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Gray Iron ASTM A48 Class 40

Posted by Penticton Foundry on September 14, 2021
An automotive bearing housing made from ASTM A 48 Class 40 gray iron.

ASTM A48 Class 40 (Related Standards – ISO 185/JL/275, SAE J431 G4000, EN-GJL-250 or 300) is a gray cast iron with a pearlitic microstructure.

Gray irons are classified into groups based on their tensile strength. For example, Class 40 requires a minimum tensile strength of 40 ksi. When choosing which class of gray iron for any application, tensile strength is the deciding factor. Specifically, a representative test bar must meet the requirements of the class to adhere to the ASTM standard.

Note: Class 40 may have lower dampening qualities compared to Class 20 or 30, but will have a higher modulus of elasticity.

Gray iron class 40 is one grade in a family of many.  Chemistry ranges are not specified in the ASTM A48 standard. Instead, chemistry and hardness values listed in this data sheet would be typical for a class 40.

Composition

 

C

Mn

Si

P

S

Min%

2.7

0.5

1.8

0

0

Max%

3.5

0.95

2.5

0.12

0.15

Physical and Mechanical Properties

UTS – Ultimate Tensile Strength (psi)

40,000 (276MPa)

Hardness (Brinell)

183 – 285

Density lb/in3 (g/cm3)

0.258 (7.15)

Thermal Conductivity Btu/hr·ft·F (W/m·K)

27 (46)

Specific Heat at 70F Btu/lb·F (J/Kg·k)

0.12 (490)

Thermal Expansion µm/m-K

11

Melting Temperature

2050 – 2120 F

Compressive Strength Ksi (MPa)

150 (1034)

The mechanical properties of the gray iron can be controlled through cooling rate, chemical composition, design of the casting, or design of the mold. It is the responsibility of the foundry to determine the best process in order to produce the required mechanical properties.

Casting

Class 40 gray iron can be cast and machined to custom dimensions. The pearlitic microstructure offers a light weight product that combines strength and wear resistance.

Read: To learn more about the differences between ductile iron and gray iron castings read this blog.

Applications

  • Automotive (brake drums, clutch plates, heads, cylinder liners, pistons)
  • Hydraulics (Bearings and Bushings)
  • Manifolds
  • Pistons
  • Spools
  • Gears
  • Wheels
  • Rams

Resource: To learn more about gray iron, check out our gray iron webpage – includes a video.

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