FIELD OF INVENTION:
This invention relates to advanced high strength steel (AHSS) and a process for
developing the same.
BACKGROUND OF THE INVENTION:
Usage of steels in the various sectors like automobile, white goods, constructions
etc. have triggered the development of newer grades of steels. Currently
automobile sectors are giving more emphasis on increasing the crush worthiness
and less fuel consumption. This can only be achieved by increasing the strength
of the steel sheet without increasing their thickness. Advance high strength steel
can be a tailor made solution to this problem.
In general, the strength ductility relationship is some what inverse particularly in
steel gamete. But the steels referred to as advanced 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:
An object of this invention is to propose an advanced high strength steel with
ultra high strength.
Another object of this invention is to propose an advanced high strength steel
with nominal ductility.
Further, object of this invention is to propose a process for developing the
advanced high strength steel.

DETAILED DESCRIPTION OF THE INVENTION:
According to this invention there is provided an advanced high strength steel
comprising (in wt%):
C: 0.1-0.3 P: 0.02-0.01
Mn: 1.5 -1.0 Ti: 0.01 - 0.005
Si: 0.50-0.20 V: 0.2 - 0.05
S: 0.015-0.010 Cr: 0.1-0.05
In accordance with this invention there is also provided a process for the
development of advanced high strength steel comprising:
subjecting the steel to the step of forgeing at 900°C-1100°C to achieve
homogenized microstructure;
hot rolling the forged material keeping FRT just above Ar3 temperature;
subjecting the steel to reheat at 900°C for 1hr;
subjecting the heated steel material to the step water quenching to produce
martensite;
cold rolling the martensite and subjecting the cold rolled material to the step of
annealing at various temperature ranging from 200°C to 700°C for 20-60 mins.
Hot rolled C-Mn-Si steel with starting microstructure of martensite 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.
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. After that the material is reheated
at ~900°C for 1hr and water quenched from that temperature to produce
martensite. Martensite inherently is a fine grained structure. This is the basic
reason for selecting martensite as a starting microstructure so that after final
processing the steel will yield ultra fine grain structure. 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 has given a property of UTS ~
1100 Mpa, % elongation of around 12%, n values (strain hardening exponent)
ranging from 0.12 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 after final
processing.

WE CLAIM:
1. An advanced high strength steel comprising:
C: 0.1-0.3 P: 0.02-0.01
Mn: 1.5 -1.0 Ti: 0.01 - 0.005
Si: 0.50-0.20 V: 0.2 - 0.05
S: 0.015-0.010 Cr: 0.1-0.05
2. The advanced high strength steel as claimed in claim 1, wherein UTS:
~1100MPa, % elongation and 12%, n values (strain hardening exponent) ranging
from 0.12 to 0.26, low angle, high angle and coincidence site lattice volume
fraction between 0.4-0.7.
3. A method for developing the advanced high strength steel comprising:
subjecting the steel to the step of forgeing at 900°C-1100°C to achieve
homogenized microstructure;
hot rolling the forged material keeping FRT just above Ar3 temperature;
subjecting the steel to air cooling reheating the steel material for 900°C;
subjecting the heated steel material to the step water quenching to produce
martensite;
cold rolling the martensite and subjecting the cold rolled material to the step of
annealing at various temperature ranging from 200°C to 700°C for 20-60 mins.