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FIELD OF INVENTION:
This invention relates to a method for production of ultra thin sheets containing
submicron to nanocrystalline grains.
BACKGROUND OF THE INVENTION:
Nanostructured materials have great importance for technological applications
due to their superior properties over the coarse grained materials. Most of the
nanocrystalline metals and alloys possess high strength, hardness, as well as
ductility. Among the different materials steel is possibly the most important
candidate for structural and other applications. Refining the microstructure of
steel to submicron (100-1000mm) or nanoscale (<100nm) is expected to enhance
its properties to a great extent. Currently there is an increasing demand to
produce high strength light weight steel sheets for auto body and packaging
industries. In order to save the fuel consumption it is necessary to reduce the
weight of the car. Reduction in weight of the steel sheet is expected to reduce
significant cost of the product. This will be possible by making thin gauge sheets
with high strength. The strength can be enhanced by refined the grains to nano
scale without sacrificing the ductility much. Several methods (ECAP, ARB) have
been developed to produce nanostructured material. However, formation of
nanograins by simple cold rolling of a single piece sheet without folding at room
temperature has not yet been reported in the literature, particularly in case of
interstitial free steel where the starting microstructure is completely ferritic in
nature.

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OBJECTS OF THE INVENTION:
An object of this invention is to propose a method for production of ultra thin
sheet containing submicron to nanocrystalline grains.
Another object of this invention is to propose a method for production of ultra thin
sheet containing submicron to nanocrystalline grains by severe uniaxial cold
rolling process at room temperature.
Further, object of this invention is to propose a method for production of ultra thin
sheet containing submicron to nanocrystalline grains which has high strength
with substantially less weight.
DETAIL DESCRIPTION OF THE INVENTION:
The chemical composition of the steel is: 0.002-0.007%C, 0.07-0.22%Mn, 0.005-
0.015%S, 0.025-0.07%P, 0.01-0.045%Si, 0.02-0.01%A1, 0.0025-0.0039%N,
0.013-0.055%Nb, 0.012-0.072%Ti, 0.001-0.001 %B (all values in wt%). The steel
was controlled hot rolled and a total of 50-95% deformation was given during hot
rolling in several passes. The Finish Rolling Temperature (FRT) was kept within
+/- 10°C of 890°C-950°C. The hot band was then subjected to cold rolling at
room temperature by an amount of 70 to 99.9%, which corresponded to final
thicknesses of around 100pm respectively. In order to confirm the formation of
nanocrystalline grains Transmission Electron Microscopy (TEM) study was
carried out using a JEOL 200kV Transmission Electron Microscope.
Dated this 7th day of August 2007.

A method for production of ultra thin sheet containing submicron to nonocrystalline grains, comprising: subjecting the steel sheet to the step of hot rolling; cold rolling the said steel sheet in the presence of a lubricant to have a final thickness in the range of 15 to 400 µm, and subjecting the said steel sheet to the step of deformation in the range of 70% to 99.5% at room temperature to obtain the grains.