What is 1.4903 steel?
1.4903 is the EN material number for X10CrMoVNb9-1, a martensitic creep-resistant steel based on 9 % chromium and 1 % molybdenum. It is known internationally as Grade 91, and in North American practice as P91 for pipe, T91 for tube and F91 for forgings.
Grade 91 differs from ordinary 9Cr-1Mo steel by the addition of vanadium (0.18 to 0.25 %), niobium (0.06 to 0.10 %) and controlled nitrogen (0.03 to 0.07 %). During tempering these elements form fine, thermally stable carbo-nitrides, principally MX particles and M23C6 carbides, which pin dislocations and sub-grain boundaries. The 100,000-hour creep rupture strength is roughly double that of unmodified 9Cr-1Mo at the same temperature.
Higher creep strength allows thinner pipe walls, lighter headers and fewer welds in supercritical and ultra-supercritical plant. Grade 91 has been the standard material for main steam lines, hot reheat lines and boiler headers since the 1980s, and is specified today across power generation, petrochemical refining and oil and gas pressure systems.
The grade demands process discipline. Its properties depend entirely on correct heat treatment and correct welding. An incorrect tempering temperature or a missed post-weld heat treatment produces material that performs worse than the cheaper steel it replaced. Forging source and certification therefore carry more weight with Grade 91 than with most alloy steels.
Is 1.4903 a stainless steel?
No. This is the most common misconception about the grade, and it comes from the numbering system rather than the metallurgy. EN material numbers beginning 1.4xxx are conventionally associated with stainless steels, so 1.4903 is frequently mislabelled as one, including by several materials databases.
EN 10020 defines a stainless steel as containing a minimum of 10.5 % chromium. 1.4903 contains 8.0 to 9.5 %. It is classified as a high-alloy creep-resistant steel. In the ISO/TR 15608 welding groups it sits in group 6.4 with other martensitic Cr-Mo-V grades, not with the stainless families.
The difference matters on receipt of goods. 1.4903 has good oxidation resistance at high temperature in service, but almost no corrosion resistance at ambient temperature. Bars and rings develop surface rust in humid storage or during sea freight unless they are oiled and sealed. We ship 1.4903 with rust-preventive coating and moisture-barrier packing as standard.
Chemical composition of 1.4903
| C | Si | Mn | P | S | Cr | Mo | Ni | V | Nb | N | Al |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 0.08–0.12 | max 0.50 | 0.30–0.60 | max 0.025 | max 0.015 | 8.0–9.5 | 0.85–1.05 | max 0.40 | 0.18–0.25 | 0.06–0.10 | 0.03–0.07 | max 0.030 |
Mechanical properties of 1.4903
Tensile and yield strength by section thickness
| Property | up to 60 mm | 60 to 150 mm | 150 to 250 mm |
|---|---|---|---|
| Tensile strength Rm (+NT) | 580–760 (84–110 ksi) | 550–730 (80–106 ksi) | 520–700 (75–102 ksi) |
| Tensile strength Rm (+QT) | 620–850 (90–123 ksi) | ||
| Min. yield strength ReH | 445 (65 ksi) | 435 (63 ksi) | |
| 0.2 % proof strength Rp0.2 (+QT) | 450 (65 ksi) | ||
| Min. elongation at fracture A | 18–20 % | ||
| Typical hardness | 190–250 HB | ||
Charpy impact energy
| Orientation | −20 °C (−4 °F) | 0 °C (32 °F) | +20 °C (68 °F) |
|---|---|---|---|
| Transverse (+NT) | 27 J | 34 J | 27–40 J |
| Longitudinal (+NT) | — | — | 40 J |
Physical properties of 1.4903
| Property | 20 °C | 400 °C | 600 °C |
|---|---|---|---|
| Density | 7.76 g/cm³ (0.280 lb/in³) | 7.68 g/cm³ | 7.60 g/cm³ |
| Modulus of elasticity | 218 GPa (31.6 × 10⁶ psi) | 196 GPa | 168 GPa |
| Thermal conductivity | 26 W/(m·K) | 29 W/(m·K) | 29 W/(m·K) |
| Specific heat capacity | 440 J/(kg·K) | 540 J/(kg·K) | 680 J/(kg·K) |
| Mean thermal expansion from 20 °C | — | 11.6 × 10⁻⁶/K | 12.3 × 10⁻⁶/K |
| Electrical resistivity | 0.60 µΩ·m | 0.90 µΩ·m | 1.10 µΩ·m |
Forging and heat treatment of 1.4903
Every mechanical property quoted above depends on correct heat treatment. Grade 91 has a narrow processing window, and a mistake inside it cannot be found by routine inspection afterwards.
| Operation | Temperature | Cooling |
|---|---|---|
| Soaking before forging | 1050 – 1100 °C (1920 – 2010 °F) | — |
| Forging range | 1100 down to 850 °C (2010 to 1560 °F) | Slow or furnace |
| Normalising (+N) | 1040 – 1080 °C (1900 – 1975 °F) | Air |
| Tempering (+NT) | 730 – 780 °C (1345 – 1435 °F) | Air |
| Quench and temper (+QT) | 1040 – 1100 °C, oil quench | Then temper 730 – 780 °C |
| Stress relief after welding | 740 – 770 °C (1365 – 1420 °F) | Slow, controlled |
Welding 1.4903 and post-weld heat treatment
1.4903 can be welded with all common arc processes, including GTAW, SMAW, GMAW, SAW and FCAW, using matching 9Cr-1Mo-V consumables. Gas fusion welding is not suitable. The grade does not tolerate a loose procedure.
- Preheat 200 to 250 °C, maintained throughout
- Interpass temperature controlled, typically 300 °C maximum
- Cool to 80 to 100 °C after welding, before PWHT
- PWHT 740 to 770 °C, hold per thickness
- Matching filler: AWS E9015-B9 or ER90S-B9
- Strict low-hydrogen practice, consumables kept baked
The cool-down step before PWHT is the one most often skipped. If the joint goes straight from welding into the tempering furnace, retained austenite has not yet transformed to martensite, and it transforms afterwards instead. That leaves untempered martensite in a joint which has already been signed off. Missing or incorrect PWHT is the leading documented cause of premature Grade 91 failures in operating plant.
Machining 1.4903
Machinability is comparable to other quenched and tempered chromium steels at similar hardness, and is governed almost entirely by the delivery condition. At 190 to 250 HB, expect cutting speeds of 30 to 50 m/min with carbide tooling, rigid clamping and flood coolant. The alloy work-hardens, and the heat has to leave through the chip rather than the tool.
We supply 1.4903 forgings as-forged with machining allowance, rough-machined to your envelope, or fully finish-machined to drawing. For rings and discs, rough machining before final heat treatment usually gives the best dimensional stability.
1.4903 equivalent grades and cross-reference
1.4903 belongs to the Grade 91 family. The designation changes with product form and standards body, but the composition is essentially the same across all of them.
| Standard or system | Designation | Product form |
|---|---|---|
| EN material number | 1.4903 | All forms |
| EN chemical designation | X10CrMoVNb9-1 | All forms |
| EN 10222-2 | X10CrMoVNb9-1 | Forgings for pressure purposes |
| UNS | K90901 | All forms |
| ASTM A182 / ASME SA-182 | F91 | Forgings, flanges, valve parts |
| ASTM A335 / ASME SA-335 | P91 | Seamless pipe |
| ASTM A213 / ASME SA-213 | T91 | Seamless tube |
| ASTM A387 / ASME SA-387 | Grade 91 | Plate |
| ASTM A234 | WP91 | Butt-weld fittings |
| GB (China) | 10Cr9Mo1VNbN | All forms |
| JIS (Japan) | STPA 28 / SFVAF 91 | Pipe / forgings |
| Common industry name | Modified 9Cr-1Mo-V, Grade 91 | — |
Forged shapes we supply in 1.4903
Round bars and rods
Solid round, square, flat and hexagonal forged bar
Hollow bars and sleeves
Bushings, shells, cylinders, forged tube blanks
Seamless rolled rings
Radial-axial rolled and open-die expanded rings
Flanges and discs
Forged flanges, blanks, discs, plates and blocks
Valve components
Bodies, bonnets, seats, seat rings, stems, wedges
Pipe fittings
Tees, Y-pieces, wyes, concentric and eccentric reducers
Custom forgings
Any profile forged to your 2D drawing or 3D model
Our 1.4903 forging capability
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu, inside the Yangtze River Delta forging cluster and about two hours from Shanghai port. We forge 1.4903 to drawing rather than selling from a standing catalogue.
- Process
- Open-die forging, seamless ring rolling, upsetting and drawing
- Machining
- As-forged with allowance, rough-machined, or finish-machined to drawing
- Heat treatment
- Normalising, tempering and quench-and-temper with recorded furnace charts
- Testing
- Chemical analysis, tensile, Charpy impact, hardness, ultrasonic examination to EN 10228-3 or ASTM A388, PMI, grain size, macro and micro examination
- Certification
- EN 10204 3.1 as standard, 3.2 with third-party inspection on request
- Export
- Seaworthy packing with rust prevention, shipped worldwide
- Quotation
- Returned within 24 hours on working days
- Factory address
- No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
- Contact
- +86 189 2135 9659 · sales@steelforgepieces.com
Applications of 1.4903 / P91 forgings
- Steam turbine rotors, casings and diaphragms
- High-pressure boiler headers and drums
- Main steam and hot reheat piping components
- Heat recovery steam generators (HRSG)
- Superheater and reheater collector components
- Petrochemical pressure vessels and reactor piping
- Valve bodies, bonnets and pressure-retaining parts
- Refinery furnace and transfer line components
- Supercritical and ultra-supercritical plant fittings
How to order 1.4903 forgings
- Send the drawing or dimensions Email a 2D drawing, 3D model or rough dimensions to sales@steelforgepieces.com. Without a drawing, send outside diameter, inside diameter, length or thickness, and quantity.
- State the standard and delivery condition Confirm EN 10222-2 X10CrMoVNb9-1 or ASTM A182 F91, and whether you need +NT or +QT.
- Confirm testing and certification Specify EN 10204 3.1 or 3.2, plus any ultrasonic examination, PMI, hardness survey or third-party inspection.
- Receive the quotation You get unit price, forging weight, lead time and Incoterms within 24 hours on working days.
Frequently asked questions about 1.4903
Is 1.4903 a stainless steel?
No. 1.4903 contains 8.0 to 9.5 % chromium, below the 10.5 % minimum that defines a stainless steel under EN 10020. It is a high-alloy creep-resistant steel, despite the 1.4xxx material number normally associated with stainless grades. It offers oxidation resistance at high temperature but rusts in humid ambient conditions.
What is the ASTM equivalent of 1.4903?
ASTM Grade 91, UNS K90901. By product form: A182 F91 for forgings, flanges and valve parts; A335 P91 for seamless pipe; A213 T91 for seamless tube; A387 Grade 91 for plate; A234 WP91 for butt-weld fittings. For forged components, specify A182 F91.
What is the tensile strength of 1.4903?
Normalised and tempered to EN 10302-2008: Rm is 580 to 760 MPa (84 to 110 ksi) up to 60 mm, 550 to 730 MPa for 60 to 150 mm, and 520 to 700 MPa for 150 to 250 mm. Quenched and tempered: 620 to 850 MPa. Minimum yield strength ReH is 445 MPa up to 60 mm and 435 MPa from 60 to 250 mm. Minimum elongation is 18 to 20 %.
What is the maximum service temperature of 1.4903?
Around 650 °C (1200 °F) continuous. Most power plant applications run it at 540 to 600 °C, where 100,000-hour creep rupture strength governs the design rather than room-temperature tensile strength. Above roughly 620 °C the creep strength falls away and P92 (1.4901) is usually specified instead.
What heat treatment is applied to 1.4903 forgings?
Soak at 1050 to 1100 °C, forge between 1100 °C and 850 °C, normalise at 1040 to 1080 °C with air cooling, then temper at 730 to 780 °C with air cooling. Tempering must stay below the Ac1 point, otherwise fresh untempered martensite forms on cooling and toughness collapses. Typical hardness after correct treatment is 190 to 250 HB.
Can 1.4903 be welded?
Yes, with all common arc processes using matching 9Cr-1Mo-V consumables, but the procedure must be tight. Preheat 200 to 250 °C, control interpass temperature, cool the joint to 80 to 100 °C so it transforms fully to martensite, then apply PWHT at 740 to 770 °C. Missing or incorrect PWHT is the leading cause of premature Grade 91 failures in service.
What is the difference between P91 and P92?
P92 (EN 1.4901, X10CrWMoVNb9-2) adds 1.5 to 2.0 % tungsten and boron while cutting molybdenum, raising 100,000-hour creep rupture strength by roughly 25 to 30 % over P91 at 600 °C. That allows thinner walls in ultra-supercritical plant. P91 stays cheaper, more available and more forgiving to weld, so it remains the default at 540 to 600 °C.
Does 1.4903 rust?
Yes. At 8.0 to 9.5 % chromium it has no meaningful ambient corrosion resistance and surface-rusts in humid storage or sea freight. Its chromium buys oxidation resistance at operating temperature, not corrosion protection at room temperature. We ship with rust-preventive oil and sealed moisture-barrier packing.
What forged shapes are available in 1.4903?
Round, square, flat and hexagonal bars; hollow bars, sleeves and bushings; seamless rolled rings; flanges, discs, blanks and plates; valve bodies, bonnets, seats and stems; and fittings including tees, Y-pieces and reducers. Custom profiles are forged to drawing.
Should I specify P91 or F91 for a forged part?
F91. ASTM A182 F91 is the specification written for forgings, flanges, forged fittings and valve parts. A335 P91 covers seamless pipe and carries different testing and dimensional requirements. Under EN, the matching forging specification is EN 10222-2 X10CrMoVNb9-1. Ordering a forging against a pipe specification is a common cause of certificate rejection at incoming inspection.
What certificates are supplied with 1.4903 forgings?
EN 10204 3.1 material certificates are supplied as standard, covering heat number, chemical analysis, mechanical test results and heat-treatment records. EN 10204 3.2 with third-party inspection is available on request, as are ultrasonic examination reports to EN 10228-3 or ASTM A388, PMI reports and hardness surveys.
Who supplies 1.4903 forgings?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, producing 1.4903 (X10CrMoVNb9-1 / P91) forgings to drawing for export worldwide. Contact +86 189 2135 9659 or sales@steelforgepieces.com. Quotations within 24 hours on working days.
Standards referenced on this page
- EN 10302-2008, Creep resisting steels, nickel and cobalt alloys
- EN 10222-2, Steel forgings for pressure purposes, Part 2: ferritic and martensitic steels with specified elevated temperature properties
- EN 10216-2:2014, Seamless steel tubes for pressure purposes, Part 2
- EN 10020, Definition and classification of grades of steel
- EN 10204, Metallic products, types of inspection documents
- EN 10228-3, Non-destructive testing of steel forgings, ultrasonic testing of ferritic or martensitic steel forgings
- ASTM A182/A182M, Forged or rolled alloy and stainless steel pipe flanges, forged fittings, valves and parts for high-temperature service
- ASTM A335/A335M, Seamless ferritic alloy-steel pipe for high-temperature service
- ASTM A213/A213M, Seamless ferritic and austenitic alloy-steel boiler, superheater and heat-exchanger tubes
Page last reviewed 3 September 2026 by Jiangyin Jiangnan Metal Co., Ltd.