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ASM Metals Handbook Volume 01 - Properties and Selection Irons, Steels, and High-Performance Allo

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80 10 269−321
2 1035 165 690 100 7 302−363
3 1205 175 827 120 4 363−444
4 1380 200 965 140 2 388−477
Sulzer (Switzerland)
GGG80 BAF 800 116 505 73 8 250−310
GGG100 1000 160 705 102 5 280−340
GGG120 1200 174 950 138 2 330−390
BCIRA (Great Britain)
950/6 950 138 670 97 6 300−310
1050/3 1050 152 780 113 3 345−355
1200/1 1200 174 940 136 1 390−400
Fig. 2 Proposed strength and elongation ranges of austempered ductile iron compared to established criteria for other
grades of ductile iron. DIS, Ductile Iron Society; BCIRA, British Cast Iron Research Association
ASM Handbook,Volume 1 Ductile Iron 01 Sep 2005
Copyright ASM International. All Rights Reserved. Page 70
Ductile Iron Applications
Ductile iron castings are used for many structural applications, particularly those requiring strength and toughness combined
with good machinability and low cost. The selection of casting, instead of mechanical fabrication, as the production process often
allows the designer to:
• Use to best advantage the combination of properties that is unique to ductile iron
• Combine several functions (or component shapes) in a single integrated configuration
• Realize the economic advantages inherent in casting, which is the simplest and most direct of the various production processes
Casting is like forming with a homogenous liquid that can flow smoothly into a wide variety of thicknesses, shapes, and
contours. The material is consistent piece to piece, day after day because it is made from a pattern that has very low wear and
dimensional change and that is produced to a specification. The microstructure is uniform, with neither directional flow lines nor
variations from weld junctions or heat-affected zones. Any porosity is predictable and remains in the thermal center. Machining
costs are low because there is less material to remove and to dispose of, castings are easier to machine, and cutting tools are
subjected to less tool wear.
Properties unique to ductile iron include the ease of heat treating because the free carbon in the matrix can be redissolved to
any desired level for hardness and strength control. Free carbon can be selectively hardened by flame, induction, laser, or electron
beam. A 650 °C (1200 °F) anneal for 3 h can produce high toughness at low temperatures. Ductile iron can be austempered to
high tensile strength, high fatigue strength, high toughness, and excellent wear resistance. Second, lower density makes ductile
iron weigh 10% less than steel for the same section size. Third, the graphite content provides damping properties for quiet
running gears. Also, the low coefficient of friction produces more efficient gear boxes. Furthermore, ductile iron has less
tendency to gear seizures from the loss of lubricant.
Experience has proved that ductile iron works in applications in which experience and handbook data say it should not. This is
because data in the literature do not describe the true properties of ductile iron, whereas it is very easy to make a prototype
casting and try it in the field. This practice has resulted in very large cost savings and superior performance compared to the
material it replaces. A ductile iron casting can be poured and shipped the same day. As-cast ductile iron castings are consistent in
dimensions and weight because there is no distortion or growth due to heat treatment.
The automotive and agricultural industries are the major users of ductile iron castings. Almost 3 × 106 tonnes (2.9 × 106 t, or
3.2 × 106 tons) of ductile iron castings were produced in the United States in 1988, the majority of components being for
automotive applications. Because of economic advantages and high reliability, ductile iron is used for such critical automotive
parts as crankshafts, front wheel spindle supports, complex shapes of steering knuckles, disk brake calipers, engine connecting
rods, idler arms, wheel hubs, truck axles, suspension system parts, power transmission yokes, high-temperature applications for
turbo housings and manifolds, and high-security valves for many various applications. It can be rolled or spun into a desired
shape or coined to an exact dimension.
The cast iron pipe industry is another major user of ductile iron.
Austempered ductile iron has resulted in many new applications for ductile iron. It is a high-strength, wear-resistant,
heat-treated material. It has more than double the strength of conventional ductile iron for a given level of ductility (Fig. 3 ).
Austempered ductile iron gets its remarkable properties from a special austempering heat treatment. The resultant strength
properties can be varied by controlling the heat treat cycle, which is described in this article in the section "Heat Treatment." In
the austempering process, good-quality ductile iron can be transformed into a superior engineering material. It cannot transform
poor-quality iron into a good-quality material.
Fig. 3 Tensile strength and elongation relationship for various ductile iron grades. Source: Ref 1
Ductile Iron Applications
Ductile iron castings are used for many structural applications, particularly those requiring strength and toughness combined
with good machinability and low cost. The selection of casting, instead of mechanical fabrication, as the production process often
allows the designer to:
• Use to best advantage the combination of properties that is unique to ductile iron
• Combine several functions (or component shapes) in a single integrated configuration
• Realize the economic advantages inherent in casting, which is the simplest and most direct of the various production processes
Casting is like forming with a homogenous liquid that can flow smoothly into a wide variety of thicknesses, shapes, and
contours. The material is consistent piece to piece, day after day because it is made from a pattern that has very low wear and
dimensional change and that is produced to a specification. The microstructure is uniform, with neither directional flow lines nor
variations from weld junctions or heat-affected zones. Any porosity is predictable and remains in the thermal center. Machining
costs are low because there is less material to remove and to dispose of, castings are easier to machine, and cutting tools are
subjected to less tool wear.
Properties unique to ductile iron include the ease of heat treating because the free carbon in the matrix can be redissolved to
any desired level for hardness and strength control. Free carbon can be selectively hardened by flame, induction, laser, or electron
beam. A 650 °C (1200 °F) anneal for 3 h can produce high toughness at low temperatures. Ductile iron can be austempered to
high tensile strength, high fatigue strength, high toughness, and excellent wear resistance. Second, lower density makes ductile
iron weigh 10% less than steel for the same section size. Third, the graphite content provides damping properties for quiet
running gears. Also, the low coefficient of friction produces more efficient gear boxes. Furthermore, ductile iron has less
tendency to gear seizures from the loss of lubricant.
Experience has proved that ductile iron works in applications in which experience and handbook data say it should not. This is
because data in the literature do not describe the true properties of ductile iron, whereas it is very easy to make a prototype
casting and try it in the field. This practice has resulted in very large cost savings and superior performance compared to the
material it replaces. A ductile iron casting can be poured and shipped the same day. As-cast ductile iron castings are consistent in
dimensions and weight because there is no distortion or growth due to heat treatment.
The automotive and agricultural industries are the major users of ductile iron castings. Almost 3 × 106 tonnes (2.9 × 106 t, or
3.2 × 106 tons) of ductile iron castings were produced in the United States in 1988, the majority