TITLE: A METHOD TO EVALUATE THE EFFECT OF ELECTRO-MAGNETIC
STIRRING ON CONTINUOUSLY CAST STEEL BILLETS BY ULTRASONIC
IMMERSION C-SCAN IMAGING.
FIELD OF THE INVENTION
The invention relates to ultrasonic immersion c-scan imaging technique to
evaluate the effect of electromagnetic stirring on continuously cast steel billets
for soundness by optimization of various parameters i.e. current, frequency,
position etc.
BACKGROUND OF THE INVENTION
Usually evaluation of the effect of electro-magnetic stirring on soundness of
continuously cast steel billets and slabs are assessed by the following methods:
1. Visual inspection of macro-etch
2. Sulphur print evaluation
But ultrasonic assessment provides through thickness information of the test
samples, whereas, macro-etching and sulphur print methods provide information
in one plane only. For more realistic assessment these methods requires large
number of test samples and hot acids which is hazardous and pollute the
atmosphere also. Ultrasonic method is pollution free and eco-friendly method
and may require less number of samples also.
To overcome the problems faced during the evaluation of cleanliness level of
steel, by above mentioned methods, a lot of interest has been shown to detect,

measure and analyze macro-level inclusions in steel using specialized ultrasonic
techniques. It is preferred ultrasonic method in comparison to other methods as
inspection could be done with a larger sample volume.
While evaluating the macro-inclusion distribution and detection, in comparison to
other methods, ultrasonic method was found to be more effective. Attenuation
measurements were found to give very low numerical values. With this
background, a high gain pulse echo ultrasonic technique was used for inclusion
detection in forgings in a quantitative manner.
Macro-etching and sulphur print methods provide information in one plane only.
For more realistic assessment these methods requires large number of test
samples and hot acids which is hazardous and pollute the atmosphere also.
OBJECT OF THE INVENTION
• The object of the invention is to evaluate the effect of electro-magnetic
stirring on soundness of high and low carbon continuously cast steel
billets.
• Another object of the invention is to reduce the use of hazardous hot
acids/chemicals for control of environment and industrial pollution.
• Other object of the invention is to reduce the running cost of repetitive
tests for quality check.

• Also the object of the invention is to make the process accessible to the
demanding industries and reduce human error.
BRIEF DESCRIPTION OF THE ACCOMPANYING TABLES. SCANNED
IMAGES & GRAPHS
• Figure 1 shows the schematic diagram of billet samples collected from
Billet Caster,
• Figure 2 shows ultrasonic C-Scan image of transverse section of non-EMS
CC billet sample of HC Grade-A.
• Figure 3 shows ultrasonic C-Scan image of transverse section of CC billet
sample of HC Grade-A EMS Current 240A and Frequency 3.5 Hz.
• Figure 4 shows ultrasonic C-Scan image of transverse section of CC billet
samples of HC Grade-A at EMS Current 260A and Frequency 3.5 Hz.
• Figure 5 shows ultrasonic C-Scan image of transverse section of CC billet
sample of HC Grade-A at EMS Current 280A and Frequency 3.5 Hz.
• Figure 6 shows ultrasonic C-Scan image of transverse section of CC billet
samples of HC Grade-A at EMS Current 300A and Frequency 3.5 Hz.
• Figure 7 shows effect of EMS current on the % equiaxed zone and %
defective area of HC Grade-A as well as LC Grade-A billet samples.

• Figure 8 shows ultrasonic C-Scan image of transverse section of non-EMS
CC billet sample of LC Grade-A.
• Figure 9 shows ultrasonic C-Scan image of transverse section of CC billet
sample of LC Grade-A at EMS Current 240A and Frequency 3.5 Hz.
• Figure 10 shows ultrasonic C-Scan image of transverse section of CC billet
of LC Grade-A at EMS Current 260A and Frequency 3.5 Hz.
• Figure 11 shows ultrasonic C-Scan image of transverse section of CC billet
sample of LC Grade-A at EMS Current 280A and Frequency 3.5 Hz.
• Figure 12 shows ultrasonic C-Scan image of transverse section of CC billet
sample of HC Grade-A at EMS Current 300A and Frequency 3.5 Hz.
• Figure 13 shows ultrasonic C-Scan image of transverse section of CC billet
sample of HC Grade-A at EMS Current 280A and Frequency 3 Hz.
• Figure 14 shows ultrasonic C-Scan image of transverse section of CC billet
of HC Grade-A at EMS Current 280A and Frequency 4 Hz.
• Figure 15 shows ultrasonic C-Scan image of transverse section of CC billet
sample of LC Grade-A at EMS Current 280A and Frequency 3 Hz.
• Figure 16 shows ultrasonic C-Scan image of transverse section of CC billet
sample of LC Grade-A at EMS Current 280A and Frequency 4 Hz.

