FIELD OF THE INVENTION:
This invention relates to a material composition for discharge/emitting
electrode wires adaptable in the emitting systems of electrostatic
precipitators.
BACKGROUND OF THE INVENTION;
The electrostatic precipitator (ESP) is basically a pollution control
equipment widely used for collecting dust particles from the flue gas
exhausted from plants such as thermal power plants, cement plants,
steel plants and glass plants.
The electrostatic precipitators are configured with a number of fields
which have collecting and emitting electrodes. A high electric field is
generated between the electrodes to charge the dust particles and collect
the charged particles on the collecting electrodes. High voltage is
generated by means of a high voltage transformer-rectifier. Rapping
mechanism is used for removing the collected dust layer from the
collecting electrodes. Cold drawn austenitic stainless steel wire of

diameter 2.7 mm in a self tensioning spiral spring type configuration is
normally sued as "emitting electrode" also called as discharge electrode
in the Electrostatic precipitator amongst other design of discharge
electrodes. The spiral spring type electrodes have significant
electrical/mechanical properties and are very efficient for high resistive
dust collection in electrostatic precipitator.
The end of the electrodes are provided with reinforced hooks, which
together with a specially holder welded with frames, form flexible links to
prevent fracture due to fatigue.
At present for the emitting electrode wire material, the austenitic
stainless steel is used. The nickel content in the material composition of
austenitic stainless steel is 25% and since the price of nickel is very high,
the cost of austenitic stainless material has become very expensive. Also,
the sources of procurement are limited, which leads to high cost.
Although, the use of austenitic steel is expensive, the main purpose of
using austenitic stainless steel material is that it can overcome the stress

corrosion factor. The phenomenon of stress corrosion cracking leads to
the failure of the material in the form of snapping of wire thereby short-
circuiting the ESP electric fields. The short-circuited electric fields will
not be available for precipitation leading to high emission through stack.
Stress corrosion cracking is cracking due to a process involving conjoint
corrosion and straining of a metal due to residual or applied stresses.
Metals are subject to corrosion. Corrosion can take many forms; the form
that concerns us here is the interaction of corrosion and mechanical
stress to produce a failure by cracking. This type of failure is known as
stress corrosion cracking, often abbreviated to SCC.
SCC is an insidious form of corrosion; it produces a marked loss of
mechanical strength with little metal loss; the damage is not obvious to
casual inspection and the stress corrosion cracking can trigger
mechanical fast fracture and catastrophic failure of components and
structures.

The phenomenon of stress corrosion cracking is complex and has many
variants. Two main variants of stress corrosion cracking are active path
dissolution and Hydrogen Embrittlement. Active path dissolution always
refers to intergranular cracking along an electro chemically active grain
boundary path. Hydrogen embrittlement (HE) can result in either an
intergranular or transgranular crack path. The determining factor is
often the strength of the steel. HE induced cracking in high strength
steel is usually intergranular and whereas in low strength steel HE
cracking is transgranular.
The temperature usually needs to be above 70°C, although SCC can
occur at lower temperatures in some situations, notably more acid
solutions. The cracking continues at low stresses and commonly occurs
as a result of residual stresses from welding or fabrication. The cracking
is normally transgranular, although it may switch to an intergranular
path as a result of sensitization of the steel.
SCC is not an inevitable process, and for most metals in most
environments it will not occur. Therefore it is possible to identify specific

combinations of metal and environment that are subject to the problem.
The exact alloy composition, microstructure and heat-treatment can have
a marked effect on SCC performance. The effects of alloying additions are
not necessarily consisting from one environment to another. Thus, higher
molybdenum content improves the resistant of low alloy steel to
carbonate-bicarbonate cracking, but makes it more susceptible to
caustic cracking. Changes in the thermo mechanical treatment of the
alloy can change the sensitivity to SCC, to mode of fracture and even the
fracture mechanism.
To overcome this stress corrosion failure it is felt that the new alternative
material composition for the emitting wire can be selected in such a way
that the material is suitable for spiral coil formation as well as to prevent
the material from stress corrosion cracking.
In this background, it has become highly essential to develop an
alternative material for emitting wire with less nickel content to cost
economics, without compromising the design/functional requirement of
the emitting wire, to avoid stress corrosion cracking and which is
adaptable in the emitting system of electrostatic precipitator.

OBJECTS OF THE INVENTION:
It is therefore an object of this invention to propose a material
composition for discharge/emitting electrode wires, which can be made
from easily available products and is economical.
It is a further object of this invention to propose a material composition
for discharge/emitting electrode wires, which is designed in a manner to .
avoid stress corrosion cracking.
Another object of this invention is to propose a material composition for
discharge/emitting electrode wires, which is adaptable in the emitting
system of electrostatic precipitator.
These and other objects of the invention will be apparent from the
ensuing description.
DESCRIPTION OF THE INVENTION:
According to this invention is provided a material composition for
discharge /emitting electrode wires, adaptable in the emitting systems of
electrostatic precipitators.

