FIELD OF THE INVENTION
The present invention relates to wear resistant screen deck for screening of the BF grade
coke of desired size and a process for developing such screen deck. The present
invention is directed to improving the wear properties of steel screen decks to achieve
higher wear resistance than mild steel and hardness over 550 BHN for favored
application in screen deck. The invention is further directed to composite deck plates
comprising deposition of a single top layer of iron based chromium carbide alloy over
mild steel base plate for BF coke screening application. The invention favours forming a
composite top layer over the screen top surface such that it favored bulk hardness of
550-560 BHN in the top hard layer. More advantageously, the minimum percentage of
primary chromium carbide has been obtained 35-40% which favours the desired wear
resistant characteristics of the deck of the invention. The process of obtaining the deck of
the invention further ensures minimal dilution of top layer with base material. The
process of the invention also ensure prevention of any propagation of cracks in base
material due to rapid cooling of the alloyed smelting bath during forming.
Advantageously, the deck of the invention involving the composite chromium carbide
layer deposition on screen deck surface ensure presence of long needle shaped crystals
with hexagonal cross section lead to adequate primary chromium carbides providing
higher wear resistance. The higher hardness (550-600 BHN) of top layer and presence of
adequate percentage of primary long and needle shaped carbides in the top layer which
resulted in the overall increase in the wear ratio (40x) of the deck plates prepared
according to the present process favoring achieving very long service life and thus having
the prospects of large scale application in steel and similar other industry.
BACKGROUND ART
The screening operation of input coke and other input raw materials to furnace, to obtain
selective sizes of granular coke is an important criteria in any integrated steel plants for
the proper functioning of the blast furnaces and also to ensure desired overall
productivity / yield of various upstream operations/sections like Coke Oven for coke
making, Sintering Plants, Raw material handling etc. The stringent quality requirement
for the upstream shops like Raw Material Handling, Coke Oven plant and Sinter Plants
have been adopted through appropriate measure to meet quality requirements of their

downstream shop e.g. the Blast Furnace(BF) operation. The major raw materials required
for iron making in blast furnace are sinter, iron ore fines, BF grade low ash coke etc. For
smooth running of furnace and to avoid choking of furnace burden, it is important to
have proper quality and sized input raw materials to BF, especially the sinter and coke, to
achieve proper burden distribution in the furnace.
Therefore, to ensure smooth and efficient furnace operation, to have the correct
sized/granulometry of raw materials all the incoming raw materials need to be properly
screened for removing the undesired size particles in the feed. In case of coke feeding to
BF, the desired size fraction is 25-80 mm for optimum furnace operation. The coke
produced in coke oven batteries are screened in self linear vibrating screens in two
stages using punched steel deck plates so as to provide the desired size of coke to blast
furnace. In the first stage of screening, the wharf coke produced in the coke oven
batteries are fed to a self linear vibrating screens having steel screen deck plates with
80mm square punched holes to remove the oversize coke particles (>80mm). The
undersize <80mm particles are again passed through another self linear vibrating
screens fitted with 25 mm square sized holes steel screen deck plates. In both these
conventional screening processes, the punched deck plates are fabricated with low alloy
steel, having poor wear resistant properties of the steel and relatively low hardness in
the range of 150-200 BHN. As a result, such existing deck plates are getting worn out at
a fast rate, resulting in very low life in the range of 2-3 months only. This results in
enlargement of slots/holes and the erosion of material leading to breaking of plates. The
early enlargement of slots/holes made in the decks and subsequent joining of adjacent
holes is conducive for large holes /open space in the deck plates, making the screening
process ineffective and uncontrolled with respect to granulometric size. These large holes
not only passing out through the screen the undesired undersize fractions of coke but
also allows some percentage of quality coke of favorable size range (25-80mm) mixed
into the undersize fractions. This is resulting in loss of yield of coke. Also the low service
life of coke screen decks results in frequent shut down of machine at least on 4 occasions
in a year and the repair/replacement consuming at least 16 Hr/screen/shut down,
sacrificing production and productivity. If the spares are not available or there occurs
substantial delay in procurement of the same , the worn out decks may cause substantial
loss of good favorable quality coke, getting mixed into the undersize coke and thereby
adversely affecting the BF performance. This mixing of screened coke sizes adds to the
circulation load of undersize fraction of coke which is not desirable at all.