• Figure 17 shows effect of EMS frequency on the % equiaxed zone and the
% defective area of HC Grade-A as well as LC Grade-A billet samples at
EMS current 280A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Stirring intensity decreases with increasing frequency and it is related to the
"skin effect" according to which eddy currents are more concentrated on the
outer part of the conductor as the frequency increases.
The following relationship describe the effect of EMS frequency on stirring
intensity, F

Where, BM = magnetic induction in the considered point inside the metal (in
Gauss)
/ = Frequency of power supply, in Hz.
The above formula shows that the stirring force is the product of B2M (f) (which
decreases with increasing frequency) and f. At frequency zero the force is zero
and at higher frequency the force approaches to zero again because the term
B2M (f) becomes very small. In between, there is a specific frequency, the so-
called optimum frequency, at which the stirring force is maximum.
The current of EMS coil controls its performance, because the stirring force (F),
acting on the liquid steel is proportional to the square of the magnetic flux (BM,

which is proportional to the current). Consequently, the current setting is the
main operational parameter, which is to be chosen as function of the casting
conditions. Generally, the current is kept constant during casting.
Theoretically, the current setting depends on the chemical composition of each
steel grade. An optimization is to be done for each individual case. Increased
casting speed as well as increased superheat needs increased current settings. In
practice however, the justification of different current setting as function of
casting speed and superheat shall have to be ascertained for each specific case.
During any metallurgical improvement obtained by EMS (such as reduction of
surface and subsurface defects, increase of equiaxed zone, decrease of axial
porosity or segregation etc.), too low current settings give insufficient
improvements, too high current settings give practically no further improvements
and spend electrical power for nothing. Moreover, too high current settings may
give rise to negative effects. Consequently, the optimum current setting is the
compromise of good results and reasonable power consumption. It needs many
casts and analysis under reproducible conditions with and without stirring, to
establish quantitatively the exact relation between improvement and current
setting.
The attempts have been made to determine the best combination of EMS current
and frequency for ensuring good surface as well as subsurface quality of CC steel
billets cast at Billets Casters. Two close casting grades, one of high carbon grade
(HC Grade-A) and another of low carbon grade (LC Grade-A) of steel billet was
considered. The chemical compositions of the above mentioned grades have
been shown in Table 1 and Table 2 respectively. The experiments were

conducted on the above grades of CC billets with EMS currents 240, 260, 280
and ,300 amperes (A), while frequency was kept constant to 3.5 Hz during
casting. In some of the heats EMS frequencies were set at 3, 3, 5 and 4 hertz
(Hz) while EMS current was kept constant during casting. In both the cases, the
corresponding CC billet samples were collected and its effect on billet quality was
assessed by using ultrasonic immersion C-Scan imaging technique.
Each billet sample of cross section of 130 x 130 mm was sliced into transverse
and longitudinal sections (approximately 20 mm thick) and ground to good
surface finish. Figure-1 shows the schematic diagram of billet samples collected
from Billet Caster. "■
All the steel billet samples were examined using the ultrasonic immersion C-Scan
imaging technique. All microstructural features observed, in each case, were
recorded and analyzed subsequently. Finally, data of axial porosity,
columnar/equiaxed zone, % defective area (which includes segregation,
inclusions, pinhole, internal as well a subsurface cracks) of the total scanned
area in each grades of steel were compared for determining the best
combination of EMS parameters.
A series of tests were carried out with the billet specimens to evaluate, and
optimize the EMS current and frequency with respect to CC steel billet quality.
These specimens were subsequently tested in a water tank using a 5 MHz
ultrasonic focused beam probe. The C-scan images were obtained with the help
of a computer controlled ultrasonic immersion C-scan system. The other details
of the equipment and testing parameters are given below:

