Title of Invention	AN IMPROVED STEEL CHEMISTRY AND PROCESSING FOR IMPROVING FORMABILITY OF BATCH ANNEALED INTERSTITIAL FREE HIGH STRENGTH STEELS FOR AUTOMOBILE BODY APPLICATIONS
Abstract	FeTiP precipitation temperature range is around 700°C and batch annealing is usually done around this temperature. As a result, precipitation of FeTiP interferes with recrystallization annealing resulting in poor {111} texture formation. Not only that, it also precipitates in preference to TiC, as a result of this most of the Ti is exhausted and C remains in solution and this adversely affects the {111} texture formation. Three different techniques have been identified for improving the Lankford parameter (average r value) by suppressing FeTiP precipitation in the steels.

Title of Invention

AN IMPROVED STEEL CHEMISTRY AND PROCESSING FOR IMPROVING FORMABILITY OF BATCH ANNEALED INTERSTITIAL FREE HIGH STRENGTH STEELS FOR AUTOMOBILE BODY APPLICATIONS

Abstract

FeTiP precipitation temperature range is around 700°C and batch annealing is usually done around this temperature. As a result, precipitation of FeTiP interferes with recrystallization annealing resulting in poor {111} texture formation. Not only that, it also precipitates in preference to TiC, as a result of this most of the Ti is exhausted and C remains in solution and this adversely affects the {111} texture formation. Three different techniques have been identified for improving the Lankford parameter (average r value) by suppressing FeTiP precipitation in the steels.

