TITLE:
Coating composition to prevent oxidation of steel during hot rolling process and ease of
pickling.
FIELD OF INVENTION:
This invention relates to a coating composition which prevent the oxidation of steel
during hot rolling process.
This invention also relates to the coating has been developed to prevent the oxidation
during hot rolling of steel. This coating reduces the material loss due to scale formation.
It can be applied before and after reheating furnace. Therefore, it can reduce the scale
formation after continuous casting, reheating furnace and subsequent rolling operation,
The coating can withstand high temperature up to 1200°C.
BACKGROUND OF THE INVENTION:
When steel is exposed to atmosphere at high temperature, oxidation takes place.
Oxidation results in scale formation which results in yield loss. Scale can reduce the
overall surface quality of hot rolled steel. Scale formation starts at different locations in
steel mill. 1st scale forms on steel slab during cooling section of casting. Further scale

formation takes place during the passage of slab through the reheating furnace. The scale
formed within reheating furnace is referred as primary scale. Secondary scale forms
during the roughing and finishing mill of hot rolling while the tertiary scale forms during
the cooling cycle on run out table. Formation and growth of each type of scale is
dependent on external factors like temperature, ambient oxygen and moisture conditions
and also on the previous scale which was formed on the surface.
Scale morphology and adhesion play critical role in final yield of material and surface
quality. In reheating furnace the scale build up can be reduced if the existing scale is
adherent in nature while loosely adherent scale is required during descaling operation. A
thin and adherent scale is again expected to form on hot rolled material after coiling for
easy pickling before cold rolling. Non-uniform scale can leave patches after pickling
which can lead to poor quality of material. Rolling oil lubrication depends on the friction
on slab surface which is governed by scale characteristics and scale can also affect the
roll condition. Degraded roll condition can again lead to poor surface quality. By
understanding the mechanism of scale formation at each stage, one can have a fair
amount of control on the scale morphology and overall surface finish of the hot rolled
material.
Different coating solutions were applied on slab fed to reheating furnace to minimize scale
growth. Scale growth reduction in the range of 30% to 98% has been reported for

different coating composition and steel chemistry combinations. Coatings act as inhibition
layer between metal / scale and atmosphere for passage of oxygen ions. Coating have
also been reported for reduction of decarburization layer during reheating. Aluminium
containing coatings are also reported to reduce fayalite formation and thereby improving
descaling efficiency. The effect of coating on existing scale layer has been reported but
with lower benefits and not much literature is available for any permissible range of scale
thickness for effective working of coating.
To overcome the challenges related to primary and secondary scale formation a coating
was developed in this invention. The coating can withstand 1200°C. Therefore, it can
prevent primary and secondary scale formation.
OBJECTS OF THE INVENTION:
An object of the present invention is to propose a coating composition which prevents
the oxidation of steel during hot rolling process.
Another object of the present invention is to propose a method which reduces the scale
formation leading to material loss due to oxidation in hot rolling operation of steel.
Still another object of the present invention is to propose a coating composition which
can sustain temperature of upto 1300°C.

Further, object of the present invention is to propose a coating composition which helps
in homogenous scale formation.
Still further object of the present invention is to propose a coating composition which help
in reducing decarburizing / nitriding or any other gaseous diffusion related phenomena
since it acts as a barrier to ionic / gaseous diffusion.
Yet another object of the present invention is to propose a coating composition which
helps in easier pickling of scale leaving behind uniform pickled surface having no scale
related defects.
BRIEF DESCRIPTION OF THE INVENTION:
This invention relates to a coating composition to prevent the oxidation of steel during hot
rolling and ease of pickling comprising:
sodium silicate 20-50 wt.% and/or Vinyl trimethoxy silane upto 20 wt.% and/or Potassium
lithium silicate upto wt. 80%;
1 to 10 wt% of Titanium isoporpoxide;
1 to 10 wt% of Aluminium isopropoxide; and
and the remainder being water.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig. 1: shows the Weight gain of coated HR samples example 1, 2, 3, and uncoated
scaled HR sample (350-1200°C)
Fig. 2: shows the Weight gain of coated HR samples example 1, 2, 3, and uncoated
scaled HR sample (350-800°C)
Fig. 3: shows the Weight gain of coated HR samples example 1,2, 3, and uncoated
scaled HR sample (800-1200°C)
Fig. 4: shows TGA of various coating compositions from 200° C temperature
DETAILED DESCRIPTION OF THE INVENTION:
The coating has following ingredients to use a) Sodium silicate b) Titanium isopopoxide
c) Aluminium isopropoxide d) Water
In all the below mentioned examples aluminium isopropoxide and Titanium isopropoxide
were dissolved in isopropanol and then used as such,
The coating compositions are given in below examples. The said coating was applied on
HR sample by dip/spray method. The coated HR samples were cured at room
temperature but it can also be cured at elevated temperature.