Name of the equipment - Multi-scan (X, Y, and Z) automatic ultrasonic
Immersion C-scan inclusion detection system
Probe - 5 MHz, 15 mm diameter., spherical focused
single crystal normal probe, focal length 1.5"
in water
Media - Water
Pulser Receiver Setting:
Make and Model - Panametrics Computer Controlled Pulser
Receiver
Model 5800
Mode - Pulse Echo
Pulse Repetition Frequency - 100 Hz
Energy - 50pJ
Damping - 50 ohm
High Pass Filter - 1 kHz
Low Pass Filter - 30 MHz
Input Attenuation - 0 dB
Output Attenuation - 7 dB
Gain - 40 dB
Scanning Setting:
Water path - 25.68 mm
Scan Length - In case of transverse billet sample 140 mm
max.
- In case of transverse billet sample 170 mm
max.
- In case of transverse billet sample 140 mm
max.

- In case of transverse billet sample 170 mm
max.
Scan Resolution - 0.4 mm
Index Resolution - 0.4 mm
Scan Mode - Bi-Directional
Calibration - In order to achieve reproducible result during
ultrasonic evaluation of macro level flaw
. counts, the equipment was standardized with
a 0.7 mm Flat Bottom Hole (FBH) in the
same billet sample. 0.7 mm Flat Bottom Hole
(FBH) resulted in 5 V peak. This peak was
indicated by yellow colour, kept as upper
threshold. 1 V peak-to-peak (i.e. 20% of full
screen height) was kept the lower threshold
as indicated by green colour.
This technique was applied to evaluate the quality of steel billet samples.
Ultrasonic C-scan can image different five intermediate layers of the billet
samples and plot in two dimensions of the final image. Therefore, all the internal
defects appeared at the final image, where as in macro-etched structure
revealed only top etched layer of the samples. One major advantage of
ultrasonic C-scan over A-scan is that classification of different kinds of defects is
possible by imaging of the defects by this method. This method also reveals
three different regions in the samples such as chilled zone, equiaxed zone and
columnar zone in different gray/colour scale.

A series of C-scan tests were carried out with varying parameter settings. The
instrument variables for these tests were as follows:
• Resolution : 0.4 mm x 0.4 mm
• Voltage setting : 20V and
• Gain : 33 dB
Grey scale was used to differentiate the results from the gated area. Referring to
ultrasonic C-scan images, and based on a grey scale that depicts attenuated ■
signals darker, one may see clear identification of defects by the darker areas.
Although not very sharp, each and every one of the areas is reproduced with a
certain degree of dimensional accuracy. However the boundary of each defect is
not well defined.
Prior to this work, the Billet Caster used a setting of 260A EMS current and 3.5
Hz EMS frequency for all the close casting grades. In this work, it has been tried
to find out the optimum combination of EMS current and frequency which will
produce billet with good internal quality consistently.
Initially EMS current was set to 240, 260 280, and 300A during casting and billet
samples were collected and examined to find out the effect of change in current.
. Samples without EMS (non-EMS) condition were also collected.
This is aluminium killed steel with carbon content 0.63%. The other details of the
grade have been shown Table 1.

