Title of Invention	"AN IMPROVED PROCESS FOR THE PREPARATION OF COPPER AND BORON CONTAINING BAINITIC STEEL OR STEEL ALLOY "
Abstract	This invention relates to an improved process for the preparation of copper and boron containing bainitic steel or steel alloy According to the process the reactants are cleaned. Pure iron is melted in a vacuum induction-melting furnace and ferro alloys are added thereto. The molten steel or steel alloy is poured into clean dry ingot moulds kept in vacuum until solidification. The ingots are homogenized and then subjected to the step of forging for further rolling. Rolled moldings are heated and then subjected to the step of air-cooling.

Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF COPPER AND BORON CONTAINING BAINITIC STEEL OR STEEL ALLOY "

Abstract

This invention relates to an improved process for the preparation of copper and boron containing bainitic steel or steel alloy According to the process the reactants are cleaned. Pure iron is melted in a vacuum induction-melting furnace and ferro alloys are added thereto. The molten steel or steel alloy is poured into clean dry ingot moulds kept in vacuum until solidification. The ingots are homogenized and then subjected to the step of forging for further rolling. Rolled moldings are heated and then subjected to the step of air-cooling.

Full Text	TITLE OF INVENTION This invention relates to an improved process for preparation of copper and boron containing bainitic steel and products thereof". OF_THE __ INVENTION The present invention relates to an improved process for preparation of copper and boron containing bainitic steel and product thereof. PRIOR ART QF THE INVENTION - The steel or steel of required far manufacture of pressure, vessels and critical components in a wide variety of engineering structures is required to have combination of high strength and toughness alonciuii the good uieldability and corrosion resistance and resistance to / hydrogen cracking are the foremost requirements of any steel or steel alloy to be used for construction of any such engineering structure, which in turn is required to be subjected to pressure (i.e. pressure vessels etc.) and/or exposed to the ; corrosive environment ships etc.). The exposure to corrosive environment: in turn initiate the corrosion, preferably, oxidation process on the exposed surfaces of the engineering structures of any type made up of steel or steel alloy. This process once initiated results in the deterioration of such engineering structures. One method of protecting the engineering B t resource as stated herein above;, from corrosive environment, that from corrosion, that is to say to enhance the corrosion resistance, is to apply a coating or the surface of such structures unhitch in turn is capable1 of protecting the exposed surface of structures or 3un The limitation of application of such coat inn that the protection is limited only upto the reds island to corrosion and that's too for the limited period, high in turn necessitates the repetition of process of coating after regular intervals. Still another limitation of such coatings is that the, upto ldabi 1 it characteristics and other mechanical properties are neither effect-ed nor improved. N -, These limitations are overcame by the improvement of the steel or steel all by itself. Such information are effected by variation in the chemical compositions » and in the process of preparation and in the process of heat treatment of each steels or steel alloys. The process of control of such properties, a--, stated herein above, in the steels or steel alloys again has the limitations of its own. Such as, the attempt to increase the strength of ah alloy normally reduce?.; its toughness and vice-versa, even for any known ultra low carbon biotitic steel.' In addition, to meet the requirements of mechanical properties, may call for requirement of either high percentage of one element or low percentage of another element and meeting these requirements will call for complex processing techniques. For example, attaining 1OO is (700MPa> of strength would require high amounts of nickel contents or elaborate processsing and heat treatment. In, order to overcome the drawbacks of known steels and steel alloys, as stated herein above, variety of steels have been used for construction of en9inee ring structures, as stated here in above, after quenching and tempering. Such steels or steel alloys after the quenching and tempering by 'known methods results in high toughness and high strength. The disadvantages of such quenched and tempered steels or steel alloys are that, these alloys suffer from inferior weld ability as their high carbon content and carbon equivalent make them susceptible to the hydrogen induced cracking. ' Another drawback of such known quenched and 1; simper eel steels or steel • alloys for construction of such engineering structures, as sheet and herein above is that, the technological problem, stated in proceeding paragraph demands stringent welding procedures and controls such 3.3 pre-heating. This adds to the cast of the components which require extensive welding. Still another drawback of such known steels or steel alloys for construction of such engineering structures as stated herein above, is that their process of preparation requires special processing facilities, like roll quenching and special rolling and heat treating facilities for processing some plates of very larqe size required for specific applications for construction of such engineering structures. Yet another drawback of such known processes or processing techniques, as Stated in preceeding paragraph, is that, setting up of such facilities of roll quenching, special rolling and heat treating, definitely acids to the cost of the process and hence to the of the products, which may int.urn make it highly uneconom j the demand happens to be low. Still further disadvantage/drawback of known hi.oh performance quenched and tempered steels or steel alloy-: is their high martensitic hardenabi1ity which rpsults in brittle heat affected zones and associated weld The ultra low carbon bainitic: steels or s I; known in prior art generally contain relatively his uhar amounts of costly alloying elements, such as molybdenum and nickel and donot contain capper and boron, The elements molybdenum and nickel are expensive and particularly nickel. OBJECTS OF THE INVENTION A main object of the present invention is to propose an improved process for preparation of copper and boron containing baintic steel and products thereof, in particular to the improved process for preparation of copper/and boron containing ultra low carbon bainitic steel and products thereof, more particularly to an improved process of preparation of copper and boron containing high performance ultra low carbon bainitic steel and the products thereof, wherein the process of present invention minimises the limitations of known such processes as stated herein above and the products produced, that is the steel or steel alloy'process disclosed herein, have the improved properties in addition to being the corrosion resx and overcomes the drawbacks of known such nr1 § allays as stated herein above. Another objects of • t h e p r e s e n t i n v v r 11.1 on is to propose improved process for preparation cooper and boron containing steel or steel alloy, ;:;s seated herein above and to the products thereof, which have-combined very high yield strength and excellent i; QUO lines •? even in the rolled condition and still, not reauirinq arr-heat treatment, hence reducing the cost of the p roc. «:!•::; and, product as well. A not tier object trf the present invention is ': o propose an improved process for preparation of copper and boron containing bainitic steel and product,--- thereof, which in turn have high strength and as w? i 1 touqlinps-j, along with good weldability and corrosion rp s L :•;' Yet another object of the present invention is to propose an improved process for preparation of high performance bainitic steel, as stated h Still another object of the present invention is to propose an improved process for the preparation of copper and boron containing bainitic steel and the products thereof, as stated herein above, which have flexibility to be used in both the conditions i.e. as rolled and in variety of heat treated conditions, and hence making the products of the present invention suitable for wider applications in wider areas of requirements. According to this invention there is provided an improved process for the preparation of copper and boron containing bainitic steel or steel alloy comprising in the following steps: (i) Cleaning and drying of pure iron stock in said approximately 10% aqueous hydrochloric acid solution until a bright surface is revealed and said rernairting reactants alongwith said pickled iron are dried in an oven at 200-250° C for two hours, (ii) Melting of pure iron between 1500-1600° C preferably at 1550° C in the vacuum induction melting furnace at vacuum of 1 Q~5 to 10~6 mm Hg in a vacuum induction melting furnace, (iii) Adding ferro alloys thereto wherein said alloying elements are carbon between 0.05 to 0.07 weight percent, mangnese between 1.5 to 1.7 weight percent, nickel between 1.0 to 1.25 weight percent, molybdenum between 0.4 to 0.45 weight percent, copper between 1.0 to 1.25 weight percent and niobium between 0.03 to 0.05 weight percent, and boron between 10 to 20 parts per million and sulphur less than 100 parts per million and balance is said pure iron. (iv) Pouring molten steel or steel alloy into clean dry ingot moulds kept in vacuum until solidification, (v) Homogenising of ingots followed by forgoing for further rolling, and (vi) Reheating the said ingots between 1100 to 1200°C and rolling followed by air cooling. In accordance with the present invention makes a disclosure of an improved process far preparation of capper and boron containing bainitic steel or ir;tr-:e.l alloy and products thereof, in particular of .:m improved process for preparation of copper and boron cant a inino ultra low carbon bainitic steel or steel ; 1 1 a . :uu! products thereof, more particularly of an improved process of preparation of copper and boron c :.;n t a :L n incj high performance ultra low carbon bainitic steel o>" steel alloy and p roduc t s thereof,.carbon is present between 0.05 to 0.07, man on SB between 1.5 to 1.7, nickel between 1.0 to 1.25, wherein b e t w e e n 0,4 to 0.45, c op p s r b e t w e e n 1 . 0 t o 1 2 I between 0.03 - 0.05, ail I present uuthin I unit in percent by weight and boron is present bcti'isfvn 10--20 parts per million and sulphur is less than 1OO p 3. r • !•; a per million and balance is pun? armco .iron easily ;sv a i 1 ib 1 e from commercial market. The preparation of high performance u 11 r .-> low carbon bainitic steel or steel alloys, as stated lie re in above, in accordance to the preferred embodiments of the process of the p resent invention, is carried out- in foil oui ing steps: (a) Cleaning and drying of reactants, (b) Melting of pure iron in the vacuum induction melting furnace (c) Addition of ferro alloys in appropriate amount;::; in accordance to the preferred embodiment of the privsent invent ion. I (d) Pouring of molten steel or stcsl alloy :wherein clean dry ingat moulds kept in vacuum until •olidification The Homogenisation of ingots followed by forging to •size suitable for further rolling (f) Reheating .below recrystal1isation temperature and rolling to the final size with sufficient reduction per pass to produce a uniformely deformed and unrecrystal 1 ised steel or stef?l alloy which on air cooling produces extremely fine granular bainitic.. -nteel or steel alloy. DESCRIPTION OF THE INVENTION b.w. in accordance to the presently disclosed invention the improved process for preparation of capper and boron containing bainitic steel or steel alloy and products thereof, particularly an impro'vad process for preparation of-copper and boron containing ultra low carbon bainitic sheet or is steel alloy and products thereof more particularly an improved process for preparation of copper and boron containing high performance ultra low carbon bainitic steel or steel alloy and products thereof are disclosed, wherein the process is characterised by first cleaning and drying of reactants, which in turn is carried out by pickling the pure iron stock in approximately 1Oth aqueous hydrochloric acid solution until a bright surface is revealed. The remaining rtactants alongwith pickled iron are dried in an oven at 20Q-25Q°C for preferably two hours. In accordance .to the process of the - present invention the second step involves melting of pure iron between 1500-1600°C preferably at about 1550 °C in th» vacuum induction melting furnace at vacuum of 1C " to 10 mm Hg. and accordance to the prefprrt'd of the presently disclosed process of this is characterised by addition of fear alloying in the appropriate amounts to the molten pure iron from second step. According to -the preferred embodiment of this invention- the alloying elements are essentially taken in Specified chemical composition comprising of carbon between 0.05 to O»07 weigtht percent, mangnese between 15 to 1.7 weight percent, nickel between 1.0 to 1,2.5, weight percent, molybdenum between 0.4 to 0.45 weight percent, copper between oil to 1.25 weight percent and niobium between 0.03 to O.O5 weight percent, and boron between 10 to 20 parts per million and sulphur less than IOO parts per million and balance is pure iron. In accordance to the * process of the present invention the fourth step comprises of pouring of th* steel or steel alloy into the already cleaned and ingot moulds and kept in- vacuum essentially unbil solidification. According to the further preferred embodiment of this invention, the fifth step is characterised b.y homogenisation of ingots from fourth step at about 1100 ?C to 12OO °C , preferably at 1130 to 1175°C for 4 to 3 Hour fallowed by forging to a size suitable far further rolling. Mare particularly, according to the fifth step, o the cast ingots are reheated between 1100 to 1200 C , preferably between 1140 to 1175°C and soaked for 4 to 5 hour* followed b'y forging to make about 90 mm thick billet* which are then ai^r cooled to roam temperature. These billets are reheated upto 950°C (below recrystallisation temperature) and soaked for about hour* before rolling in the si:;th step of the process of thi* invention. According to the preferred embodiment of the prorns-r, of this invention, the rolling ia carried out in fnu.H-.iple passes without intermedi ater re--heatinq . The rol 1 inn in Accordance to this preferred embodiment results in 20-25V, reduction in each pass and is continued till the plate? thickness of 12.5np is achieved, which on air cooling results in the desired extremely fine granular, copper and boron containing, high performance ultra low carbon bainitic steel or steel alloy. The developed steel or steel alloy