Title of Invention	"A PROCESS FOR PREPARATION OF NICKEL BASE SUPER ALLOY WITH IMPROVED HIGH TEMPRETURE PERFORMANCE DUCTIBILITY"
Abstract	The commercially available super alloys suffer from degradation in rupture-life and ductility due to heat treatment environment relates of the known process. To obtain super alloy with improved creep strength, rupture-life and ductility a process is proposed according to which a charge of alloying elements namely nickel pellet, molybdenum, cobalt and chronium is subjected to the step of vacuum induction melting. Carbon pellets are added to the molten charge. Subsequently aluminium and titanium is added thereto in a sequential order, and also zicronium sponge and ferro-boron was added in a sequential order. The molten metal is then poured into a mould and the ingot formed thereby is subjected to surface machining. A stub made of same alloy is welded to the ingot and the ingot melted again by variable are remelting method. The melted alloy is cast into an ingot which is machined, forged, hot rolled, cold rolled and annealed to obtain the desired super alloy sheets

Title of Invention

"A PROCESS FOR PREPARATION OF NICKEL BASE SUPER ALLOY WITH IMPROVED HIGH TEMPRETURE PERFORMANCE DUCTIBILITY"

Abstract

The commercially available super alloys suffer from degradation in rupture-life and ductility due to heat treatment environment relates of the known process. To obtain super alloy with improved creep strength, rupture-life and ductility a process is proposed according to which a charge of alloying elements namely nickel pellet, molybdenum, cobalt and chronium is subjected to the step of vacuum induction melting. Carbon pellets are added to the molten charge. Subsequently aluminium and titanium is added thereto in a sequential order, and also zicronium sponge and ferro-boron was added in a sequential order. The molten metal is then poured into a mould and the ingot formed thereby is subjected to surface machining. A stub made of same alloy is welded to the ingot and the ingot melted again by variable are remelting method. The melted alloy is cast into an ingot which is machined, forged, hot rolled, cold rolled and annealed to obtain the desired super alloy sheets

