, tempering inside the 425–565 °C embrittlement band, or an as-cast carbide network never broken up by sufficient forging reduction.
What can Jiangyin Jiangnan Metal forge in AISI 440B?
440B is a made-to-order grade for us: we buy the heat against your specification rather than pulling it from stock, which is why the drawing, the governing specification and the required certificate all matter at enquiry stage rather than after the order is placed.
- Rolled ring OD
- 200–1,500 mm25 mm minimum wall
- Disc diameter
- ≤ 1,000 mmdiscs, hubs, blanks
- Shaft length
- ≤ 3,000 mmØ60–500 mm
- Bar diameter
- 40–400 mmround, square, flat, hex
- Single piece
- ≤ 2,000 kgin this grade
- Condition
- Annealed or H&Tto a stated HRC band
- Lead time
- 8–14 weekstypical, heat bought to order
- Certificate
- EN 10204 3.13.2 on request
The figures above are the practical envelope for 440B specifically. The plant envelope across all grades is considerably larger: seamless rolled rings to 2,500 mm outside diameter, shafts to 8 m and single pieces to 8,000 kg. A high-carbon martensitic stainless is limited by crack sensitivity and by billet availability rather than by press capacity. Send the drawing and we will confirm size, weight and lead time for your part before quoting.
Forging
1 t, 3 t, 5 t and 9 t open-die hammers; 4,500 t and 5,000 t hydraulic presses; radial-axial ring mills with a 6 m ring line.
Heat treatment
Bogie-hearth furnaces to 1,200 °C with ±5 °C uniformity and chart recording; warm oil, water and forced-air quenching with controlled transfer times; sub-zero treatment on request.
Inspection
Optical emission spectrometer, universal tensile machine, Charpy impact machine, hardness testers, magnetic particle and penetrant lines, ultrasonic flaw detection, metallographic microscope.
Machining
Vertical and horizontal lathes, boring mills and machining centres for rough or finish machining to drawing, with in-process dimensional records.
Which standards and certificates apply to 440B forgings?
Material and product
- ASTM A473: stainless steel forgings. Cite this for a forged part
- ASTM A276: stainless bars and shapes
- ASTM A314: billets and bars for forging
- ASTM A484: general requirements for stainless bars
- JIS G4303: SUS 440B bars
- EN 10088-3: where 1.4112 / X90CrMoV18 is called up
- GB/T 1220: where 9Cr18MoV or 9Cr18 is called up
- EN 10204 3.1 standard, 3.2 with third-party witness
Testing and examination
- Hardness: ASTM E18 (Rockwell), ASTM E10 (Brinell)
- Tensile: ASTM E8/E8M
- Impact: ASTM E23, where the order requires it
- Ultrasonic: ASTM A388 or EN 10228-3
- Penetrant: ASTM E165 / ISO 3452
- Magnetic particle: ASTM E1444
- Grain size ASTM E112; carbide distribution by micrograph
- Passivation: ASTM A967 where specified
Quality management is certified to ISO 9001:2015. Third-party witness certificates are issued through the inspection body you nominate: Lloyd's Register, DNV, Bureau Veritas, ABS, TÜV or SGS. Customers keep an unrestricted right to witness any production stage, including chemistry, forging, heat treatment and mechanical testing, arranged with our QA team at no charge.
How do you specify an AISI 440B forging order?
Name the grade and the standard together
Write
AISI 440B / UNS S44003and the product-form specification. "440B" on its own leaves the acceptance requirements undefined.Cite the forging specification, not the bar specification
ASTM A473 covers stainless forgings. A276 is bars and shapes. On a forged ring or shaft, A473 is the correct citation.
State the delivery condition explicitly
Annealed for machining, or hardened and tempered to a stated HRC band. If hardened, give the band you will accept, for example "55–58 HRC" rather than "58 HRC", because a single number is not a testable requirement.
Say where the hardness is measured
Surface, mid-radius, or a traverse. On a heavy section these differ, and the argument is much cheaper before the order than after delivery.
Decide the austenitising intent
Maximum hardness (nearer 1066 °C) or maximum corrosion resistance (nearer 1010 °C). We will set the cycle accordingly and chart it.
Call out sub-zero treatment if dimensions are critical
Gauge blocks, bearing races and precision seats need it. It is not in the default cycle.
Define NDE and the acceptance class
"UT per EN 10228-3 quality class 3" or "UT per ASTM A388 with acceptance to the purchase order". An unqualified "ultrasonic test" is not a specification.
Give quantity, date, Incoterm and destination
Quantity drives the melt: small orders are consolidated onto a larger heat, which affects both price and schedule.
Drawing callout you can copy
MATERIAL: AISI 440B / UNS S44003 (SUS 440B). If EN is required,
state 1.4112 / X90CrMoV18 separately - it is NOT identical
SPECIFICATION: ASTM A473 (stainless forgings); ASTM A276 for bar
Revision per contract date
FORGING: Preheat 760-816 C, forge 1038-1150 C, finish above 927 C,
furnace or lime cool, minimum 4:1 reduction
POST-FORGE: Full anneal 843-871 C, furnace cool. Report hardness
CONDITION: [ ] Annealed for machining, approx. 223 HB
[ ] Hardened and tempered to ____ - ____ HRC
HARDENING: Austenitise 1010-1066 C, quench warm oil (or air per section),
temper ____ C minimum 2 h. Do NOT temper 425-565 C
SUB-ZERO: -73 C between quench and temper if dimensional stability
is required, followed by the normal temper
CHEMISTRY: Report all elements. C 0.75-0.95, Cr 16.0-18.0, Mo 0.75 max
HARDNESS: Per ASTM E18, ____ locations, traverse on sections over 50 mm
NDE: UT per EN 10228-3 quality class 3 (or ASTM A388)
PT per ASTM E165, Type I Method C
SURFACE: Passivate per ASTM A967 after final grinding (if required)
CERTIFICATE: EN 10204 3.1 (3.2 with third-party witness if stated on the PO)
MARKING: Heat number, specification, condition and drawing number,
low-stress stamped or vibro-etched
Seven mistakes buyers make with AISI 440B
Treating 1.4112 as an exact equivalent
X90CrMoV18 has a higher molybdenum band and a vanadium addition. Order the one your drawing actually calls for, or ask for dual certification before the melt.
Specifying 440B for chloride service
The passive film on a high-carbon 440 grade does not survive seawater or chloride process streams. Hardness does not help. Change grade, not heat treatment.
Accepting annealed material for a corrosion duty
440B is only corrosion resistant hardened and tempered. Annealed parts left in service will rust.
Tempering in the 425–565 °C band
It embrittles the steel and reduces corrosion resistance at the same time. If a drawing calls for it, question the drawing.
Writing a single hardness number
"58 HRC" is not testable. Give a band, and say where on the part it is measured.
Buying a solid block and machining a ring out of it
On a ring geometry, rolling the ring rather than boring a disc typically halves the purchased weight. See the worked example.
Leaving the post-forge anneal off the purchase order
If it is not written down, a subcontractor may air cool the forging. The cracks appear later, after the machining cost has been added.
Tool 5 of 6
AISI 440B forging weight calculator
Pick a shape, enter the finished dimensions, and get the net weight at 7.74 g/cm³ plus the rough forging weight we quote against.
Net finished weight at density 7.74 g/cm³. The rough forging adds your selected machining allowance and is the figure we quote against. Our single-piece limit in 440B is 2,000 kg; confirm larger sizes with us before designing to them.
Tool 6 of 6
AISI 440B RFQ writer
Fill in what you know and it writes a complete, unambiguous enquiry you can paste into email or WhatsApp. Nothing is submitted from this tool. The text stays in your browser.
We answer enquiries within 24 hours with price, lead time and the standards we will certify to.
Ask for an AISI 440B / UNS S44003 quotation
Send the drawing, the specification, the delivery condition and the quantity. Jiangyin Jiangnan Metal Co., Ltd. answers within 24 hours with price, lead time and the certificate we will issue.
sales@steelforgepieces.com
Drawings in PDF, STEP or DWG.
Telephone and WhatsApp
Factory address
No.1 Chengxiqiao Road, Zhouzhuang Town,
Jiangyin City, Jiangsu Province, China
What to send
Grade, specification, dimensions, quantity, delivery condition and hardness band, certificate type and required date.
Where is AISI 440B used?
Cutlery and blades
Kitchen and professional knives, scissors, industrial blades. 440B is the choice when a blade needs more edge life than 440A and more toughness and stain resistance than 440C. Wet-use kitchen knives are the classic case.
Bearings and races
Hardened balls, rolling elements, races and rings for bearings running in fresh water, steam, food or mildly corrosive media where a through-hardened stainless is required.
Valve components
Valve seats, seat rings, stems, bodies, bonnets and trim where the wear face carries the duty and the medium is mild.
Pump parts
Pump shafts, sleeves, wear rings, plungers and pivot pins in fresh water, condensate and light hydrocarbon service.
Measuring and instruments
Gauge blocks, precision instrument parts and measuring tools, where dimensional stability after sub-zero treatment is as important as hardness.
Moulds, dies and tooling
Plastic mould inserts and dies handling corrosive polymers, where a stainless tool steel is wanted rather than a conventional tool steel.
Surgical and dental instruments
Instruments that must hold an edge through repeated autoclave cycles and cleaning.
Nozzles and wear parts
Nozzles, bushings, guides and wear plates in abrasive but non-chloride service.
Two worked examples
Example 1: ring rolling versus machining a disc
Given. A finished 440B ring, 620 mm OD × 480 mm ID × 210 mm high.
Method. Net volume = π/4 × (0.620² − 0.480²) × 0.210 = 0.02540 m³. At 7,740 kg/m³ that is about 197 kg finished. Rolled as a ring with 25% stock, the forging is roughly 246 kg. Machined instead from a solid forged disc of the same outside diameter and height, the input billet is about 491 kg, so roughly 294 kg of 440B would be bought, forged, annealed and then cut away.
Result. Ring rolling halves the purchased weight on this geometry, and it also gives circumferential grain flow, which matters on a race or a seat ring. This is usually the single biggest decision on a 440B order, and it is why we ask for the finished drawing rather than a billet size.
Example 2: choosing the hardness band for a valve seat ring
Given. A seat ring in condensate service at 80 °C, moderate impact from seating, wear from throttling, and a requirement that the part not rust in a wet shutdown.
Assessment. The maximum-hardness route, austenitising near 1066 °C and tempering at 150 °C for 58 HRC, gives the best wear life and the worst impact behaviour, with roughly 9 J Izod. The seating impact argues for backing off. Tempering at 315 °C gives 54–56 HRC with better toughness, and it is still comfortably below the 425 °C line where corrosion resistance falls away.
Decision. Specify AISI 440B / UNS S44003 per ASTM A473, hardened and tempered to 54–56 HRC, temper 315 °C, hardness traverse at mid-radius, passivated per ASTM A967. If wear later proves to govern and seating impact turns out to be mild, the same drawing can be re-issued at 57–58 HRC without changing the material or the forging route.
Glossary
| Term | Meaning |
|---|---|
| AISI 440B | High-carbon martensitic stainless steel, 0.75–0.95% C and 16–18% Cr, the middle grade of the 440 family. Also UNS S44003 and SUS 440B. |
| UNS S44003 | Unified Numbering System designation for 440B. The unambiguous way to name the steel on a drawing or purchase order. |
| 1.4112 / X90CrMoV18 | European grade often cross-referenced to 440B. Higher molybdenum and a vanadium addition make it a near, not exact, equivalent. |
| Martensitic stainless steel | A stainless steel that transforms to hard martensite on quenching, so it can be hardened by heat treatment. Ferromagnetic, unlike austenitic 304 or 316. |
| Austenitising | Heating to 1010–1066 °C so carbon dissolves into austenite before quenching. Its temperature sets the balance between hardness and corrosion resistance. |
| Retained austenite | Austenite that fails to transform during the quench. It lowers hardness and transforms slowly in service, causing dimensional growth. |
| Sub-zero treatment | Cooling to about −73 °C between quench and temper to convert retained austenite and stabilise dimensions. The normal temper follows it. |
| Temper embrittlement | Loss of toughness and corrosion resistance caused by tempering in the 425–565 °C range. Avoided absolutely in this grade. |
| Ruling section | The greatest thickness heat must travel through during heat treatment. It sets soak time, not the part's overall size. |
| Grinding burn | Local re-tempering caused by grinding heat, which removes hardness and corrosion resistance at the surface and can leave residual tensile stress. |
| Passivation | Chemical treatment, usually to ASTM A967, that removes free iron and restores the passive chromium oxide film after machining and grinding. |
| EN 10204 3.1 / 3.2 | Certificate types. 3.1 is issued by the manufacturer's own independent inspection function; 3.2 is countersigned by a third party or the buyer's representative. |
| Open-die forging | Hot working between flat or simply shaped dies with the workpiece manipulated between blows. Suits one-off and small-batch parts and heavy sections. |
| Seamless rolled ring | A ring produced by piercing a billet and rolling it out on a ring mill, giving circumferential grain flow and no weld seam. |
AISI 440B frequently asked questions
What is AISI 440B stainless steel?
AISI 440B is a high-carbon martensitic stainless steel containing 0.75–0.95% carbon and 16.0–18.0% chromium, designated UNS S44003 and SUS 440B. It is hardenable by heat treatment to a maximum of 58 HRC and is used in the hardened-and-tempered condition for cutlery, bearing races, valve seats, pump parts and measuring instruments. Jiangyin Jiangnan Metal Co., Ltd. forges it to drawing in Jiangyin, Jiangsu, China.
What is the chemical composition of AISI 440B?
In weight percent: carbon 0.75–0.95, chromium 16.0–18.0, molybdenum 0.75 maximum, manganese 1.00 maximum, silicon 1.00 maximum, phosphorus 0.040 maximum, sulphur 0.030 maximum, iron balance at roughly 80%.
What hardness can AISI 440B reach?
58 HRC maximum, obtained by austenitising at 1010–1066 °C, quenching in warm oil or air, and tempering at about 148–177 °C. Tempering higher trades hardness for toughness: roughly 56–57 HRC at 205 °C, 54–56 HRC at 315 °C and 52–54 HRC at 370 °C. In the annealed condition 440B is about 223 HB, which is the machining condition, not a service condition.
Is AISI 440B the same as 1.4112 or X90CrMoV18?
No. They are near equivalents rather than identical. EN 1.4112 (X90CrMoV18) runs 0.85–0.95% carbon, 17–19% chromium and 0.9–1.3% molybdenum, and adds 0.07–0.12% vanadium. AISI 440B caps molybdenum at 0.75% and specifies no vanadium. A heat can meet one specification and fail the other, so order to the designation your drawing actually states, or request dual certification before the heat is melted.
Is SUS 440B the same as AISI 440B?
Yes. SUS 440B in JIS G4303 carries the same 0.75–0.95% carbon, 16–18% chromium and 0.75% maximum molybdenum as AISI 440B / UNS S44003. Material can be certified to both designations on the same certificate.
What is the difference between 440A, 440B and 440C?
Only the carbon content, and everything that follows from it. 440A carries 0.60–0.75% carbon and reaches about 56 HRC with the best corrosion resistance of the three. 440B carries 0.75–0.95% and reaches about 58 HRC. 440C carries 0.95–1.20% and reaches about 60 HRC with the highest wear resistance, the lowest toughness and the lowest corrosion resistance. All three carry 16–18% chromium.
Is AISI 440B magnetic?
Yes. 440B is ferromagnetic in every condition, annealed, hardened or tempered, because it is a martensitic stainless steel rather than an austenitic one. Hardened 440B even makes a fair permanent magnet. Do not specify it where a non-magnetic part is required.
Does AISI 440B rust?
It can. 440B has corrosion resistance broadly similar to Type 410: adequate in mild atmospheres, fresh water, steam, ammonia, many petroleum products and organic media, and in some mild acids. It is not suitable for seawater, chlorides or working acid concentrations. Corrosion resistance is only obtained in the hardened-and-tempered condition with the temper below about 425 °C, on a clean, passivated surface.
What is the density of AISI 440B?
7.74 g/cm³, or 0.280 lb/in³. The forging weight calculator on this page uses that figure. The published melting point is 1482 °C (2700 °F).
How is AISI 440B forged?
Preheat slowly to 760–816 °C, then heat to 1038–1177 °C and soak through the section at roughly 30 minutes per 25 mm. Forge with frequent reheats and aim for at least 4:1 reduction to break up the as-cast carbide network. Do not forge below 927 °C. Cool in the furnace or in warm dry lime or ash, then full anneal at 843–871 °C immediately.
Why must 440B be annealed immediately after forging?
Because 440B air-hardens. A forging left to cool on the shop floor transforms to untempered martensite and can crack hours later without any further handling. Controlled cooling followed by a full anneal at 843–871 °C with a slow furnace cool is what prevents that, and it should be written on the purchase order if a subcontractor does the forging.
Can AISI 440B be welded?
Welding is not recommended. The grade hardens in air, so the heat-affected zone becomes untempered martensite and cracks. If welding is unavoidable, preheat to about 260 °C, then apply a post-weld treatment at 732–760 °C for about 6 hours with a slow furnace cool. Austenitic 309 or 310 filler gives a softer, more ductile weld. A welded part must be re-hardened and re-tempered to be regarded as meeting the grade.
Can AISI 440B be machined after hardening?
Practically, no. Above about 50 HRC machining is finished and grinding takes over. All machining is done in the fully annealed condition at roughly 223 HB, using carbide or ceramic tooling with chip breakers, and grinding stock is left on tolerance features for finishing after heat treatment.
What temperature is 440B tempered at?
Between 150 °C and 370 °C, for at least one hour per 25 mm of section and never less than two hours, applied immediately after quenching. Tempering at 148–177 °C gives the maximum 58 HRC. Higher temperatures inside that range trade hardness for toughness.
Why should 440B never be tempered between 425 °C and 565 °C?
That range causes temper embrittlement and a marked loss of corrosion resistance at the same time, so the part becomes both more brittle and less stainless. Tempering between 600 °C and 675 °C is a separate operation used to soften a part to roughly 35–45 HRC so it can be machined again; it is not a service condition for this grade.
Is AISI 440B good for knives?
Yes, in the right place. 440B holds an edge better than 440A and is tougher and more stain resistant than 440C, which makes it a good choice for kitchen and professional knives used wet, and for scissors and industrial blades. For a hard-use blade where edge retention dominates, 440C is normally preferred; for maximum corrosion resistance, 440A.
What standards cover AISI 440B forgings?
ASTM A473 for stainless steel forgings, which is the correct citation for a forged part, with ASTM A276 for bars and shapes, ASTM A314 for billets and bars for forging and ASTM A580 for wire. JIS G4303 covers SUS 440B, EN 10088-3 covers the near-equivalent 1.4112, and GB/T 1220 covers 9Cr18MoV. Certificates are issued to EN 10204 3.1 as standard and 3.2 with third-party witness.
What sizes of 440B forgings can Jiangyin Jiangnan Metal make?
