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AUSTENITIC CAST IRONS
These are Irons alloyed with high percentages
of Nickel and Chromium. Basically they are the iron equivalents of
Stainless steel in their properties, but alas not their looks. Two
basic types are available based on the type of carbon. The graphite
appears as either flake, as in grey iron or spheroidal as in SG irons.
The SG versions having greater mechanical properties than the flake.
Both types, because of the high Nickel, have similar properties of
heat resistance and good resistance to salt water and other corrosive
materials.
They can exhibit low levels of magnetic permeability i.e. they can be
non magnetic.
Main uses : sea water pump and valve parts and high temperature ovens
/ furnaces.
The Flake graphite grades are denoted with
a prefix of 'F'
The SG grades are denoted with a prefix 'S'
Flake grades have a tensile of 170 to 240 N/mm.sq
SG grades are stronger with a tensile of 370 to 490 N/mm.sq
- AUSTENITIC CAST IRONS
A family of austenitic, high alloy
Ductile Irons identified by the trade name "Ductile
Ni-Resist" have been produced for many years to meet a
wide range of applications requiring special chemical, mechanical
and physical properties combined with the economy and ease of
production of Ductile Iron. Ductile Ni-Resist irons containing
18-36% nickel and up to 6% chromium combine tensile strengths of
55-80 ksi (380-550 MPa) and elongations of 4-40% with the following
special properties:
- corrosion, erosion and wear resistance,
- good strength, ductility and oxidation
resistance at high temperatures,
- toughness and low temperature stability,
- controlled thermal expansion,
- controlled magnetic and electrical
properties and
- good castability and machinability.
Specifications
and Recommendations
The ASTM and ASME
specifications for Ductile Ni-Resist Irons and lists typical
applications for each grade. This section contains further information
on international specifications for these materials. The applications
listed for each grade take advantage of the following general
characteristics.
Type D-2,
the most commonly used grade, is recommended for service requiring
resistance to corrosion, erosion and frictional wear up to temperatures
of 1400oF (760oC).
Type D-2B,
provides higher resistance to erosion and oxidation than Type D-2 and is
also recommended for use with neutral and reducing salts.
Type D-2C,
is recommended where resistance to corroision is less severe and high
ductility is required.
Type D-2M
(2 classes) is recommended for cryogenic applications requiring
structural stability and toughness.
Type D-3
exhibits excellent elevated temperature properties and resistance to
erosion. It is recommended for applications involving thermal shock and
thermal expansion properties similar to ferritic stainless steels.
Type D-3A
provides good resistance to galling and wear, and intermediate thermal
expansion.
Type D-4
provides resistance to corrosion, erosion and oxidation that is superior
to Types D-2 and D-3.
Type D-5 is
recommended for applications requiring miniumu thermal expansion.
Type D-5B
should be used in aplications requiring minimum thermal stresses, and
good mechanical properties and resistance to oxidation at high
temperatures.
Type 5-S
provides excellent resistance to oxidation when exposed to air at
temperatures up to 1800oF (980oC) and is also
recommended for applications involving thermal cycling at temperatures
up to 1600oF (870oC).
Selection of General Engineering
Grades
Part of Austentitic Cast Iron BS 3468: 1986
| F1 |
Good resistance to
corrosion of dilute acids, alkalis and sea water.
Good heat resistance. Mining and flanges. |
| F2 |
Similar to F1 but
with more corrosion resistance to alkalis |
| S2 |
Similar to F2 but
with superior mechanical problems: marine |
| S5 |
Excellent
resistance to growth and scaling up to 850 deg. C
Low thermal expansion and good thermal shock resistance |
These metals are
melted with an electric furnace rather than the coke fired cupola
