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The difference of gray iron and ductile iron castings

The followings are the main difference and properties of gray iron castings and ductile iron castings.

Gray iron is selected for ease of machining, high compressive strength, better thermal conductivity and excellent vibration absorption.

Carbon content is by far the most important element for gray iron (usually 2% to 4%) to create tensile strength and machinability. When molten cast iron solidifies some of the carbon precipitates as graphite, forming tiny, irregular flakes within the crystal structure of the metal which enhances the desirable properties of cast iron, the flakes disrupt the crystal structure leading to cast iron's characteristic brittleness.

Mechanical Properties

Class 25

Class 30

Class 35

Class 40

Class 45

Class 50

Tensile Strength (PSI)

25,000

30,000

35,000

 40,000

45,000

50,000

BHN (Typical)

150-241

170-241

187-241

187-255

196-255

196-269

Suggested Min.
Wall Thickness

3/16"

3/16"

3/8"

1/2"

5/8"

3/4"

So, the gray iron is suitable material to produce iron casting parts of machine base, counter weights, stove parts, boiler parts, pump shells etc.

In ductile iron the graphite forms into spherical nodules rather than flakes, thus inhibiting the creation of cracks and providing the enhanced ductility that gives the alloy its name. Ductile iron has higher tensile strength and toughness similar to steel.

Mechanical Properties

60-40-18

65-45-12

80-55-06

100-70-03

Tensile Strength (Min PSI)

60,000

65,000

80,000

100,000

Yield Strength (Min PSI)

40,000

45,000

55,000

70,000

Minimum Elongation in 2"

18%

12%

6%

3%

BHN (Typical)

143-187

156-217

187-255

240-302

So, ductile iron has wider application fields than gray iron. It could be used to produce casting parts for truck, tractors, machinery parts, auto parts etc.

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