Some of the prior Patents and publications in the related field are briefly described in the
following paragraphs to illustrate the state of the prior art.
The prior publication no. WO/2007/069970 dated 21.06.2007 entitled "SCREENING
ARRANGEMENT" states in its abstract about a screening arrangement in a vibrating
screen for screening of material, such as crushed stone, gravel or the like. Said screening
arrangement having one or more screening decks placed at different heights and
provided with directing means, where the directing means are provided on the underside
of at least one upper screening deck to direct the screened material upstream onto a
screening deck located below the at least one upper screening deck.
International publication number WO 2005/077551 dated 25.08.2005 is prior Patent
publication that states in its abstract regarding a screening deck for screening of
material, such as crushed stone, gravel or the like, the screening deck comprising
screening elements and where at least one side of each screening element is not parallel
with a longitudinal direction (A) of the screening deck and that the screening deck
includes at least two different types of said screening elements and that different
screening elements are arranged at different heights in the screening deck for creating
narrowing passages or winding paths for the material on the screening deck .
The above two cited prior publications are substantially same inventions which do not
direct to any means for enhancement of the operating life of the screen deck nor it refers
to screening of coke and dealing with associated constraints thereof, to meet the
requirement of the BF operation in steel plants.
Prior publication number WO 2003/066243 dated 14.08.2003 entitled "SCREEN DECK"
states in its abstract about a screen deck runner assembly suitable for use in a vibratory
screening machine characterized by the assembly including a saddle member, being
configured and dimensioned to removably straddle a screen deck runner and to engage
a screen panel.
Thus this cited prior art is speaks in particular about the construction of the screen deck
runner assembly and nothing about the performance improvement of the machine in
terms of strength, hardness and wear resistance of the screen material or any means to

improve such properties of screen material to enhance service life of the screening
machine.
Prior publication number WO 2004/099560 A1 dated 18.11.2004 entitled "EROSION
RESISTANT SAND SCREEN" states in its abstract about a sand screen comprising a
perforated base pipe and an erosion resistant micro porous sleeve. The erosion resistant
micro porous material of the sleeve is preferably selected from among the group
comprising microporous polymeric foams, microporous metal foams, microporous carbide
monoliths, microporous nitride monoliths.
Though this cited prior art is directed to the erosion resisting property of the sand
screening sleeve element but is different in application as of the screening of BF grade
coke. It is clearly apparent from the cited prior art that the basic inventive intent is
directed to sand screening wherein the micro porous sleeve is erosion resistant and may
be made of material including carbide monoliths, but the present invention is distinctly
different dealing with the problem of operating life enhancement for the screening deck
for BF grade coke to selective desired size of 25mm-80mm, by overlaying metallic
carbide composite on said MS plate to develop the wear resistant screen.
There has been therefore a persistent need to develop steel screen having higher
hardness and wear resistance preventing enlargement of holes of screening deck, by
favored deposition of metallic carbide composite material on the top layer of screen deck
and thereby ensuring selective size of screened material e.g. coke sinter and the like,
that would favor the down stream operation using such coke of desired range in BF for
longer run without requiring any repair and replacement affecting the productivity. The
screen deck with metallic carbide and preferably the chromium carbide composite
deposition on MS base plate provide an economic and simple means to enhance the
performance of such screen providing consistently preferred range of granulometric size
range of good quality coke and avoiding mixing with undersized coke and overcoming the
limitations due to undesirable circulation load of undersize fraction of coke in BF.
OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to provide a composite screen deck
involving a base plate such as of MS base plate so as to achieve desired high hardness

and wear resistance favoring effective screening of the hard coke to provide consistently
good quality coke of desired size range of 25-80mm, avoiding enlargement of holes in
said screen deck and enhanced operating life of said screen without repair/replacement,
ensuring higher productivity in BF operation.
A further object of the present invention directed to said screen deck with metallic
carbide deposited top layer to enhance the wear resistance of screen decks to reduce
maintenance and arrest loss of desired quality grade materials, in BF operation due to
mixing of preferred and undesired granulometric sizes.
A further object of the present invention directed to said screen deck with metallic
carbide deposited top layer having enhanced high hardness and wear resistance
properties and thus favoring reduced down time and sacrificing quality, higher
productivity and yield of the Blast Furnace operation.
A still further object of the present invention directed to said powder metallurgical metal
carbide coated screen deck wherein minimum percentage of primary chromium carbide is
to be obtained in the range 35-40%, thus providing high hardness in the order of 550-
600VHN and the over all wear ratio of 40x for the deposited wear resistant iron-
chromium carbide composite layer, having selective as deposited chemistry.
Another object of the present invention directed to the process of depositing chromium
carbide and more particularly iron-chromium carbide composite on the MS base plate of
said screen deck for coke screening wherein the invention further ensures minimal
dilution of top layer with base material. The process of the invention also ensures
prevention of any propagation of cracks in base material due to rapid cooling of the
alloyed smelting bath during forming and thus providing longer and reliable performance
of said screen deck.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a screen
deck with improved wear properties comprising:

a base plate and
atleast one layer of chromium carbide metallic alloy deposition theron wherein the alloy
comprises C: 4-5%,Si: 0.5-1.0%, Mn: 0.8-1.2 % ,Cr: 25-30 % and Fe-balance.
According to an aspect of the invention the screen deck with improved wear properties
comprises of a base plate comprising mild steel base plate.
In accordance with a preferred aspect in the screen deck with improved wear properties
of the invention, the total thickness of the deck comprises about 10 mm wherein the top
layer of chromium carbide metallic alloy deposition comprise 2-2.5 mm and the base
plate comprise 7.5-8.0 mm with holes therethrough the deck obtained of either plasma
or electro discharge machining..
According to another aspect in the screen deck with improved wear properties of the
invention the plate size is in the range of from 3/8" to 1-1/2" in thickness, widths from
4' to 8' and lengths from 8' to 20'.
Preferably, the screen deck with improved wear properties of the invention involve the
overlay deposit comprising of one or two layers measuring 1/4" or 3/8" thickness.
In accordance with a further aspect in the screen deck with improved wear properties the
bead width vary typically in the range of 1- V2" wide and are randomly check cracked.
According to yet further preferred aspect of the invention the screen deck with improved
wear properties of the invention comprises the overlay deposit composition comprising

from 15% to 30% Chromium, 3.0% to 4.5% carbon, Manganese and Silicon from 1% to
4% and Optionally Molybdenum up to 3%.
Importantly, the screen deck with improved wear properties of the invention achieves the
hardness of the deposit layer varies in the range of 400 BHN to 600 BHN preferably 550-
600 BHN.
In accordance with yet another aspect of the invention there is provided a method for the
manufacture of a screen deck with improved wear properties as above comprising:
preparing the alloy with desired composition ;
welding the powder alloy into the top surface of the base plate; and
cutting desired holes with either plasma or electro discharge machining techniques.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING
EXAMPLE
The present invention is directed to achieving enhanced hardness and wear resistance
properties in the screen deck top layer by depositing iron-chromium carbide composite
top layer by powder metallurgical process in order to provide enhanced service life of
decks for coke screening avoiding hole enlargement on coke screen leading to mixing
with undesirable undersized coke, and thereby reducing the machine down time, increase
machine availability for higher production and improving the yield. The improved
performance of the screen deck for coke screening also ensure maintaining consistently
good quality granule in the desired size range of 25-80mm which in turn help achieving
balanced load distribution and improved performance and yield of the Blast Furnace using
such coke.

The method for developing the high hardness and high wear resistance of coke screen
top layer, an iron based chromium carbide metallic alloy composition was selectively
obtained through trials and testing. Various alternative methods are tested for optimum
performance for manufacture of such composite overlay on MS plate for screen deck
application for coke screening. The common method of depositing such metallic carbide
overlay comprise:
a. Arc welding process using (i) Open Arc or (ii) Submerged Arc or Fusion bond
Welding.
b. Base plate configuration comprising (i) Flat plate or Table design, or Cylindrical
drum.
The selection of any of the combinations of the above variables bear significant impact on
the quality, consistency, and integrity and wear properties of the plate.
An embodiment of the present invention for achieving favored metallic carbide composite
overlay on screen deck for coke screening providing desired hardness and wear
resistance properties in the deposited layer are may be better under stood from the
following example:
EXAMPLE:
BASIC PROCESS STEPS:
Flat plates of IS 2062 grade steel of required sizes are procured for Overlaying with
metallic carbide composite. There are different options for configuring the plate for
overlay process. The present embodiment of the invention selected the option for overlay
by placing the Flat plate of selective size and thickness on a specially designed Flat Table,
known to be the Table method of configuring. The obvious advantage with this
configuration is the ease of plate handling while depositing the metallic carbide layer. The
Flat plate obtained for overlaying is just placed on the table and suitably clamped in
position. Either an open arc or Fusion Bond welding process carries out the
overlay/deposit/weld on said flat plate on table. The flat plate with the deposited overlay
of selective composition is then subjected to a straightening or flattening process and

then trimmed to size on a plasma-cutting machine. The process is simple and need no
special skill for production of such overlaid screen deck plate. But some complexity arises
at times during the welding of base plates of less than ¾" thick. Distortions in the form of
large humps affect adversely the deposit integrity. Thus whenever a hump is
encountered by the welding arc, penetration and dilution of the base plate increases. This
lead to a chemistry of the deposition in the hump portion that is not capable to
demonstrate the desired properties of hardness and wear resistance in the overlay. This
problem is therefore adequately addressed to ensure uniform chemistry and properties in
the deposited overlay, ensuring minimum distortions and the allied problems, by
selecting preferred size/thickness of base plate and controlled weld parameters for
overlaying with open arc process or SAW at controlled heat input rate.
THE DECK CONSTRUCTION:
Chromium Carbide Overlay on MS Plates of the invention comprised of a mild steel base
plate onto which a highly abrasive resistant welded overlay is deposited using an open
arc or submerged arc process. Plate sizes typically range from 3/8" to 1-1/2" in
thickness, widths from 4' to 8' and lengths from 8' to 20'. The overlay deposit consists of
one or two layers measuring 1/4" or 3/8" thick. Bead widths vary according to the
method of manufacture but typically about 1-1/2" wide and are randomly check cracked.
Check cracking occurs as a natural phenomenon during welding and is controlled by the
chemical composition of the overlay or by cooling methods.
According to an embodiment of the present invention, to achieve desired improved wear
properties in overlay weld deposit on screen deck for favored application in screening of
Coke, with reduced down time avoiding enlargement of holes, and ensuring consistently
improved performance in BF operation, an iron base chromium carbide metallic alloy
composition has been selected. Said composition of the selective alloy comprised the
following chemistry by wt. percent:
C: 4-5%, Si:0.5-1.0%, Mn: 0.8-1.2%, Cr:25-30% and balance Fe.
It has also been designed to have composite deck plates of different thickness in place of
a single material. The present embodiment of the invention, the base plate of mild steel
was selected having thickness in the range of 7.5-8.0 mm and preferably 8mm. To

achieve a hard surface over the mild steel base at least one single layer of the above said
alloy was deposited by powder metallurgy technique. The alloy was first prepared in the
designed chemistry and then automatically welded to have the desired thickness in a
single layer. For this submerged arc method was used for fusion of the powder alloy into
the top surface of the base plate. Since the total thickness of the plate has to be
maintained to 10 mm, the top layer was maintained at 2-2.5 mm, over said base plate of
8mm thickness. By this way a set of deck plates were manufactured using the above
alloy deposit over mild steel base plates.
After the overlaying of the screen deck plates with suitable alloy composition/properties
and straightened/flattened to eliminate weld distortions and cut to finish size by plasma
cutting machine, the required numbers of holes/slots of required sizes are cut with
plasma cutting machine such as to favor obtaining coke in the desired size range of
25mm to 80mm after screening of quenched coke, crushed by vibratory screen.
Thus the process of developing the screen deck for screening of coke having favored
hardness/wear resistant properties to ensure desired enhanced operating life of the
screen deck and consistently supplying good quality coke of desired size range of 25mm
to 80mm for BF operation, comprising the following steps:
a. Obtaining MS Flat Plate of selective size and thickness usually about 8mm thick,
widths from 4' to 8' and lengths from 8' to 20'.
b. Laying the Flat plate on a specially designed Flat table and suitably clamped to
arrest/limit distortion/localized hump formation, within limits during over laying of
the composite metallic carbide deposition by the powder metallurgical process.
c. An iron based chromium carbide metallic alloy composition has been selected for
overlaying composition of the selective alloy comprised the following chemistry by
wt. percent:
C: 4-5%, Si:0.5-1.0%, Mn: 0.8-1.2%, Cr:25-30% and balance Fe.
d. Either an Open arc or Fusion Bond or Submerged Arc welding process is carried
out to overlay/deposit/weld on said flat plate on table.
e. The submerged arc method is also used for fusion of the powder alloy into the top
surface of the base plate. Since the total thickness of the plate has to be
maintained to 10 mm, the top layer was maintained at 2-2.5 mm, in incremental
widths of 1-1/2" in each pass, over said base plate of 8mm thick MS plate, with

