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AISI 418 (Alloy 615, S41800) Stainless Steel

AISI 418 stainless steel is a martensitic stainless steel formulated for primary forming into wrought products. Cited properties are appropriate for the heat treated (HT) condition. 418 is the AISI designation for this material. S41800 is the UNS number. And Alloy 615 is the common industry name.

It has a fairly high base cost among wrought martensitic stainless steels. In addition, it has a fairly high tensile strength and a moderately high embodied energy.

The graph bars on the material properties cards below compare AISI 418 stainless steel to: wrought martensitic stainless steels (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

330

Elastic (Young's, Tensile) Modulus

200 GPa 29 x 106 psi

Elongation at Break

17 %

Fatigue Strength

520 MPa 75 x 103 psi

Poisson's Ratio

0.28

Reduction in Area

50 %

Shear Modulus

77 GPa 11 x 106 psi

Shear Strength

680 MPa 98 x 103 psi

Tensile Strength: Ultimate (UTS)

1100 MPa 160 x 103 psi

Tensile Strength: Yield (Proof)

850 MPa 120 x 103 psi

Thermal Properties

Latent Heat of Fusion

270 J/g

Maximum Temperature: Corrosion

390 °C 730 °F

Maximum Temperature: Mechanical

770 °C 1410 °F

Melting Completion (Liquidus)

1500 °C 2740 °F

Melting Onset (Solidus)

1460 °C 2660 °F

Specific Heat Capacity

470 J/kg-K 0.11 BTU/lb-°F

Thermal Conductivity

25 W/m-K 15 BTU/h-ft-°F

Thermal Expansion

10 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

2.8 % IACS

Electrical Conductivity: Equal Weight (Specific)

3.1 % IACS

Otherwise Unclassified Properties

Base Metal Price

15 % relative

Density

8.0 g/cm3 500 lb/ft3

Embodied Carbon

2.9 kg CO2/kg material

Embodied Energy

41 MJ/kg 18 x 103 BTU/lb

Embodied Water

110 L/kg 13 gal/lb

Common Calculations

PREN (Pitting Resistance)

19

Resilience: Ultimate (Unit Rupture Work)

170 MJ/m3

Resilience: Unit (Modulus of Resilience)

1830 kJ/m3

Stiffness to Weight: Axial

14 points

Stiffness to Weight: Bending

24 points

Strength to Weight: Axial

38 points

Strength to Weight: Bending

29 points

Thermal Diffusivity

6.7 mm2/s

Thermal Shock Resistance

40 points

Alloy Composition

Among wrought stainless steels, the composition of AISI 418 stainless steel is notable for including tungsten (W). Tungsten interacts with other alloying elements to a greater extent than usual, which makes it hard to broadly characterize its effects.

Iron (Fe) 78.5 to 83.6
Chromium (Cr) 12 to 14
Tungsten (W) 2.5 to 3.5
Nickel (Ni) 1.8 to 2.2
Manganese (Mn) 0 to 0.5
Silicon (Si) 0 to 0.5
Molybdenum (Mo) 0 to 0.5
Carbon (C) 0.15 to 0.2
Phosphorus (P) 0 to 0.040
Sulfur (S) 0 to 0.030

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

Followup Questions

Similar Alloys

Further Reading

ASTM A565: Standard Specification for Martensitic Stainless Steel Bars for High-Temperature Service

Advanced Materials in Automotive Engineering, Jason Rowe (editor), 2012

ASTM A959: Standard Guide for Specifying Harmonized Standard Grade Compositions for Wrought Stainless Steels

Properties and Selection: Irons, Steels and High Performance Alloys, ASM Handbook vol. 1, ASM International, 1993

Corrosion of Stainless Steels, A. John Sedriks, 1996

ASM Specialty Handbook: Stainless Steels, J. R. Davis (editor), 1994

Advances in Stainless Steels, Baldev Raj et al. (editors), 2010

CRC Materials Science and Engineering Handbook, 4th ed., James F. Shackelford et al. (editors), 2015