FIELD OF INVENTION
The present invention relates to a development of ultra high strength steel
grade with nominal ductility adaptable to manufacture automobile parts.
BACKGROUND OF THE INVENTION
Design applications for steel products have been necessitated the
development of new grade steels with ultra high strength. To increase the
strength to weight ratio of the automobile appliances will eventually lead to a
decrease in the fuel consumption and an increase in the passenger safety. In
general, the strength ductility relationship is somewhat inverse particularly in
steel gamete. So a special emphasis made to develop as advance high
strength steels (AHSS) possess very high strength with nominal ductility. A
special chemistry and processing route has been invented which can lead to
a development of new grade of AHSS family.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a development
of advance high strength steel grade adaptable to manufacture automobile
appliances which eliminates the disadvantages of prior art.

Another object of the present invention is to propose a development of
advance high strength steel grade adaptable to manufacture automobile
appliances which increase strength to weight ratio.
A further object of the present invention is to propose a development of
advance high strength steel grade adaptable to manufacture automobile
appliances which increases the safety of the passenger.
SUMMARY OF INVENTION
Hot rolled C-Mn-Si steel with starting microstructure of ferrite-bainite is given
cold deformation to different percentages starting from 20 to 85. The cold
deformed steels are again recrystallized annealed at various temperatures
ranging from 200 to 700°C for 20-60 mins.
DEATILED DESCRIPTION OF THE INVENTION
The steel studied contain (in wet%):
C: 0.1-0.3
Mn: 1.5 or less
Si: 0.50 or less
S: 0.015 or less
P: 0.02 or less
Ti: 0.01 or less
V: 0.2 or less
Cr: 0.1 or less

PROCESS PARAMETERS
The steel is made in the air induction furnace and subsequently forged at
900-1100°C with different amount of deformation and temperature at each
stroke 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 and this has
given UTS:~550Mpa and Elongation:~20%.
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. This will yield a steel with UTS ~ 850 Mpa and % elongation of around
15%, n values (strain hardening exponent) from 0.21 to 0.26, low angle, high
angle and coincidence site lattice volume fraction ranging between 0.4-0.7;
0.6-0.3 and ~0.1, respectively.

WE CLAIM
1. Development of advance high strength steel family with ultra high
strength steel and nominal ductility, the chemistry of steel
comprises:-
C: 0.1-0.3
Mn: 1.5 or less
Si: 0.50 or less
S: 0.015 or less
P: 0.02 or less
Ti: 0.01 or less
V: 0.2 or less
Cr: 0.1 or less
2. The steel as claimed in claim 1 wherein the said steel on undergoing
forging at 900-1100°C followed by hot rolling with FRT just above Ar3
results in YS 400 MPa , UTS 550 MPa and Elongation 20%.
3. The steel as claimed in claim 1 wherein the said hot rolled steel when
cold rolled (20-85%) and recrystallised annealed at 200°C to 700°C
for 20-60 mins results in YS- 750 MPa, UTS- 850 MPa and elongation
15%, n values (strain hardening exponent) ranging from 0.21 to
0.26, low angle, high angle and coincidence site lattice volume
fraction ranging between 0.4-0.7; 0.6-0.3 and ~0.1 respectively.

Hot rolled C-Mn-Si steel with starting microstructure of ferrite-bainite is given
cold deformation to different percentages starting from 20 to 85. The cold deformed steels are again recrystallized annealed at various temperatures ranging from 200 to 700°C for 20-60 mins.