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The differences between grey iron and ductile iron

The difference in appearance of grey iron and ductile iron are not obvious. In general, the color of the fracture is different, the bright white one is ductile iron and the gray one is gray cast iron.

Mechanical properties

1. Gray cast iron
American Standard ASTM requirements on the hardness of gray cast iron castings (ASTM A48-92) is for the main consideration of tensile strength gray iron castings for engineering. Gray cast iron has low mechanical properties the tensile strength of cast iron is only 31k psi and does not show the yield strength, but it has high wear-resistant damping performance, the damping resistance, wear resistance, cast ability, machinability are better. The bed, cabinet, base, rails and other parts that demand less strength and withstand pressure, gray cast iron is the best choice.

2. Ductile cast iron
Ductile iron has high plasticity and good toughness, the tensile strength of ductile iron is 60k psi and the yield strength of ductile iron is 40k psi, it can be comparable to carbon steel in strength. So it is often used to produce iron parts which require high strength, toughness and complex shapes.

Its cast performance is better than steel, mainly used to manufacture machine parts with mechanical complexity and a larger load, such as crankshaft, connecting rod, gear, camshaft. Iron foundry can also make recirculating ball type, worm fan steering parts in trucks, buses, construction vehicles. Sometimes it is made into the base and large ductile iron castings.
In the case of low tensile strength and elongation requirements, iron foundry can use grey iron instead of ductile iron according to Dandong Foundry.

Material Grades

1. Gray cast iron (ASTM A48-2000)
When ordering or producing cast iron, according to the performance of separate casting specimen grey iron is divided into a number of levels, each level uses a number followed by a letter, numbers indicate the minimum tensile strength of the individual casting test bars, the letter says the specifications of test bars.
For example, gray iron casting, ASTM A48, 30B indicates that this grey iron is produced according to ASTM A48, the minimum tensile strength of 30 thousand pounds /2 inch (207 MPa); the nominal diameter of test bar is 1.2 inches (30.5 mm).

2. Ductile cast iron (ASTM A536-84)
Casting grades is expressed by "tensile strength - yield strength - elongation". For example: grade: 80-55-06 is on behalf that the tensile strength is 80,000 pounds / inch 2 (552 MPa), the yield strength is 55,000 pounds / inch 2 (379 MPa), the elongation is 6.0% (2 inches or 50 mm).

Ductile iron and gray cast iron each have their own advantages, in industrial producing and daily life, buyers should learn to avoid weaknesses, so that iron castings can serve for economic development better.

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