FIELD OF INVENTION
The present invention relates to an improved process for
continuous casting of steel. More particularly, the
invention relates to a process for continuous casting of Zr
bearing steel, and prevents the casting nozzle from being
choked or blocked when liquid steel is cast as a slab.
BACKGROUND OF THE INVENTION
Zr bearing (Zr 0.10 to 0.15%) medium carbon steel is
continuously cast in slab casters. This grade is prone to
nozzle clogging/choking during the process of continuous
casting. Casting is aborted sometimes due to partial
choking of subentry nozzle (SEN) or ladle nozzle. Incidence
of Crusty meniscus and viscous mould slag are of frequent
occurrence. These sometimes result in breakout during the
process. During earlier attempts in slab caster, only part
of liquid steel could be cast (50 %) , as casting process
had to be aborted due to choking of subentry nozzle as
mentioned above. Slabs of this grade are therefore
traditionally made through ingot casting route by rolling
the ingots, and then processing the slabs to plates.
The difficulties faced during conventional casting have
been analyzed and it is found that the clogging behavior is
due to the formation of complex Al-Zr-oxinitride. Crusty
meniscus is due to formation of high-melting ZrO2, Al2O3,
ZrN, and low meniscus temperature. The viscous mould slag
formation is due to deterioration of mould slag during
casting operation. It has been found that this viscous slag

is responsible for lack of lubrication and eventual
breakout.
Due to low superheat casting, the meniscus temperature
reduces. ZrO2 and Al2O3 are responsible for nozzle
deposition and eventual choking.
OBJECTS OF THE INVENTION
Accordingly, one object of the present invention is to over
come the castability problems as in the prior art so that
such steel can be manufactured through continuous casting
process.
Another object of the present invention is to provide the
optimum remedial measures.
Yet another object of the invention is to provide a process
for continuous casting of Zr bearing medium carbon steel.
SUMMARY OF THE INVENTION
According to one aspect of the present invention a process
for improving castability of Zr-bearing steel is provided
for continuous casting, said process comprising steps of:
selecting a batch composition of raw material comprising C,
Mn, Si, N, Cr, S, P, Zr, Al, Fe selected in specific wt %;
melting said batch composition for liquification to form
liquid steel and pouring said liquid steel from ladle into
a tundish of continuous casting machine;

pouring the liquid steel from the tundish through subentry
nozzle to the mould of continuous casting, and casting
machine into slabs of desired cross-section.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides an improved process for
producing continuously cast Zr-bearing grade steel by
selecting a batch composition of raw materials as specified
in table 1. It is noted from table 1 that the chemical
composition produced by the process of the present
invention differs from the known grade steel in respect of
the following :
i) increase in C, Mn, Zr and
ii) decrease in Si, Cr, Mo, Al
The selected batch composition of raw materials is melted
in a electric arc furnace and vacuum arc degassing unit.
The liquid steel from the vacuum arc degassing unit is then
transferred into ladle. The liquid steel from the ladle is
then poured into the tundish of continuous casting machine
at a temperature range of 1550 to 1560 C. The liquid steel
from the tundish is poured in the mould of continuous
casting and cast into slabs of desired cross-section. The
parameters for the process of continuous casting of slabs
are shown in table 2.


The carbon equivalent Cp mentioned above in the table 1 is
defined by-
Cp = %C + 0.04% Mn + 0.10% Ni + 0.7% N - 0.14% Si - 0.04%
Cr - 0.10% Mo - 0.24% Ti


From table 2 the difference of the process of the present
invention with respect to the known process are as follows:
a. Superheat , i.e. the difference between the actual
temperature of liquid steel and the temperature of
liquefaction determined empirically from the chemical
composition of the stainless steel, is greater in the
present process by 20°C than in the conventional

process. Superheat temperature in the present process
is 50 - 60°C
b. Secondary cooling intensity, i.e. amount of cooling
water in litre used in the secondary cooling zone of
continuous casting machine, per kg of steel, is more
in the invented process by 0.15 lit/kg of steel
compared with the known process, the cooling intensity
in the present process is found to be 0.8 lit/kg; and
c. Speed of casting, i.e. the length of slab in meter
cast per minute, is higher in the invented process by
0.1 m/min compared with the known process. The speed
in the present process is 0.8 meter / minute.
d. Thickness of the mould powder cover on meniscus of
steel in mould is greater by 20-25 mm. from the known
process
e.'SEN depth decreased by 20 mm from the known process
f. ZrO coated Al-graphite SEN is used
It has been found that the castability of the steel
produced by the process of the present invention is very
good, and complete casting is possible. On the other hand
the castability in the known and conventional process is
found to be poor, and only 50% of liquid steel could be
cast, leading to the rejection of a large amount of liquid
steel in tundish.

WE CLAIM
1. A process for improving castability of Zr-bearing
steel for continuous casting, said process comprising
steps of:
selecting a batch composition of raw material
comprising C, Mn, Si, N, Cr, S, P, Zr, Al, Fe selected
in specific wt % ;
melting said batch composition for liquification to
form liquid steel and pouring said liquid steel from
ladle into a tundish of continuous casting machine;
pouring the liquid steel from the tundish to the mould
of continuous casting machine, and casting into slabs
of desired cross-section.
2. Process as claimed in claim 1, wherein said batch
composition comprises 0.31 to 0.34 % weight C, 0.82 to
0.88 % weight Mn, 0.55 to 0.65 % weight Si, 40-60 ppm
N, 0.82 to 0.88 % weight Cr, upto 0.015 weight % S,
upto 0.015 weight % P, Al/Zr ratio of 0.2-0.3, and
balanced wt. % Fe.
3. Process as claimed in claims 1 and 2, wherein the
batch composition comprises Zr ranging from 0.12 to
0.16 weight %.

4. Process as claimed in any preceding claims, wherein Al
to Zr ratio ranges from 0.2 to 0.3.
5. Process as claimed in claim 1, wherein temperature of
liquid steel in the tundish ranges from 1550°C to
1560°C.
6. Process as claimed in claim 1, wherein the casting is
superheat temperature during casting ranges from 50°C
to 60°C.
7. Process as claimed in any preceding claims comprising
a secondary cooling intensity of 0.8 1/kg
approximately.
8. Process as claimed in any preceding claims comprising
casting speed of 0.8 m/min approximately.
9. A composition for producing Zr-bearing steel
comprising percentage weight C : 0.31 to 0.34, Mn:.
0.82-0.88, Si: 0.55-0.65, N: 40-60 ppm, Cr: 0.82 to
0.88, S: 0.015 max, P: 0.015 max, Zr: 0.12 to 0.16,
Al/Zr ratio-0.2 to 0.3, Fe-balance.

ABSTRACT

TITLE : A PROCESS FOR IMPROVING CASTABILITY OF Zr
BEARING STEEL
The present invention relates to a process for
improving castability of Zr-bearing steel for
continuous casting. The process steps comprises
selecting a batch composition of raw material
comprising C, Mn, Si, N, Cr, S, P, Zr, Al, Fe selected
in specific wt %. The batch composition is melted for
liquification to form liquid steel and pouring said
liquid steel from ladle into a tundish of continuous
casting machine. The liquid steel from the tundish is
poured to the mould of continuous casting machine, and
cast into slabs of desired cross-section.