EN 1.4903, commonly known as F91 (often referenced as P91 in power-generation specifications), is a 9% chromium, molybdenum-vanadium-niobium alloyed creep-resistant steel developed for high-temperature and high-pressure service. It is widely used in modern and retrofit power plant systems because it combines strong long-term creep strength with good oxidation resistance and a favorable strength-to-weight ratio compared to older Cr-Mo steels.
In practical terms, F91 allows designers to run higher steam temperatures and pressures or to reduce wall thickness for the same duty, supporting higher efficiency and lower fuel consumption. The material is typically supplied in normalized and tempered condition, and performance in service depends heavily on correct heat treatment, fabrication control and qualified welding procedures. For critical applications, the material certificate EN 10204 / 3.1 provides the verified chemistry, heat treatment condition and mechanical test results for the delivered batch.
| Element | Typical range (wt. %) |
|---|---|
| C | 0.08 – 0.12 |
| Si | 0.20 – 0.50 |
| Mn | 0.30 – 0.60 |
| P | ≤ 0.020 |
| S | ≤ 0.010 |
| Cr | 8.0 – 9.5 |
| Mo | 0.85 – 1.05 |
| V | 0.18 – 0.25 |
| Nb | 0.06 – 0.10 |
| N | 0.03 – 0.07 |
| Fe | Balance |
| Property | Typical value (normalized & tempered) |
|---|---|
| Tensile strength (Rm) | per standard / see EN 10204 3.1 certificate |
| Yield strength (Rp0.2) | per standard / see EN 10204 3.1 certificate |
| Elongation (A5) | per standard / see EN 10204 3.1 certificate |
| Hardness | per standard / see EN 10204 3.1 certificate |
| Creep rupture strength | designed for long-term service at high temperature |
Exact values are stated on the material certificate EN 10204 / 3.1.
1.4903 / P91 is supplied as seamless pipe, tube, forged bar and plate. It is delivered in normalized and tempered condition for high-temperature pressure service.
Range: on request
Centerless grinding available on request.
F91 provides significantly higher creep strength than older Cr-Mo steels, allowing higher steam temperatures and pressures (or reduced wall thickness for the same duty). This supports higher plant efficiency and lower fuel use. The 9% chromium level also improves oxidation resistance compared to low-alloy boiler steels.
Yes. Welding typically requires controlled preheat, suitable filler materials and post-weld heat treatment (PWHT) to restore the correct microstructure and creep properties. Strict control of heat input and interpass temperature is critical for long-term reliability in pressure service.
In many power-generation specifications, F91 (P91) is selected for higher creep strength and improved efficiency potential. Compared to older steels such as 1.4913, it generally enables higher design temperatures or thinner sections. 1.4923 is also used for high-temperature pressure duty, but grade selection depends on code, form availability and design requirements.
F91 is commonly supplied in normalized and tempered condition. The verified heat treatment condition, chemistry and test results are stated on the EN 10204 / 3.1 certificate. For critical components, consistency of heat treatment is essential for creep performance.
Yes, forged/rolled bar can be supplied for machining, and centerless ground shafts are available on request when tight tolerances and surface finish are required. Provide your diameter, length, tolerance and surface requirements when requesting a quote.
Certificates: EN 10204 / 3.1
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