Page 73 - Mechanical Behavior of Materials

74 Chapter 3 A Survey of Engineering Materials

Figure 3.6 Effects of alloying additions and processing (x-axis) on the yield strength of steel.
Alloying iron with carbon and other elements provides substantial strengthening, but even
higher strengths can be achieved by heat treating with quenching and tempering. The highest
strengths are obtained by combining alloying with special processing, such as ausforming or
maraging. (Adapted from an illustration courtesy of R. W. Landgraf, Howell, MI.)

systems, and the current publication on the UNS System (SAE, 2008) for a description of those
designations and their equivalence with other specifications.
The AISI and SAE designations for various steels are coordinated between the two organiza-
tions and are nearly identical. Details for common carbon and low-alloy steels are given in Table 3.5.
Note that in this case there is usually a four-digit number. The first two digits specify the alloy
content other than carbon, and the second two give the carbon content in hundredths of a percent.
For example, AISI 1340 (or SAE 1340) contains 0.40% carbon with 1.75% manganese as the only
other alloying element. (Percentages of alloys are given on the basis of weight.)
The UNS system has a letter followed by a five-digit number. The letter indicates the category
of alloy, such as F for cast irons, G for carbon and low-alloy steels in the AISI–SAE naming system,
K for various special-purpose steels, S for stainless steels, and T for tool steels. For carbon and low-
alloy steels, the number is in most cases the same as that used by AISI and SAE, except that a zero
is added at the end. Thus, AISI 1340 is the same steel as UNS G13400.
Some particular classes of irons and steels will now be considered.

3.3.2 Cast Irons
Cast irons in various forms have been used for more than two thousand years and continue to be
relatively inexpensive and useful materials. The iron is not highly refined subsequent to extraction
from ore or scrap, and it is formed into useful shapes by melting and pouring into molds. The
temperature required to melt iron in a furnace is difficult to achieve. As a result, prior to the modern
industrial era, there was also considerable use of wrought iron, which is heated and forged into
useful shapes, but never melted in processing. Several different types of cast iron exist. All contain
large amounts of carbon, typically 2 to 4% by weight, and also 1 to 3% silicon. The large amount