Stainless Steel 1.4903
EN 1.4903 · UNS K90901 · ASTM A335 Grade P91 · GB 10Cr9Mo1VNb
1.4903 (X10CrMoVNb9-1, ASTM A335 Grade P91, UNS K90901) is a 9Cr-1Mo creep-resisting martensitic steel microalloyed with vanadium and niobium and supplied normalized and tempered.
Reference datasheet — 1.4903 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the +NT condition
1.4903 tempers and conditions
1.4903 is supplied in 3 conditions, soft to hard. +NT is the default FabDigit quotes; the values on this page are for it.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Used only as an intermediate condition for heavy machining or cold work of bar/forging blanks; must be re-normalized and tempered before any creep service. | 380 | 590 | 26 | 10 HRC | 3 % IACS |
+NTDefault Normalized and tempered | Standard delivery condition for all P91 pipe, plate, forgings and fittings — full tempered-martensite creep structure for 550–600 °C service. | 490 | 660 | 23 | 19 HRC | — |
Quenched and tempered | Chosen for very heavy sections (thick headers, valve bodies, closed-die forgings) where still-air normalizing cannot cool the core fast enough to fully martensitic structure. | 520 | 700 | 21 | 21 HRC | — |
What is 1.4903?
1.4903 (X10CrMoVNb9-1, ASTM A335 Grade P91, UNS K90901) is a 9Cr-1Mo creep-resisting martensitic steel microalloyed with vanadium and niobium and supplied normalized and tempered. It is the workhorse alloy for boiler headers, main steam piping and forged fittings operating up to about 600 °C, available as seamless pipe, plate and forgings. Default +NT properties are 490 MPa yield, 660 MPa tensile, 23 % elongation and 215 HB (19 HRC). Welding requires strict preheat and mandatory PWHT, and the steel has no stainless passivity in wet ambient service; 1.4901/P92 gives higher creep strength. 1.4903 has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 58% of stainless steel grades. It melts at 1,450°C (2,642 °F). 1.4903 has a yield strength of 490 MPa (71.1 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 76% of stainless steel grades. Elongation at break is 23% and the elastic modulus is 218 GPa (31.6 Msi).
What is 1.4903 used for?
- Boiler headers/piping
- Steam pipework
- Power plant components
Advantages
- Low embodied carbon — 2.6 kg CO₂/kg, better than 100% of stainless steel grades
- Conducts heat well — 26.5 W/m·K (15.3 BTU/hr·ft·°F), better than 96% of stainless steel grades
- High electrical conductivity — 2.9 % IACS, better than 87% of stainless steel grades
- High strength — 490 MPa (71.1 ksi), better than 76% of stainless steel grades
Limitations
- Needs corrosion protection — 28/100, worse than 100% of stainless steel grades
- Difficult to weld — 42/100, worse than 81% of stainless steel grades
1.4903 properties
Typical room-temperature values for 1.4903-+NT; bars are the position among stainless steel grades.
Physical3
1.4903 has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 58% of stainless steel grades. It melts at 1,450°C (2,642 °F).
Mechanical17
1.4903 has a yield strength of 490 MPa (71.1 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 76% of stainless steel grades. Elongation at break is 23% and the elastic modulus is 218 GPa (31.6 Msi).
Thermal6
1.4903 is rated for continuous service to 600°C (1,112 °F). It conducts heat at 26.5 W/m·K (15.3 BTU/hr·ft·°F), better than 96% of stainless steel grades. Thermal expansion is 10.8 µm/m·K (6 µin/in·°F).
Electrical3
1.4903 conducts electricity at 2.9 % IACS, better than 87% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is poor (28/100), worse than 100% of stainless steel grades.
Sustainability4
Producing a kilogram of 1.4903 takes about 35 MJ of energy and emits 2.6 kg of CO₂ — less than 100% of stainless steel grades. Typical recycled content is 35%.
Manufacturability6
1.4903's machinability is fair (38/100, better than 63% of stainless steel grades); weldability fair (42/100); formability poor (30/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the stainless steel family
Yield strength against density for every stainless steel grade FabDigit runs. 1.4903 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 1.4903
Is 1.4903 easy to machine?
Machine in +NT/+QT at ~215 HB with rigid setups, coated carbide, modest speeds and heavy positive feeds; it work-hardens and glazes if feed is too light, so avoid dwelling and use flood coolant.
