I
Iron Alloys
ron castings are produced by a variety of molding methods and are available with a wide range of properties. Cast iron is a generic term that designates a family of
metals that include gray, ductile, aus- tempered ductile, carbidic austempered ductile, compacted graphite, malleable, white and alloyed irons. Because of their excellent proper- gr y and ductile
Because of their excellent proper- ties and castability, gray and ductile irirons are the dominant metals
ties and castabilit
ns are the dominant metals produced in metalcasting facilities today. Gray cast irons are the preferred material when the
designer is seeking low cost complex geometries with strength and high density. For applor applicications in which thermal conductivity is needed, compacted graphite n (CGI) is an ideal can- or higher strength
densit didate ations in
which thermal conductivity is needed, compacted graphite iriron (CGI) is an ideal can- didate. For higher strength applications, ductile iron can be used.
applications, ductile ir n can be used. Austempering of ductile iron creates addition- al opportunities by further
ustempering of
ductile ir n creates addition- al opportunities by further
improving strength, fatigue resistance, and wear resistance.
Properties T e basic strength and hardness of
all iron alloys is provided by the metal- lic structures containing graphite. T e properties of the iron matrix can range from those of soft, low-carbo
modulus of elasticity varies with the class of iron and the shape (sphericity) and volume fraction of the graphite phase (percent free carbon).
high silicon content, cast irons inherinherently resist oxidation and corrosion by developing a tightly dhering oxide and subscale to repel further atta k. Iron castings
Because of their relativel high silicon content,
Because of their relatively ently resist oxidation and
ast irons
corrosion by de eloping a tightl adhering oxide and subscale to repel further attack. Iron castings
are used in applications where this resistance provides long
are used in applications where this resistance provides long
from those of soft, low-carbon steel (18 ksi/124 MPa) to those of hardened, high-carbon steel (230 ksi/1,586 MPa). T e modulus of elasticity varies with the class of iron and the shape (sphericity) and volume fr ction of the graphite phase (percent free carbon).
steel (18 ksi/124 MPa) to those of hardened, high-carbon steel (230 ksi/1,586 MPa).
life. Resistance to heat, oxidation and corrosion are appreciably enhanced with alloyed irons. Properties of the cast iron family can be adjusted over a wide range and enhanced by heat treatment. Annealing produces a matrix of soft machinable ferrite. In limited situations, this an- nealing can be accomplished at sub- critical temperatures. Heating above critical temperatures takes the carbon from the graphite and places it in the is engineered material can be
nealing can be accomplished at sub- critical temperatures. Heating abo critical temperatures takes the carbo from the graphite and places it in the matrix.
conventional heat treating or surface hardening (
Types ypes
Gray iron—Flake graphite provides gray iron with unique properties (such as excellent machinability) at hardness levels that produce superior wear-resistant charac- teristics, the ability to resist galling
and excellent vi-
matrix. T is engineered material can be through-hardened and tempered using entional heat treating or surface able 1).
through-hardened and tempered using co
hardening (Table 1). T ese adjustments create the diff erent members of the cast on family.
ese adjustments
create the diff erent members of the cast iriron famil
The main shank of the planter row unit was converted from 17 stamped steel parts to three ductile iron castings, the no-till coulter arm was consolidated from fi ve steel parts to one casting, and the parallel arm was consolidated from seven parts to one.
2016 CASTING SOURCE DIRECTORY METAL CASTING DESIGN & PURCHASING 15
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