White
Irons
These irons, on fracture appear as white silvery fractures. The carbon
in the iron is no longer free grey coloured graphite but is locked in
chemical compositions of hard wearing carbides. The unalloyed White
Irons have a hardness of 200-350 BHN the lower end of the hardness
scale can be machined but generally are used as cast.
The
use of white irons is generally in low impact abrasive situations such
as liner plates and abrasive material pump cases.
Ni-Hard
( Nickel - Chromium Alloyed )
In
these irons a development of iron-chromium carbides produce a tougher
more abrasion resistant iron. The variation of carbon content effects
the toughness and abrasion resistance. Greater carbon increases the
resistance to abrasion, however at the loss of toughness and vice
versa lowering the carbon increases toughness but decreases the
resistance to wear. Hardness ranges dependent on section thickness can
be between 450-600 BHN
The
use for Ni-Hards is in pulverizing, crushing and impact wear plates
also in heavy duty pump casings and impellers for slurry and gravel
applications.
High
Chromium Alloys
These
irons produce a more continuous structure of iron-chromium carbides.
After heat treatment these irons have a hardness range of 600-650 BHN
All
the white irons are difficult to machine, however advances in ceramic
machining tips have vastly improved the prospects.