Figure 2 shows the ultrasonic C-Scan image of transverse section of non-EMS
billet sample of HC Grade-A. It can be easily observed that there is a very small
equiaxed zone with a large columnar zone and a huge defective area in non-EMS
billet samples when compared with the EMS billet samples. After use of EMS,
there was significant improvement in quality of CC billets in terms of larger%
equiaxed zone, small axial porosity and low% defective areas, which is desirable.
It is also evident from the Figures 3-6 which show the ultrasonic G-Scan images
of transverse sections of CC billet sample of HC Grade-A, at EMS current 240,
260, 280 and 300A.
Figure 7 demonstrates the quantitive values of the effect of EMS current on the
quality of HC Grade-A billet samples in terms of % equiaxed zone and the %
defective area of total area. It is clear that the equiaxed zone in non-EMS
samples is only 15% whereas it is 35, 39, 47 and 45% in EMS billet samples at
the EMS current 240, 260, 280 and 300A respectively. Similarly, the defective
area in the non-EMS billet sample is as high a 19% of the total area of the billet
sample, while it is 15, 13, 10 and 10% in EMS billet samples at the EMS current
240, 260, 280 and 300A respectively.
In can be, therefore, concluded that the % of equiaxed zone increase sharply
with the increase in EMS current. It is most significant at EMS current 280A after
that it increases marginally. Similarly, the % total defective area in the billet
sample, with respect to the total area of billet section, also decreases
considerably with increase in EMS current up to 280A after that it does not
decrease further.

LC Grade-A
This is a cold heading quality grade and its application is for high tensile
fasteners. The details of this grade have been shown in Table 2.
Figure 8 shows the ultrasonic C-Scan image of transverse section of non-EMS
billet sample LC Grade-A. It can be easily observed that there is a very small
equiaxed zone with a large columnar zone and a huge defective area in non-EMS
billet samples when compared with the EMS billet samples. When EMS was used,
there was significant improvement in quality of CC billets in terms of larger %
equiaxed zone, small axial porosity and low % defective areas, which is
desirable. It is also evident from the Figures 9-12 which show the ultrasonic C-
Scan images of transverse sections of billet sample of LC Grade-A at EMS current
240, 260, 280 and 300A.
Figures 7 demonstrates the quantative values of the effect of EMS current on the
quality of LC Grade-A billet samples in term % equiaxed zone and the %
defective area of total area. It is clear that the equiaxed zone in non-EMS sample
is only 12% whereas, in EMS billet samples, it is 33, 37, 39 and 37% at the EMS
current 240, 260, 280 and 300A .respectively. Similarly, the defective area in the
non-EMS billet sample is as high as 22% of the total area of the billet sample,
while, in EMS billet samples, at the EMS current 240, 260, 280 and 300A, it is 19,
17, 13 and 13% respectively.
Hence, it can be concluded that the % equiaxed zone increases sharply with the
increasing EMS current. It is most significant at EMS current 280A after that it

increases marginally. Similarly, the % total defective area in the billet sample,
with respect to the total are of billet section, also decreases considerably with
increase in EMS current up to 280A and after that it does not decrease further.
Optimization of EMS frequency
After optimization of EMS current, EMS frequency was, then, set to 3, 3, 5
(existing practice) and 4 Hz, keeping EMS current constant at 280 during casting
and billet samples were collected. These billet samples were also ultrasonically
analyzed and evaluated.
Figures 13 and 14 shows the ultrasonic C-Scan image of transverse section of
billet samples of HC Grade-A at EMS current 280 A and EMS frequency 3 Hz and
4 Hz respectively whereas Figures 15 and 16 show the ultrasonic C-Scan image
of transverse section of billet samples of LC Grade-A at EMS current 280A and
EMS frequency 3 and 4 Hz respectively. In both the grades, it was found'that
quality of the billet samples appears sounder, in terms of the % equiaxed zone,
axial porosity and the % defective areas, when the EMS frequency was 3.5 Hz,
when compared to the same with the EMS frequency 3 Hz and 4 Hz.
Figure 13 demonstrate the quantitative values of the effect of EMS frequency on
the quality of billet samples of both the grades in term of the % equiaxed zone
and the % defective area of total area.
It is obvious that the equiaxed zone in non-EMS HC Grade-A samples is only
15% whereas, in EMS billet samples, it is 33, 47 and 48% at the EMS frequency

