All metals may be classified as
ferrous or nonferrous. A ferrous metal has iron as its main element. A metal is
still considered ferrous even if it contains less than 50 percent iron,
as long as it contains more iron
than any other one metal. A metal is nonferrous if it contains less iron than
any other metal.
Ferrous
Ferrous metals include cast iron,
steel, and the various steel alloys, The only difference between iron and steel
is the carbon content. Cast iron contains more than 2-percent carbon, while
steel contains less than 2 percent. An alloy is a substance composed of two or
more elements. Therefore, all steels are an alloy of iron and carbon, but the
term “alloy steel” normally refers to a steel that also contains one or more
other elements. For example, if the main alloying element is tungsten, the
steel is a “tungsten steel” or “tungsten alloy.” If there is no alloying
material, it is a “carbon steel.”Ferrous metals are those that contain iron as the base metal. The properties of ferrous metals may be changed by adding various alloying elements. The chemical and mechanical properties need to be combined to produce a metal to serve a specific purpose. The basic ferrous metal form is pig iron. Pig iron is produced in a blast furnace that is charged with an iron ore, coke, and limestone. The four principal iron ores are
hematite, limonite, magnetite and goethite.
Nonferrous
Nonferrous metals include a great many metals that are used mainly for metal plating or as alloying elements, such as tin, zinc, silver, and gold. However, this post will focus only on the metals used in the manufacture of parts, such as aluminum, magnesium, titanium, nickel, copper, and tin alloys.
CAST IRON
Cast iron is a metal that is widelv used. It is a hard, brittle metal that has good wear resistance. Cast iron contains 2 to 4 percent carbon. White cast iron is very hard and is used mostly where abrasion and wear resistance is required. White cast iron may be made into malleable iron by heating it; then cooling it very slowly over a long period of time. Malleable iron is stronger and tougher than white cast iron; however, it is much more expensive to produce. Gray iron is another form of cast iron. It is used mostly for castings because of its ability to flow easily into complex shapes
Wrought iron is an iron that has had most of its carbon removed. It is tough; however, it can be bent or twisted very easily. Wrought iron is used mostly in ornamental ironwork,such as fences and handrails, because it is welded or painted easily and it rusts very slowly.
STEEL
Steel is an alloy of iron and
carbon or other alloying elements. When the alloying element is carbon, the
steel is referred to as carbon steel. Carbon steels are classified by the percentage of carbon in “points”
or hundredths of 1 percent they contain.
Low Carbon Steel
(Carbon content up to 0.30
percent or 30 points).This steel is soft and ductile and can be rolled,
punched, sheared, and worked when either hot or cold. It is easily machined and
can be readily welded by all methods. It does not harden to any great amount;
however, it can be easily case- or surface-hardened.
Medium Carbon
Steel
(Carbon content from 0.30 to 0.50
percent or 30 to 50 points).This steel may be heat-treated after fabrication.
It is used for general machining and forging of parts that require surface hardness
and strength. It is made in bar form in the cold-rolled or the normalized and
annealed condition. During welding, the weld zone will become hardened if
cooled rapidly and must be stress-relieved after welding.
High Carbon
Steel
(Carbon content from 0.50 to
1.05% or 50 to 105 points) This steel is used in the manufacture of drills,
taps, dies, springs, and other machine tools and hand tools that are heat
treated after fabrication to develop the hard structure necessary to withstand
high shear stress and wear. It is manufactured in bar, sheet, and wire forms,
and in the annealed or normalized condition
in order to be suitable for machining before heat treatment. This steel is
difficult to weld because of the hardening effect of heat at the welding joint.
Tool Steel
(carbon content from 0.90 to 1.70
percent or 90 to 170 points) This steel is used in the
manufacture of chisels, shear blades, cutters, large taps, woodturning tools,
blacksmith’s tools, razors, and other similar parts where high hardness is
required to maintain a sharp cutting edge. It is difficult to weld due to the
high carbon content.
High-Speed Steel
High-speed steel is a
self-hardening steel alloy that can withstand high temperatures without
becoming soft. High speed steel is ideal for cutting tools because of its
ability to take deeper cuts at higher speeds
than tools made from carbon steel.
Tungsten Carbide
Tungsten carbide is the hardest
man-made metal. It is almost as hard as a diamond. The metal is molded from
tungsten and carbon powders under heat and pressure. Tools made from this metal
can cut other metals many times faster than high speed steel tools.
Alloy Steels
Steel is manufactured to meet a
wide variety of specifications for hardness, toughness, machinability, and so
forth. Manufacturers use various alloying elements to obtain
these characteristics. When
elements other than carbon, such as chromium, manganese, molybdenum, nickel,
tungsten, and vanadium are used. The resulting metals are called alloy
.
No comments:
Post a Comment