1. Field of invention:
The present invention relates to a method for sample preparation for
sub-surface characterization of hot rolled steel sheets through
Transmission electron microscopy.
2. Back ground of the invention:
Sub-surface properties of Hot Rolled steel colls are important from
alloying elements segregation and coatability point of view. Several
researchers have reported the different alloying elements segregation
phenomenon at the sub-surface level during the hot rolling process.
Depending on the Finish Roil Temperature (FRT) and Coiling
Temperature (CT), different alloying elements present in the steel
gets time to segregate at the sub-surface level. Several
characterization techniques like X-Ray photo Electron Spectroscopy
(XPS), Glow Discharge Optical Emission Spectroscopy (GDOES) and
Auger Electron spectroscopy (AES) etc. are available to Identify the
alloying elements getting segregated. The present innovation has
tried to look into the morphology of alloying elements segregated
through Transmission Electron Microscopy (TEM) by adapting a
special sample polishing techniques.
3. Objects of the present invention:
It is therefore an object of the present invention to propose a
method of sample preparation for sub-surface characterization of hot

rolled steel sheets through TEM which eliminates the disadvantages
of prior Art.
Another object of the present Invention Is to propose a method of
sample preparation for sub-surface characterization of hot rolled steel
sheets through TEM which helps in one sided sample thinning
technique keeping the other side intact during polishing is carried
out.
A further object of the present invention is to propose a method of
sample preparation for sub-surface characterization of hot rolled steel
sheets through TEM which helps to look morphology of alloying
elements segregated through TEM.
4. Summary of invention:
There is several sample preparation techniques are avallabie to
observe the surface morphology by Transmission Electron Microscope
(TEM) like Carbon Extraction Replica, Cross sectional TEM etc. Each
technique has its own advantages and disadvantages. In present
innovation a special one sided sample thinning technique keeping
another side intact during polishing is carried out. As high
temperature oxide is formed at the surface during hot rolling, so one
of the two surfaces was kept intact during complete sample thinning
technique by polishing paper. After thinning down to 100 µm, the
Sample Was put under electro polishing instrument where thinning up

to 1 µm was done as per convention. During this thickness reduction process, the side
of the sample having oxide scale will be reduced much slower than the other side, as a
consequence the sub-surface will be observed under the TEM.
5. BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE:
Fig.1 - shows a schematic diagram for sample preparation technique.
Fig.2 - shows TEM picture of sub-surface morphology of hot-rolled steel adopting
special sample preparation method.
6. A preferred embodiment of the Invention:
As shown in Fig.l, the initial thickness of the samples (S) along with both sides oxide
layer (1) is 3 mm + 16-20 µm. The thickness reduction was carried out keeping one
side of the sample untouched (4). The thinning was done by normal emery paper
technique till the sample (S) thickness is reduced to 100 µm. During thinning process
one side of the sample (4) (which will be untouched) was made attached with a holder
by applying adhesive which can be removed easily during subsequent thinning
operations. Now the 100 µm thick sample (S) consists of one side oxide layer (6) of 8-
10 urn and rests having bulk steel. After the initial thinking, the thinned sample is put
inside the electro polishing chamber. During the electro thinning

operation the oxide removal rate is slower than the steei removal
rate. As a consequence of which the sample was preferentially
thinned form steel side (5) and at the end, the electron transparent
region had been formed adjacent to the oxide containing side (6).
Then the sample (S) is put under Transmission Electron Microscope
and necessary tests to be carried out.
7. TEST RESULT:
By the above mentioned technique it is possible to look into sub
surface morphology under Transmission electron Microscopy. The sub
surface morphology along with surface oxides as shown in Fig-2 can
be seen by adopting this technique.

KEY FEATURES
Reference Character Feature Figure
S Sample 1a, 1b, 1c
1 Oxide layer 1a
2 Base steel 1a, 1b, 1c
3 Thinning from this
side up to 100µm 1b
4 No thinning from the
side 1(b)
5 Thinned steel layer 1(c)
6 One side oxide layer 1(c)
7 Oxide layer 2

WE CLAIM
1. A method for sample preparation for sub-surface phenomenon and alloying
segregation of hot rolled steel sheets through transmission electron microscopy
comprises:
- a oxide coated steel sample of 3mm + 16-20 µm thick;
- thinning of the sample at one side (3) by emery paper technique till the
sample (S) thickness is reduced to 100 µm;
- holding the other side (4) of the sample (S) with a holder by applying
adhesive; and
- electroplating from the thinned surface (5) of the sample (S) to reduce up
1µm;
characterised in that said electroplating on the surface reduces the oxide
scale and form electron transparent region adjacent to oxide layer for
vision of sub-surface phenomenon and alloying segregation when placed
under Transmission Electron Microscopy (TEM).
2. A method for sample preparation for sub-surface phenomenon and alloying
segregation of hot rolled steel sheets through transmission electron microscopy

as substantially described and illustrated herein with reference to accompanying
drawings.

The present invention relates to a method for sample preparation for sub-surface
phenomenon and alloying segregation of hot rolled steel sheets through transmission
electron microscopy comprises a oxide coated steel sample of 3mm + 16-20 urn thick
and thinning of the sample at one side (3) by emery paper technique till the sample (S)
thickness is reduced to 100 µm and holding the other side (4) of the sample (S) with a
holder by applying adhesive and electroplating from the thinned surface (5) of the
sample (S) to reduce up 1 µm characterised in that said electroplating on the surface
reduces the oxide scale and form electron transparent region adjacent to oxide layer for
vision of sub-surface phenomenon and alloying segregation when placed under
Transmission Electron Microscopy (TEM).