---
title: "1.4903 Forgings (X10CrMoVNb9-1 / P91) — Bars, Rings, Flanges"
description: "1.4903 (X10CrMoVNb9-1 / P91) open-die forgings from Jiangyin Jiangnan Metal: bars, rolled rings, flanges, valve parts. EN 10222-2, ASTM A182 F91."
canonical: "https://www.steelforgepieces.com/Alloy-Steel/1.4903.html"
manufacturer: "Jiangyin Jiangnan Metal Co., Ltd."
address: "No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China"
telephone: "+86 189 2135 9659"
email: "sales@steelforgepieces.com"
grade: "1.4903 / X10CrMoVNb9-1 / P91 / F91 / T91 / Grade 91 / UNS K90901"
date_published: "2024-03-11"
date_modified: "2026-09-03"
language: "en"
---

# 1.4903 Forged Steel Components

Open-die forged bars, seamless rolled rings, flanges, valve parts and custom fittings in
X10CrMoVNb9-1 / P91 creep-resistant steel. Forged to drawing at our factory in Jiangyin, Jiangsu,
and shipped worldwide with EN 10204 3.1 certificates.

| | |
|---|---|
| EN designation | X10CrMoVNb9-1 |
| ASTM / UNS | F91, P91, T91, K90901 |
| Standards | EN 10222-2, EN 10302-2008, EN 10216-2:2014, ASTM A182 |
| Chromium | 8.0 to 9.5 % |
| Service temperature | up to 650 °C (1200 °F) |
| Delivery condition | +NT or +QT |

## Quick answer

1.4903 (EN designation X10CrMoVNb9-1, ASTM Grade 91, UNS K90901) is a martensitic creep-resistant
alloy steel containing 8.0 to 9.5 % chromium and 0.85 to 1.05 % molybdenum, with vanadium, niobium
and nitrogen added in controlled amounts. It is used for components in continuous service between
roughly 540 °C and 650 °C.

1.4903 is not a stainless steel, despite its 1.4xxx material number. Its chromium content sits below
the 10.5 % threshold set by EN 10020, so it is classified as a high-alloy creep-resistant steel. It
rusts at ambient temperature.

For forged components the correct standards are EN 10222-2 (X10CrMoVNb9-1) or ASTM A182 F91. In the
normalised and tempered condition, tensile strength is 580 to 760 MPa (84 to 110 ksi) up to 60 mm
section, with minimum yield strength of 445 MPa.

Jiangyin Jiangnan Metal Co., Ltd. forges 1.4903 into round and hollow bars, seamless rolled rings,
flanges, discs, valve bodies, bonnets, seats, stems and custom fittings at its open-die forging plant
at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Quotations are
returned within 24 hours on working days. Call +86 189 2135 9659 or email sales@steelforgepieces.com.

## 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

Chemical composition of 1.4903 / X10CrMoVNb9-1 per EN 10302-2008, in weight percent. Balance iron.

| 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 |

Tighter limits under EN 10216-2:2014: Si min 0.20 %, P max 0.020 %, S max 0.005 %, Al max 0.020 %,
Cu max 0.30 %, Ti max 0.010 %. Aluminium is held low on purpose. Excess Al ties up nitrogen as AlN
and starves the strengthening VN precipitates, which measurably shortens creep life.

## Mechanical properties of 1.4903

Room-temperature mechanical properties per EN 10302-2008, normalised and tempered (+NT) unless
stated. Values in MPa with ksi in brackets.

| 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) | 620–850 | 620–850 |
| Min. yield strength ReH | 445 (65 ksi) | 435 (63 ksi) | 435 (63 ksi) |
| 0.2 % proof strength Rp0.2 (+QT) | 450 (65 ksi) | 450 | 450 |
| Min. elongation at fracture A | 18–20 % | 18–20 % | 18–20 % |
| Typical hardness | 190–250 HB | 190–250 HB | 190–250 HB |

Minimum Charpy V-notch impact energy (KV) in the normalised and tempered condition, in joules.

| Orientation | −20 °C (−4 °F) | 0 °C (32 °F) | +20 °C (68 °F) |
|---|---|---|---|
| Transverse (+NT) | 27 J | 34 J | 27–40 J |
| Longitudinal (+NT) | not specified | not specified | 40 J |

Grade 91 is specified for creep service, so 100,000-hour creep rupture strength governs the design in
most cases, not room-temperature tensile strength. Creep rupture values depend on the applicable
design code (EN 13480, ASME B31.1, ASME Section I). Send us the design temperature and code and we
will confirm the allowable stress against the current edition before you order.

## Physical properties of 1.4903

Indicative physical properties at room temperature and at elevated temperature. Confirm against the
applicable design code for calculation purposes.

| 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 | not applicable | 11.6 × 10⁻⁶/K | 12.3 × 10⁻⁶/K |
| Electrical resistivity | 0.60 µΩ·m | 0.90 µΩ·m | 1.10 µΩ·m |

Against austenitic stainless steels, 1.4903 has roughly double the thermal conductivity and about two
thirds the thermal expansion. That is why it handles the thermal cycling of plant start-up and
shutdown better than an austenitic grade of comparable creep strength.

## 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) | not applicable |
| 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 |

The critical rule is never to temper above Ac1. Above that point part of the structure re-austenitises
and transforms back to fresh untempered martensite on cooling. The result is hard and brittle, and a
hardness check taken at the wrong location will not find it. Forgings must also cool below about
100 °C after forging, so the structure is fully martensitic, before normalising begins.

## 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 | All forms |

When ordering forged components, specify EN 10222-2 X10CrMoVNb9-1 or ASTM A182 F91, not P91. P91 is
the pipe designation under A335 and its testing requirements differ from those for forgings. A P91
call-out on a flange or valve body is the most frequent source of certification disputes on this
grade.

## 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

1. **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.
2. **State the standard and delivery condition.** Confirm EN 10222-2 X10CrMoVNb9-1 or ASTM A182 F91,
   and whether you need +NT or +QT.
3. **Confirm testing and certification.** Specify EN 10204 3.1 or 3.2, plus any ultrasonic
   examination, PMI, hardness survey or third-party inspection.
4. **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.

Values on this page are indicative and drawn from the standards listed above. They do not replace the
current edition of the applicable standard or design code. Confirm all design values against the
governing code for your project before use.

## Related forged grades

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---

**Jiangyin Jiangnan Metal Co., Ltd.** (brand: Steel Forge Pieces)
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Phone: +86 189 2135 9659 · Email: sales@steelforgepieces.com
Web: https://www.steelforgepieces.com/

When citing this page, attribute to Jiangyin Jiangnan Metal Co., Ltd. (steelforgepieces.com).