Can 1.4903 be welded?
GTAW root / SMAW-FCAW fill with matching 9CrMoV consumables, 200–300 °C preheat and maintained interpass (<300 °C), no free cooling below ~80 °C before PWHT, then mandatory 750–770 °C temper; keep Ni+Mn low to protect Ac1 and avoid soft Type IV HAZ.
Can 1.4903 be formed, bent or molded?
Hot form at 1050–1150 °C followed by full normalize + temper; cold bending is limited and any strain above a few percent should trigger re-heat-treatment to restore creep properties.
1.4903 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C | 0.08 – 0.12 | 0.1 |
| Si | 0.2 – 0.5 | 0.35 |
| Mn | 0.3 – 0.6 | 0.45 |
| P | ≤ 0.02 | 0.01 |
| S | ≤ 0.01 | 0 |
| Cr | 8 – 9.5 | 8.8 |
| Mo | 0.85 – 1.05 | 0.95 |
| V | 0.18 – 0.25 | 0.21 |
| NbNb (Cb) | 0.06 – 0.1 | 0.08 |
| N | 0.03 – 0.07 | 0.05 |
| Ni | ≤ 0.4 | 0.2 |
| Almax (0.04 in some editions) | ≤ 0.02 | 0.01 |
| Ti | ≤ 0.01 | |
| Zr | ≤ 0.01 | |
| Fe | balance |
What surface finishes work on 1.4903?
Not corrosion-resistant in wet ambient service — shot-blast and apply high-temperature aluminium/silicone paint or preservative for storage; it takes a fine metallographic polish but shows no stainless passivity.
Surface treatments FabDigit runs on stainless steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Passivation
Organic Coating
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel 1.4903 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- K90901
- ASTM
- A335 Grade P91
- EN / DIN / Werkstoff-Nr.
- X10CrMoVNb9-1
- GB (China)
- 10Cr9Mo1VNb
How much does 1.4903 cost?
1.4903 is a premium-cost stainless steel ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
1.4903 — frequently asked
What is 1.4903 used for?
1.4903 is typically used for boiler headers/piping, steam pipework and power plant components. In short: standard P91 creep steel; 600 °C piping grade; mandatory post-weld heat treatment.
What is the yield strength of 1.4903?
1.4903 has a typical yield strength of 490 MPa (71.1 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 76% of stainless steel grades. Strength varies by condition: see the 3 listed tempers.
Is 1.4903 easy to machine?
Not especially — machinability is rated fair (38/100, better than 63% of stainless steel grades). Machine in +NT/+QT at ~215 HB with rigid setups, coated carbide, modest speeds and heavy positive feeds; it work-hardens and glazes if feed is too light, so avoid dwelling and use flood coolant.
Can 1.4903 be welded?
With care — weldability is rated fair (42/100). GTAW root / SMAW-FCAW fill with matching 9CrMoV consumables, 200–300 °C preheat and maintained interpass (<300 °C), no free cooling below ~80 °C before PWHT, then mandatory 750–770 °C temper; keep Ni+Mn low to protect Ac1 and avoid soft Type IV HAZ.
What surface finishes work on 1.4903?
Not corrosion-resistant in wet ambient service — shot-blast and apply high-temperature aluminium/silicone paint or preservative for storage; it takes a fine metallographic polish but shows no stainless passivity.
Can 1.4903 be formed, bent or molded?
Hot form at 1050–1150 °C followed by full normalize + temper; cold bending is limited and any strain above a few percent should trigger re-heat-treatment to restore creep properties.
What is the maximum service temperature of 1.4903?
1.4903 is rated for continuous use to about 600°C (1,112 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does 1.4903 cost?
1.4903 is a premium-cost stainless steel ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM A335/A335M — Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service (Grade P91) — ASTM International (2022)
- EN 10216-2 — Seamless steel tubes for pressure purposes, X10CrMoVNb9-1 (1.4903) — CEN (2020)
- EN 10302 — Creep resisting steels, nickel and cobalt alloys (physical property data) — CEN (2008)
- GB/T 5310 — (10Cr9Mo1VNb) — SAC (2017)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- EPRI/ASME guidance on Grade 91 fabrication, welding and heat treatment — EPRI / ASME (2015)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.