White cast irons are widely used in abrasive wear applications
involved in the crushing, grinding, milling and handling of abrasive
materials such as minerals and ores, both dry and as slurries.
Three types of irons are commonly used:
White Iron is unalloyed cast iron with low carbon and silicon
content such that the structure is hard brittle iron carbide with no
free graphite. These irons are limited in application because of the
lack of impact resistance and the difficulty in maintaining the
structure in thicker sections. In some cases the castings are
designed and produced to have a white structure in certain areas and
a grey or flake structure elsewhere to improve toughness.
Martensitic white cast irons containing nickel and chromium are
commonly known as Ni-Hards. There are two general types containing
4% Ni-2% Cr, and 8% Cr-6% Ni. Both have a structure of iron and
chromium carbides in a matrix of martensite and bainite, but the
higher alloy content materials have a type of carbide which is
discontinuous and confers greater impact and corrosion resistance.
These irons can be used as cast, but heat treatment improves the
hardness and resistance to surface cracking and spalling.
High Chromium cast irons have typical compositions of 15%Cr-3%Mo and
23-28%Cr and a superior combination of abrasion resistance and
toughness. In some cases they may be used as cast, but are normally
air hardened to develop the optimum properties.
Some of these irons may also be machined after annealing and then
hardened to produce a machined abrasion resistant part.
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