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).
| Fe | 87.3 to 90.3 | |
| Cr | 8.0 to 9.5 | |
| Mo | 0.85 to 1.1 | |
| Mn | 0.3 to 0.6 | |
| Si | 0.2 to 0.5 | |
| V | 0.18 to 0.25 | |
| Ni | 0 to 0.4 | |
| C | 0.080 to 0.12 | |
| Nb | 0.060 to 0.1 | |
| N | 0.030 to 0.070 | |
| P | 0 to 0.025 | |
| S | 0 to 0.025 | |
| Al | 0 to 0.020 | |
| Ti | 0 to 0.010 | |
| 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