1.3.1 Steel

Any review of modern armor materials must start with steel. According to
the [American Steel Manufacturers] ASM-96 guide there are literally hundreds
of steels in use throughout the world, but only a few qualify as good
armor material.

Firstly the type of steel must be relatively cheap as its still the most common
material used in tank armor accounting for about ½ the weight. In order to
survive the pressure and strain of impact, this steel must be both strong and
ductile. A class of steels -that currently fit the bill- have been developed
called ‘high strength low alloy steel’ [HSLA], and the most common of these
in research papers is ‘Type 4340 steel’. This steel features low carbon [0.3—
0.5%], with moderate manganese content [1—3%] and good ductility [on the
order of 8—10%] and strength [~1.0—1.1 GPa – ultimate tensile strength].
The hardness range from ~250—300 Brinell Hardness Number [BHN, a
rating system for metal hardness] to BHN 350—390. Other steels are available
that are stronger like ‘Maraging Steel’ and harder like ‘Tool Steel’,
but tests reveal these offer only 90% of the resistance of RHA.