Alloy Cast Irons Alloy Cast Irons Alloy Cast Irons
Introduction
ALLOY CAST IRONS are considered to be those casting alloys based on the iron-carbon-silicon system that
contain one or more alloying elements intentionally added to enhance one or more useful properties. The
addition to the ladle of small amounts of substances (such as ferrosilicon, cerium, or magnesium) that are used
to control the size, shape, and/or distribution of graphite particles is termed inoculation rather than alloying.
The quantities of material used for inoculation neither change the basic composition of the solidified iron nor
alter the properties of individual constituents. Alloying elements, including silicon when it exceeds about 3%,
are usually added to increase the strength, hardness, hardenability, or corrosion resistance of the basic iron and
are often added in quantities sufficient to affect the occurrence, properties, or distribution of constituents in the
microstructure.
In gray and ductile irons, small amounts of alloying elements such as chromium, molybdenum, or nickel are
used primarily to achieve high strength or to ensure the attainment of a specified minimum strength in heavy
sections. Otherwise, alloying elements are used almost exclusively to enhance resistance to abrasive wear or
chemical corrosion or to extend service life at elevated temperatures.

Additional comments :

The strengthening effects of the various alloying elements in gray and ductile irons are dealt with in the articles
"Gray Iron" and "Ductile Iron" in this Volume. This article discusses abrasion-resistant chilled and white irons,
high-alloy corrosion-resistant irons, and medium-alloy and high-alloy heat-resistant gray and ductile irons.
Table 1 lists approximate ranges of alloy content for various types of alloy cast irons covered in this article.
Individual alloys within each type are made to compositions in which the actual ranges of one or more of the
alloying elements span only a portion of the listed ranges; the listed ranges serve only to identify the types of
alloys used in specific kinds of applications.