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Eternal
F91 (ASTM A182 Grade F91) is a 9Cr-1Mo-V-Nb martensitic heat-resistant steel, specifically developed for high-temperature, high-pressure operating conditions in supercritical and ultra-supercritical thermal power units; it is the core material for supercritical critical valves as designated by the National Energy Administration.
F91 forged steel components manufactured by Jiangyin Eternal Heavy Industry Co., Ltd. are widely used in the manufacture of high-temperature, high-pressure valves for supercritical power units of 600 MW and above, including gate valves, globe valves, check valves and control valves. Under operating conditions where steam temperatures exceed 560 °C and pressures exceed 22 MPa, F91 has become the material of choice for pressure-bearing components such as valve bodies, bonnets and discs, owing to its excellent resistance to high-temperature oxidation and steam corrosion.
Element | C | Si | Mn | P | S | Cr | Mo | Ni | V | Nb | N |
(%) | 0.08~0.12 | 0.20~0.50 | 0.30~0.60 | ≤0.020 | ≤0.010 | 8.00~9.50 | 0.85~1.05 | ≤0.40 | 0.18~0.25 | 0.06~0.10 | 0.03~0.07 |
Item | Data |  |
Heat treatment | Normalizing + Tempering（N+T） | |
Normalizing temperature | 1040℃~1090℃ | |
Tempering temperature | 730℃~780℃ | |
Tensile strength Rm | 630~830 MPa | |
Minimum yield strength ReL | ≥450 MPa | |
Minimum elongation A | ≥20% | |
Minimum cross-sectional contraction rate Z | ≥40% | |
Minimum impact energy KV₂ (20℃) | ≥40 J | |
Hardness HBW | 180~248 | |
Maximum service temperature | 650℃ |
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The use of an electric arc furnace (EAF) combined with VODC vacuum refining and electroslag remelting (ESR) ensures low gas content (H ≤ 1.5 × 10⁻⁴, O ≤ 30 × 10⁻⁴) and high purity.
The forging ratio of the main cross-section should be ≥3 (for electroslag remelted ingots) or ≥4 (for non-electroslag remelted ingots) to ensure a dense and uniform microstructure.
By strictly adhering to the normalising and tempering process, a tempered martensitic microstructure with fine MX precipitation phases is achieved, with hardness precisely controlled between 180 and 248 HBW.
Ultrasonic testing shall be carried out on a piece-by-piece basis, with quality grades not lower than Grade 2 for individual defects, a reduction of 2 grades in the base wave, and Grade I for defects in dense areas. Acceptable grain size grades for F91: Grades 3 to 5.
Application | Typical Conditions |
Supercritical thermal power plant（593℃） | Main steam pipeline valves, reheater valves |
Ultra-supercritical thermal power plant（620℃+） | High-temperature and high-pressure steam trap, three-way valve body |
Power station boiler | F91 forged steel gate valve, globe valve body |
Nuclear power plant conventional island | High-temperature steam pipeline valves |
Petrochemical industry | High-temperature reactor connection flange |
How should F91 forged steel components be heat treated?
A normalising and tempering process must be used, with a normalising temperature of 1040–1080 °C and a tempering temperature of 730–780 °C. The final microstructure should be tempered martensite, with a hardness of 196–248 HBW. Improper heat treatment will significantly reduce high-temperature creep properties.
What is the difference between F91 and F22?
What are the common quality defects in F91 forgings?
How should the grade of forged steel components be selected?
