DESC:PRIORITY STATEMENT
The present application hereby claims priority from Indian patent application with the application number 202341024813, filed on 31 March 2023, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD OF INVENTION
The present invention in general is related to the field of titanium metallurgy. More specifically, the present invention relates to 4 millimeters or below cold rolled sheets and its manufacturing methods.

BACKGROUND OF INVENTION
Titanium alloys typically have high specific strength, are corrosion resistant, and creep resistant at moderately high temperatures. For these reasons, titanium alloys are used in many aerospace, aviation, defense, marine and automotive applications, including, for example, elements of take-off and landing devices, engine frames, body armor, vehicle bodies, and mechanical fasteners.
Reducing the weight of an aircraft or other motorized vehicle allows for fuel economy. Therefore, for example, in the aerospace industry, there is a serious incentive to reduce the weight of the aircraft. Titanium and titanium alloys are effective materials in providing weight reduction when used in aircraft due to their high specific strength and other useful mechanical properties.
Titanium alpha plus beta alloys exhibit poor cold workability. Due to poor cold workability titanium sheets are manufactured through pack rolling route. In this method we don’t have a control on oxidation and adiabatic temperature raise during rolling of sheets, which will result low yield strength due to beta microstructure along with grain boundary alpha. Further cleaning of sheets are more challenging to achieve surface finish and desired thickness.
At present, we could not find any literature disclosing bulk production of Ti-6Al-4V cold rolled thin sheets due to its poor cold workability.
With this background, in order to overcome and retain good volume fraction of primary alpha and transformed beta, the present invention discloses a novel method of manufacturing 4 mm or below cold rolled Ti6Al4V sheets.

OBJECT OF THE INVENTION
The principal object of the present invention is to provide a method of manufacturing Ti6Al4V cold rolled sheets of size 4 mm and below for strategic applications.
Another object of the present invention is to disclose 4mm or below cold rolled Ti6Al4V sheets.

SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the disclosure. This summary is neither intended to identify key or essential inventive concepts of the disclosure nor is it intended for determining the scope of the disclosure.

To overcome the problems mentioned above, the present invention discloses a method for manufacturing Ti6Al4V cold rolled sheets of thickness 4mm and below from ingot of diameter 850, comprising the steps of forging and hot rolling the ingot into sheets with a thickness of 5-6 mm and dimensions of 800 X L mm; heat treating the said hot rolled sheets at a near beta transverse temperature (950-880°C) for process annealing to retain a high-volume fraction of beta phase; pickling the annealed sheets in 2%HF+20% HNO3 solution to remove oxide scales for cold rolling; cold rolling the sheets up to 20 to 30% thickness reduction with intermediate annealing at 820°C for 2 hours; rolling the sheets to a final thickness ranging from 4 millimeters to 0.8 millimeters; and annealing, degreasing, and flash pickling the rolled sheets to improve appearance and surface topology.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 illustrates the microstructure of the Ti6Al4V cold rolled sheets of 4mm and below sizes in accordance with an embodiment of the present invention.

DESCRIPTION OF THE INVENTION
The present invention discloses a method of manufacturing Ti6Al4V cold rolled sheets of size 4 mm and below for strategic applications.
TITAN31 is one of the most commercially used titanium alloys under classification of alpha plus beta alloy. This alloy is equivalent to Ti6Al4V or Grade 5 and typical composition of Titan 31 alloy in weight percent is as follows: Aluminium (Al) - 5.5-6.75, Vanadium (V) - 3.5-4.5, Iron (Fe) - 0.3, Oxygen (O) - 0.2, Carbon (C) - 0.08, Nitrogen - 0.05, Hydrogen - 0.0125 and balance Titanium (Ti).
The principle alloying elements in this grade are Aluminium and Vanadium. Aluminium is an alpha (a) phase stabilizer and Vanadium is a beta (ß) phase stabilizer. This alloy is generally hot deformed either in the a+ß phase region or ß phase region due to the possibility of cracking at low temperatures.
The Hexagonal closed packed (HCP) a and Body Centered Cubic (BCC) ß titanium phase transformations makes the alloy more difficult to process in the a+ß phase region.
The deformation in the ß phase is comparatively easier due to the greater number of active slip systems in the bcc ß titanium. The high-volume fraction of ß phase at room temperature will provides good cold workability.
Production of Titan31 ingots starts with blending of titanium sponge, master alloys and other alloying elements. This alloy mix is pressed in a hydraulic press to form a “compact”. Number of these compacts are plasma welded together to form a electrode. The electrodes are multiple melted in a vacuum arc remelting furnace to ensure an acceptable degree of homogeneity, resulting final ingot dia of 850. Subsequently the ingot is forged and hot rolled to 5-6 mm X 800 X L mm thick sheets.
The hot rolled sheets are heat treated at near beta transverse temperature called process annealing at 950-880 oC, to retain the high-volume fraction of beta in the material which will improve the cold workability. Subsequently the 5-6 millimeter sheets are pickled in 2%HF+20% HNO3 to removal of oxide scales for cold rolling. The sheets are cold rolled up to 30% with intermediate annealing at 900-790 oC for 2 hours and rolled to range of 4 millimeters to 0.8 millimeters. Further the sheets are Annealed, degreased and flash pickled to improve the appearance and surface topology.
ADVANTAGES AND APPLICATION
The present invention is used to produce sheets which are used in various critical application. The said sheets are used as feed stock for dome forging in Space, aerospace, Additive manufacturing, Naval and nuclear applications.
,CLAIMS:CLAIMS:
We Claim
1. A method for manufacturing Ti6Al4V cold rolled sheets of thickness 4mm and below from ingot of diameter 850, comprising the steps of:
a. Forging and hot rolling the ingot into sheets with a thickness of 5-6 mm and dimensions of 800 X L mm;
b. Heat treating the said hot rolled sheets at a near beta transverse temperature (950-880°C) for process annealing to retain a high-volume fraction of beta phase;
c. Pickling the annealed sheets in 2%HF+20% HNO3 solution to remove oxide scales for cold rolling;
d. Cold rolling the sheets up to 20 to 30% thickness reduction with intermediate annealing at 820°C for 2 hours;
e. Rolling the sheets to a final thickness ranging from 4 millimeters to 0.8 millimeters; and
f. Annealing, degreasing, and flash pickling the rolled sheets to improve appearance and surface topology.

2. A method for manufacturing Ti6Al4V cold rolled sheets as claimed in claim 1, wherein the composition of Titan 31 ELI ingots comprises in weight percent: Aluminium (Al) - 5.5-6.75, Vanadium (V) - 3.5-4.5, Iron (Fe) - 0.3, Oxygen (O) - 0.2, Carbon (C) - 0.08, Nitrogen - 0.05, Hydrogen - 0.0125 and balance Titanium (Ti)

3. The method for manufacturing Ti6Al4V cold rolled sheets as claimed in claim 1, wherein the hot rolled sheets are subjected to a solution heat treatment before the process annealing step to enhance the homogeneity and remove residual stresses.

4. The method for manufacturing Ti6Al4V cold rolled sheets as claimed in claim 1, wherein the cold rolling process includes multiple rolling to achieve the desired thickness reduction, with each rolling followed by an intermediate annealing step to prevent excessive work hardening.