The thickness of the coating was maintained up to 200 micron more precisely in the range
of 10-50 micron preferable 15-30 micron.
Thermal gravimetric analysis of coated film was performed up to 1200°C in ambient
atmosphere. The weight loss with respect to temperature is shown in drawing no.4.
The coated samples of hot rolled steel of various coating compositions mentioned in
subsequent examples are performed in TGA up to 1200°C with heating rate of 10°C/min
in ambient atmosphere. The weight gain of the coated HR sample with temperature is
shown in drawing no. 1, 2 and 3.
The drawing no 1 shown the graph of temperature gain of coated and uncoated HR
samples from 350-1200°C. Considering the percentage weight gain of sample at 1200°C,
the uncoated samples shows the highest weight gain as expected followed by example 1
& 2 and the least weight gain is shown by example 3. The application area for example
3 can be in-between the air mist cooling stage of casting upto the reheating furnace. In
these areas, the slab continuously faces temperature in excess of 1000°C and example
3 shows the best results.
The drawing no 2 shown the graph of temperature gain of coated and uncoated HR
samples from 350-800°C. Considering the percentage weight gain of samples at 800°C,
the sample 3 shows the highest weight gain followed by uncoated sample, example 1 and
the least weight gain is shown by example 2. The application area for

example 2 can be in-between the primary descalar upto the run out table, In these areas,
the slab continuously faces temperature below 800°C and example 2 shows the best
results.
The drawing no 3 shown the graph of temperature gain of coated and uncoated HR
samples from 800-1200°C. Considering the percentage weight gain of samples at
1100°C, the uncoated sample shows the highest weight gain followed by example 2 while
examples 1 & 3 are showing almost similar weight gain. Example 1 shows higher weight
gain in the temperature range of 1100°C to 1200°C compared to example 3. The
application area for example 1 can be the air mist cooling area of caster upto the entry of
reheating furnace while example 3 has application area exclusively in the reheating
furnace and can also be used in area of example 1, as discussed above. The coated
(Example 1,2 &3) hot rolled samples were pickled in acid solution and uniform and easy
removal of scale was observed.
Example: 1
The coating has composition of
a) Sodium silicate (up to 50 wt%)
b) Titanium isopopoxide {up to 10%)
c) Aluminium isopropoxide (up to 10%)
d) Water (remaining)

Example: 2
The coating has composition of
a) Vinyl trimethoxy silane (up to 20 wt%)
b) Titanium isopropoxide (up to 10%)
c) Aluminium isopropoxide (up to 10%)
d) Acidic Water (remaining)
Example: 3
The coating has composition of
a) Potassium lithium silicate (up to 80 wt %)
b) Titanium isopropoxide (up to 10 wt%)
c) Aluminium isopropoxide (up to 10 wt%)
d) Water (remaining)

WE CLAIM:
1. A coating composition to prevent the oxidation of steel during hot rolling and ease
of pickling comprising:
sodium silicate 20-50 wt.% and/or Vinyl trimethoxy silane upto 20 wt.% and/or
Potassium lithium silicate upto wt. 80%;
1 to 10 wt% of Titanium isoporpoxide;
1 to 10 wt% of Aluminium isopropoxide; and
and the remainder being water
2. The composition as claimed in claim 1 wherein aluminium isopropoxide and
Titanium isoporpoxide is dissolved in isopropanol.
3. The composition as claimed in claim 1, wherein the thickness of the coating was
maintained upto 200 micron preferably 10-50 micron.
4. The composition as claimed in claim 1, wherein a coated material was found to
withstand a temperature of 1200°C.