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Home > Ordnance Documents and other related manuals > > Grey Cast Iron
Figure 3. Converting Iron Ore to Iron.
Steel

Metal Properties, Characteristics, Uses, And Codes
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METAL PROPERTIES, CHAR, USES, AND CODES - OD1643 - LESSON 1/TASK 1
(b) Capabilities.
Cast  iron  is  commonly  brazed  or  bronze
welded, but it can be gas or arc welded, hardened, or machined.
(c) Limitations.  Cast iron must be preheated prior to welding;
it cannot be cold-worked.
(d) Grey Cast Iron.
If molten pig iron is permitted to cool
quite slowly, the chemical compound of iron and carbon breaks up to a
certain extent; much of the carbon separates out as tiny flakes of
graphite scattered throughout the metal.  This graphitic carbon, so-
called  to  distinguish  it  from  combined  carbon,  causes  the  gray
appearance of a fracture which characterizes ordinary gray cast iron.
Since graphite is an excellent lubricant, and since the metal is
filled with tiny flaky cleavages, it is not difficult to understand
why gray cast iron is so easy to machine, and why it cannot withstand
a heavy shock.
Gray cast iron consists of from 90 to 94 percent
metallic  iron  with  varying  proportions  of  carbon,  manganese,
phosphorus,  sulfur,  and  silicon.
Special  high-strength  grades
contain 0.75 to 1.5 percent nickel and 0.25 to 0.5 percent chromium,
or 0.25 to 1.25 percent molybdenum.  Commercial gray iron has 2.5 to
4.5 percent carbon.  Of this quantity, about 1 percent of the carbon
is combined with the iron, while about 2.75 percent remains in the
free  or  graphitic  state.
In  the  production  of  gray  cast  iron,
silicon  content  is  usually  increased,  since  this  facilitates  the
formation of graphitic carbon.
The combined carbon (iron carbide),
which is a small percentage of the total carbon present in cast iron,
is known as cementite.  In general, the more free (graphitic) carbon
present in cast iron, the lower the combined carbon content and the
softer the iron.
(e) White Cast Iron.
When gray cast iron is heated to the
molten state, the carbon completely dissolves in the iron.
If this
molten  metal  is  cooled  quickly,  the  two  elements  remain  in  the
combined state, and white cast iron is formed.
The carbon in this
type of iron is generally from 2.5 to 4.5 percent by weight and is
referred to as combined carbon.
White cast iron is very hard and
brittle,  often  impossible  to  machine,  and  has  a  silvery  white
fracture surface.
(f) M a l l e a b l e  C a s t  I r o n .
Malleable  cast  iron
is
made  by  heating  white  cast  iron  to  between
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