FIELD OF THE INVENTION
The present invention relates to the development of micro-alloyed high tensile
strength steel. More particularly the invention relates to development of carbon
manganese 440 Tensile strength formable and weldable steel adaptable to
internal and external members for automobile appliances.
BACKGROUND OF THE PRESENT INVENTION
The modern automobile industry is driven by some important factors such as
(a) Energy saving or less fuel consumption
(b) Less emission
(c) Improved passenger safety
(d) Low cost manufacturing etc.
In order to satisfy all these basic conditions, the modern car manufacturing
involves more high strength steel grade which also be combined with degree of
formability.
The formable high strength steels are usually expensive and the manufacturing
steps require special facility like continuous annealing.
The present invention gives a solution to the problem. Chemical composition and
processing route are such that the manufacturing of this steel grade is less
expensive. Moreover, this grade is exclusively suitable for batch annealing
process.

OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose an improved carbon-
manganese 440 tensile strength steel formable and weldable quality adaptable to
manufacture of automobile body which eliminates the disadvantages of prior art.
Another object of the present invention is to propose an improved carbon-
manganese 440 tensile strength steel formable and weldable quality adaptable to
manufacture of automobile body which is applicable and usable for a wide range
of automobile application.
A further object of the present invention is to propose an improved carbon-
manganese 440 tensile strength steel formable and weldable quality adaptable to
manufacture of automobile body which is suitable for producing through batch
annealing route.
A still further object of the present invention is to propose an improved carbon-
manganese 440 tensile strength steel formable and weldable quality adaptable to
manufacture of automobile body which is cost savings.
An yet further object of the present invention is to propose an improved carbon-
manganese 440 tensile strength steel formable and weldable quality adaptable to
manufacture of automobile body which saves energy consumption.
A still further object of the present invention is to propose an improved carbon-
manganese 440 tensile strength steel formable and weldable quality adaptable to
manufacture of automobile body which are in great demand by automobile

A still further object of the present invention is to propose an improved carbon-
manganese 440 tensile strength steel formable and weldable quality adaptable
to manufacture of automobile body which are in great demand by automobile
industry due to increased concerns on safety and need to reduce green house
gas emissions.
SUMMARY OF THE INVENTION
The present invention consist of a steel grade for automobile structural
application with a medium draw comprises high strength and appreciable
drawability manufactured through an economic processing route It is a low
carbon based steel composition, strengthened by suitable addition of
manganese.
The processing schedule including steel making, hot rolling, cold rolling and
annealing have been determined appropriately so as to achieve desire
drawability and strength. The material is also adequately weldable.
CHEMICAL COMPOSITION


PHYSICAL PROCESSING
a) hot charging of slabs to reheat furnace
b) Slab drop out @ around 1200°C
c) Finish rolling @ higher than Ar3 temperature
d) Coiling @ less than 620°C-650°C
e) Batch annealing @ temperature 700°C-720°C
f) Skin pass rolling @ 1.0% temper elongation


WE CLAIM;
1. A carbon manganese steel having 440 MPa tensile strength of durable
' and weldable quality adaptable to mainly for manufacturing of
automotive body and appliances; having the composition in weight %:
- %C =0.080-0.10;
%Mn = 1.65 or less;
%S = 0.015 or less;
%P = 0.035 or less;
%Si = 0.05 or less;
%A1 = 0.02 or more;
%MA (Micro Alloy) = 0.030 or less;
%N = 60 (ppm) or less; and
Fe and unavoidable impurities (the residual).
2 A process of manufacturing coil by the steel as claimed in claim 1,
comprising the steps of;
- manufacturing of slab from the liquid steel;
- hot charging of slabs to reheat furnace;
- finish rolling @ higher than Ar3 temperature 900-910°C;
- coiling @ less than 620°C-650°C;
- batch annealing @ temperature 700-720°C; and
- skin pass rolling @ 1.07 temper elongation.

ABSTRACT

TITLE: DEVELOPMENT OF CARBON- MANGANESE 440 MPa TENSILE
STRENGTH STEEL
Development of an improved carbon manganese 440 MPa tensile strength
formable and weldable quality steel adaptable to mainly for manufacturing of
automotive body and appliances comprising: %C = 0.080-0.10; %Mn = 1.65
max; %S = 0.015 max; %P = 0.035 max; %S1 = 0.05 max, %A1 = 0.02 mm;
%MA (Micro Alloy) = 0.030 max; %N = 60 (ppm) max; and Fe and unavoidable
impurities (the residual) and the process of operating the steel as claimed in
claim 1 to form coil comprising; manufacturing of slab from the liquid steel; hot
charging of slabs to reheat furnace; finish rolling @ higher than Ar3
temperature 900-910°C, coiling @ less than 620°C-650°C, batch annealing @
temperature 700-720°C; skin pass rolling @ 1.07 temper elongation