The present Invention relates to an improved / ladle treatment process
for manufacture of cold rolled non-oriented (CRNO) electrical
steel of reduced core loss.
The CRNO electrical steel of grades such as M47, M45
and M43 of American Iron and Steel Institute and corresponding
ASTM Grades 47P 380, 47F 290 and 47F 230 respectively, produced
in the existing process is found to be of relatively high core
loss of 3.32-8.01 Watt/kg owing to eddy current and magnetic
hysteresis effect when used as rotating parts in electric motors
and generators with an increased energy loss and heat generation
therein.
The object of the present invention is to provide a
process of manufacturing cold rolled non-oriented (CRNO)
electrical steel of relatively low core loss.
The invented process is suitable for producing CRNO
electrical steel of grades such as M27, M22 and M19 of American
Iron and steel Institute and of corresponding ASTM grades 47F 190,
47F 185 and 47G 174 respectively, in the BOF (Basic Oxygen
Furnace) - VAD (Vacuum Decarburisation) - Ingot route, containing
0.006 to 0.02596 by weight of c + s, i.e. total carbon and sulphur
content, 2.40 to 2.90% by weight of Si + Al, i.e. total silicon
and aluminium content 710-4o ppm of N and Otot i.e. total nitrogen
and free and bound oxygen content, each.
The chemical compositions of CRNO electrical steel
produced in the invented and the existing processes are presented
in Table I which also includes the core loss value of the steels
produced in the invented and existing processes.
The steps followed in the present invention for over-
coming the disadvantages of the existing process are : (a) to
adopt a deoxidation method which does not require addition of
any deoxidiser to the molten iron during tapping thereof and
which delays the deoxidation process; (b) to add Aluminium to
molten steel for deoxidation in a modified scheme; (c) to add
FeSi to molten steel for alloying in a modified scheme; and
(d) to add flux mix containing lime and spur with Aluminium as
required for enhancing Nitrogen removal from liquid steel.
The quantity of Aluminium addition at varying,Oxygen
content of molten steel, and the quantity of FeSi addition at
varying Si content of molten steel done in the invented process
are presented in Table III.
The distinguishing features of the invented process
from the prior art process are :-
(a) In the existing process, addition of deoxidiser and
alloy to molten steel is done during tapping from converter to
ladle. As a result the reduction in carbon and nitrogen content
of steel is inadequate.
In the invented process the addition of deoxidiser
and alloy to molten steel is not done during tapping from
converter to ladle. As a result the reduction in carbon and
nitrogen content of steel is adequate./
(b) In the existing process the slag added for refining
steel in VAD comprises 300-500 kg of lime, 50-100 kg of spur and
250-400 kg of Al in a 66t bath. As a result reduction in carbon
and nitrogen oontent of steel is inadequate.
In the Invented process the slag added for refining
steel by Vacuum Arc Degassing (VAD) treatment comprises 800 kg
lime, 200 kg spur, 200-691 kg aluminium (Table III) and 1112-2779
kg FeSi (Table III) in a 66t bath. As a result the reduction in
carbon and nitrogen content of steel is adequate.
(c) In the existing process, the steel produced contains
(by weight %) carbon - 0.025 to 0.030, sulphur - 0.008 to 0.013,
nitrogen - 60 to 70 ppm and total oxygen - 70 to 80 ppm. As a
result the core loss is relatively high.
In the invented process, the steel produced contains
(by weight %) carbon - 0.005 to 0.020, sulphur - 0.001 to 0.005,
nitrogen - 10 to 40 ppm and total oxygen - 10 to 40 ppm.
As a result the core loss is relatively low.
The various steps followed in the process is Illustrated
in the accompanying drawings in which «
Figure 1 is a flow chart showing the steps followed
in the invented process in sequence.
The invented process is described fully and particularly,
without restricting the scope of the invention in any manner,
to comprise following steps in sequence :-
i) producing molten steel heat in Basic Oxygen Furnace (BOF]
in the known manner;
ii) tapping the molten steel into a ladle;
iii) subjecting the molten metal to Vacuum Arc Degassing
(VAD) treatment;
iv) casting the molten steel into ingots;
v) cold rolling the steel in known manner;
characterised in that -
(a) the temperature, C- and S-content of the heat in Basic
Oxygen Furnace (BOF) before tapping is maintained at
1660°C, 0.04% and 0.03% by weight respectively;
(b) tapping is done in a red hot clean ladle without
addition of any deoxidiser and alloy for enhancing
reduction in carbon and nitrogen content of steel;
(c) Vacuum Arc Degassing (VAD) treatment is carried out in
the process at secondary voltage of 250-290V by raising
the temperature of the heat to 1650 C by arcing,
rinsing the heat with Ar at a flow rate of 5-6 Nm/hr
and at a vacuum level of 300 mbar, changing the vacuum
level to less than 100 mbar, degassing for 10 min at Ar
flow rate of 10 Um /hr with increase in the degassing
time by 5 min for every 0.002% (by weight) reduction in
C ontent below 0.02% level, by adding slag comprising
800 kg lime, 200 kg spur, 200-691 kg aluminium, 556-1390
kg FeSi with Ar purging at the flow rate of 10-12 Nnr/hr
for 15 min at leas than 100 mbar vacuum level, adding
balance 556-1390 kg FeSi and Ilmenite with Ar purging
for 10 min at a flow rate of 10-12 Nm5/hr at less than
100 mbar vacuum level, adding required amount of CaSi
wire at a rate of 0.6 kg/t with Ar purging at a flow
rate of 5-6 Nnr/hr at atmospheric pressure for 3 min;
(d) the steel ingot produced is of chemical composition
(by weight %): C - 0.005 to 0.02, Mn - 0.20 to 0.25,
S - 0.001 to 0.005, P - 0.010 to 0.025, Al - 0.20 to
0.40, Si - 2.2 to 2.5, N - 10 to 40 ppm, 0tot - 10 to
40 ppm, Fe - balance»
The chemical composition of CRND electrical steel of
grade M27, M22 and M19 produced in the invented process are
presented in Table II which includes also the core loss value
for each grade.
The performance of the CRND electrical steel produced
in the invented process has been tested at the users1 level
and found to be superior to that of the steel produced in the
existing process.
We Claim :-
1. An improved ladle treatment process for manufacture of
cold rolled non-oriented (CRNO) electrical steel of reduced core
loss, comprising the following steps in sequence :-
i) producing molten steel heat in Basic Oxygen Furnace
(BOF) in the known manner;
ii) tapping the molten steel into a ladle;
iii) subjecting the molten metal to Vacuum Arc Degassing
(VAD) treatment;
iv) casting the molten steel into ingots;
v) cold rolling the steel in known manner;
characterised in that -
(a) the teaperature, C- and S-ccntent of the heat produced
in Basic Oxygen Furnace (BOF) before tapping is maintained
at 1660°C, 0.0496 and 0.0396 by weight respectively;
(b) tapping is done in a red hot clean ladle without
addition of any deoxidiser and alloy for enhancing
reduction in carbon and nitrogen content of steel;
(c) Vacuum Arc Degessing (VAD) treatment is carried out by
raising the temperature of the heat to 1650°C by arcing,
rinsing the bea* witn Ar at a fl0¥ rate o£ $-6 Nor/hr and
at a vacuum level of 300 mbar, changing the vacuum level
to less than 100 mbar, degassing for 10 min at Ar flow
rate of 10 NM3/hr with increase in the degassing time by
5 min for every 0.00296 (by weight) reduction in C content
below 0.0296 level, by adding slag comprising 800kg lime,
200 kg spur, 200-691 kg aluminium, 556-1390 kg FeSi with
Ar purging at the flow rate of 10-12 Nnr/hr for 15 min at
less than 100 mbar vacuum level, adding balance 556-1390
kg FeSi and Ilmenite with Ar purging for 10 min at a
flow rate of 10-12 Itor/hr at less than 100 mbar vacuum
level, adding required amount of CaSi wire at a rate of
0.6 kg/t with Ar purging at a flow rate of 5-6 lto5/hr
at atmospheric pressure for 5 min; and
(d) the steel ingot produced is of chemical composition (by
weight %)i C - 0.005 to 0.02, Mn - 0.20 to 0.25,
S - 0.001 to 0.005, P - 0.01 to 0.025, Al - 0.20 to 0.40,
Si - 2.0 to 2.5, N - 10 to 40 ppm, 0t t - 10 to 40 ppm,
Fe - balance*
2. The process as claimed in claim 1, wherein the chemical
composition of CRND electrical steel equivalent to grade M27
produced is (by weight #): C - 0.020 max, Mn - 0.20 to 0.25,
P - 0.025 max, S - 0.005 max, Si - 2.0 to 2.2t Al - 0.20 to 0.30,
N - 40 ppm max, 0+j. - 40 ppm max, Fe - balance.
3. The process as claimed in claim 1, wherein the chemical
composition of CRND electrical steel equivalent to grade M22
produced is (by weight %): C - 0.018 max, Mn - 0.20 to 0.25,
P - 0.025 max, S - 0.005 max, Si - 2.2 to 2.4, Al - 0.25 to 0.35,
N - 40 ppm max, 0+ t - 40 ppm max, Fe - balance.
4. The process as claimed in claim 1, wherein the chemical
composition of CRNO electrical steel equivalent to grade M19
produced is (by weight %)i C - 0.015 max, Mn - 0.20 to 0.25,
P - 0.025 max, S - 0.005 max, Si - 2.3 to 2.5, Al - 0.30 to 0.40,
N - 40 ppm max, 0tot -40 ppm max, Fe - balance.
Dated this 26th day of March 1999.

An improved ladle treatment process for manufacture of
cold rolled non-oriented (CRNO) electrical steel of reduced core
loss, comprising the following steps in sequence :-
i) producing molten steel heat in Basic Oxygen Frunace
(BOF) in the known manner;
ii) tapping the molten steel into a ladle;
iii) subjecting the molten metal to Vacuum Arc Degassing (VAD)
treatment;
iv) casting the molten steel into ingots;
v) cold rolling the steel in known manner;
characterised in that -
(a) the temperature, C- and S-content of the heat produced
in Basic Oxygen Furnace (BOF) before tapping is maintained
at 1660°C, 0.04% and 0.03% by weight respectively;
(b) tapping is done in a red hot clean ladle without addition
of any deoxidiser and alloy for enhancing reduction in
carbon and nitrogen content of steel;
(c) Vacuum Arc Degassing (VAD) treatment is carried out by
raising the temperature of the heat to 1650°C by arcing,
rinsing the heat with Ar at a flow rate of 5-6 Nm3/hr
and at a vacuum level of 300 mbar, changing the vacuum
level to less than 100 mbar, degassing for 10 min at Ar
flow rate of 10 Nm3/hr with increase in the degassing
time by 5 min for every 0,002% (by weight) reduction in
C content below 0.02% level, by adding slag comprising
800 kg lime, 200 kg spur, 200-691 kg aluminium, 556-1390
kg FeSi with Ar purging at the flow rate of 10-12 Nm3/hr
for 15 min at less than 100 mbar vacuum level, adding
belance 556-1390 kg FeSi and Ilmenite with Ar purging
for 10 min at a flow rate of 10-12 Nm3/hr at less than
100 mbar vacuum level, adding required amount of CaSi
wire at a rate of 0.6 kg/t with Ar purging at a flow
rate of 5-6 Nm3/hr at atmospheric pressure for 5 min;
and

(d) the steel ingot produced is of chemical composition
(by weight %): C - 0.005 to 0.02, Mn - 0.20 to 0.25,
S - 0.001 to 0.005, P - 0.01 to 0.025, Al - 0.20 to
0.40, Si - 2.0 to 2.5, N - 10 to 40 ppm, 0tot-10 to
40 ppm, Fe - balance.
Reference: Figure 1 of the accompanying drawing.