FIELD OF INVENTION
The present invention relates to a process and an apparatus for generating
multiphases in steel sheets by adapting an enhanced cooling technique.
BACKGROUND OF INVENTION
Different phases of steel have distinct strength levels. These phases can be
developed by heating the steel to 1000°C and cooling to room temperatures. The
cooling is defined in terms of cooling rates. Cooling is achieved in wire mills
producing steel rods by using water in water boxes. For a fixed layout and
process conditions, the cooling rates remain fixed. Any change in the cooling rate
can be achieved by either changing the process conditions, or by upgrading the
lay-out of the wire mill. Both of these possibilities entail huge cost and time.
To produce new grades of steels, it is necessary to produce new phases in the
steel. A phase constitutes a metallurgical entity characterized by a distinct
hardness level, wherein the phase is a metallurgical entitu characterized by
ferrite, bainite, pearlite, austenite or martensite. A multi-phase steel is a steel
having one or more phases each phase existing in the steel in predefined
proportions varying between 0 and 100%.
There is a continual need to produce new grades of steels with leaner
chemistries.

OBJECTS OF INVENTION
It is therefore an object of the invention to propose a process of generating
multiphases in steel sections by adapting an enhanced cooling technique.
Another object of the invention is to propose a process of generating
multiphases in steel sections by adapting an enhanced cooling technique, in
which nano-coolant is adapted to implement enhanced cooling technique.
A still another object of the invention is to propose a process of generating
multiphases in steel sections by adapting an enhanced cooling technique, which
provides new grade of steels with leaner chemistry.
A further object of the invention is to propose an apparatus for generating
multiphases in steel sections by adapting an enhanced cooling technique, the
cooling technique being implemented by using a nano-coolant.
SUMMARY OF INVENTION
Accordingly, there is provided a process for generating multi-phases in steel
strips by adapting an enhanced cooling technique in the wire-rod mill, the
process comprising the steps of placing a steel strip in a controlled atmosphere
furnace pre-heated to 950°C; heating the steel strip in the furnace upto a
temperature between 800-1000°C, the heating rate being 4 to 8°/sec; and

cooling the hot strip by impinging nano coolant to enhance the cooling rate,
wherein, each of the multiphase is brought about by employing cooling rates
defined either by the conventional time-temperature transformation curve, or by
the continuous cooling transformation curve, the phases brought about in the
steel strip evolving from a single austenite phase, the nano-coolant being
produced employing nano-particles in an aqueous medium, and the produced
steel comprises Carbon: 0.001-0.05, Manganese: 0.01-0.14, Aluminium: 0.001-
0.04, Silicon: 0.001-0.03, Sulphur: 0.001-0.01, Phosphorus: 0.001-0.02,
Titanium: 0.002-0.04, Niobium: 0.001-0.04, and Nitrogen: 0.0001-0.0035.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure - 1 schematically shows an apparatus for enhanced cooling of
hot steel plates by impingement of water-based titanium-
oxide nano fluid.
Figure - (2a) graphically illustrates a comparative result of temperature
time data of a steel plate cooled by water and that by nano-
fluid
Figure - (2b) graphically illustrates a variation of viscosity with
temperature in respect of water-based and nano-fluid based
cooling
Figure - (3a) SEM photograph of the top surface of a steel plate after
having cooled with water

Figure - 3(b) SEM photograph of the top surface of an identical steel plate
having cooled with nano-fluid
Figure - 3(c) SEM photograph of the cross-section of a steel surface after
having cooled with water
Figure - 3(d) SEM photograph of the cross-section of a steel surface after
having cooled with nano-fluid
Figure - 3(e) SEM photograph showing a magnified view of the encircled
portion of figure 3(d)
Figure-3(f) showing the EDS of the top surface generated just afer
cooling the top surface of the steel sheet by nano-fluid
DETAILED DESCRIPTION OF THE INVENTION
Figure-1 shows an apparatus to implement a process for enhanced cooling of hot
steel plates in the run-out table of an industrial rolling mill. As shown in Figure-1,
a tank (D) is filled with nanofluid. The nanofluid is transferred up to a dispensing
unit (A) using a pump (E). A pre-heated steel plate (B) is placed over a
refractory brick (C) so that the heat loss is minimized during the implementation
of cooling step. The nano-fluid pumped from the tank (D) is allowed to fall on
the preheated steel plate (B), through a nozzle (A).

In order to determine the phase-generation effects on the steel sheets while
implementing the cooling technique, and further to make a comparison of the
cooling effect by using the nano-coolant and by using water, a total of nine
thermocouples (G) are placed on the surface of the plate (B) where the nano-
fluid is incident. A cooling curve of the nano-fluid is obtained by putting the
average temperature from the data recorded by all the nine thermocouples (G)
versus time. The steps are thereafter repeated by allowing a jet of water instead
of the nanofluid to be impinged on an equivalent steel plate (B) under the same
process conditions, and a cooling curve of water is plotted in the same manner.
A collection tank (H) for collection of the liquid after impingement on the steel
sheet, is disposed at the bottom of the apparatus for reuse of the liquid.
The steel plate (B) was initially put in a controlled atmosphere furnace that is
pre-heated to 950°C. The plate (B) was heated to a desired temperature of
850~900°C maintaining a heating rate of 5°C/sec. The plate (B) was then
brought out of the furnace with tongs and placed in an inverted position with the
plate surface having the thermocouple (G) facing towards the refractory bricks
(C).
Figure-2(a) shows a graphical comparison of the temperature-time data of the
steel plate cooled by water and that by a water based TiO2 nano-fluid. In the
same graph, the continuous cooling transformation (CCT) graph for the steel
composition has been superimposed. The CCT curve exhibits a 50% phase
transformation. From Figure 2(a) it is clearly established that the cooling rate for

