Table 4. Property Comparisons for Ductile Iron Grades (ASTM A536)
Property Heat Treatment
60-40-18 1 65-45-12 2 80-50-06 2 100-70-03 3 120-90-02 4
Tensile Strength
Yield Strength
% Elongation (min. 2 in.)
60,000 psi (413 MPa) 40,000 psi (276 MPa) 18 65,000 psi (448 MPa) 45,000 psi (310 MPa) 12 80,000 psi (551 MPa) 55,000 psi (379 MPa) 6 100,000 psi (689 MPa) 70,000 psi (482 MPa) 3 120,000 psi (827 MPa) 90,000 psi (620 MPa) 2
primarily due to the matrix structure that contains the spherical graphite. Distinctions between grades are the result of differences in composition, in the cooling rate of the casting or as the result of heat treatment. Minor differences in composition or the addition of alloys may be used to enhance the desired microstructure.
Comparing Capabilities: Gray And Ductile Iron
Hardness: Hardness is the most
commonly determined property of metal because it is a simple test, and many useful properties are directly re-
lated to hardness. Within a class or type of gray iron, hardness is a good indica- tor of engineering properties, but this relation is not useful between types of gray iron because differences in graphite structure have more of an effect on tensile properties than on hardness. Specifying the hardness at a designated area on each casting is an excellent method of establishing testing consistency in production. Compression strength correlates well with hardness for all types of iron. Hardness usually gives a good indication of tool life in machining. The hardness of gray iron (shown
Brinell Hardness
Poisson’s Ratio
130-170 0.28 150-220 0.28 170-250 0.28 241-300 0.28 240-300 0.28
Tensile Elastic Modulus
24.5 Msi (169 GPa) 24.5 Msi (169 GPa) 24.5 Msi (169 GPa) 25.5 Msi (176 GPa) 25.5 Msi (176 Gpa)
in Table 3) cannot be compared directly to the hardness of other metals for an indication of proper- ties such as machinability or wear resistance. In a particular size or type of casting, gray iron also can be designated by its Brinell hardness. Because of the minimum influ- ence of ductile iron’s spheroidal graphite on mechanical properties, hardness is a useful test for ductile iron and can be directly related to other properties. The relationship between tensile properties and hard- ness is reliable with a typical micro- structure and chemical analysis.
42 | METAL CASTING DESIGN & PURCHASING | Sept/Oct 2014
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