Title of Invention

"AN IMPROVED PROCESS FOR PREPARATION OF COPPER AND BORON CONTAINING BAINITIC STEEL ALLOY AND PRODUCTS THEREOF"

Abstract This invention relates to an improved process for the preparation of copper and boron containing bainitic steel or steel alloy and products thereof. According to the process pure iron is subjected to the steps of melting and deoxidation. Ferro alloys are then added to the deoxidized molten iron. The mixture is subjected to the steps of salt treatment and tapping. The molten steel or steel alloy is poured into clean dry ingot moulds. The moulded alloy is forged to a size suitable for further rolling and is rolled to the final size with sufficient reduction per pass to produce a uniformely deformed steel or steel alloy which on air cooling produces extremely fine granular bainitic steel or steel alloy.
Full Text TITLE OF INVENTION
An improved process for preparation of copper and boron containing bain.tt.ic steel and products thereof„
FIELD OF THE INVENTION
The present invention relates to an improved process for preparation of copper anc! boron containing hainitic steel and products thereof:,
PRIOR ART
The steel or steel alloy required for manufacture of pressure vessels and critical components in a wide variety of engineering structures is required to have combination of high strength and toughness a 1 o n Q w i. t h g o o d w e 1 d a b i 1 i t y a n d c o r r o s i on re s i s t a n c e a n d 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 in required to be subjected to pressure (i„e„ pressure vessels etc,) and/or exposed to the corrosive
eng iron merit (i.e. ships etc.) and/or various/types of attacks,, like kinetic energy attack,, mo men tun attack . or shock wave attack. The exposure to corrosive
e n v i r o n m e n t i n t u r n i n i t i a t e the c o r r o s i. o n , p r e f e r a b 1 y ,,
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 r u c. t u r e s, as s t a t. e d h e r e i. n above , f r o m c o r r o s i v e environment, i, that is from corrosion,, that is to say to enhance the corrosion,, that is to say to enhance the corrosion resistance,, is to apply a coating on the surface of such structures,, which in turn is capable of protecting the exposed surface of structures or super structures or pressure vessels,, as the case may be,, from corrosive attack or say from initiation of corrosion process,, Such coatings are known in the prior art and are being used exhaustively.
The limitation of application of such coatings is that the protection is limited only upto the resistance to corrosion and that's too for the limited period,, which in turn necesitat.es the repetition of process of coating after reqular intervals,,
S t i 1.1 a n o t h e r 1 i m i. t. a t i. o n o f s u c h c o a t i n q s is that the, weldability characteristics and other i ii e c h a n i c. a 1. p r o p e r t. i. e s ,, p a r t i c. u 1 a r 1 y t h e s t. r e n g t h r elated properties are neither effected nor improved.
These limitations are overcome by the improvement of the steel or steel alloy itself, Such improvements are effected by variation in the chemical compositions and in the process of preparation and in the process of heat treatment of such steels or steel alloys.
The process of control of such properties, as 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 an alloy normally reduces its toughness and vice-versa,, In addition, to meet the requirements of mechanical properties, in ay 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 100 Ksi (700Mpa) of strength would require high amounts of nickel contents or elaborate processing and heat treatment.
The requirement of the heat treatment as one of the essential step of the known methods of the prior art, as stated above sometimes introduces various defects leading to higher rejection rate.
One of the known such defects, as stated above is heterogeneity, which in turn is introduced due to non-uniform heating.
Another known such defect is possibility of property variation, which in turn is introduced due to faulty stacking and quenching in the heat treatment from batch to batch.
Still another known such defect is the increase in the cost of the process and hence the cost of the products.
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 engineering 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 weldability as their higher carbon content and carbon equivalent make them susceptible to the hydrogen induced cracking.
Another drawback of such known quenched and tempered steels or steel alloys for construction of such engineering structures, as stated herein above is that,, the technological problem, stated in proceeding paragraph damands stringent welding procedures and controls such as p re--heat ing,, This adds to the cost of the components which require extensive welding,,
Still another drawback of such known steels or steel alloys for construction of such engineeing 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 large size required for specific application's for c. o n s t r u c t i o r 'i o f s u c. h e n g i n e e r i r i g s t r u c. t u r e s ,
Yet. another drawback of such known processes or processing techniques., as stated in proceeding p a r- a g r a p h ., i s t h at, set t i. n g u p o f s u c h f a c: i. 1 i. t i. e s o f roll quenching,, special rolling and heat treating,, definitely adds to the cost of the process and hence to the cost of the products,, which may in turn make it highly uneconomical if the demand happens to be l&w.