the water-based TiO2 nano-fluid is much faster than that of water, till the
temperature for forming bainite grain structure attains. This difference in the
cooling rates produces a very distinct changes in the microstructures of the steel
plate after cooling by water and that by the nano-fluid as shown in Figures 3(a-
e). To begin with, the hot plate (B) right at the onset of cooling, remains in
austenite range, and the phase transformation occurs as the cooling progresses.
Clearly, the polygonal ferrite grains are observed on top surface of the steel plate
(B) where water was incident. By contrast, the surface appeared rather rough
with visible undulations on top surface of the steel plate (B) where the nano-fluid
was impinged. The difference clearly shows in the micrographs taken from the
cross-section of the above two samples as well. In the water cooled plate, only
ferrite grains are observed, wherein, a distinct two phase microstructure is seen
in case of the nanofluid cooled steel. Figure 3(e) shows a second phase grains,
on a magnified scale which is bainite. The micro-hardness taken from the matrix
phase and the second phase are 111 VPN and 141 VPN respectively. Obviously,
the matrix phase consists of polygonal ferrite grains. The micro-hardness of the
low carbon bainite was reported to be 150VPN by a group of researchers [5] for
bainite forming at a temperature similar to that in the present invention (650°C).
Thus, it is concluded that while a ferrite-bainite structure is obtained during
nano-fluid cooling, only ferrite is obtained after cooling by water, which interalia
shows that the cooling has been more servere in the former case. This is also
quite apparent from Figure 3(a). accordingly, an enhanced cooling technique by
adapting a nano-coolant is enabled to generate multiphases in steel sheets.

Reference Patents
• Rapidly disintegrating tablets comprising titanium dioxide nano-powders.
1044/KOL/2009 dated 07.08.2009
• A process and Apparatus for application of Coolants to achieve Higher
Cooling Rates In the Water Boxes of a Wire Rod Mill. - 291/KOL/2009
dated 16.02.2009
• A process and an apparatus for Large-scale synthesis of nano-fluids.
293/KOL/2009 dated 16.02.2009
• A Method for Faster Cooling Rate by a New Medium For Run Out Table of
Hot Strip Mill (Application No. 430/KOL/2007).

WE CLAIM
1. A process for generating multi-phases in steel strips by adapting an
enhanced cooling technique in the wire-rod mill, comprising the steps of:-
- placing a steel strip in a controlled atmosphere furnace pre-heated to
950°C;
- heating the steel strip in the furnace upto a temperature between 800-
1000°C, the heating rate being 4 to 8°/sec; and
- cooling the hot strip by impinging nano coolant to enhance the cooling
rate, wherein,
- each of the multiphases is brought about by employing cooling rates
defined either by the conventional time-temperature transformation curve,
or by the continuous cooling transformation curve,
- the phases brought about in the steel strip evolving from a single
austenite phase,
- the nano-coolant being produced employing nano-particles in an aqueous
medium, and
- the produced steel comprises Carbon: 0.001-0.05, Manganese: 0.01-0.14,
Aluminium: 0.001-0.04, Silicon: 0.001-0.03, Sulphur: 0.001-0.01,

Phosphorus: 0.001-0.02, Titanium: 0.002-0.04, Niobium: 0.001-0.04, and
Nitrogen: 0.0001-0.0035.
2. The process as claimed in claim 1, wherein the nano particles are selected
from a group comprising metallic, metal-oxide, carbon based and polymer
based particles.
3. The process as claimed in claim 1 to 3, wherein the nano-particles are
enabled to get self-stabilised or stablised using a surfactant of polymeric
origin.
4. The process as claimed in claim 1 to 3, wherein the process is enabled to
bring about at least a two-phase microstructure in the steel, wherein a
matrix phase exhibits polygonal ferrite grains, and wherein a second
phase exhibits a bainite grain structure.
5. An apparatus for generating multiphases in steel plates by adapting an
enhanced cooling technique, the enhanced cooling technique being
implemented through impingement by nano-coolants on the steel plates
produced in a wire rod mill and transferred in heated condition for cooling
by the apparatus, the apparatus comprising:
- a tank filled with a nano-coolant, the nano-fluid from the tank being
transferable to atleast dispensing means;

- a first base-support to place the heated steel strips, the base, support
atleast having a refractory-lined second support base to minimize heat
loss; and
- the at least one dispensing means is enabled to impinge nano-coolant on
the heated surface of the steel plates to generate mulitphases in the steel
plates.
6. A process for generating multi-phases in steel strips by adapting an
enhanced cooling technique in the wire-rod mill, as substantially herein
described with reference to the accompanying drawings.

The invention relates to a process for generating multi-phases in steel strips by
adapting an enhanced cooling technique in the wire-rod mill, comprising the
steps of placing a steel strip in a controlled atmosphere furnace pre-heated to
950°C; heating the steel strip in the furnace upto a temperature between 800-
1000°C, the heating rate being 4 to 8°/sec; and cooling the hot strip by
impinging nano coolant to enhance the cooling rate, wherein, each of the
multiphases is brought about by employing cooling rates defined either by the
conventional time-temperature transformation curve, or by the continuous
cooling transformation curve, the phases brought about in the steel strip evolving
from a single austenite phase, the nano-coolant being produced employing nano-
particles in an aqueous medium, and the produced steel comprises Carbon:
0.001-0.05, Manganese: 0.01-0.14, Aluminium: 0.001-0.04, Silicon: 0.001-0.03,
Sulphur: 0.001-0.01, Phosphorus: 0.001-0.02, Titanium: 0.002-0.04, Niobium:
0.001-0.04, and Nitrogen: 0.0001-0.0035.