in accordance to the process, of the present invention as disclosed herein above, has been found to be useful in as rolled state and even in a variety of heat treatment conditions, if desired. The heat treatment is performed by simple and convenient method’ as described herein above, for fifth step. The developed steel or steel allay was subjected to the aging, which in turn has further resulted in the improvement of the desired mechanical properties such a.3 yield strength, ultimate utensil strength and chirpy energy etc. as' it is clearly understood from the following table-I, which illustrates effect of water quenching and air cooling on the steel or steel alloy prepared in accordance to the process of this invention. TABLE- I : EFFECTS OF ABING (HEAT TREATMENT) ON MECHANICAL PROPERTIES. • YS means yield'.-strength, UTS means-ultimate tensile strength CE means charpy energy WQ means quenched at 945 C for 45 minutes AC means air' cooled at 945°C for 45 minutes (Table REMOVED) The developed alloy when observed for micrastrur.:tur under- .optical microscope has shown the uniformly fine microstructure,r(asi it is clear/understood from the micrograph shown belows- It is understood from the forgoing description that the process disclosed herein above, definitely has overcome the drawbacks of such known processes and definitely has the advantage .of producing the' copper and boron •containing high-performance, ultra low carbon b^iriitic steel or steel alloy. The presence of chromium is totally eliminated and the 'weight percentage of expensive elements, an stated hrin wbovfi iai rduc»d. The combined weight prM-r:"n i-. q«? of copper niobium and boron is maintained between l.O to 1.35 weight percent. The foregoing process was performed by using following specific chemical composition;-- Silicon, aluminium and titanium were added only in traces to act as deoxidising and denitriding agent:. The developed alloy was tested for its mechanical properties, which were observed to be (Table REMOVED) The foregoing examples and the data of the developed steel or steel alloy in accordance to the process of the present invention are not intended to limit the scone of the present invention. Any steel or s THE all developed in accordance to the process of the invention having chemical composition, as djsc1osed herein above may full within the scope of the presently disclosed invention. 1 CLAIM: 1. An improved process for the preparation of copper and boron containing bainitic steel or steel alloy comprising in the following steps: (i) Cleaning and drying of pure iron stock in said approximately 10% aqueous hydrochloric acid solution until a bright surface is revealed and said remaining reactants alongwith said pickled iron are dried in an oven at 200-250° C for two hours, (ii) Melting of pure iron between 1500-1600° C preferably at 1550° C in the vacuum induction melting furnace at vacuum of 10~5 to 10 6 mm Hg in a vacuum induction melting furnace, (iii) Adding ferro alloys theretc wherein said alloying elements are carbon between 0.05 to 0.07 weight percent, mangnese between 1.5 to 1.7 weight percent, nickel between 1.0 to 1.25 weight percent, molybdenum between 0.4 to 0.45 weight percent, copper between 1.0 to 1.25 weight percent and niobium between 0.03 to 0.05 weight percent, and boron between 10 to 20 parts per million and sulphur less than 100 parts per million and balance is said pure iron. (iv) Pouring molten steel or steel alloy into clean dry ingot moulds kept in vacuum until solidification, (v) Homogenising of ingots followed by forgoing for further rolling, and (v) Reheating the said ingots between 1100 to 1200°C and rolling followed by air cooling. 2. An improved process as claimed in claim 1, wherein said fifth step comprises of reheating the said cast ingots preferably between 1140 to 1175°C and soaked for 4 to 5 hours followed by forging to make about 90 mm thick billets which in turn is subsequently followed by air cooling to room temperature. 3. An improved process as claimed in claim 1, wherein the said billets are reheated upto 950°C and soaked for about hours before rolling. 4. An improved process as claimed in claim 1, wherein said rolling is carried out in multiple passes without intermediate re-heating. 5. An improved process as claimed in claim 1, wherein said heat treatment is performed by similar process of the said fifth step. 6. An improved process as claimed in claim 1, wherein said combined weight percentage of copper niobium and boron is maintained between 1.0 to 1.35 weight percent 7. An improved process as claimed in preceding claims wherein said chemical composition of said alloying elements is specifically: C = 0.06 wt.% Mn = 1.5 wt.% Ni = 1.0 wt.% Mo = 0.45 wt.% Cu = 1.2 wt.% Nb = 0 05 wt.% B = 10-20 ppm S 100 8. An improved process for preparation of copper and boron containing baimitic steel or steel alloy and products thereof substantially as herein described and illustrated in the foregoing specific example.

Full Text

TITLE OF INVENTION
This invention relates to an improved process for preparation of copper and boron containing bainitic steel and products thereof".
OF_THE __ INVENTION
The present invention relates to an improved process for preparation of copper and boron containing bainitic steel and product thereof.
PRIOR ART QF THE INVENTION -
The steel or steel of required far manufacture of pressure, vessels and critical components in a wide variety of engineering structures is required to have combination of high strength and toughness alonciuii the good uieldability and corrosion resistance and resistance to
/
hydrogen cracking are the foremost requirements of any steel or steel alloy to be used for construction of any such engineering structure, which in turn is required to be subjected to pressure (i.e. pressure vessels etc.) and/or exposed to the ; corrosive environment ships etc.). The exposure to corrosive environment: in turn initiate the corrosion, preferably, oxidation process on the exposed surfaces of the engineering structures of any type made up of steel or steel alloy. This process once initiated results in the deterioration of such engineering structures.
One method of protecting the engineering B t resource as stated herein above;, from corrosive environment, that
from corrosion, that is to say to enhance the corrosion resistance, is to apply a coating or the surface of such structures unhitch in turn is capable1 of protecting the exposed surface of structures or 3un The limitation of application of such coat inn that the protection is limited only upto the reds island to corrosion and that's too for the limited period, high in turn necessitates the repetition of process of coating after regular intervals.
Still another limitation of such coatings is that the, upto ldabi 1 it characteristics and other mechanical properties are neither effect-ed nor improved.
N -,
These limitations are overcame by the improvement of the steel or steel all by itself. Such information are effected by variation in the chemical compositions
»
and in the process of preparation and in the process of heat treatment of each steels or steel alloys.
The process of control of such properties, a--, stated herein above, in the steels or steel alloys again has the limitations of its own. Such as, the attempt to increase the strength of ah alloy normally reduce?.; its toughness and vice-versa, even for any known ultra low carbon biotitic steel.' In addition, to meet the requirements of mechanical properties, may call for requirement of either high percentage of one element or low percentage of another element and meeting these requirements will call for complex processing techniques. For example, attaining 1OO is (700MPa> of strength would require high amounts of nickel contents or elaborate processsing and heat treatment.
In, order to overcome the drawbacks of known steels and steel alloys, as stated herein above, variety of steels have been used for construction of en9inee ring structures, as stated here in above, after quenching and tempering. Such steels or steel alloys after the quenching and tempering by 'known methods results in high toughness and high strength.
The disadvantages of such quenched and tempered steels or steel alloys are that, these alloys suffer from inferior weld ability as their high carbon content and carbon equivalent make them susceptible to the hydrogen induced cracking.
' Another drawback of such known quenched and 1; simper eel steels or steel • alloys for construction of such engineering structures, as sheet and herein above is that,
the technological problem, stated in proceeding paragraph demands stringent welding procedures and controls such 3.3 pre-heating. This adds to the cast of the components which require extensive welding.
Still another drawback of such known steels or steel alloys for construction of such engineering structures as stated herein above, is that their process of preparation requires special processing facilities, like roll quenching and special rolling and heat treating facilities for processing some plates of very larqe size required for specific applications for construction of such engineering structures.
Yet another drawback of such known processes or processing techniques, as Stated in preceeding paragraph, is that, setting up of such facilities of roll quenching, special rolling and heat treating, definitely acids to the cost of the process and hence to the of the
products, which may int.urn make it highly uneconom j the demand happens to be low.
Still further disadvantage/drawback of known hi.oh performance quenched and tempered steels or steel alloy-: is their high martensitic hardenabi1ity which rpsults in brittle heat affected zones and associated weld
The ultra low carbon bainitic: steels or s I; known in prior art generally contain relatively his uhar amounts of costly alloying elements, such as molybdenum and nickel and donot contain capper and boron, The elements molybdenum and nickel are expensive and particularly nickel.
OBJECTS OF THE INVENTION
A main object of the present invention is to propose an improved process for preparation of copper and boron containing baintic steel and products thereof, in particular to the improved process for preparation of copper/and boron containing ultra low carbon bainitic steel and products thereof, more particularly to an improved process of preparation of copper and boron containing high performance ultra low carbon bainitic steel and the products thereof, wherein the process of present invention minimises the limitations of known such processes as stated herein above and the products
produced, that is the steel or steel alloy'process disclosed herein, have the improved properties in addition to being the corrosion resx and overcomes the drawbacks of known such nr1 § allays as stated herein above.
Another objects of • t h e p r e s e n t i n v v r 11.1 on is to propose improved process for preparation cooper and boron containing steel or steel alloy, ;:;s seated herein above and to the products thereof, which have-combined very high yield strength and excellent i; QUO lines •? even in the rolled condition and still, not reauirinq arr-heat treatment, hence reducing the cost of the p roc. «:!•::; and, product as well.
A not tier object trf the present invention is ': o propose an improved process for preparation of copper and boron containing bainitic steel and product,--- thereof, which in turn have high strength and as w? i 1 touqlinps-j, along with good weldability and corrosion rp s L :•;'
Yet another object of the present invention is to propose an improved process for preparation of high performance bainitic steel, as stated h Still another object of the present invention is to propose an improved process for the preparation of copper and boron containing bainitic steel and the products thereof, as stated herein above, which have flexibility to be used in both the conditions i.e. as rolled and in variety of heat treated conditions, and hence making the products of the present invention suitable for wider applications in wider areas of requirements.
According to this invention there is provided an improved process for the preparation of copper and boron containing bainitic steel or steel alloy comprising in the following steps:
(i) Cleaning and drying of pure iron stock in said approximately 10% aqueous hydrochloric acid solution until a bright surface is revealed and said rernairting reactants alongwith said pickled iron are dried in an oven at 200-250° C for two hours, (ii) Melting of pure iron between 1500-1600° C preferably at 1550° C in the vacuum induction melting furnace at vacuum of 1 Q~5 to 10~6 mm Hg in a vacuum induction melting furnace, (iii) Adding ferro alloys thereto wherein said alloying elements are carbon between 0.05 to 0.07 weight percent, mangnese between 1.5 to 1.7 weight percent, nickel between 1.0 to 1.25 weight percent, molybdenum between 0.4 to 0.45 weight percent, copper between 1.0 to 1.25 weight percent and niobium between 0.03 to 0.05 weight percent, and boron between 10 to 20 parts per million and sulphur less than 100 parts per million and balance is said pure iron.
(iv) Pouring molten steel or steel alloy into clean dry ingot moulds kept in vacuum until solidification,
(v) Homogenising of ingots followed by forgoing for further rolling,
and (vi) Reheating the said ingots between 1100 to 1200°C and rolling
followed by air cooling.
In accordance with the present invention makes a disclosure of an improved process far preparation of capper and boron containing bainitic steel or ir;tr-:e.l alloy and products thereof, in particular of .:m improved process for preparation of copper and boron cant a inino ultra low carbon bainitic steel or steel ; 1 1 a . :uu! products thereof, more particularly of an improved process of preparation of copper and boron c :.;n t a :L n incj high performance ultra low carbon bainitic steel o>" steel alloy and p roduc t s thereof,.carbon is present between 0.05 to 0.07, man on SB between
1.5 to 1.7, nickel between 1.0 to 1.25, wherein b e t w e e n 0,4 to 0.45, c op p s r b e t w e e n 1 . 0 t o 1 2 I between 0.03 - 0.05, ail I present uuthin I unit in percent by weight and boron is present bcti'isfvn 10--20 parts per million and sulphur is less than 1OO p 3. r • !•; a per million and balance is pun? armco .iron easily ;sv a i 1 ib 1 e from commercial market.
The preparation of high performance u 11 r .-> low carbon bainitic steel or steel alloys, as stated lie re in above, in accordance to the preferred embodiments of the process of the *p resent invention, is carried out- in foil oui ing steps:
(a) Cleaning and drying of reactants,
(b) Melting of pure iron in the vacuum induction
melting furnace
(c) Addition of ferro alloys in appropriate amount;::;
in accordance to the preferred embodiment of the privsent
invent ion.
I (d) Pouring of molten steel or stcsl alloy :wherein clean dry ingat moulds kept in vacuum until •olidification
The Homogenisation of ingots followed by forging to •size suitable for further rolling
(f) Reheating .below recrystal1isation temperature and rolling to the final size with sufficient reduction per pass to produce a uniformely deformed and unrecrystal 1 ised steel or stef?l alloy which on air cooling produces extremely fine granular bainitic.. -nteel or steel alloy.
DESCRIPTION OF THE INVENTION
b.w. in accordance to the presently disclosed invention the improved process for preparation of capper and boron containing bainitic steel or steel alloy and products thereof, particularly an impro'vad process for preparation of-copper and boron containing ultra low carbon bainitic sheet or is steel alloy and products thereof more particularly an improved process for preparation of copper and boron containing high performance ultra low carbon bainitic steel or steel alloy and products thereof are disclosed, wherein the process is characterised by first cleaning and drying of reactants, which in turn is carried out by pickling the pure iron stock in approximately 1Oth aqueous hydrochloric acid solution until a bright surface is revealed. The remaining rtactants alongwith pickled iron are dried in an oven at 20Q-25Q°C for preferably two hours.
In accordance .to the process of the - present invention the second step involves melting of pure iron between 1500-1600°C preferably at about 1550 °C in th» vacuum induction melting furnace at vacuum of 1C " to 10 mm Hg.
and accordance to the prefprrt'd of the presently disclosed process of this is characterised by addition of fear alloying
in the appropriate amounts to the molten pure
iron from second step.
According to -the preferred embodiment of this invention- the alloying elements are essentially taken in Specified chemical composition comprising of carbon between 0.05 to O»07 weigtht percent, mangnese between 1*5 to 1.7 weight percent, nickel between 1.0 to 1,2.5, weight percent, molybdenum between 0.4 to 0.45 weight percent, copper between oil to 1.25 weight percent and niobium between 0.03 to O.O5 weight percent, and boron between 10 to 20 parts per million and sulphur less than IOO parts per million and balance is pure iron.
In accordance to the * process of the present invention the fourth step comprises of pouring of th* steel or steel alloy into the already cleaned and ingot moulds and kept in- vacuum essentially unbil solidification.
According to the further preferred embodiment of this invention, the fifth step is characterised b.y homogenisation of ingots from fourth step at about 1100 *?C to 12OO °C , preferably at 1130 to 1175°C for 4 to 3 Hour* fallowed by forging to a size suitable far further
rolling. Mare particularly, according to the fifth step,
o the cast ingots are reheated between 1100 to 1200 C ,
preferably between 1140 to 1175°C and soaked for 4 to 5 hour* followed b'y forging to make about 90 mm thick billet* which are then ai^r cooled to roam temperature. These billets are reheated upto 950°C (below recrystallisation temperature) and soaked for about hour* before rolling in the si:;th step of the process of thi* invention.
According to the preferred embodiment of the prorns-r, of this invention, the rolling ia carried out in fnu.H-.iple passes without intermedi ater re--heatinq . The rol 1 inn in Accordance to this preferred embodiment results in 20-25V, reduction in each pass and is continued till the plate? thickness of 12.5np is achieved, which on air cooling results in the desired extremely fine granular, copper and boron containing, high performance ultra low carbon bainitic steel or steel alloy.
The developed steel or steel alloy in accordance to the process, of the present invention as disclosed herein above, has been found to be useful in as rolled state and even in a variety of heat treatment conditions, if desired.
The heat treatment is performed by simple and convenient method’ as described herein above, for fifth step.
The developed steel or steel allay was subjected to the aging, which in turn has further resulted in the improvement of the desired mechanical properties such a.3 yield strength, ultimate utensil strength and chirpy energy etc. as' it is clearly understood from the following table-I, which illustrates effect of water quenching and air cooling on the steel or steel alloy prepared in accordance to the process of this invention.
TABLE- I : EFFECTS OF ABING (HEAT TREATMENT) ON MECHANICAL PROPERTIES.
• YS means yield'.-strength,
UTS means-ultimate tensile strength
CE means charpy energy
WQ means quenched at 945 C for 45 minutes AC means air' cooled at 945°C for 45 minutes
(Table REMOVED)
The developed alloy when observed for micrastrur.:tur under- .optical microscope has shown the uniformly fine microstructure,r(asi it is clear/understood from the micrograph shown belows-
It is understood from the forgoing description that the process disclosed herein above, definitely has overcome the drawbacks of such known processes and definitely has the advantage .of producing the' copper and boron •containing high-performance, ultra low carbon b^iriitic steel or steel alloy.
The presence of chromium is totally eliminated and the 'weight percentage of expensive elements, an stated h*r*in wbovfi iai r*duc»d. The combined weight prM-r:"n i-. *q«? of copper niobium and boron is maintained between l.O to 1.35 weight percent.
The foregoing process was performed by using following specific chemical composition;--