Full Text	This invention relates to a process for preparation of nickel base super alloy sheets with improved creep strength, rupture-life and ducility. More particularly, the invention relates to a modified improved process for preparation of nickel base superalloy incorporating modifications in chemical composition and heat-treatment environment which enhance high temperature performance of the alloy, as compared to the existing corresponding Nimonic 263 class of alloys being used for high temperature applications in aircraft-engines. The existing Nimonic-263 class of nickel base superalloy, is essentially gamma prime (M3 Al, Ti) strengthened solid solution of Ni-Cr-Co alloy which is used extensively for aero-engine applications where high temperature creep properties are most important. The phenomenon of creep is of engineering significance during high temperature service of superalloys. Due to prominent creep resistance coupled with fairly good formability, this alloy is one of the most widely accepted material for the sheet-metal components of gas-turbine, which is a critical sub-system of aircraft engines. The other important application of this alloy is in the combustion chamber of aero-engines. In addition, this alloy has many other important applications such as jet pipes, ducting, swirlers and liners in combustor and casings and fasteners etc. The existing Nimonic-263 class of nickel based superalloy comprises of nickel, chromium, cobalt, molybdenum, titanium, aluminium and carbon. It is generally prepared by double melting routes. In this known process, the above alloy composition is first melted in a vacuum, induction furnace and ingot is cast. The same ingot is used as electrode in the vacuum arc remelting (VAR) unit. The second melting step of VAR process is essentially used to achieve uniform distribution of the alloy-constituents in the solidified material i.e. to minimise segregation of some of the constituents at a particular place. The material is then further homogenised at high temperature and is forged by press forging. The forged ingots are hot-rolled and subsequently cold-rolled. Thereafter the material is annealed at high temperature of the order of 1100 to 1150 degree celcius in air for about half an hour. The material is then heated at lower temperature of the order of 800 degree celcius for about 8 hours. In 1990s the new class of high performance aero-engines, in civilian and military sectors, demand for an alloy with better performance parameters namely rupture-life and creep ductility than what is available from the existing known Nimonic-263 class of nickel base super-alloys. Further the process of making such Nimonic-263 class of alloys requires press-forging which is a slow process and needs number of heat-soaking cycles over a considerable time. The primary object of this invention is to propose a process for the preparation of nickel base super alloy having high temperature performance namely creep strength, ductility and rupture life of the commercially available Nimonic 263 alloy. Another object of the present invention is to propose a process for the preparation of nickel base super alloy with modified alloy chemistry to reduce "degradation" in the rupture-life and ductility caused by the heat treatment environment, as occurring in the known process of preparation of Nimonic-263 alloy. Still another object of this present invention is to propose a process for the preparation of nickel base super alloy which is an economical and faster process. According to the present invention, there is provided a process, for preparation- ofjickel base super alloy sheets with improved creep strength, rupture-life and ductility comprising the steps of: (a) subjecting a charge of alloying constituents comprising nickel pellets,, molybdenum, cobalt and chromium to the step of vacuum induction melting, (b) adding carbon pellets to the molten charge, (c) subsequently adding aluminium and titanium in a sequential order, (d) further adding Zirconium sponge and ferro-boron in a sequential order, (e) pouring the molen alloy into a mould, (f) machining the ingot obtained form step (e) to eliminate surface contaminations, removing all scales and pits till bright surface appears, (g) fabricating a stub from the above alloy following the steps (a) to (f) and welding the stub to the ingot obtained from step (f), (h) melting-the ingot obtained from step (g) in a crucible by variable arc remelting (VAR) method, wherein arc is struck between the ingot and the crucible wall, pouring the molten alloy into a mould to obtain a VAR ingot, (i) heating and forging the VAR ingot, repeating these steps till desired size of slab obtained, removing the cracked ends and surface defects by machining, (j) hot rolling the slab obtained form step (i) to sheets of desired thickness, (k) cold rolling the hot rolled sheets obtained from step (j) by annealing, repeating the steps of cold rolling and annealing till the nickel base super alloy sheets of desired thickness are obtained. In accordance with the present invention the vacuum induction furnace is initially charged with nickel pellets (49.1% to 59.1% of overall alloy wt.), molybdenum (5.6% to 6.1% of overall alloy wt.), cobalt (14% to 21% of overall alloy wt.) and chromium (19% to 21% of overall alloy wt.). After achieving vacuum in the furnace equivalent to pressure exerted by mercury column of height equal to thousandth part of one milli-meter, the charge is melted and carbon pellets (0.4% to 0.08% of overall alloy wt.) are added. Subsequently, aluminium (0.3% to 0.6% of overall alloy wt.) and titanium (1.9% to 2.4% of overall alloy wt.) are added in the above sequence. As per this invention, two more micro-alloying elements, namely zirconium sponge (0.03% to 0.15% of overall alloy wt) and ferro-boron (05 ppm to 90 ppm) are also added strictly as per this sequence, soon after addition of aluminium and titanium. The molten metal is then teemed into a mould, preferably a mild steel mould, of appropriate size. The VIM ingot is surface-machined to eliminate the contamination. Entire surface of the machined ingot is visually examined and surface defects like pits and scale are ground till the bright surface appeared. A small stub is in-situ welded to the VIM ingot which is used as an electrode in this step. It is centered to ensure uniform... -5-gap between electrode and the crucible wall. The arc is struck in the crucible and the current is gradually increased to attain a desired melt rate. In order to reduce shrinkage porosity in the alloy the current is reduced gradually during the final stage of remelting to provide hot topping effect to the ingot. All surface defects of the VAR ingots are first removed and these are conditioned for forging. The VAR ingots are then soaked at high temperatures, between 112 0 to 1180 degree celsius for 12 to 18 hours in air. The forging operation is carried out generally by press forging method. As per this invention, the forging operation can also be done by hammer forging method which is faster and requires less number of heat-soaking cycles ; thereby resulting in economical processing of the alloy. Therefore hammer forging is preferred in this invention. During each operation of hammer forging, the height of the ingot is progressively reduced. Between two cycles of forgings, the ingot is again soaked at temperatures between 1120 to 1180 degree celcius, for 20 to 40 minutes. In the final forging operation, the finish temperature is between 940 to 970 degree celcius. Finally, height of the ingots is reduced to desired size. These forged slabs are cleared of cracked ends and surface defects. These are then soaked at temperatures between 1120 to 1180 degree celsius for 5 to 6 hours. These slabs are hot-rolled down to sheets of desired thickness. The hot-rolled sheets are subjected to sand blasting to remove surface scaling. The sheets are given vacuum annealing at 1000 to 1060 degree celsius wherein annealing time is decided by formula, time = 30 minutes x sheet thickness in mm, and argon-quenched to relieve stresses. Finally the sheets are reduced to desired thickness by repeated cold rolling and annealing cycles. Thickness reduction of 10-30% is aimed during each cold-rolling operation. For the heat-treatment, the cold-rolled sheets are generally annealed in air at temperatures of 1100 to 1150 degee celcius for 15 to 30 minutes. Annealing of cold rolled sheets improves deep-drawing ability of the super alloy; howeves: annealing in air environment lowers the creep strength, rupture-life and ductility properties. The above degradation of properties in this alloy gets reduced if the annealing treatment is carried out in yacuum. Therefore, as per this invention, annealing treatment is preferebly done in vacuum of pressure equal to about 0.00001 milli-meter column of mercury. These sheets after annealing in vacuum are ready for use by the customers. The invention is now illustrated but not limited, by the following working example: Working Example: For a 17 Kg melt, a charge of 8.44 kg of nickle pellets, 3.57 kg of chromium, 3.4 kg of cobalt and 1.003 kg of molibdenum pellets was prepared and melted in the vacuum induction furnace with a vacuum equivalent to pressure exerted by thousandth part of one millimeter column of mercury, when the charge has melted, 0.0102 kg of carbon pellets were added and the whole material was allowed to boil for some time. Then 0.442 kg of titanium sponge and 0.136 kg of aluminum granules were added to the melt in this sequence. When the above material had melted fully and was ready for pouring into the mould, 0.0102 kg of zirconium sponge and 0.0056 kg of ferro-boron were added in this sequence just before pouring into a mild steel mould. When the mould had solidified , it was subjected to re-melt under vacuum arc remelting ( VAR ) method. Here a stub of about 5 cm diameter and 10 cm length was fabricated out of this alloy and was in-situ welded to the ingot obtained from above step. The arc was struck in the crucible at about 30 volt and the current was gradually increased to 3000 amperes to attain a melt rate of 3.5 kg per minute. The current was reduced to about 2000 amperes during the final stages of remelting. By the time this process is over, the melted electrode i.e. ingot drops down on the stub in form of droplets and gets gradually solidified in the copper crucible. The solidified ingot from the VAR unit is taken out and the stub is removed. The VAR ingot is then soaked at 1160 degree celcius in air for 15 hours. Subsequently hammer forging was carried out. The finish forging temperature was 950 degree celcius. The forged slab was again soaked at 1160 degree celcius for 5 hours and hot rolled from 10 mm to 3.5 mm thickness. The hot rolled slab was sand blasted to remove surface scaling and was given vacuum annealing treatment at 1050 degree Celsius for 30 min per mm thickness followed by argon quench. About 20% reduction of thickness was achieved during each rolling operation. The sheets were cold rolled down to 0.91 mm thicknes with repeated intermediate annealing treatments. Finally, the sheets were annealed in vacuum eqvivalent to 0.00001 mm mercury pressure, at 1120 degree Celsius for 30 minuntes. WE CLAIM: 1. A process for preparation of nickel base super alloy sheets with improved creep strength, rupture-life and ductility comprising the steps of: (a) subjecting a charge of alloying constituents comprising nickel pellets, molybdenum, cobalt and chromium to the step of vacuum induction melting, (b) adding carbon pellets to the molten charge, (c) subsequently adding aluminium and titanium in a sequential order, (d) further adding Zirconium sponge and ferro-boron in a sequential order, (e) pouring the molten alloy into a mould, (f) machining the ingot obtained form step (e) to eliminate surface contaminations, removing all scales and pits till bright surface appears, (g) fabricating a stub from the above alloy following the steps (a) to (f) and welding the stub to the ingot obtained from step (f), (h) melting the ingot obtained from step (g) in a crucible by variable arc remelting (VAR) method, wherein arc is struck between the ingot and the crucible wall, pouring the molten alloy into a mould to obtain a VAR ingot, (i) heating and forging the VAR ingot, repeating these steps till desired size of slab obtained, removing the cracked ends and surface defects by machining, (j) hot rolling the slab obtained form step (i) to sheets of desired thickness, (k) cold rolling the hot rolled sheets obtained from step (j) followed by annealing, repeating the steps of cold rolling and annealing till the nickel base super alloy sheets of desired thickness are obtained. 2. A process as claimed in claim 1 wherein nickel pellets, molybdenum, cobalt and chromium are present in 49.1% to 59.1% of overall alloy wt, 5.6%-6.1% of overall alloy wt. 14% to 21% of overall alloy wt and 19% to 21% of overall alloy wt respectively. 3. A process as claimed in claim 1 wherein 0.04% to 0.08% of overall weight of carbon pellets are added to the molten charge. 4. A process as claimed in claim 1 wherein 0.3% to 0.6% of overall wt of aluminium and 1.9% to 2.4% of overall alloy wt of titanium are added to the molten metal in a sequential order. 5. A process as claimed in claim 1 wherein 0.03% to 0.15% of overall alloy wt of zirconium sponge and 05 ppm to 90 ppm of ferro-boron are added to the molten metal in a sequential order. 6. A process as claimed in claim 1 wherein the step of heating the VAR ingot comprises the step of soaking at temperature between 1120-1180°C for 12-18 hours in air, which is followed by the step of forging. 7. A process as claimed in claim 6 wherein between two steps of forging, the ingot is again soaked at temperatures between 1120-1180°C for 20-40 minutes. 8. A process as claimed in claim 5 and 6 wherein in the final forging operation, the finish temperature is between 940-970°C. 9. A process as claimed in claim 1 wherein said forged slabs are soaked at temperature between 1120-1180°C for 5-6 hours. 10. A process as claimed in claim 1 wherein said hot rolled sheets are subjected to sand blasting before the step of cold rolling. 11. A process as claimed in claim 1 wherein the said cold rolled sheets are subjected to vacuum annealing at temperatures of 1100-1150°C for 15-30 minutes. 12. A process for preparation of nickel base super alloy sheets with improved creep strength, rupture-life and ductility substantially as herein described and illustrated in the example.

Full Text

This invention relates to a process for preparation of nickel base super alloy sheets with improved creep strength, rupture-life and ducility. More particularly, the invention relates to a modified improved process for preparation of nickel base superalloy incorporating modifications in chemical composition and heat-treatment environment which enhance high temperature performance of the alloy, as compared to the existing corresponding Nimonic 263 class of alloys being used for high temperature applications in aircraft-engines.
The existing Nimonic-263 class of nickel base superalloy, is essentially gamma prime (M3 Al, Ti) strengthened solid solution of Ni-Cr-Co alloy which is used extensively for aero-engine applications where high temperature creep properties are most important. The phenomenon of creep is of engineering significance during high temperature service of superalloys. Due to prominent creep resistance coupled with fairly good formability, this alloy is one of the most widely accepted material for the sheet-metal components of gas-turbine, which is a critical sub-system of aircraft engines. The other important application of this alloy is in the combustion chamber of aero-engines. In addition, this alloy has many other important applications such as jet pipes, ducting, swirlers and liners in combustor and casings and fasteners etc.
The existing Nimonic-263 class of nickel based superalloy comprises of nickel,
chromium, cobalt, molybdenum, titanium, aluminium and carbon. It is generally prepared by
double melting routes. In this known process, the above alloy composition is first melted in a
vacuum, induction furnace and ingot is cast. The same ingot is used as electrode in the vacuum
arc remelting (VAR) unit. The second melting step of VAR process is essentially used to achieve
uniform distribution of the alloy-constituents in the
solidified material i.e. to minimise segregation of some of the constituents at a particular place. The material is then further homogenised at high temperature and is forged by press forging. The forged ingots are hot-rolled and subsequently cold-rolled. Thereafter the material is annealed at high temperature of the order of 1100 to 1150 degree celcius in air for about half an hour. The material is then heated at lower temperature of the order of 800 degree celcius for about 8 hours.
In 1990s the new class of high performance aero-engines, in civilian and military sectors, demand for an alloy with better performance parameters namely rupture-life and creep ductility than what is available from the existing known Nimonic-263 class of nickel base super-alloys. Further the process of making such Nimonic-263 class of alloys requires press-forging which is a slow process and needs number of heat-soaking cycles over a considerable time.
The primary object of this invention is to propose a process for the preparation of nickel base super alloy having high temperature performance namely creep strength, ductility and rupture life of the commercially available Nimonic 263 alloy.
Another object of the present invention is to propose a process for the preparation of nickel base super alloy with modified alloy chemistry to reduce "degradation" in the rupture-life and ductility caused by the heat treatment environment, as occurring in the known process of preparation of Nimonic-263 alloy.
Still another object of this present invention is to propose a process for the preparation of nickel base super alloy which is an economical and faster process.

According to the present invention, there is provided a process, for preparation- ofjickel base super alloy sheets with improved creep strength, rupture-life and ductility comprising the steps of: (a) subjecting a charge of alloying constituents comprising nickel pellets,, molybdenum, cobalt and chromium to the step of vacuum induction melting, (b) adding carbon pellets to the molten charge, (c) subsequently adding aluminium and titanium in a sequential order, (d) further adding Zirconium sponge and ferro-boron in a sequential order, (e) pouring the molen alloy into a mould, (f) machining the ingot obtained form step (e) to eliminate surface contaminations, removing all scales and pits till bright surface appears, (g) fabricating a stub from the above alloy following the steps (a) to (f) and welding the stub to the ingot obtained from step (f), (h) melting-the ingot obtained from step (g) in a crucible by variable arc remelting (VAR) method, wherein arc is struck between the ingot and the crucible wall, pouring the molten alloy into a mould to obtain a VAR ingot, (i) heating and forging the VAR ingot, repeating these steps till desired size of slab obtained, removing the cracked ends and surface defects by machining, (j) hot rolling the slab obtained form step (i) to sheets of desired thickness, (k) cold rolling the hot rolled sheets obtained from step (j) by annealing, repeating the steps of cold rolling and annealing till the nickel base super alloy sheets of desired thickness are obtained.
In accordance with the present invention the vacuum induction furnace is initially charged with nickel pellets (49.1% to 59.1% of overall alloy wt.), molybdenum (5.6% to 6.1% of overall alloy wt.), cobalt (14% to 21% of overall alloy wt.) and chromium (19% to 21% of overall alloy wt.). After achieving vacuum in the furnace equivalent to pressure exerted by mercury column of height equal to thousandth part of one milli-meter, the charge is melted and carbon pellets (0.4% to 0.08% of overall alloy wt.) are added. Subsequently, aluminium (0.3% to 0.6% of overall alloy wt.) and titanium (1.9% to 2.4% of overall alloy wt.) are added in the above sequence. As per this invention, two more micro-alloying elements, namely zirconium sponge (0.03% to 0.15% of overall alloy wt) and ferro-boron (05 ppm to 90 ppm) are also added strictly as per this sequence, soon after addition of aluminium and titanium. The molten metal is then teemed into a mould, preferably a mild steel mould, of appropriate size. The VIM ingot is surface-machined to eliminate the contamination. Entire surface of the machined ingot is visually examined and surface defects like pits and scale are ground till the bright surface appeared. A small stub is in-situ welded to the VIM ingot which is used as an electrode in this step. It is centered to ensure uniform...
-5-gap between electrode and the crucible wall. The arc is struck in the crucible and the current is gradually increased to attain a desired melt rate. In order to reduce shrinkage porosity in the alloy the current is reduced gradually during the final stage of remelting to provide hot topping effect to the ingot.
All surface defects of the VAR ingots are first removed and these are conditioned for forging. The VAR ingots are then soaked at high temperatures, between 112 0 to 1180 degree celsius for 12 to 18 hours in air. The forging operation is carried out generally by press forging method. As per this invention, the forging operation can also be done by hammer forging method which is faster and requires less number of heat-soaking cycles ; thereby resulting in economical processing of the alloy. Therefore hammer forging is preferred in this invention. During each operation of hammer forging, the height of the ingot is progressively reduced. Between two cycles of forgings, the ingot is again soaked at temperatures between 1120 to 1180 degree celcius, for 20 to 40 minutes. In the final forging operation, the finish temperature is between 940 to 970 degree celcius. Finally, height of the ingots is reduced to desired size.
These forged slabs are cleared of cracked ends and surface defects. These are then soaked at temperatures between 1120 to 1180 degree celsius for 5 to 6 hours. These slabs are hot-rolled down to sheets of desired thickness. The hot-rolled sheets are subjected to sand blasting to remove surface scaling. The sheets are given vacuum annealing at 1000 to 1060 degree celsius wherein annealing time is decided by formula, time = 30 minutes x sheet thickness in mm, and argon-quenched to relieve stresses. Finally the sheets are reduced to desired thickness by repeated cold rolling and annealing cycles. Thickness reduction of 10-30% is aimed during each cold-rolling operation.
For the heat-treatment, the cold-rolled sheets are generally annealed in air at temperatures of 1100 to 1150 degee celcius for 15 to 30 minutes. Annealing of cold rolled sheets improves deep-drawing ability of the super alloy;
howeves: annealing in air environment lowers the creep strength, rupture-life and ductility properties. The above degradation of properties in this alloy gets reduced if the annealing treatment is carried out in yacuum. Therefore, as per this invention, annealing treatment is preferebly done in vacuum of pressure equal to about 0.00001 milli-meter column of mercury. These sheets after annealing in vacuum are ready for use by the customers.
The invention is now illustrated but not limited, by the following working example:
Working Example:
For a 17 Kg melt, a charge of 8.44 kg of nickle pellets, 3.57 kg of chromium, 3.4 kg of cobalt and 1.003 kg of molibdenum pellets was prepared and melted in the vacuum induction furnace with a vacuum equivalent to pressure exerted by thousandth part of one millimeter column of mercury, when the charge has melted, 0.0102 kg of carbon pellets were added and the whole material was allowed to boil for some time. Then 0.442 kg of titanium sponge and 0.136 kg of aluminum granules were added to the melt in this sequence. When the above material had melted fully and was ready for pouring into the mould, 0.0102 kg of zirconium sponge and 0.0056 kg of ferro-boron were added in this sequence just before pouring into a mild steel mould.
When the mould had solidified , it was subjected to re-melt under vacuum arc remelting ( VAR ) method. Here a stub of about 5 cm diameter and 10 cm length was fabricated out of this alloy and was in-situ welded to the ingot obtained from above step. The arc was struck in the crucible at about 30 volt and the current was gradually increased to 3000 amperes to attain a melt rate of 3.5 kg per minute. The current was reduced to about 2000 amperes during the final stages of remelting. By the time this process is over, the melted electrode i.e. ingot drops down on the stub in form of droplets and gets gradually solidified in the copper crucible.
The solidified ingot from the VAR unit is taken out and the stub is removed. The VAR ingot is then soaked at 1160
degree celcius in air for 15 hours. Subsequently hammer forging was carried out. The finish forging temperature was 950 degree celcius. The forged slab was again soaked at 1160 degree celcius for 5 hours and hot rolled from 10 mm to 3.5 mm thickness. The hot rolled slab was sand blasted to remove surface scaling and was given vacuum annealing treatment at 1050 degree Celsius for 30 min per mm thickness followed by argon quench. About 20% reduction of thickness was achieved during each rolling operation. The sheets were cold rolled down to 0.91 mm thicknes with repeated intermediate annealing treatments. Finally, the sheets were annealed in vacuum eqvivalent to 0.00001 mm mercury pressure, at 1120 degree Celsius for 30 minuntes.

WE CLAIM:
1. A process for preparation of nickel base super alloy sheets with improved creep
strength, rupture-life and ductility comprising the steps of:
(a) subjecting a charge of alloying constituents comprising nickel pellets, molybdenum, cobalt and chromium to the step of vacuum induction melting,
(b) adding carbon pellets to the molten charge,
(c) subsequently adding aluminium and titanium in a sequential order,
(d) further adding Zirconium sponge and ferro-boron in a sequential order,
(e) pouring the molten alloy into a mould,
(f) machining the ingot obtained form step (e) to eliminate surface contaminations, removing all scales and pits till bright surface appears,
(g) fabricating a stub from the above alloy following the steps (a) to (f) and welding the stub to the ingot obtained from step (f),
(h) melting the ingot obtained from step (g) in a crucible by variable arc remelting (VAR) method, wherein arc is struck between the ingot and the crucible wall, pouring the molten alloy into a mould to obtain a VAR ingot,
(i) heating and forging the VAR ingot, repeating these steps till desired size of slab obtained, removing the cracked ends and surface defects by machining,
(j) hot rolling the slab obtained form step (i) to sheets of desired thickness,
(k) cold rolling the hot rolled sheets obtained from step (j) followed by annealing, repeating the steps of cold rolling and annealing till the nickel base super alloy sheets of desired thickness are obtained.
2. A process as claimed in claim 1 wherein nickel pellets, molybdenum, cobalt and
chromium are present in 49.1% to 59.1% of overall alloy wt, 5.6%-6.1% of overall
alloy wt. 14% to 21% of overall alloy wt and 19% to 21% of overall alloy wt
respectively.
3. A process as claimed in claim 1 wherein 0.04% to 0.08% of overall weight of carbon pellets are added to the molten charge.
4. A process as claimed in claim 1 wherein 0.3% to 0.6% of overall wt of aluminium and 1.9% to 2.4% of overall alloy wt of titanium are added to the molten metal in a sequential order.
5. A process as claimed in claim 1 wherein 0.03% to 0.15% of overall alloy wt of zirconium sponge and 05 ppm to 90 ppm of ferro-boron are added to the molten metal in a sequential order.
6. A process as claimed in claim 1 wherein the step of heating the VAR ingot comprises the step of soaking at temperature between 1120-1180°C for 12-18 hours in air, which is followed by the step of forging.
7. A process as claimed in claim 6 wherein between two steps of forging, the ingot is again soaked at temperatures between 1120-1180°C for 20-40 minutes.
8. A process as claimed in claim 5 and 6 wherein in the final forging operation, the finish temperature is between 940-970°C.
9. A process as claimed in claim 1 wherein said forged slabs are soaked at temperature between 1120-1180°C for 5-6 hours.
10. A process as claimed in claim 1 wherein said hot rolled sheets are subjected to sand blasting before the step of cold rolling.
11. A process as claimed in claim 1 wherein the said cold rolled sheets are subjected to vacuum annealing at temperatures of 1100-1150°C for 15-30 minutes.
12. A process for preparation of nickel base super alloy sheets with improved creep strength, rupture-life and ductility substantially as herein described and illustrated in the example.

Documents:

1542-del-1996-abstract.pdf

1542-del-1996-claims.pdf

1542-del-1996-complete specification (granted).pdf

1542-del-1996-correspondence-others.pdf

1542-del-1996-correspondence-po.pdf

1542-del-1996-description (complete).pdf

1542-del-1996-form-1.pdf

1542-del-1996-form-2.pdf

1542-del-1996-gpa.pdf

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Patent Number

195206

Indian Patent Application Number

1542/DEL/1996

PG Journal Number

29/2008

Publication Date

26-Sep-2008

Grant Date

08-Dec-2006

Date of Filing

11-Jul-1996

Name of Patentee

THE CHIEF CONTROLLER, RESEARCH AND DEVELOPMENT, MINISTRY OF DEFENCE, GOVERNMENT OF INDIA

Applicant Address

TECHNICAL COORDINATION DTE., B-341, SENA BHAWAN DHQ P.O., NEW DELHI-110011

Inventors:

#	Inventor's Name	Inventor's Address
1	SANNALA SRINIVAS	TECHNICAL COORDINATION DTE., B-341, SENA BHAWAN DHQ P.O., NEW DELHI-110011
2	MANIK CHANDRA PANDEY	TECHNICAL COORDINATION DTE., B-341, SENA BHAWAN DHQ P.O., NEW DELHI-110011

PCT International Classification Number

C22C 019/05

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA