FIELD OF INVENTION
The present invention relates to heavily single reduced ultra low carbon thin steel
sheet with high r bar value. More particularly, the invention relates to a process
of producing very thin (190-250 µm) ultra low carbon steel sheet with high r bar
value by cold rolling of hot rolled sheet and subsequent temper rolling of
annealed cold rolled material.
BACKGROUND OF THE INVENTION
Low carbon steel sheets are largely used for the production of Tin plate. Tin
plate is the material used more widely in cans for foods, beverages and for other
sophisticated applications. The term Tin plate refers to low carbon mild steel
sheet with a thin layer of tin coating on each surface of the material.
This low carbon steel having higher carbon than the ultra low carbon steel has
the disadvantages during deep drawing when r bar value achieved is low. The
term r bar can also be called as Lankford parameter which determines the
drawability of a sheet material. This property is commonly represented in terms
of the average r-value written as r or rm, which is defined by the relationship f or
rm = (r0 + 2r45 + r90)/4 where the subscripts 0, 45 and 90 refer to the inclination

of the longitudinal axes of tensile sample to the rolling direction of the sheet,
while an individual r value is the ratio of the strain in the width direction/strain in
the thickness direction.
Because of this low r bar value, it becomes difficult to manufacture a complicated
shape with this steel after deep drawing. The property of 'Formability' is also low.
Formability can be specified as deep drawability which is the capacity to achieve
high degree of plastic flow in the plane of the sheet, while offering sufficient
resistance to flow in the thickness direction. This is closely related to texture and
r bar value of the steel sheet. Another area where the improvement can be made
is the reduction in weight.
Hence there exists a need to improve the deep drawing, r bar value, formability
and also for reduction in weight of low carbon thin steel sheet.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a process for manufacturing
heavily single reduced ultra low carbon thin steel sheet which is capable of
achieving high r bar value in the steel sheet after temper reduction.

Another object of the invention is to propose a process for manufacturing heavily
single reduced ultra low carbon thin steel sheet which is able to produce
optimum amount of strength and formability without much loss in ductility in thin
steel sheet.
Yet another object of the invention is to propose a process for manufacturing
heavily single reduced ultra low carbon thin steel sheet which is capable of
producing light weight products.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. la - shows the (111) pole figure of hot rolled sheet according to invention.
Fig. lb - shows the (111) pole figure of Primary cold rolled sheet with increased
texture strength according to invention.
Fig. lc - shows the (111) pole figure of annealed steel sheet with marginal drop
of texture intensity according to invention.
Fig. Id - shows the (111) pole figures of secondary cold rolling with marginal
strengthening of textures according to invention.
Fig. 2a - shows the texture of hot rolled sheet according to invention.
Fig. 2b - shows the texture with increased intensity of the steel sheet after
primary cold rolling according to invention.

Fig. 2c - shows the texture of the steel sheet with strong r fibre after annealing
according to invention.
Fig. 2d - shows the texture with marginal improvement of texture strength after
secondary cold rolling.
Fig. 3 - a flow chart of the process of manufacturing according to invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
According to the invention, the process to produce very thin steel sheet with high
r bar value in the single reduced condition helps to reduce the weight of the
product and improve formability along with high resistance to indentation for a
product to be used in packaging applications.
The present invention provides production of very thin (190-250 µm) ultra low
carbon single reduced steel sheet with high r bar value in the single reduced
state. The annealing parameters and the amount of temper reduction in the
specified composition range have been optimized to achieve high r bar value in
the steel sheet after temper reduction. The r bar value has direct impact on the
formability and the deep drawability. The resulted material is to be used to
produce light weight products especially for production of beverage cans.

The chemical composition of the steel is: 0.001-0.005%C/ 0.05-0.2%Mn/ 0.004-
0.012%S/ 0.005-0.015%P/ 0.002-0.010%Si/ 0.020-0.045%AI/ 0.025-0.008%N/
0.004-0.030%Nb/ 0.01-0.05%Ti (all values in wt%). The steel was controlled hot
rolled and during hot rolling total amount of deformation applied is in the range
of 50-90%. The Finish Rolling Temperature (FRT) is kept within 875°C-975°C.
The coiling temperature of the hot rolled material is in the range 650°C-775°C.
Cold rolling is applied to the hot rolled sheet to reduce the thickness. The cold
rolled steel is subjected to batch annealing treatment for 6 to 12 hours in the
temperature range 600 to 700°C. The annealed material is given high amount of
temper rolling. The amount of temper rolling applied 25 to 45%. The thickness
of the sheet achieved after moderate amount of temper rolling is in the range of
190 to 250 urn. The sample for X-Ray diffraction (XRD) is prepared by manual
polishing technique. Crystallographic textures is determined from the mid
thickness regions of the sheets using a Philips X-Ray diffractometer. ODFs
(Orientation Distribution functions) were measured using MTM-FHM software and
2 = 45° sections (Bunge notation) are determined therefrom. The average r bar
value is also calculated using the same software.
Formability of steel sheets is greatly enhanced by the presence of strong and
homogenous γ fibre texture. The resistance to indentation of a steel sheet is
determined by the amount of deformation applied to the sheet. Optimum
amount of strength and formability without much loss in ductility can be

controlled by controlling the amount of second reduction applied to the sheet for
the production of beverage cans. Figure 1 (a-d) show the (111) pole figure of the
steel sheets from the hot rolling stage to successive processing. The (111) pole
figure of the hot rolled sheet is shown in figure 1(a). The texture here has been
found almost random. Cold rolling leads to increase in the texture strength
[Fig.1b]. As a result of annealing the texture intensity drops marginally, however,
the (111) pole density increases. The texture of the sheet strengthens marginally
as a result of second cold rolling. The texture developed during each stage of
processing has also been depicted in the form of 2 = 45° sections of the ODFs
which are presented in figure 2 (a-d). Fig. 2(a) shows the texture of the hot
rolled sheet. The texture here can be found very weak with maximum ODF
intensity 2 times random. No clear γ and α could be found here. The texture
intensity increases to 13 times random as a result of primary cold rolling
[Fig.2b]. The texture here can be described as combination of strong γ and α
fibre texture. Annealing of the cold rolled sheet produces a strong Γ fibre at the
expense of α fibre [Fig.2c]. The ODF intensity found here 10 times random. The
annealed sheet was further given second reduction. Second reduction leads to
improvement in the texture strength marginally [Fig.2d]. The ODF intensity rose
marginally to 11 times random. At this stage the Γ fibre almost retained,
however, very small amount of α fibre could also be observed. The r bar value
obtained as a result of annealing is in the range 1.80 to 2.05. Second reduction
does not lead to significant deterioration of the average r bar value, which is

found to be in the range 1.75 to 1.90. Figure 3 show the schematic flow chart of
the present invention.
Temper rolling is light cold reduction of the cold rolled and annealed sheet. In
the present invention the reduction is primarily applied in the room temperature,
which is cold reduction. In the present invention hot rolling reduction in thickness
is negligible compared to cold rolling. Depending upon the amount of temper
rolling applied in the cold rolled and annealed sheet, the steel sheet is
categorized whether it would be single reduced or double reduced. The present
invention is single reduced steel although the amount of temper rolling is little bit
higher.
111 pole figures means projection of <111> plane normal. This is a standard
way to represent the texture developed in the steel sheet.
Y fibre is a metallurgical terminology which is used world wide to express the
orientation of aggregate of crystals in a material. The gamma (γ) fibre actually
indicates <111> direction of the crystals present in the material and is parallel to
the normal direction of the sheet.
Alpha (α) fibre is <110> direction of the crystals and is parallel to rolling
direction of the sheet.

2 = 45° section is one of the sections in Euler space. The Euler space is used to
define the position of a crystal. This space has definite Euler angle (1, , 2)
values. Several sections can be sliced from the Euler box. 2 = 45° section is one
of the constant section which has been used to represent the crystal orientations
generated in the steel sheet after novel treatment.
The present invention involves a combined process of annealing and second
reduction that leads to development of steel sheet with average r bar value in
the range 1.75 in a thin steel sheet having thickness 190-250 µm. Achieving of
such high r bar value in this thin steel sheet after temper reduction makes the
steel sheet suitable for light weight beverage applications.

WE CLAIM
1. Heavily single reduced ultra low carbon thin steel sheet with high r bar
value and the process for manufacturing the same comprising:
a thin ultra low carbon steel sheet containing in terms of percent by
weight, C- 0.001-0.005%, Mn- 0.05-0.2%, S- 0.004-0.012%, P- 0.005-
0.015%, Si- 0.002-0.010%, Al- 0.020-0.045%, N- 0.0025-0008%, Nb-
0.004-0.030% and Ti- 0.01-0.05% and the rest being Fe;
characterized in that the r bar value of the said steel sheet is in the range
of 1.75 to 1.90 after temper rolling.
2. Ultra low carbon thin steel sheet as claimed in claim 1, wherein the
reduced thickness of the steel sheet is 190-250 µm.
3. A process for manufacturing heavily single reduced ultra low carbon thin
steel sheet with high r bar value comprising:
controlled hot rolling of the steel;
cooling of the hot rolled steel sheet;
cold rolling of the hot rolled sheet to reduce the thickness;
batch annealing of the cold rolled steel sheet;
temper rolling of the annealed steel sheet to further reduce the thickness;

4. A process as claimed in claim 3, wherein the hot rolling is carried out in
the temperature range 875°C-975°C and the amount of hot rolling applied
50-90%.
5. A process as claimed in claim 3, wherein the cooling temperature of the
steel sheet after hot rolling is in the range of 650°C-775°C.
6. A process as claimed in claim 3, wherein the annealing temperature is
used in the range of 600 to 700°C.
7. A process as claimed in claim 3, wherein the batch annealing treatment is
carried out for 6 to 12 hours.
8. A process as claimed in claim 3, wherein the amount of temper rolling
applied is 25 to 45%.

Heavily single reduced ultra low carbon thin steel sheet containing in terms of percent by weight, C- 0.001-0.005%, Mn- 0.05-0.2%, S- 0.004-0.012%, P- 0.005-0.015%, Si- 0.002-0.010%, Al- 0.020-0.045%, N- 0.0025-0008%, Nb- 0.004-0.030% and Ti- 0.01-0.05% and the rest being Fe, has high average r bar value of 1.75 tol.9 and reduced thickness in the range of 190 µm to 250um. The process for manufacturing the ultra low carbon thin steel sheet consists of
controlled hot rolling, cooling of the hot rolled steel sheet, cold rolling of the hot
rolled sheet to reduce thickness followed by batch annealing of the cold rolled steel sheet and then temper rolling of the annealed steel sheet to reduce the thickness further.