Silicon, aluminium and titanium were added only in traces to act as deoxidising and denitriding agent:.
The developed alloy was tested for its mechanical properties, which were observed to be
(Table REMOVED)
The foregoing examples and the data of the developed steel or steel alloy in accordance to the process of the present invention are not intended to limit the scone of the present invention. Any steel or s THE all developed in accordance to the process of the
invention having chemical composition, as djsc1osed herein above may full within the scope of the presently disclosed invention.

1 CLAIM:
1. An improved process for the preparation of copper and boron
containing bainitic steel or steel alloy comprising in the following
steps:
(i) Cleaning and drying of pure iron stock in said approximately 10% aqueous hydrochloric acid solution until a bright surface is revealed and said remaining reactants alongwith said pickled iron are dried in an oven at 200-250° C for two hours,
(ii) Melting of pure iron between 1500-1600° C preferably at 1550° C in the vacuum induction melting furnace at vacuum of 10~5 to 10 6 mm Hg in a vacuum induction melting furnace,
(iii) Adding ferro alloys theretc wherein said alloying elements are carbon between 0.05 to 0.07 weight percent, mangnese between 1.5 to 1.7 weight percent, nickel between 1.0 to 1.25 weight percent, molybdenum between 0.4 to 0.45 weight percent, copper between 1.0 to 1.25 weight percent and niobium between 0.03 to 0.05 weight percent, and boron between 10 to 20 parts per million and sulphur less than 100 parts per million and balance is said pure iron.
(iv) Pouring molten steel or steel alloy into clean dry ingot moulds kept in vacuum until solidification,
(v) Homogenising of ingots followed by forgoing for further rolling, and
(v) Reheating the said ingots between 1100 to 1200°C and rolling followed by air cooling.
2. An improved process as claimed in claim 1, wherein said fifth step
comprises of reheating the said cast ingots preferably between 1140 to
1175°C and soaked for 4 to 5 hours followed by forging to make about
90 mm thick billets which in turn is subsequently followed by air
cooling to room temperature.
3. An improved process as claimed in claim 1, wherein the said billets
are reheated upto 950°C and soaked for about hours before rolling.
4. An improved process as claimed in claim 1, wherein said rolling is
carried out in multiple passes without intermediate re-heating.
5. An improved process as claimed in claim 1, wherein said heat
treatment is performed by similar process of the said fifth step.
6. An improved process as claimed in claim 1, wherein said combined
weight percentage of copper niobium and boron is maintained
between 1.0 to 1.35 weight percent
7. An improved process as claimed in preceding claims wherein said
chemical composition of said alloying elements is specifically:
C = 0.06 wt.%
Mn = 1.5 wt.%
Ni = 1.0 wt.%
Mo = 0.45 wt.%
Cu = 1.2 wt.%
Nb = 0 05 wt.%
B = 10-20 ppm
S 100
8. An improved process for preparation of copper and boron containing baimitic steel or steel alloy and products thereof substantially as herein described and illustrated in the foregoing specific example.

Documents:

401-del-1997-abstract.pdf

401-del-1997-claims.pdf

401-del-1997-correspondence-others.pdf

401-del-1997-correspondence-po.pdf

401-del-1997-description (complete).pdf

401-del-1997-form-1.pdf

401-del-1997-form-19.pdf

401-del-1997-form-2.pdf

401-del-1997-form-3.pdf

401-del-1997-gpa.pdf

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Patent Number

213241

Indian Patent Application Number

401/DEL/1997

PG Journal Number

01/2008

Publication Date

04-Jan-2008

Grant Date

24-Dec-2007

Date of Filing

20-Feb-1997

Name of Patentee

THE CHIEF CONTROLLER, DEFENCE RESEARCH & DEVELOPMENT ORGANISATION,

Applicant Address

MINISTRY OF DEFENCE, GOVT. OF INDIA, TECHNICAL COORDINATION, DTE., B-341 SENA BHAWAN, DHQ P.O. NEW DELHI 110011 INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	SHRI GIRISH JAYANTRAO KULKARNI, SCEENTIST 'C'	NAVEL MATERIALS RESEARCH LABORATORY, RESEARCH AND DEVELOPMENT ORGANISATION, MINISTRY OF DEFENCE, BOMBAY INDIA.
2	DR. DIPAK KUMAR BISWAS	SCIENTIST 'F' NOVEL MATERIALS RESEARCH LABORATORY, RESEARCH AND DEVELOPMENT ORGANISATION, MINISTRY OF DEFENCE, BOMBAY INDIA.

PCT International Classification Number

C22C 038/42

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA