ABRASION
RESISTANT IRONS
White
Irons,
Ni-Hard and
High Chromes:
BS4844 ASTM
A532
BS 4844
ASTMA532
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.
Chemical composition of
unalloyed and low alloy
grades
BS 4844 White Irons
Most Common Grade 1A
|
Grade
|
Carbon
%
|
Silicon
%
|
Manganeses
%
|
Chrome
%
|
Phosphorus
%
|
1A
|
2.4
to 3.4
|
0.5
to 1.5
|
0.2
to 0.8
|
2.0
Max
|
O.15
Max
|
1B
|
2.4 to
3.4
|
0.5 to
1.5
|
0.2 to
0.8
|
2.0 Max
|
0.50
Max
|
1C
|
2.4 to
3.0
|
0.5 to
1.5
|
0.2 to
0.8
|
2.0 Max
|
0.15
Max
|
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
pulverising, crushing and impact wear plates also in heavy duty pump
casings
and impellers for slurry and gravel applications.
Chemical composition of
nickel chromium alloys
BS 4844 Ni-Hard Irons
Most Common Grade 2B
|
Grade
|
Carbon
%
|
Silicon
%
|
Manganese
%
|
Nickel
%
|
Chrome
%
|
2A
|
2.7 to
3.2
|
0.3 to
0.8
|
0.2 to
0.8
|
3.0 to
5.5
|
1.5 to
3.5
|
2B
|
3.2
to 3.6
|
0.3
to 0.8
|
0.2
to 0.8 |
3.0
to 5.5
|
1.5
to 3.5
|
2C
|
2.4 to
2.8
|
1.5 to
2.2
|
0.2 to
0.8 |
4.0 to
6.0
|
8.0 to
10.0
|
2D
|
2.8 to
3.2
|
1.5 to
2.2 |
0.2 to
0.8 |
4.0 to
6.0 |
8.0 to
10.0 |
2E
|
3.2 to
3.6
|
1.5 to
2.2 |
0.2 to
0.8 |
4.0 to
6.0 |
8.0 to
10.0 |
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.
They are nearly impossible to drill and tap and hace steel
inserts cast into the casting to allow drilling and tapping to take
place.
Chemical Composition of
High Chrome irons
BS 4844
Most Common Grade 3E
|
Grade
|
Carbon
%
|
Silicon
%
|
Manganese
%
|
Moly.%
|
Nickel
%
|
Chrome
%
|
Copper
%
|
3A
|
1.8 to
3.0
|
1.0 Max
|
0.5 to
1.50
|
2.5 Mx
|
2.0 Max
|
14 to
17
|
2.0 Max
|
3B
|
3.0 to
3.6
|
1.0 Max |
0.5 to
1.5 |
3.0 Max
|
2.0 Max |
14 to
17
|
2.0 Max |
3C
|
1.8 to
3.0
|
1.0 Max |
0.5 to
1.5 |
3.0 Max
|
2.0 Max |
17 to
22
|
2.0 Max |
3D
|
2.0 to
2.8
|
1.0 Max |
0.5 to
1.5 |
1.5 Max
|
2.0 Max |
22 to
28
|
2.0 Max |
3E
|
2.8
to 3.5
|
1.0
Max |
0.5
to 1.5 |
1.5
Max
|
2.0
Max |
22
to 28
|
2.0
Max |
3F
|
2.0 to
2.7
|
1.0 Max |
0.5 to
1.5 |
2.5 Max
|
2.0 Max |
11 to
13
|
2.0 Max |
3G
|
2.7 to
3.4
|
1.0 Max |
0.5 to
1.5 |
3.0 Max
|
2.0 Max |
11 to
13
|
2.0 Max |