Still further disadvantage/drawback of known high performance quenched and tempered steels or steel alloys is their high martensitic hardenah.il ity which results in brittle heat affected zones and associated w e 1 d c: r a c k i n g .
The low carbon taainitic steels or steel alloys known in prior art generally contain relatively higher amounts of costly alloying elements,, such as molybdenum and nickel and do not contain copper and boron. The elements molybdenum and nickel are expensive and part icu1 ar1y nickel.
OBJECTS OF THE INVENTION
A primary object of the present invention is to propose an improved process for preparation of copper and boron containing bainitic steel and products thereof,, wherein the process of present invention avoids the disadvantages of the known art.
Another object of this invention is to propose a process for preparation of copper and boron containing bainitic steel and products thereof having improved mechanical properties,, particularly strength r e I a t e cl p r o p e r ties, in addition t o b OB i n g c o r r o s i o n resistant.
Still another object of the present invention is to propose an improved process for preparation of
copper and boron containing bainitic steel or steel alloy products thereof, which have high yield strength arid excellent, toughness even in the as rolled condition and still not requiring any heat treatment,, hence reducing the cost of the process and product as well,,
Yet another object of the present invention is to propose an improved process for preparation of high strength bainitic steel containing copper and boron as alloying elements having better grain refinement.,, uniform fine microstrueture and overcome the d e f e c i. s / d r a w b a c k s o f h e t e r o g e n e i t y .
A further object of the present invention is to
propose an improved process for the preparation of
copper and boron containing taainitic steel and the
products thereof, which have flexibility to be used in
both the conditions i „ e „ as rolled arid in variety of
heat t r e a t e d c. o n d i. t i. o n s .
Further an object of the present invention is to have an improved process for the preparation of copper and boron containing bainitic steel and the
products thereof, as stated herein above, which have onvercome the drawback of the property variation, that is the products prepared according to process of the present invention as disclosed herein below have the uniform properties over the entire area of the end use product.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention there is provided an improved process for preparation of copper and boron bainitic steel and product thereof comprising in the steps of:
a) Melting pure iron at temperature range of 1400-
1700°C;
b) graphite is then added to increase carbon content to
allow the reacting mass to deoxide;
c) adding ferro alloying elements as herein described to
the deoxidized molten iron;
d) treating the molten iron with a salt as herein
described;
e) tapping at a temperature of 1550 to 1650°C as herein
described;
f) pouring of molten steel alloy into clear dry ingot
moulds;
g) forging at 1000 to 1250°C as herein described; rolling to the required size by soaking/and heating
/ repeatably to produce a uniformaly deformed steel
which on air cooling produces extremely fine granular bainitic steel or steel alloy.
The preparation of high strength,, low carbon
taa.in.itic steel or steel alloys,, as stated herein above,,
in accordanre to the preferred embodiments of the
process, of the present invention,, is carried out. in
f o 1 1 o w i. r i q s t e p s s
a) Cleaning and drying of re act. ants;
b) Melting of pure iron;
c ) d e o x i d a t i o n $
d) addition of ferro alloys to the deoxidized
moI ten iron;
e) salt treatment;
f ) tapping;
g) pouring of molten steel or steel alloy into
c 1 e an d r y i n g o t. in o u 1 d s 5
f o r q i n g t o a B i z e s u i t a b 1 e f o r f u r t h e r r o 11 i. n g 5
v o 1 1 i. n g t o t h e final s i. z e w i. t h s u f f i. c i e n t reduction per pass to produce a uniformely deformed steel or steel alloy which on air cooling produces extremely fine granular bainitic steel or steel alloy.
The alloying element used comprises carbon (C) present between O.29 to 0,32, mangnese (Hn) between .1.2 to 1.5, nickel (Mi) between .1.75 to 2.OO, molybdenum (Mo) between 0.3 to 0,,5,; copper (Cu) between J. . 2 to !niobium (Mb) between 0.04 to 0.5, copper (Cu) between 1.2 to 1 „ 4 ., niobium (Nh) betwr^n 0.04-O.06, si 1 icone (Si) between 0.75 to ',00,, phosphorus (P) less than 0..02, sulphur (S) 'ess than 0.02? chromium (Cr) between 0 „ 5 t.: 0 ,. 3 ,, boron ( B ) less t h a n O . 0 0 2 O a n d t. i t a n i u m ("1" i) b e t K •"• e r i O . 0 4 i:. o 0 „ 0 6 s all p r e s e n t w i t. h i n these I i m i t B in percent by weight and oxygen (O2) is present, less than 50 parts per million (ppm) and nitrogen (N2) is less than 1.00 parts per million (ppm) and hydrogen (H2) is less than 2 parts per million (ppm) and balance is iron.
In accordance to the presently disclosed invention the improved process for preparation of copper and boron containing bainitic steel and steel alloy and products thereof, particularly an improved process for preparation of copper and boron containing low carbon bainitic steel or steel alloy and products thereof, more particularly an improved process for p re? pa rat.ion of copper and boron containing high 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 1.0'X, aqueous hydrochloric acid solution until a bright surface is revealed., The remaining react ants a long with pickled iron are dried in an oven at 20O—250'C for preferably two hours.
In accordance to the process of the present, invention the first, step involves melting of pure iron between .1400-1700' C preferably at about 1500 to 1600'C in a furnace,, such as an air induction melting furnace,.
According to the preferred embodiment, to the graded scrap, the graphite is added, which in turn increases the carbon content to the desired level in accordance to the preferred embodiment of this invention and the reacting mass is allowed to deoxidise,,
After the step of deoxidation, the ferro alloying elements are added in the appropriate amounts to the molten pure iron, which in turn adjust the possible loss of each of the alloying element in the me 11. „
According to the preferred embodiment of this invention the alloying elements comprise of carbon (C) present between 0 „ 29 to 0.32., mangnese (Mn) between 1.2
to 1,5, nickel (Ni) between 1.75 to 2.00, molybdenum (Mo) between O.3 to 0 . 5 =, copper ( Cu ) between i,,2 to .1. „ 4,
niobium (Mb) between 0.04 0,, 06, si 1 icons (Si) between
0.75 to 1.00, phosphorus (P) less than O..O2,, sulphur (S) less then 0.02, chromium (Cr) between 0.5 to 0.8, boron (B) less than O.OO20 and titanium (Ti) between O..O4 to O.O6, all present in percent by weight and oxygen (02) is present less than 5O parts per million (pprn) and nitrogen £N2) is less than .1.00 parts per million (ppm) and hydrogen (H2) is less than 2 parts per million (ppm) and balance is iron.
The reacting mass is treated with salt, preferably the sodium chloride salt,, During this step a sign if icant amount. of inclusion removal takes place. "!"11 e sal t,, p a r t i. c u 1 a r 1 y sod i u m c h 1 o r ids v a p p o r i s e s , i n the melt and comes out in the form of bubbles,, These upcoming bubbles form vapour phases like SiC14 and Aid4 on reaction with the inclusions. The sulfide inclusions re removed by formation of sodium sulfide.
The molten steel or steel alloy is poured into the already cleaned and dried ingot moulds after
tapping it at the temperature of about 1550 to 1650'C,
preferably at the temperature of about 1575 to 16iO'C.
The melt is c as tec!, preferably in the form of round
ingot, more preferably round ingots of diameter about
110 to 125mm.
The ingots formed are soaked at about 1000C to 1250'C,, preferably at .1.170 to 1.225'C for about 160 to 19O minutes followed by forging to a size suitable for further rolling, preferably to the size from 150 mm X 100 inn: to about. 50 to 60 mm square cross section,, More particularly,, according to the process of this .invention the cast ingots are reheated between 1OOO to 1200'C, preferably between 11OO to 1.1.55 'C and soaked at this temperature for about two hours followed by forging to make about 6.4 mm thick and 200 to 250 mm wide plates which are then air cooled to room temperature. These plates are reheated upto 300'C and soaked for 2 hours before rolling in the steps of the process of this invention„
R o I I i n q i s c a r r i. e d o u t i n rn u 11 i p 1 e pas is e s „ The rolling in accordance to this preferred embodiment
results in 15 20% reduction in each pass and is
continued till the plate thickness of about 6., 0 to 6U5 mm is achieved, which on air cooling results in the desired extremely fine granular., copper and boron containing3 high strength, low carbon bainitic steel or steel allay.
'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 c o n d i t. i o n s ,, i. -f d e B i r e d „
T h e d e v e 1 o p e c:! s t e e 1 o r B tee!!. alloy was subjected ho the test of reduction of .inclusion. The
following Table 1 clearly indicates about 62% reduction
of inclusion contents when compared to the steel prepared by conventional technique. This further resulted in the improvement of the desired met a 1 1 ogr aphic and mechanical properties,, such as yield strength,, ultimate ten si 1 strength , hardness and c harpy energy etc,, of the steel or steel alloy prepared in accordance to the process of this invention
TABLE 1 (Table Removed)
The developed alloy when observed for micrOBtrueture
under optical microscope in as rolled condition, has
shown the uniformly fine grained hainitic lath
structure, as it is clear/understood from the
micrographs shown below at two different magnifications.
Micrograph 'A' of Fig. 1 of the accompanying drawings
shows the micros-trueture at the magnification of X500
and micrograph 'B' of Fig,, 2 shows at rnagnification of
X1OOO„
It is understood from the forgoing description that the process disclosed herein above,, definitely has over-come the drawbacks of such known processes and definitely has the advantage of producing the copper and boron containing high strength, low carbon ba.init.ic steel or steel alloy having comparable hardness and i.ensile properties.
The weight percentage of expensive elements,, as stated herein ahove is reduced„ The combined weight percentage of copper, niobium and boron is maintained between 1.2 to 1.50 weight percent,,
The foregoing process was performed for 50 kg and 50O kg production scales and it was observed that the developed steel or steel alloy,, when strictly prepared in accordance to the process of the present invention has improved metal lographic. and mechanical properties with reduction in inclusion and no property variation ,.
Any steel or steel alloy developed in accordance to the process of the present invention isaving chemical composition, as disclosed herein above may fall within the scope of the presently disclosed invention„




WE CLAIM;
1. An improved process for preparation of copper and boron bainitic steel and product thereof comprising in the steps of:
a) melting pure iron at temperature range of 1400-
1700°C characterised by;
b) adding graphite to step (a) to increase carbon content
to allow the reacting mass to deoxide;
c) adding ferro alloying elements as herein described to
the deoxidized molten iron;
d) treating the molten iron with a salt as herein
described;
e) tapping at a temperature of 1550 to 1650°C as herein
described;
f) pouring of molten steel alloy into clear dry ingot
moulds;
g) forging at 1000 to 1250°C as herein described;
h) rolling to the required size by soaking as herein described and heating repeatably to produce a uniformaly deformed steel which on air cooling produces extremely fine granular bainitic steel or steel alloy.
2. An improved process as claimed in preceedings claims,
wherein the said ferro alloying elements comprises of carbon
(C) between 0.29 to 0.32, manganese (Mn) between 1.2 to
1.5, nickel (Ni) between 1.75 to 2.00, molybdenum (Mo)
between 0.3 to 0.5, copper (Cu) between 1.2 to 1.4, niobium
(Nb) between 0.04-0.06, silicone (Si) between 0.75 to 1.00,
phosphorus (P) less than 0.02, sulphur (S) less than 0.02,
chromium (Cr) between 0.5 to 0.8, boron (B) less than
0.0020 and titanium (Ti) between 0.04 to 0.06, all within
these limits in percent by weight and oxygen (O2) less than
50 parts per million (ppm) and nitrogen (N2) less than 100
parts per million (ppm) and hydrogen (H2) less than 2 parts
per million (ppm) and balance iron.
3. An improved process as claimed in claim 1, wherein the step
(d) of treating the molten iron with a salt, is sodium chloride,
then removing sodium sulfide formed.
4. An improved process as claimed in claim 1, wherein the step
(e) of tapping is carried at preferably 1575 to 1610°C
followed by pouring of the said molten steel or steel alloy
into the already cleaned and dried ingot moulds in the said
seventh stage and casting, preferably in the form of round
ingots.
5. An improved process as claimed in claim 1, wherein in the
step (h) the cast ingots are soaked preferably between 1770-
1225°C for about 160 to 190 minutes followed to give the
size from 150 mm to 100 mm preferably 50 to 60 mm
square cross section, which is turn is subsequently followed
by air cooling to room temperature.
6. An improved process as claimed in claim 5, wherein the said
cast ingots are preferably reheated between 1000 to 1200°C,
preferably between 1100 to 1155°C and socked at this
temperature for about two hours followed by forging to make
about 6.4 mm thick and 200 to 250 mm wide plates which
are then air cooled to room temperature.
7. An improved process as claimed in claim 6, wherein the said
plates are reheated upto 800°C and soaked for about 2
hours before rolling.
8. An improved process as claimed in claim 7, wherein the said
rolling is carried out by repeatably soaking and heating
without intermediate re-heating by soaking and heating
repeatedly.
9. An improved process as claimed in claim 2, wherein the said
combined weight percentage of copper niobium and boron is
maintained between 1.2 to 1.50 weight precent.
10. An improved process for preparation of copper and boron containing bainitic steel or steel alloy and products thereof substantially as herein described.

