Innovate and improve. It might seem
simplistic, but these two words describe
mankind’s inherent desire to develop and
advance technologies. Each new development usually is followed by countless
updates and enhancements, a large step
followed by myriad small steps, until another big step starts the cycle over.
The progression of the vast technological eras likewise is somewhat simplified. The three eras—the Stone Age, the
Bronze Age, and the Iron Age—are broad
divisions that don’t capture the essence
of thousands of years of innovations and
improvements. It took more than three
steps to go from chipping away at stones
to developing the many steel alloys that
make modern life possible. Even the
names are deceiving. Bronze is an alloy of copper and tin, whereas iron is an
element that rarely is used by itself. The
Steel Age would be a better term.
Iron, the Father of
“Plain carbon steel consists of iron, carbon, and manganese, as well as small
amounts of residual elements such as
sulfur, phosphorus, and silicon,” said
Karl Hoes, welding instructor for The
Lincoln Electric Co. It doesn’t take much
carbon and manganese to turn iron into
steel. For example, a typical plain carbon steel, AISI 1018, has 0.15 to 0.20
percent carbon and 0.60 to 0.90 percent
manganese. That’s just one of thousands
of variations of steel. The percentages
of carbon, silicon, and manganese can
be changed, and other elements can be
added, to improve steel’s characteristics—principally its strength, hardness,
wear resistance, corrosion resistance,
machinability, and hardenability (how it
reacts to heating and quenching).
Steels often are categorized into broad
• Plain carbon steels are iron alloys
with a carbon content less than 2 per-
cent, manganese less than 1.65 percent,
and silicon deoxidizers less than 0.6 per-
cent by weight. They can be designated
further as low carbon, medium carbon,
• Alloy steels add a variety of ele-
ments up to 50 percent by weight, typi-
cally benefiting hardenability.
• High-strength, low-alloy (HSLA)
steels are defined primarily by mechanical strength. Developed in the 1980s,
their high strength allows automotive
and heavy equipment designers to use
thinner material while maintaining component integrity. These steels, listed in
the 9000 series of steels by the Society
of Automotive Engineers, exhibit low carbon and excellent weldability.
• Stainless steels include any steel
alloy with more than 10. 5 percent chromium by weight and are grouped into
families based on their crystalline microstructure. The most common family is the
austenitic or chrome-nickel grade, which
can’t be hardened by heat treatment.
• Tool steels are compounds developed for extreme resistance to wear and
heat. As their name implies, they are
used to make tooling for shaping, forming, or cutting other steels.
Adding Chrome and Moly
While chromium can add corrosion resistance in stainless steel grades, it doesn’t
help steel to resist rust when it contributes less than 10. 5 percent of the steel’s
content. However, chromium does have
The filler metals suggested for joining chrome-moly steel— ER80S-D2, ER70S- 6, and
ER70S- 2—are available as all-position products, which is helpful when welding something
as complex as an airframe.