Full Text	2 FIELD OF THE INVENTION The present invention relates to development of a metallurgical process to improve physical properties of steel. More particularly the present invention relates to development of a metallurgical process and chemistry of steel to Improve formabillty of batch annealed interstitial free high strength steels adaptable to automobile body applications. BACKGROUND OF THE INVENTION Application of interstitial free high strength (IFHS) steels in the automotive industry has increased significantly in the last couple of decades due to their excellent deep drawability coupled with adequate strength. Deterioration of drawability has been noticed in this grade, as compared to normal IF steels, which is very often been attributed to the presence of P, the principal solid solution strengthening element in this grade. It is assumed that P precipitates as FeTiP which leads to the deterioration of both drawability and loss of strength. This effect is more pronounced in batch annealed IFHS steels, as the long soaking allows sufficient time for this precipitation to occur. 3 OBJECTS OF TH E INVENTION It is therefore, an object of the present invention to propose a process and chemistry of steel for improving formability of batch annealed interstitial free high strength steels adaptable to automobile body application which eliminates the disadvantages of prior art Another object of the present invention is to propose a process and chemistry of steel for improving formability of batch annealed interstitial free high strength steels adaptable to automobile body application which helps to increase the formability properties of steel. A further object of the present invention is to propose a process and chemistry of steel for improving formability of batch annealed interstitial free high strength steels adaptable to automobile body application which increases strength by batch annealing process. A still further object of the present invention is to propose a process and chemistry of steel for improving formability of batch annealed interstitial free high strength steels adaptable to automobile body application which improves steel chemistry. 4 SUMMARY OF THE INVENTION FeTiP precipitation temperature range Is around 700°C and batch annealing Is usually done around this temperature. As a result, precipitation of FeTiP interferes with recrystallization annealing resulting in poor {111} texture formation. Not only that, it also precipitates in preference to TIC, as a result of this most of the Ti is exhausted and C remains in solution and this adversely affects the {111} texture formation. Three different techniques have been Identified for improving the Lankford parameter (average r value) by suppressing FeTiP precipitation in the steels. DETAILED DESCRIPTION OF THE INVENTION The IFHS steels studied contain (In wt %): C: 0.002-0.005 Al: 0.02-0.07 Mn: 1.5 or less TI: 0.1 or less Si: 0.05 or less Nb: 0.05 or less S: 0.05 or less B: 30 ppm or less P: 1.5 or less N: 80 ppm or less 5 To improve the formability and therefore, the Lankford parameter, the major goal Is to produce a very large volume fraction of {111} oriented grains during recrystallization annealing. The first and foremost condition for this is to make the matrix free of interstltlals, mainly C and N Two techniques have been identified to achieve this based on: 1. The chemistry 2. The processing parameters Chemistry: Ti level in the steel should be just above the stoichiometric rqulrment for fixing N and C so that is does not get any chance to form FeTiP. For 30-40 ppm carbon and 30-40 ppm N, 0.02 to 0.05 Ti is ideal. Process Paramenters: Processing of IFHS steels consists of hot rolling, cold roiling and annealing. During hot rolling, the coiling temperature plays a vital role. If IFHS steels are coiled at a much higher temperature, which 6 does not lie in the temperature range for the precipitation of FeTiP, much better results will be obtained. Coiling at 580-650°C produces Tl4C2S2 which causes carbon to be taken out of solid solution. On the contrary, when the same steel is coiled at a somewhat lower temperature (470-570°C) no precipitation of Tl4 C2S2 takes place. This is the reason why even when an IFHS steel is annealed at 670- 750° (within the precipitation regime of FeTiP) after cold rolling, coiling at a higher temperature results better average r value of >1.9 as compared to temperature results better average r value of >1.9 as compared to Another important parameter is the temperature of annealing after coid roiling. It has been observed that annealing at 670-750°C produces poorer {111} texture than after annealing at 770-860°C. This is also attributed to the formation of FeTiP precipitate instead of any carbide at 670-750°C annealing temperature. However, at 770- 850°C annealing temperature, Tl4C2S2 forms and presence of FeTiP is not observed. Higher average r value (~2.4) is obtained in the latter as compared to in the former one. 7 WE CLAIM 1. An improved steel chemistry and processing for improving formabillty of batch annealed interstitial free high strength steels adaptable to automobile body applications comprising:- - an improved chemistry of steel having a composition of: (in wt %) (In wt %) C: 0.02-0.005 Al: 0.02-0.07 Mn: 1.5 or less Tl: 0.1 or less Sl: 0.05 or less Nb: 0.05 or less S: 0.05 or less B: 30 ppm or less P: 1.5 or less N: 80 ppm or less 2. An improved process for improving formability of batch annealed interstitial free high strength steel comprises:- - Hot rolling and coiling of steel at a temperature 580°-650pC - a cold rolling and 8 - a batch annealing at 770°C-8500 C 3. The steel chemistry as claimed in claim 1, wherein Ti level in the steel should be just above the stoichlmetric requirement for fixing C and N which result in better formability in IFHS steels. 4. The process as claimed in ciaim 2, wherein annealing temperature at 770°C-850°C results in the formation of Tl4C2S2 precipitation, eliminating the presence of FeTIP precipitation. 5. An improved steel chemistry and processing for improving formability of batch annealed interstitial free high strength steels adaptable to automobile body applications as substantially illustrated and described herein. FeTiP precipitation temperature range is around 700°C and batch annealing is usually done around this temperature. As a result, precipitation of FeTiP interferes with recrystallization annealing resulting in poor {111} texture formation. Not only that, it also precipitates in preference to TiC, as a result of this most of the Ti is exhausted and C remains in solution and this adversely affects the {111} texture formation. Three different techniques have been identified for improving the Lankford parameter (average r value) by suppressing FeTiP precipitation in the steels.

Full Text

2
FIELD OF THE INVENTION
The present invention relates to development of a metallurgical
process to improve physical properties of steel. More particularly the
present invention relates to development of a metallurgical process
and chemistry of steel to Improve formabillty of batch annealed
interstitial free high strength steels adaptable to automobile body
applications.
BACKGROUND OF THE INVENTION
Application of interstitial free high strength (IFHS) steels in the
automotive industry has increased significantly in the last couple of
decades due to their excellent deep drawability coupled with
adequate strength. Deterioration of drawability has been noticed in
this grade, as compared to normal IF steels, which is very often been
attributed to the presence of P, the principal solid solution
strengthening element in this grade. It is assumed that P
precipitates as FeTiP which leads to the deterioration of both
drawability and loss of strength. This effect is more pronounced in
batch annealed IFHS steels, as the long soaking allows sufficient time
for this precipitation to occur.

3
OBJECTS OF TH E INVENTION
It is therefore, an object of the present invention to propose a
process and chemistry of steel for improving formability of batch
annealed interstitial free high strength steels adaptable to automobile
body application which eliminates the disadvantages of prior art
Another object of the present invention is to propose a process and
chemistry of steel for improving formability of batch annealed
interstitial free high strength steels adaptable to automobile body
application which helps to increase the formability properties of steel.
A further object of the present invention is to propose a process and
chemistry of steel for improving formability of batch annealed
interstitial free high strength steels adaptable to automobile body
application which increases strength by batch annealing process.
A still further object of the present invention is to propose a process
and chemistry of steel for improving formability of batch annealed
interstitial free high strength steels adaptable to automobile body
application which improves steel chemistry.

4
SUMMARY OF THE INVENTION
FeTiP precipitation temperature range Is around 700°C and batch
annealing Is usually done around this temperature. As a result,
precipitation of FeTiP interferes with recrystallization annealing
resulting in poor {111} texture formation. Not only that, it also
precipitates in preference to TIC, as a result of this most of the Ti is
exhausted and C remains in solution and this adversely affects the
{111} texture formation. Three different techniques have been
Identified for improving the Lankford parameter (average r value) by
suppressing FeTiP precipitation in the steels.
DETAILED DESCRIPTION OF THE INVENTION
The IFHS steels studied contain (In wt %):
C: 0.002-0.005 Al: 0.02-0.07
Mn: 1.5 or less TI: 0.1 or less
Si: 0.05 or less Nb: 0.05 or less
S: 0.05 or less B: 30 ppm or less
P: 1.5 or less N: 80 ppm or less

5
To improve the formability and therefore, the Lankford parameter,
the major goal Is to produce a very large volume fraction of {111}
oriented grains during recrystallization annealing. The first and
foremost condition for this is to make the matrix free of interstltlals,
mainly C and N Two techniques have been identified to achieve this
based on:
1. The chemistry
2. The processing parameters
Chemistry:
Ti level in the steel should be just above the stoichiometric rqulrment
for fixing N and C so that is does not get any chance to form FeTiP.
For 30-40 ppm carbon and 30-40 ppm N, 0.02 to 0.05 Ti is ideal.
Process Paramenters:
Processing of IFHS steels consists of hot rolling, cold roiling and
annealing. During hot rolling, the coiling temperature plays a vital
role. If IFHS steels are coiled at a much higher temperature, which

6
does not lie in the temperature range for the precipitation of FeTiP,
much better results will be obtained. Coiling at 580-650°C produces
Tl4C2S2 which causes carbon to be taken out of solid solution. On the
contrary, when the same steel is coiled at a somewhat lower
temperature (470-570°C) no precipitation of Tl4 C2S2 takes place.
This is the reason why even when an IFHS steel is annealed at 670-
750° (within the precipitation regime of FeTiP) after cold rolling,
coiling at a higher temperature results better average r value of >1.9
as compared to temperature results better average r value of >1.9 as compared to
Another important parameter is the temperature of annealing after
coid roiling. It has been observed that annealing at 670-750°C
produces poorer {111} texture than after annealing at 770-860°C.
This is also attributed to the formation of FeTiP precipitate instead of
any carbide at 670-750°C annealing temperature. However, at 770-
850°C annealing temperature, Tl4C2S2 forms and presence of FeTiP is
not observed. Higher average r value (~2.4) is obtained in the latter
as compared to in the former one.

7
WE CLAIM
1. An improved steel chemistry and processing for improving
formabillty of batch annealed interstitial free high strength steels
adaptable to automobile body applications comprising:-
- an improved chemistry of steel having a composition of:
(in wt %) (In wt %)
C: 0.02-0.005 Al: 0.02-0.07
Mn: 1.5 or less Tl: 0.1 or less
Sl: 0.05 or less Nb: 0.05 or less
S: 0.05 or less B: 30 ppm or less
P: 1.5 or less N: 80 ppm or less
2. An improved process for improving formability of batch annealed
interstitial free high strength steel comprises:-
- Hot rolling and coiling of steel at a temperature 580°-650pC
- a cold rolling and

8
- a batch annealing at 770°C-8500 C
3. The steel chemistry as claimed in claim 1, wherein Ti level in the
steel should be just above the stoichlmetric requirement for fixing
C and N which result in better formability in IFHS steels.
4. The process as claimed in ciaim 2, wherein annealing temperature
at 770°C-850°C results in the formation of Tl4C2S2 precipitation,
eliminating the presence of FeTIP precipitation.
5. An improved steel chemistry and processing for improving
formability of batch annealed interstitial free high strength steels
adaptable to automobile body applications as substantially
illustrated and described herein.

FeTiP precipitation temperature range is around 700°C and batch
annealing is usually done around this temperature. As a result,
precipitation of FeTiP interferes with recrystallization annealing
resulting in poor {111} texture formation. Not only that, it also
precipitates in preference to TiC, as a result of this most of the Ti is
exhausted and C remains in solution and this adversely affects the
{111} texture formation. Three different techniques have been
identified for improving the Lankford parameter (average r value) by
suppressing FeTiP precipitation in the steels.

Documents:

00534-kol-2007-claims.pdf

00534-kol-2007-correspondence others 1.1.pdf

00534-kol-2007-correspondence others.pdf

00534-kol-2007-description complete.pdf

00534-kol-2007-form 1.pdf

00534-kol-2007-form 18.pdf

00534-kol-2007-form 2.pdf

00534-kol-2007-form 3.pdf

00534-kol-2007-gpa.pdf

534-KOL-2007-(23-03-2012)-ABSTRACT.pdf

534-KOL-2007-(23-03-2012)-CLAIMS.pdf

534-KOL-2007-(23-03-2012)-DESCRIPTION (COMPLETE).pdf

534-KOL-2007-(23-03-2012)-EXAMINATION REPORT REPLY RECEIVED.pdf

534-KOL-2007-(23-03-2012)-FORM-1.pdf

534-KOL-2007-(23-03-2012)-FORM-2.pdf

534-KOL-2007-(23-03-2012)-OTHERS.pdf

534-KOL-2007-(23-03-2012)-PETITION UNDER RULE 137.pdf

534-KOL-2007-(30-04-2012)-AMANDED PAGES OF SPECIFICATION.pdf

534-KOL-2007-(30-04-2012)-CORRESPONDENCE.pdf

534-KOL-2007-CORRESPONDENCE.pdf

534-KOL-2007-EXAMINATION REPORT.pdf

534-KOL-2007-FORM 18.pdf

534-KOL-2007-FORM 3.pdf

534-KOL-2007-GPA.pdf

534-KOL-2007-GRANTED-ABSTRACT.pdf

534-KOL-2007-GRANTED-CLAIMS.pdf

534-KOL-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

534-KOL-2007-GRANTED-FORM 1.pdf

534-KOL-2007-GRANTED-FORM 2.pdf

534-KOL-2007-GRANTED-LETTER PATENT.pdf

534-KOL-2007-GRANTED-SPECIFICATION.pdf

534-KOL-2007-OTHERS.pdf

534-KOL-2007-REPLY TO EXAMINATION REPORT.pdf

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Patent Number

253202

Indian Patent Application Number

534/KOL/2007

PG Journal Number

27/2012

Publication Date

06-Jul-2012

Grant Date

04-Jul-2012

Date of Filing

02-Apr-2007

Name of Patentee

TATA STEEL LIMITED

Applicant Address

JAMSHEDPUR

Inventors:

#	Inventor's Name	Inventor's Address
1	PAMPA GHOSH	R&D, TATA STEEL LIMITED JAMSHEDPUR 831001
2	DEBASHISH BHATTACHARJEE	R&D, TATA STEEL LIMITED JAMSHEDPUR 831001
3	R K RAY	R&D, TATA STEEL LIMITED JAMSHEDPUR 831001

PCT International Classification Number

C21D8/02,C22C38/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA