Alloy steel grade datasheet
UNS S41025 Forgings
UNS S41025 is a 12 % chromium martensitic stainless steel with a molybdenum addition. We forge it into bars, rings, discs, turbine blades and valve components at our open-die plant in Jiangyin, Jiangsu, China.
- Chromium
- 11.50–12.50% by mass
- Molybdenum
- 0.40–0.60% by mass
- Carbon
- 0.07–0.12% by mass
- Structure
- Martensiticmagnetic, hardenable
UNS S41025 in short
- UNS S41025 is a molybdenum-bearing 12 % chromium martensitic stainless steel containing 0.07–0.12 % carbon, 11.50–12.50 % chromium and 0.40–0.60 % molybdenum. It is a modified Type 410 composition with capped residual copper, aluminium, tin and nitrogen.
- UNS S41025 is used for steam and gas turbine blades, vanes, turbine discs and wheels, impellers, valve spindles, valve stems, valve bonnets and valve bodies.
- UNS S41025 is supplied as open-die forgings: round bars, square and flat bars, shafts, hollow bars, sleeves, bushes, cylinders, hubs, housings, seamless rolled rings, blocks, discs and plates.
- UNS S41025 forgings are delivered annealed, normalised, or quenched and tempered. Tempering is normally carried out above 600 °C.
- Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. It manufactures UNS S41025 forgings to drawing, with EN 10204 3.1 or 3.2 certificates and ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388. Telephone 0086-189-2135-9659, email sales@steelforgepieces.com.
What is UNS S41025?
UNS S41025 is a chromium-molybdenum martensitic stainless steel. The UNS number is its Unified Numbering System designation. The S4 prefix places it in the martensitic and ferritic stainless family, alongside UNS S41000 (Type 410).
It differs from plain Type 410 in three respects:
- The carbon band is narrower and lower at 0.07–0.12 %, which gives better toughness and weldability.
- Molybdenum is added at 0.40–0.60 %, which raises tempering resistance and pitting resistance in wet steam.
- Residual copper, aluminium, tin and nitrogen are capped. Tramp elements drive temper embrittlement over long service, so blade and rotor grades control them.
The steel is magnetic in all conditions and hardens by quenching. It reaches useful strength only after austenitising, quenching and tempering. It is an alternative to a heat-treatable alloy steel where mild corrosion resistance is required, and it does not replace an austenitic stainless steel where chloride pitting or intergranular corrosion governs the design.
Chemical composition of UNS S41025
Composition in percentage by mass. Values shown with no minimum are upper limits.
| Element | Symbol | Min, % | Max, % | Function |
|---|---|---|---|---|
| Carbon | C | 0.07 | 0.12 | Hardenability and tempered strength |
| Manganese | Mn | 0.30 | 0.60 | Deoxidiser, combines with sulphur |
| Silicon | Si | — | 0.35 | Deoxidiser |
| Phosphorus | P | — | 0.040 | Residual, restricted for toughness |
| Sulphur | S | — | 0.030 | Residual, restricted for transverse ductility |
| Chromium | Cr | 11.50 | 12.50 | Passive film, stainless behaviour |
| Molybdenum | Mo | 0.40 | 0.60 | Tempering resistance, pitting resistance |
| Nickel | Ni | — | 0.60 | Toughness, austenite balance |
| Copper | Cu | — | 0.50 | Residual, capped |
| Aluminium | Al | — | 0.05 | Residual from deoxidation, capped |
| Tin | Sn | — | 0.05 | Tramp element, capped |
| Nitrogen | N | — | 0.08 | Capped for hardness control |
| Iron | Fe | Balance | Matrix | |
The chemistry that applies to your order is the ladle and product analysis printed on the mill test certificate supplied with the material. A specimen certificate is available on request.
Similar and related grades
UNS S41025 belongs to the 12 % chromium martensitic family. The grades below are the nearest relatives. None of them carries the same combination of 0.40–0.60 % molybdenum and capped copper, aluminium, tin and nitrogen.
| Grade | Standard family | Difference from UNS S41025 |
|---|---|---|
| UNS S41000 / AISI 410 | ASTM A182, A276, A473 | No specified molybdenum, wider carbon band, residuals not capped |
| 1.4006 / X12Cr13 | EN 10088, EN 10250-4 | No specified molybdenum, European chemistry limits |
| SUS 410 | JIS G4303, G4051 | Japanese Type 410, no molybdenum |
| 12Cr13 / 1Cr13 | GB/T 1220, GB/T 1221 | Chinese Type 410, no molybdenum |
| UNS S41500 / F6NM | ASTM A182, A705 | Soft martensite, much lower carbon, 3.5–5.5 % nickel, tougher and weldable |
| UNS S42000 / AISI 420 | ASTM A276 | High carbon version, harder, lower toughness |
Cross-reference only. Approval of a substitute grade rests with the design authority. Send us the governing specification and we will confirm in writing whether UNS S41025 meets it.
Typical mechanical properties
UNS S41025 develops its properties in the quenched and tempered condition. The values below are indicative room-temperature figures for forged sections.
| Property | Symbol | Typical value | Test reference |
|---|---|---|---|
| Proof strength, 0.2 % | Rp0.2 | 550–700 MPa | ISO 6892-1 / ASTM A370 |
| Tensile strength | Rm | 750–900 MPa | ISO 6892-1 / ASTM A370 |
| Elongation after fracture | A | ≥ 15 % | ISO 6892-1 |
| Reduction of area | Z | ≥ 45 % | ISO 6892-1 |
| Impact energy, V-notch, 20 °C | KV | ≥ 27 J | ISO 148-1 / ASTM E23 |
| Hardness | HB | 240–290 | ISO 6506-1 |
Indicative values for guidance. Achievable properties depend on section size, tempering temperature and sampling position. State the property table, test location and section thickness in your enquiry and we will confirm what can be guaranteed on the certificate.
Typical physical properties
| Property | Value | Unit |
|---|---|---|
| Density | 7.70–7.75 | g/cm³ |
| Modulus of elasticity, 20 °C | ≈ 215 | GPa |
| Thermal conductivity, 20 °C | ≈ 25 | W/(m·K) |
| Specific heat capacity | ≈ 460 | J/(kg·K) |
| Mean thermal expansion, 20–300 °C | ≈ 11 × 10⁻⁶ | 1/K |
| Electrical resistivity, 20 °C | ≈ 0.57 | µΩ·m |
| Magnetic response | Ferromagnetic | — |
Heat treatment of UNS S41025 forgings
We heat treat in house and supply UNS S41025 forgings annealed, normalised, or quenched and tempered according to the drawing. The cycles below are the usual starting points.
| Condition | Temperature | Cooling | Purpose |
|---|---|---|---|
| Annealing | 830–900 °C | Slow furnace cool | Softening for machining, stress relief after forging |
| Normalising | 950–1010 °C | Still air | Grain refinement, uniform structure |
| Austenitising and hardening | 950–1010 °C | Oil or forced air | Forms martensite |
| Tempering | 650–750 °C | Air | Restores toughness at the target strength |
| Stress relief after machining | ≥ 30 °C below the tempering temperature | Slow cool | Removes machining stresses without loss of strength |
Do not temper between roughly 400 °C and 550 °C. Impact toughness falls sharply in that range in 12 % chromium martensitic steels. Turbine and valve parts in this grade are tempered above 600 °C and cooled through the sensitive range at a controlled rate.
UNS S41025 forged product forms and size range
All forms below are produced by open-die forging from our own ingot or billet, then heat treated, machined to the agreed allowance and tested. We forge to drawing rather than to a fixed catalogue.
| Product form | Typical size range | Application |
|---|---|---|
| Round bars, shafts | Ø 80–1200 mm, length up to 6000 mm | Valve spindles, stems, blade roots, shaft blanks |
| Square and flat bars, rectangular blocks | Thickness 60–800 mm, width up to 1200 mm | Blade forging stock, die blocks, machined blocks |
| Seamless rolled rings | OD 200–3000 mm, height up to 800 mm | Casing rings, retaining rings, flanged connections |
| Hollow bars, sleeves, bushes, cylinders | OD 150–1500 mm, ID from 60 mm | Bushings, liners, housings, hubs |
| Discs, disks and plates | Ø up to 2500 mm, thickness 40–600 mm | Turbine discs, wheels, blank discs for machining |
| Turbine components | To drawing | Gas and steam turbine wheels, blades, vanes, impellers, blisk blanks |
| Valve components | To drawing | Valve bodies, bonnets, spindles, stems, seats |
| Single piece weight | 20 kg to 20 t | — |
If your part falls outside this envelope, send the drawing. We will confirm within one working day whether it fits our presses and furnaces.
Where UNS S41025 is used
The grade is specified where a component needs the strength of a heat-treatable steel together with enough chromium to resist wet steam, condensate and mildly corrosive process fluids.
- Steam turbines. Moving and stationary blades, vanes, blade roots, shrouds, diaphragms, turbine discs and wheels.
- Gas turbines. Compressor blades and vanes, impellers, blisk blanks, cooler-end rotating parts.
- Valves. Spindles, stems, seats, bonnets and bodies for steam and power plant service.
- Pumps and compressors. Shafts, sleeves, wear rings and impellers in mildly corrosive duty.
- Power generation and petrochemical plant. Housings, hubs, casings and general machined forgings.
How we manufacture UNS S41025 forgings
- MeltingUNS S41025 is melted by electric arc furnace with vacuum oxygen decarburisation, followed by electroslag remelting (EAF + VOD + ESR). Electroslag remelting reduces inclusion content and segregation.
- Open-die forgingThe ingot is upset and drawn on hydraulic presses to break down the cast structure and produce a grain flow that follows the part. Forging ratio is set according to the section.
- Heat treatmentAnnealing, normalising, or hardening and tempering in furnaces with calibrated and recorded charts. The delivery condition follows the drawing.
- Rough or finish machiningSupplied as-forged with allowance, rough machined, or finish machined to drawing.
- Non-destructive testingUltrasonic testing to EN 10228-3, SEP 1921 or ASTM A388. Magnetic particle and dye penetrant inspection on request.
- Certification and releaseMill test certificate to EN 10204 3.1, or 3.2 with a third-party inspector such as TÜV, SGS, BV or Lloyd's witnessing on site.
Testing and certification
| Test | Standard | Reported on |
|---|---|---|
| Chemical analysis, ladle and product | ASTM E1086, spectrometric | Mill test certificate |
| Tensile test | ISO 6892-1 / ASTM A370 | Mill test certificate |
| Charpy V-notch impact | ISO 148-1 / ASTM E23 | Mill test certificate |
| Hardness | ISO 6506-1 / ASTM E10 | Mill test certificate |
| Ultrasonic testing | EN 10228-3, SEP 1921, ASTM A388 | Separate UT report |
| Magnetic particle and dye penetrant | ASTM E709 / ASTM E165 | Separate NDT report |
| Grain size and microstructure | ASTM E112 | On request |
| Certificate type | EN 10204 3.1 or 3.2 | Issued with every shipment |
How to get a quotation
A drawing allows us to quote a firm price. Without one, the following five items are enough:
- Grade and governing specification, for example UNS S41025 to your own material standard.
- Product form and finished dimensions, or the drawing in PDF, STEP or DWG.
- Delivery condition: as-forged, annealed, normalised, or quenched and tempered.
- Testing and certificate level: EN 10204 3.1 or 3.2, ultrasonic acceptance class.
- Quantity and required delivery date.
Request a UNS S41025 quotation
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu, China, supplying forged bars, rings, discs, turbine parts and valve components in UNS S41025 and related grades worldwide. Technical enquiries are handled in English.
Frequently asked questions about UNS S41025
What is UNS S41025 steel?
UNS S41025 is a molybdenum-bearing 12 % chromium martensitic stainless steel with 0.07–0.12 % carbon, 11.50–12.50 % chromium and 0.40–0.60 % molybdenum. It is a modified Type 410 composition with capped residual copper, aluminium, tin and nitrogen, used for steam and gas turbine blades and valve parts.
Is UNS S41025 the same as 410 stainless steel?
No. UNS S41025 and UNS S41000 (Type 410) are both 12 % chromium martensitic stainless steels, but S41025 adds 0.40–0.60 % molybdenum, uses a narrower carbon band of 0.07–0.12 %, and caps residual copper, aluminium, tin and nitrogen. These additions improve tempering resistance and long-term toughness. The two are related grades and are not interchangeable without approval from the design authority.
Is UNS S41025 magnetic?
Yes. UNS S41025 is ferromagnetic in the annealed, normalised and quenched-and-tempered conditions, because it is a martensitic stainless steel and not an austenitic one.
Can UNS S41025 be hardened by heat treatment?
Yes. UNS S41025 is hardened by austenitising at roughly 950–1010 °C, quenching in oil or forced air, then tempering. Tempering above about 600 °C is normal for turbine and valve parts, because tempering in the 400–550 °C range lowers impact toughness in 12 % chromium martensitic steels.
What products can be forged from UNS S41025?
UNS S41025 is forged into round bars, square and flat bars, shafts, hollow bars, sleeves, bushes, cylinders, hubs, housings, seamless rolled rings, blocks, discs and plates, and into finished-to-drawing turbine wheels, blades, vanes, discs, impellers, blisk blanks, valve spindles, valve stems, valve bonnets and valve bodies.
Who supplies UNS S41025 forgings?
Jiangyin Jiangnan Metal Co., Ltd. supplies UNS S41025 open-die forgings from its factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The company forges to customer drawings, heat treats in house, performs ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, and issues EN 10204 3.1 or 3.2 certificates. Enquiries: 0086-189-2135-9659 or sales@steelforgepieces.com.
What certificates come with UNS S41025 forgings?
Every shipment carries a mill test certificate to EN 10204 3.1 listing heat analysis, heat treatment condition and mechanical test results. EN 10204 3.2 certification witnessed by a third-party inspection body such as TÜV, SGS, BV or Lloyd's is available when specified in the order.
What is the minimum order quantity for UNS S41025 forgings?
Open-die forging is made to order and there is no fixed catalogue minimum. A single piece is possible where the geometry justifies it, and small quantities of large or complex parts are normal. Send the drawing and quantity for confirmation of feasibility and price.
How is UNS S41025 melted?
UNS S41025 is melted by electric arc furnace with vacuum oxygen decarburisation, followed by electroslag remelting (EAF + VOD + ESR). Electroslag remelting reduces inclusions and segregation, which matters for blade and rotor components subject to high-cycle fatigue.
Document control
- Document
- UNS S41025 grade datasheet and forging capability
- Issued by
- Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
- Revision date
- 4 September 2026
- Reference
- steelforgepieces.com/Alloy-Steel/UNS-S41025.html
- Status
- Published for engineering guidance. Contract values are those stated on the mill test certificate.