لخّصلي

The earth contains a large number of metals which are useful to man.Any carbon content above that percentage is present in the form of flaky graphite.A certain number of non-ferrous metals, including aliminium and zine, are also important, but even today the majority of our engineering products are of iron or steel.The process of smelting consists of heating the ore in a blast furnace with coke and limestone, and reducing it to metal.These non-metallic constituents of cast-iron include carbon, silicon and sulphur, and the presence of these substances affects the behaviour of the metal.The non-metallic constituents of the ore combine with the limestone to form a liquid slag.We can melt this down again in another furnace - a capula - with more coke and limestone, and tap it out into a ladle or directly into moulds.Iron which contains a negligible quantity of carbon, for example wrought-iron, behaves differently from iron which contains a lot of carbon.Moreover, iron possesses magnetic properties, which have made the development of electrical power possible.The ore becomes molten, and it oxides combine with carbon from the coke.Steel contains no free graphite, and its carbon content ranges from almost nothing to 1 1/2 %.This is cast-iron.

The earth contains a large number of metals which are useful to man. One
of the most important of these is iron. Modern industry needs considerable
quantities of this metal, either in the form of iron or in the form of steel. A
certain number of non-ferrous metals, including aliminium and zine, are also
important, but even today the majority of our engineering products are of iron or
steel. Moreover, iron possesses magnetic properties, which have made the
development of electrical power possible.
The iron ore which we find in the earth is not pure. It contains some
impurities which we must remove by smelting. The process of smelting consists
of heating the ore in a blast furnace with coke and limestone, and reducing it to
metal. Blasts of hot hair enter the furnace from the bottom and provide the
oxygen which is necessary for the reduction of the ore. The ore becomes molten,
and it oxides combine with carbon from the coke. The non-metallic constituents
of the ore combine with the limestone to form a liquid slag. This floats on top of
the molten iron, and passes out the furnace through a tap. The metal which
remains is pig-iron.
We can melt this down again in another furnace – a capula - with more
coke and limestone, and tap it out into a ladle or directly into moulds. This is
cast-iron. Cast-iron does not have the strength of steel. It is brittle and may
fracture under tension. But it possesses certain properties which make it very
useful in the manufacture of machinery. In the molten state it is easy to machine
it. Cast-iron contains small proportions of other substances. These non-metallic
constituents of cast-iron include carbon, silicon and sulphur, and the presence of
these substances affects the behaviour of the metal. Iron which contains a
negligible quantity of carbon, for example wrought-iron, behaves differently
from iron which contains a lot of carbon.
The carbon in cast-iron is present partly as free graphite and partly as a
chemical combination of iron and carbon which we call cementite. This is a very
hard substance, and it makes the iron hard too. However, iron can only hold
about 1½% of cementite. Any carbon content above that percentage is present in
the form of flaky graphite. Steel contains no free graphite, and its carbon content
ranges from almost nothing to 1½%. We make wire and tubing from mild steel
with a very low carbon content, and drills and cutting tools from high carbon