Chrome-moly F91 / P91 (UNS K90901)
Chrome-moly F91 / P91 (UNS K90901) — 9Cr-1Mo-V creep-strength-enhanced steel for supercritical power plants.
| UNS number | K90901 |
| Material family | Alloy steel |
| Product specifications | ASTM A182 F91, A234 WP91, A335 P91 |
| Density (typical) | 7.85 g/cm³ (7850 kg/m³) |
| Weight of 6" Sch 40 pipe | 28.26 kg/m |
Specifications by product form
One alloy is ordered under different ASTM/ASME numbers depending on form: forged flanges and fittings, wrought buttweld fittings, and pipe or tube. For Chrome-moly F91 / P91 the usual specifications are ASTM A182 F91, A234 WP91, A335 P91. Quote both the specification and the UNS number on purchase orders to avoid ambiguity.
Chemical and mechanical limits differ between these specifications — always check the edition of the standard named on your order and the mill test certificate.
Chemical composition & mechanical properties
| Property | Alloy steel F91 |
|---|---|
| Family | Alloy steel |
| UNS | K90901 |
| EN / W.Nr | – – |
| Basis spec | ASTM A182 |
| Density g/cm³ | 7.77 |
| Chemical composition, % | |
| C | 0.08–0.12 |
| Mn | 0.30–0.60 |
| P | 0.020 |
| S | 0.010 |
| Si | 0.20–0.50 |
| Cr | 8.0–9.5 |
| Ni | 0.40 |
| Mo | 0.85–1.05 |
| N | 0.03–0.07 |
| Nb | 0.06–0.10 |
| V | 0.18–0.25 |
| Al | 0.02 |
| Mechanical properties (min) | |
| Tensile strength | 585 MPa (85 ksi) |
| Yield strength (0.2%) | 415 MPa (60 ksi) |
| Elongation | 20% |
| Hardness (max) | 248 HB |
| PREN (min, from spec) | – |
Single values are maximums; ranges are min–max; "bal" = balance. Limits are typical of the basis specification for that product form — forgings, pipe and fittings specifications differ slightly. Always check the exact specification, edition and the mill test certificate.
Frequently asked questions
What is the UNS number of Chrome-moly F91 / P91?
K90901.
Which ASTM specifications cover Chrome-moly F91 / P91?
ASTM A182 F91, A234 WP91, A335 P91.
What is the density of Chrome-moly F91 / P91?
About 7.85 g/cm³ (7850 kg/m³), used for weight calculations.
Last updated 2026-11-02