FIELD OF THE INVENTION
The present invention relates to a process for development of an
high strength steels. More particularly the present invention relates
to a process for development of an ultra high strength steels.
BACKGROUND OF THE INVENTION
To increase the strength to weight ratio of the automobiles which will
eventually lead to a decrease in the fuel consumption and an
increase in the passenger safety there has been an increased
emphasis on the development of new advanced high strength sheet
steels (AHSS), categorically for this purpose.
Design applications for steel products have necessitated the
development of new steels with unique properties. In general, the
strength ductility relationship is some what inverse particularly in
steel gamete. But the steel referred to as advance high strength
steels (AHSS) possess very high strength with nominal ductility.
There are some chemistries and processing routes suggested in the

invention which can lead to a development of certain grades of AHSS
family.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a
process for development of an ultra high strength steels which
eliminates the disadvantages of prior art.
Another object of the present invention is to propose a process for
development of an ultra high strength steels which increases strength
to weight ratio.
A further object of the present invention is to propose a process for
development of an ultra high strength steels which is adaptable to
automobile industry

A still further object of the present invention is to propose a process for development of
an ultra high strength steels which takes care of passengers safety when used in
automobile can body.
SUMMARY OF THE INVENTION

is made in the air induction furnace and subsequently forged at 900-1100° C with
different amount of deformation and temperature at each stoke to achieve
homogenized microstructure. The forged material is hot rolled and the FRT is kept just
above Ar3 temperature. The steel is then air cooled. The hot rolled structure is
observed to be ferrite-bainite. After that the material is intercritically annealed at

the temperature range of 700°C 800°C for 1 hour and water
quenched from that temperature to produce ferrite-martensite. The
intercritical annealing temperature are selected to vary the amount of
ferrite and austensite at that temperature, which ultimately controlled
the amount of two phases after cooling. The basic aim is to achieve
two kinds of grain size distribution after the final processing.
The hot rolled material is then cold rolled to different percentage of
reduction starting from 20 to 85 %. The cold rolled material is then
subjected to annealing at various temperatures ranging from 200°C
to 700°C for 20-60 mins.
RESULT
1. The above chemical composition of steel yield the following
properties after subsequent treatment UTS 1200 and EL-8%

2. After hot rolling and inter-critical annealing the microstructure is
composed of martensite and (10-35) % ferrite depending on annealing
temperature.
3. The final microstructure after cold rolling and annealing composed of
bimodal grain size distribution. Ferrite grain size is ~10-15µm and
martensite grain size is ~ 1-µm.
4. The hot rolled material when cold rolled (20-85%) and recrystallized
annealed at 200° C to 700PC for 20-60 minutes results in YS: ~ 1100MPa,
UTS: ~1200MPa and Elongation:~ 8%.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention can now be described in detail with the help of the figure of the
accompanying drawing in which
Figure 1 shows Fe-C phase diagram (only the steel part) showing the Ar3 and Ar1 lines.

WE CLAIM
1. A process for development of ultra high strength steel from ferrite martensite
starting microstructure, the process comprising:
- forging the steel at 900° - 1100° with different amount of deformation and
temperature at each stoke to achieve homogenized microstructure;
- hot rolling the forged material;
- air cooling the said steel;
- annealing inter critically the hot rolled material at the temperature range of 700°
- 800° for one hour;
- water quenching the annealed material from that temperature to produce ferrite
- martensite;
characterized in that,
- the hot rolled material is then cold rolled to different percentage of reduction
from 20 to 85 % and the said cold rolled material is then recrystallized annealed
at 200° C to 700° C for 20 - 60 minutes to produce the ultra high strength steel
having a composition by % by weight,
C-0.1-0.5%
Mn - 1.5 % or less
Si - 0.50 % or less
S - 0.015 % or less
Ti - 0.01 % or less
P - 0.02 % or less
V - 0.2 % or less
Cr-0.1 % or less

2. The process as claimed in claim 1, wherein the cold rolling the annealing
produces the final microstructure of ultra high strength steel of bimodal grain-
size-distribution and yields a ferrite grain size of 10 - 15 µm.
3. The process as claimed in claim 1, wherein the microstructure after hot rolling
and inter-critical annealing is composed of martensite and 10-35 % of ferrite
depending on the annealing temperature.
4. An ultra high strength steel having a final microstructure of bimodal grain size
distribution and ferrite grain size of 10 - 15 µm and martensite grain size of 1
µm comprising by % by weight;
C-0.1-0.5%
Mn - 1.5 % or less
Si - 0.50 % or less
S - 0.015 % or less
Ti - 0.01 % or less
P - 0.02 % or less
V - 0.2 % or less
Cr - 0.1% or less
5. An ultra high strength steel as claimed in claim 4, wherein the said steel acquires
yield strength of 1100MPa, tensile strength of 1200MPa and elongation of 8 %.

The present invention relates to a process for development of ultra high strength
steel from ferrite martensite starting microstructure. The process comprises of
forging the steel at 900° - 1100° with different amount of deformation and
temperature at each stoke to achieve homogenized microstructure. The forged
material is not rolled and air cooled. The material is then intercritically annealed
at the temperature range of 700° C - 800° C for one hour and water quenched
from that temperature to produce ferrite - martensite. The hot rolled material is
then cold rolled to different percentage of reduction from 20 to 85 % and the
said cold rolled material is then recrystallized annealed at 200° C to 700° C for 20
- 60 minutes to produce the ultra high strength steel having a composition by %
weight of C - 0.1 - 0.3 %, Mn - 1.5 % or less, Si - 0.50 % or less, S - 0.015 %
or less, Ti - 0.01 % or less, P - 0.02 % or less, V - 0.2 % or less, cr - 0.1 % or
less.