3, 3.5 and 4 Hz respectively. Similarly, the defective area in the non-EMS billet
sample is as high as 19% of the total area of the billet sample, while, in EMS
billet samples, at the EMS frequency 3, 3.5 and 4 Hz, it is 18, 10 and 11%
respectively. Hence, it can be concluded that, in this case, the % equiaxed zone
increases sharply with the increasing EMS frequency. It is most significant at
EMS frequency 3.5 Hz after that it increases marginally. Similarly, the % total
defective area in the billet sample, with the respect to the total area of billet
section, also decreases considerably with increase in EMS frequency up to 3.5 Hz
and after that it starts increasing.
In case of LC Grade-A, in non-EMS samples it is 12% only whereas, in EMS billet
samples, it is 28, 39 and 37% at the EMS frequency 3, 3.5 and 4 Hz respectively.
Similarly, the defective area in the non-EMS billet sample is as high as 22% of
the total area of the billet sample, while, in EMS billet samples, at the EMS
frequency 3, 3.5 and 4 Hz, it is 21, 13 and 16% respectively. Hence, it can be
concluded that, in this case also, the % equiaxed zone increases with the
increase in EMS frequency. It is most significant at EMS frequency 3.5 Hz and
after that it increases marginally. The % total defective area in the billet sample,
with respect to the total area of billet section, also decreases considerably with
increase in EMS frequency up to 3.5 Hz and after that it starts increasing further.
It was observed that billet samples contain large axial porousity with lot of
subsurface defects also. Therefore EMS frequency should not be increased
further.

WE CLAIM:
1. A method to determine the grain-structure and casting defects in a Cast
Steel Billet by ultrasonic immersion C-Scan imaging, comprising the steps
of:
- calibrating an ultra sound equipment to achieve reproducible result
during evaluation of macro level flow counts of the equipment;
- standardizing Ultrasonic C-Scan image in different five intermediate
layers of the billet and arrange the data in two dimensions image
scale;
- selecting optimum electromagnetic stirring current;
- selecting electromagnetic stirring frequency;
- carrying out an Electro Magnetic stirring test on the casted billet;
and
- detecting the defect including microstructure of the billet.

2. The method as claimed in claim 1 wherein calibration of the equipment is
carried on a 0.7 mm flat bottom hole (FBH) in the same billet showing 5V
peaks in the scale wherein upper threshold peak shows yellow colour and
IV peak to peak (i.e. 20% of full screen height) was kept lower threshold
as green colour.
3. The method as claimed in claim 1 wherein standardization reveals three
different regions in the billet such as chilled zone, equiaxed zone and
column Zone in different gray/colour scale wherein a gray scale depicts a
clear identification of defect by darker signal.
4. The method as claimed in claim 1 wherein selection of optimization of
electromagnetic stirring current by conducting a trial test to set 240, 260,
280 and 300A on billets and selecting the best result obtained from the
test.

5. The method as claimed in claim 1 wherein selection of optimum frequency
of sound by conducting a trial test to set 3, 4, 5 Hz at different EMS
current and selecting best result obtained from the test.
6. The method as claimed in claim 1 wherein % of equiaxed zone increase
with increase of EMS current up to 280A.
7. The method as claimed in claim 1 wherein defect areas decrease over
EMS current 280A.
8. The method as claimed in claim 1 wherein % of equiaxed zone increase
sharply with the increasing of EMS frequency upto 3.5 Hz.
9. The method as claimed in claim 1 wherein % of defect decreases with the
increase of EMS frequency upto 3:5 Hz.
10. The method as claimed in claim 1 wherein testing parameter settings are
Resolution: 0.4mm X 0.4 mm
Voltage settings: 20V and
Gain : 33 dB

ABSTRACT

A METHOD TO DETERMINE THE GRAIN STRUCTURE AND
CASTING DEFECT IN CAST STEEL BILLET BY ULTRASONIC
IMMERSION C-SCAN IMAGING
The present invention is provided with a method to determine the grain-structure
and casting defects in a Cast Steel Billet by ultrasonic immersion C-Scan imaging,
comprising calibrating an ultra sound equipment to achieve reproducible result
during evaluation of macro level flow counts of the equipment; standardizing
Ultrasonic C-Scan image in different five intermediate layers of the billet and
arrange the data in two dimensions image scale; selecting optimum
electromagnetic stirring current; selecting electromagnetic stirring frequency;
carrying out an Electro Magnetic stirring test on the casted billet; and detecting
the defect including microstructure of the billet.