controlled parameters for favored controlled heat input rate to arrest
distortion/hump formation and favor achieving desired properties in resulting
composite overlay.
f. A set of deck plates were manufactured using the above alloy deposit over mild
steel base plates.
g. Overlaying of the screen deck plates with over layed alloy composition/properties
and straightened/flattened to eliminate weld distortions and cut to finish size by
plasma cutting machine.
h. The required numbers of holes/slots of required sizes/shape are cut with plasma
cutting machine such as to favor obtaining coke in the desired size range of
25mm to 80mm after screening of coke.
TESTS & RESULTS:
Overlay deposit chemistry has been analyzed to identify the as deposited elements
comprising,
Chromium in the range from 15% to 30%, Carbon from 3.0% to 4.5%, Manganese and
Silicon varying from 1% to 4% each and Molybdenum existing up to 3%.
The hardness of the deposited layer(s) found to vary in the range from 400 BHN to 600
BHN, and typically 550-600 BHN. The finished plates are formed and fabricated, using
straightening/flattening and trimmed to finish sizes by plasma cutting machine. Holes of
selective numbers are cut with either plasma or electro discharge-machining (EDM)
techniques for desired accuracy and tolerance.
Sustained monitoring of performance of the metallic carbide deposited deck plates,
according to the present embodiment of the invention, in the plant have shown that
there has not been any wearing out of material even after 22 months of use. The
undersize coke samples were collected regularly and analyzed for various size fractions
namely, +25, +15, +10 and -10mm. Since there has not been any wearing out of
material, the samples of undersize coke collected after 20 month of use there has not
been any oversize coke (+25mm) in the same, as compared to presence of about 5% of

size fraction of +25mm collected along with under sized coke after 3-4 months use of
conventional screen deck.
It is thus possible by way of the present invention to develop screen deck plates with
overlay of metallic carbide, and preferably iron-chromium carbide having selective
chemistry of the deposited layer, providing superior hardness and wear resistance
properties and thereby enhancing the life of the screen deck delivering consistently
screened coke in the desired size range of 25mm to 80mm, reduced down time of
screening machine, and improved output/productivity of the screen deck ensuring
uninterrupted good quality and proper size of input coke for BF operation favoring
uniform load distribution and higher yield.

WE CLAIM:
1. A screed deck with improved wear properties comprising:
a base plate and
atleast one layer of chromium carbide metallic alloy deposition thereon wherein the alloy
comprises C: 4-5%,Si: 0.5-1.0%, Mn: 0.8-1.2 % ,Cr: 25-30 % and Fe-balance.
2. A screen deck with improved wear properties as claimed in claim 1 wherein the base
plate comprises mild steel base plate.
3. A screen deck with improved wear properties as claimed in anyone of claims 1 or 2
wherein the total thickness of the deck comprises about 10 mm wherein the top layer of
chromium carbide metallic alloy deposition comprise 2-2.5 mm and the base plate
comprise 7.5-8.0 mm with holes therethrough the deck obtained of either plasma or
electro discharge machining..
4. A screen deck with improved wear properties as claimed in anyone of claims 1 to 3
comprising plate size in the range of from 3/8" to 1-1/2" in thickness, widths from 4' to
8' and lengths from 8' to 20'.
5. A screen deck with improved wear properties as claimed in anyone of claims 1 to 4
wherein the overlay deposit comprise of one or two layers measuring 1/4" or 3/8"
thickness.

6. A screen deck with improved wear properties as claimed in anyone of claims 1 to 5
wherein the bead width vary typically in the range of 1- ½" wide and are randomly check
cracked.
7. A screen deck with improved wear properties as claimed in anyone of claims 1 to 6
wherein the overlay deposit composition comprise from 15% to 30% Chromium, 3.0% to
4.5% carbon, Manganese and Silicon from 1% to 4% and Optionally Molybdenum upto
3%.
8. A screen deck with improved wear properties as claimed in anyone of claims 1 to 7
wherein the hardness of the deposit layer varies in the range of 400 BHN to 600 BHN
preferably 550-600 BHN.
9. A method for the manufacture of a screen deck with improved wear properties as
claimed in anyone of claims 1 to 8 comprising:
preparing the alloy with desired composition ;
welding the powder alloy into the top surface of the base plate; and
cutting desired holes with either plasma or electro discharge machining techniques.
10. A screen deck with improved wear properties and its method of manufacture
substantially as herein described and illustrated with reference to the accompanying
examples.

The invention relates to a wear resistant screen deck for screening of the BF grade coke of desired size and its process of manufacture. The composite deck plates comprising deposition of a top layer of iron based chromium carbide alloy over mild steel base plate for BF coke screening application. The composite top layer favored attaining bulk hardness of 550-560 BHN. More advantageously, the primary chromium carbide has
been obtained in the range of 35-40% providing desired wear resistant characteristics of
the deck. The process of the invention further ensures minimal dilution of top layer with
base material and prevents propagation of any cracks in base material due to rapid cooling. The chromium carbide layer ensure presence of long needle shaped crystals with hexagonal cross section leading to adequate primary chromium carbides providing higher wear resistance and increase in the wear ratio (40x) of the deck plates. The invention thus favours achieving very long service life and thus having the prospects of large scale application in steel and similar other industry.