In this grade, seamless rolled rings 200–1,500 mm outside diameter with a 25 mm minimum wall, discs to 1,000 mm diameter, shafts to 3,000 mm length, bar from Ø40 mm to Ø400 mm and single pieces to 2,000 kg. The plant envelope across all grades is larger, with rings to 2,500 mm, shafts to 8 m and single pieces to 8,000 kg, but high-carbon martensitic stainless is limited by crack sensitivity and billet availability. Send the drawing and we confirm size, weight and lead time before quoting.
What is the lead time for AISI 440B forgings?
Eight to fourteen weeks is typical, because the heat is bought against your specification rather than pulled from stock. Third-party witnessed release adds one to two weeks. Small quantities are consolidated onto a larger heat, which affects both price and schedule, so state quantity and required date at enquiry stage.
Do you supply 9Cr18MoV or 9Cr18 to Chinese standards?
Yes. 9Cr18MoV and 9Cr18 in GB/T 1220 are the nearest Chinese grades, with 9Cr18MoV corresponding more closely to EN 1.4112 than to AISI 440B. State the governing GB standard and any additional test requirements on the order and Jiangyin Jiangnan Metal Co., Ltd. will certify to it, including cross-certification against UNS S44003 where a project needs both callouts.
References and data sources
- ASTM A473, Standard Specification for Stainless Steel Forgings. The product-form specification for forged UNS S44003.
- ASTM A276/A276M, Standard Specification for Stainless Steel Bars and Shapes; ASTM A314 billets and bars for forging; ASTM A484 general requirements; ASTM A580 wire.
- JIS G4303, Stainless steel bars: SUS 440B.
- EN 10088-3, Stainless steels: technical delivery conditions for semi-finished products, bars and rods, grade 1.4112 / X90CrMoV18.
- GB/T 1220, Stainless steel bars: 9Cr18 and 9Cr18MoV.
- Carpenter Technology, CarTech 440B stainless technical datasheet. Annealing, hardening, tempering, hot-working and corrosion guidance.
- AZoM, Stainless Steel Grade 440B (UNS S44003) datasheet. Composition, physical properties and heat-treatment summary.
- ASM Handbook, Volume 1, Properties and Selection: Irons, Steels and High-Performance Alloys, ASM International. Martensitic stainless steels.
- ASM Handbook, Volume 14A, Metalworking: Bulk Forming, ASM International. Forging of stainless steels.
- ASTM E18 hardness, E8/E8M tensile, E23 impact, A388 and EN 10228-3 ultrasonic examination, E165 penetrant examination, A967 passivation.
- EN 10204, Metallic products: types of inspection documents, CEN.
Standards are cited by number; always work to the revision in force at your contract date. Property values on this page are published typical figures for screening and are not design allowables. Test results on our certificates are independent and traceable to calibrated equipment.
About the manufacturer, and how to cite this page
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, with 460 employees including 9 senior and 32 intermediate engineers. The plant runs 1 t to 9 t open-die hammers, 4,500 t and 5,000 t hydraulic presses and radial-axial ring mills with a 6 m ring line, with in-house heat treatment, machining, mechanical testing and non-destructive examination. Alongside AISI 440B / UNS S44003 the company forges carbon, alloy and tool steels, the martensitic, precipitation-hardening and duplex stainless families, and nickel and cobalt high-temperature alloys. Quality management is certified to ISO 9001:2015; material is supplied with EN 10204 3.1 certification as standard and 3.2 with third-party witness on request.
Cite this page
Jiangyin Jiangnan Metal Co., Ltd. (2026). AISI 440B / UNS S44003 forgings: composition, heat treatment and ordering guide. Updated 13 September 2026. Retrieved from https://www.steelforgepieces.com/Alloy-Steel/AISI-440B.html
Contact for technical questions or a quotation: Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China · 0086-189-2135-9659 · sales@steelforgepieces.com · WhatsApp
AISI 440B, UNS S44003 and SUS 440B are generic public designations, not trademarks. Material produced by Jiangyin Jiangnan Metal Co., Ltd. is correctly described as AISI 440B / UNS S44003 forged to ASTM A473 or the specification stated on the order.