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ASTM A369 Grade FP91 High-Chromium Steel

ASTM A369 grade FP91 is an alloy steel formulated for primary forming into wrought products. Cited properties are appropriate for the normalized and tempered condition.

It has a fairly low thermal conductivity among wrought alloy steels in the same category. In addition, it has a fairly high base cost and a fairly high embodied energy.

The graph bars on the material properties cards below compare ASTM A369 grade FP91 to: wrought alloy steels in the same category (top), all iron alloys (middle), and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.

Mechanical Properties

Brinell Hardness

200

Elastic (Young's, Tensile) Modulus

190 GPa 28 x 106 psi

Elongation at Break

19 %

Fatigue Strength

320 MPa 46 x 103 psi

Poisson's Ratio

0.28

Shear Modulus

75 GPa 11 x 106 psi

Shear Strength

410 MPa 60 x 103 psi

Tensile Strength: Ultimate (UTS)

670 MPa 97 x 103 psi

Tensile Strength: Yield (Proof)

460 MPa 67 x 103 psi

Thermal Properties

Latent Heat of Fusion

270 J/g

Maximum Temperature: Mechanical

600 °C 1100 °F

Melting Completion (Liquidus)

1460 °C 2660 °F

Melting Onset (Solidus)

1420 °C 2580 °F

Specific Heat Capacity

470 J/kg-K 0.11 BTU/lb-°F

Thermal Conductivity

26 W/m-K 15 BTU/h-ft-°F

Thermal Expansion

13 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

8.9 % IACS

Electrical Conductivity: Equal Weight (Specific)

10 % IACS

Otherwise Unclassified Properties

Base Metal Price

7.0 % relative

Density

7.8 g/cm3 490 lb/ft3

Embodied Carbon

2.6 kg CO2/kg material

Embodied Energy

37 MJ/kg 16 x 103 BTU/lb

Embodied Water

88 L/kg 10 gal/lb

Common Calculations

PREN (Pitting Resistance)

13

Resilience: Ultimate (Unit Rupture Work)

110 MJ/m3

Resilience: Unit (Modulus of Resilience)

560 kJ/m3

Stiffness to Weight: Axial

14 points

Stiffness to Weight: Bending

25 points

Strength to Weight: Axial

24 points

Strength to Weight: Bending

22 points

Thermal Diffusivity

6.9 mm2/s

Thermal Shock Resistance

18 points

Alloy Composition

Among alloy steels, the composition of ASTM A369 grade FP91 is notable for including zirconium (Zr) and containing a comparatively high amount of chromium (Cr). Zirconium is used to improve ductility. Chromium is used to improve corrosion resistance and most mechanical properties (particularly at higher temperatures).

Iron (Fe) 87.3 to 90.3
Chromium (Cr) 8.0 to 9.5
Molybdenum (Mo) 0.85 to 1.1
Manganese (Mn) 0.3 to 0.6
Silicon (Si) 0.2 to 0.5
Vanadium (V) 0.18 to 0.25
Nickel (Ni) 0 to 0.4
Carbon (C) 0.080 to 0.12
Niobium (Nb) 0.060 to 0.1
Nitrogen (N) 0.030 to 0.070
Phosphorus (P) 0 to 0.025
Sulfur (S) 0 to 0.025
Aluminum (Al) 0 to 0.020
Titanium (Ti) 0 to 0.010
Zirconium (Zr) 0 to 0.010

All values are % weight. Ranges represent what is permitted under applicable standards.

Followup Questions

Similar Alloys

Further Reading

ASTM A369: Standard Specification for Carbon and Ferritic Alloy Steel Forged and Bored Pipe for High-Temperature Service