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.
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.
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
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