commonly used. Nickel increases the hardness, tensile
characteristics. The spark streams vary from a few tiny
strength, and elastic limit of steel without appreciably
shafts to a shower of sparks several feet in length. Few
decreasing the ductility. It also intensifies the hardening
nonferrous metals give off sparks when touched to a
effect of heat treatment. SAE 2330 steel is used
grinding stone. Therefore, these metals cannot be
extensively for aircraft parts such as bolts, terminals,
successfully identified by the spark test.
keys, clevises, and pins.
Wrought iron produces long shafts that are a dull
red color as they leave the stone, and they end up a
white color. Cast iron sparks are red as they leave the
high in hardness, strength, and corrosion-resistant
stone, but turn to a straw color. Low-carbon steels give
properties. SAE 51335 is particularly adaptable for
off long, straight shafts that have a few white sprigs. As
heat-treated forgings that require greater toughness and
the carbon content of the steel increases, the number of
strength than may be obtained in plain carbon steel. It is
sprigs along each shaft increases, and the stream
used for such articles as the balls and rollers of
becomes whiter in color. Nickel steel causes the spark
stream to contain small white blocks of light within the
CHROMIUM-NICKEL OR STAINLESS
main burst.
STEELS.--These are corrosion-resisting metals. The
anticorrosive degree is determined by the surface
Types, Characteristics, and Uses of Alloyed Steels
temperature, and concentration of the corrosive agent.
While the plain carbon type of steel remains the
principal product of the steel mills, so-called alloy or
The principal part of stainless steel is chromium, to
special steels are being turned out in ever increasing
which nickel may or may not be added. The corrosion-
tonnage. Let us now consider those alloyed steels and
resisting steel most often used in aircraft construction is
their uses in aircraft.
known as 18-8 steel because of its content of 18 percent
chromium and 8 percent nickel. One of the distinctive
CARBON STEELS.--Steel containing carbon in
features of 18-8 steel is that its strength may be
percentages ranging from 0.10 to 0.30 percent are
increased by cold-working.
classed as low-carbon steel. The equivalent SAE
numbers range from 1010 to 1030. Steels of this grade
Stainless steel may be rolled, drawn, bent, or
are used for making such items as safety wire, certain
formed to any shape. Because these steels expand about
nuts, cable bushings, and threaded rod ends.
50 percent more than mild steel and conduct heat only
Low-carbon steel in sheet form is used for secondary
about 40 percent as rapidly, they are more difficult to
structural parts and clamps, and in tubular form for
weld. Stainless steel, with but a slight variation in its
moderately stressed structural parts.
of an aircraft. Some of its more common applications
Steels containing carbon in percentages ranging
are in the fabrication of exhaust collectors, stacks and
from 0.30 to 0.50 percent are classed as
manifolds, structural and machined parts, springs,
medium-carbon steel. This steel is especially adaptable
castings, and tie rods and cables.
for machining or forging and where surface hardness is
desirable. Certain rod ends and light forgings are made
CHROME-VANADIUM STEELS.--These are
from SAE 1035 steel.
made of approximately 0.18 percent vanadium and
about 1.00 percent chromium. When heat-treated, they
Steel containing carbon in percentages ranging
have strength, toughness, and resistance to wear and
from 0.50 to 1.05 percent are classed as high-carbon
fatigue. A special grade of this steel in sheet form can
steel. The addition of other elements in varying
be cold-formed into intricate shapes. It can be folded
quantities adds to the hardness of this steel. In the fully
and flattened without signs of breaking or failure. SAE
heat-treated condition, it is very hard and will withstand
6150 is used for making springs; and chrome-vanadium
high shear and wear and have little deformation. It has
with high-carbon content, SAE 6195, is used for ball
limited use in aircraft. SAE 1095 in sheet form is used
for making flat springs, and in wire form for making
coil springs.
CHROME-MOLYBDENUM S T E E L S . --
Molybdenum in small percentages is used in combina-
NICKEL STEELS.--The various nickel steels
tion with chromium to form chrome-molybdenum
are produced by combining nickel with carbon steel.
steel, which has various uses in aircraft. Molybdenum
Steels containing from 3 to 3.75 percent nickel are
is a strong alloying element, only 0.15 to 0.25 percent
2-27