According to this invention is further provided, a method for the
production of a material composition for discharge/emitting electrode
wires, adaptable in the emitting systems of electrostatic precipitators.
Austenitic stainless steels have attractive properties such as high
strength, toughness, and formability and corrosion resistance. High Mn-
N austenitic steels in which Ni is replaced with cost effective Mn is
developed. These steels costs 7 to 8 times lower than steels with high Ni.
But since Mn is not a strong austenitic stabilizer as Ni, the same
austenitic stability can be obtained by replacing the Nickel by combining
Mn with N is these stainless steel alloys.
Nitrogen, is not only an austenitic stabilizer but also improves resistance
to localized corrosion, strengthening and retardation of sensitization.
Cobalt is another alloying element which can replace Nickel with regard
to stabilizing the austenite phase.
The addition of Mn to stainless steels, however, decreases the corrosion
resistance significantly, and it is minimized by addition of higher levels of
Cr, Mo and N.

In the material composition according to the invention, the percentage
of materials like carbon, silicon, phosphorus, sulphur, chromium,
molybdenum, copper are maintained the same and that of the
austenitic stainless steel. The proportions of these constituents are
provided in weight percentages as follows:
Phosphorous-0.005% to 0.050% by weight
Sulphur-.005% to 0.050% by weight
Chromium-5% to 30% by weight
Silicon-0.1% to 1.0% by weight
Molibdinum-1.0% to 10% by weight
Carbon-0.001% to 0.1% by weight
Copper-0.25% to 5% by weight
However the percentage of material like manganese is altered from the
original value of 2.8% by weight to a value to 15 to 33% by weight.
The proportion of nickel is altered from 25% to a new proportion of 0
to 9.9%. Nitrogen is added in 0.3% and cobalt may be optionally
added and is present in 0 to 1.9% by weight.

In a preferred embodiment according to the invention, the proportion
of carbon, silicon, phosphorus, sulphur, chromium, molybdenum and
copper are maintained the same as in austenitic stainless steel and as
provided hereinbefore, but manganese is present in 15 to 17% and
nickel is present in 7 to 9.9% by weight. Nitrogen is present in 0.3%
by weight.
In another preferred embodiment according to the invention, the
proportion of carbon, silicon, phosphorus, sulphur, chromium,
molybdenum and copper are maintained the same as in austenitic
stainless steel and as provided hereinbefore, but manganese is
present in 28 to 33%. Nickel in 0.3%, nitrogen in 0.3% and
additionally cobalt is present in 0.5 to 1.9%.
The compositions are formed by standard alloying procedures, such
as basic oxygen steel making in an LD converter. The carbon rich
molten pig iron is made into steel by blowing oxygen through molten
pig iron which lowers the carbon content of the alloy and changes it

into low-carbon steel. The process is basic due to the pH of the
refractories-calcium oxide and magnesium oxide-that line the vessel
to withstand the high temperature of molten metal. The steel is
further refined in the ladle furnace, by adding alloying material to give
the steel special properties as required . After the steel is removed
from the BOS vessel, the slag, filled with impurities, is poured off and
cooled.
The invention will now be explained in greater detail with the help of
the following non-limiting examples.
Example-1
An austenitic steel composition was prepared by alloying an austenitic
stainless steel composition with manganese and nitrogen, so that in
the final composition the percentage of materials like carbon, silicon,
phosphorous, sulphur, chromium, molybdenum, copper are
maintained same as that the austenitic stainless steel material but
the composition percentage of manganese is 17% by weight and that
of Nickel is altered to 9.9%. Also nitrogen by 0.3% is added to the
composition.

Example-II
An austenitic steel composition was prepared in which carbon, silicon,
phosphorus, sulphur, chromium, molybdenum, copper are maintained
same as that of the austenitic stainless steel material but the weight
percentage of manganese is altered to 33% and that of Nickel is altered
to 0%. Also Nitrogen is 0.3% and cobalt in 1.9% by weight, is added.

WE CLAIM:
1. An alloy composition for discharge emitting electrode wires,
comprising Phosphorous-0.005% to 0.050% by weight,
Sulphur-.005% to 0.050% by weight, Chromium-5% to 30% by
weight, Silicon-0.1% to 1.0% by weight, Molibdinum-1.0% to
10% by weight, Carbon-0.001% to 0.1% by weight, Copper-
0.25% to 5% by weight and manganese in 15 to 33% by weight,
nickel from 0 to 9.9% by weight, nitrogen in 0.3% by weight and
cobalt in 0 to 1.9% by weight.
2. The alloy composition as claimed in claim 1, wherein
manganese is present in 15 to 17%, nickel in 7 to 9.9%,
nitrogen is present in 0.3% and cobalt is present in 0% by
weight.
3. The alloy composition as claimed in claim 1, wherein
manganese is present in 28 to 33%, nickel in 0.3%, nitrogen in
0.3% and cobalt in 0.5 to 1.9% by weight.

An alloy composition For discharge emitting electrode wires, comprising Phosphorous-0.005% to 0.050% by weight, Sulphur- .005% to 0.050% by weight, Chromium-5% to 30% by weight, Silicon-
0.1% to 1.0% by weight, Molibdinum-1.0% to 10% by weight, Carbon- 0.001% to 0.1% by weight, Copper-0.25% to 5% by weight and manganese in 15 to 33% by weight, nickel from 0 to 9.9% by weight, nitrogen in 0.3% by weight and cobalt in 0 to 1.9% by weight.