METAL PROPERTIES, CHAR, USES, AND CODES - OD1643 - LESSON 1/TASK 1
Characteristics of Steel and Cast Iron.
(1) Basic Substance. The basic substance used to make both steel
and cast iron (gray and malleable) is the metal, iron in the form of
pig iron. Pig iron is produced from iron ore, which occurs chiefly
in nature as an oxide, the two most important oxides being hematite
(2) Iron Ore. Iron ore is reduced to pig iron in a blast furnace,
and the impurities are removed in the form of slag (figure 2 on the
following page). Raw materials charged into the furnace include iron
ore, coke, and limestone.
The pig iron produced is used to
manufacture steel or cast iron.
To convert iron ore to iron, the
iron ore is smelted with coke and limestone in a blast furnace
(figure 3 on page 13) to remove from it the oxygen (the process of
reduction) and earth foreign matter.
Limestone is used to combine
with the earth matter to form a liquid slag; coke is used to supply
the chemical element of carbon needed for the reduction and
carburization of the ore.
The iron ore, limestone, and coke are
charged into the top of the furnace. Rapid combustion, with a blast
of preheated air into the smelter, causes a chemical reaction in
which the oxygen is removed from the iron. The iron melts, and the
molten slag, consisting of limestone flux and ash from coke, together
with compounds formed by the reaction of the flux with substances
present in the ore, floats on the heavier iron liquid. Each material
is then separately drawn off.
(3) Plain Carbon Steel. Plain carbon steel consists of iron and
carbon, the latter being the hardening element. Tougher alloy steel
contains other elements, such as chromium, nickel, and molybdenum.
Cast iron is nothing more than basic carbon steel with more carbon
added together with silicon.
The carbon content range for steel is
0.03 to 1.7 percent, and for cast iron 4.5 percent.
Steel is produced in a variety of melting furnaces:
open-hearth, Bessemer converter, crucible electric-arc, and induction.
Most carbon steel is made in open-hearth furnaces, while alloy steel is
melted in electric-arc and induction furnaces. Steel, often considered
as the master metal, is available in large quantities in both