Documents:

636-del-1997-abstract.pdf

636-del-1997-claims.pdf

636-del-1997-complete specifiction (granted).pdf

636-del-1997-correspondence-others.pdf

636-DEL-1997-Correspondence-PO.pdf

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

636-del-1997-drawings.pdf

636-del-1997-form-1.pdf

636-del-1997-form-19.pdf

636-del-1997-form-2.pdf

636-del-1997-form-3.pdf

636-del-1997-gpa.pdf


Patent Number 232929
Indian Patent Application Number 636/DEL/1997
PG Journal Number 13/2009
Publication Date 27-Mar-2009
Grant Date 23-Mar-2009
Date of Filing 14-Mar-1997
Name of Patentee THE CHIEF CONTROLLER RESEARCH & DEVELOPMENT
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 VINAY PRABHAKAR DESHMUKH SCIENTIST "C" NAVAL MATERIAL RESEARCH LABORATORY, MUMBAI, INDIA.
2 SHRI VASANT VISHNJU MODAK SCIENTIST "D" NAVAL MATERIAL RESEARCH LABORATORY, MUMBAI, INDIA.
3 SHRI SUNIL KAUSHAL SCIENTIST "B" NAVAL MATERIAL RESEARCH LABORATORY, MUMBAI, INDIA.
4 DR. DIPAK KUMAR BISWAS SCIENTIST "F" NAVAL MATERIAL RESEARCH LABORATORY, MUMBAI, INDIA.
5 DR. SHASHI BHUSHAN SCIENTIST "D" VEHICLE RESEARCH DEVELOPMENT ESTABLISHMENT, AHAMADNAGAR; RESEARCH AND DEVELOPMENT ORGANISATION, MINISTRY NOF DEFENCE, INDIA.
PCT International Classification Number C22C 38/16
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA