FIELD OF INVENTION
The present invention relates to a method to detect the defects of metal casting.
More particularly the present invention relates to a method to detect, measure
the inclusion bands in continuous cast steel billets using ultrasonic Immersion C-
scan immersion system and analyze the inclusion bands using an image analysis
software.
BACK GROUND OF THE INVENTION
In recent years, there has been a tremendous increase in the production of
continuously cast steel, since the process of continuous casting is a faster
method of steel casting from liquid steel at reduced production cost when
compared with the conventional ingot route of casting. However, at the same
time, more attention has been paid to improve product quality with respect to
overall cleanliness level in order to improve reliability of the finished products
which has led to production of continuously cast product of high quality. A clean
steel greatly effect many physical and mechanical propertied like fatigue life,
machinability and corrosion resistance. Steel with respect to macroscopic oxide
inclusions are a prerequisite for improved surface finish and prolonged lifetime of
components as well as for the application of increasingly stringent forming

processes. Presence of macro-inclusions can generate sliver defects during cold
rolling for thinner gauge steel strips and can also become the reason for wire
breakage during wire drawing for very thin sections.
Continuous casting of steel through curved type of moulds generally causes the
formation of inclusion concentration bands towards the inner radius of the
strand, the location and severity of which depends on the casting conditions like
casting speed, cooling condition etc. and condition of steel making practices.
During solidification, the large size inclusion or bubbles holding the inclusions are
caught during floatation and form a band towards the inner radius of the strand.
Location of these bands close to the surface can cause surface defects like cracks
and also can cause problems in further processing/rolling of these billets. The
extreme cases these bands may be the cause for typical cobble formation during
rolling or rejection of the coils after finish rolling
The inclusion bands generally located towards the inner radius of continuously
cast (CC) strands in curved moulds are the most troublesome location due to
accumulation of harmful macro-inclusion at these spots. It is important to
monitor the severity of these bands with respect to its concentrations and size
distributions to reduce the problems in further processing of these steel
products.
MIDAS ( Mannesmann Inclusion Detection by Analyzing Surfboard ) is the most
popular method in European Countries to quantify the inclusion concentration in
these bands. However, this method needs special cross hot rolling of the CC
Billet/slab/bloom samples cut to specific dimensions and directions. The hot
rolling refines the grain structure in the sample to improve transmission of

ultrasonic waves and close up the pores/voids etc. present in the cast structure.
The process of sample making and sample preparation takes a lot of time and
decision based on the ultrasonic measurements are delayed. At the same time,
the shape, size and location of the macro-level globular inclusion are disturbed
during rolling.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a method to detect,
measure and analyze inclusion bands in continuous cast steel billet using
ultrasonic C-scan immersion system which overcomes the draw backs of earlier
method for assessing the inclusion concentration in the inclusion bands in
continuous casting.
Another object of the present invention is to Propose a method to detect,
measure and analyze inclusion bands in continuous cast steel billet using
ultrasonic C-scan immersion system which helps in assessing severity levels (in
terms of inclusion concentration) of inclusion bands in CC strands (Particularly
Globular macro inclusion).
A further object of the present invention is to propose a method to detect,
measure and analyze inclusion bands in continuous cast steel billet using
ultrasonic C-scan immersion system which correlates between the ultrasonic
parameter (Ultrasonic Counts) using computer controlled Automatic "C" scan
immersion and image Analysis System and the Size and distribution of macro
inclusions measured in optical microscope.

A still further object of the present invention is to propose a method to detect,
measure and analyze inclusion bands in continuous cast steel billet using
ultrasonic C-scan immersion system which helps in correlation between the
ultrasion parameter (ultrasonic Counts) and the impact properties of these
inclusion bands.
An yet further object of the present invention is to propose a method to detect,
measure and analyze inclusion bands in continuous cast steel billet using
ultrasonic C-scan immersion system which ensures the products sent to the
customers free from harmful macro-inclusion which may cause further
processing problems at their end.
SUMMARY OF THE INVENTION
In the present method, rolling is not required and grain refinement of the cast
sample is obtained by homogenizing of the sample at 1260°C in a heat treatment
furnace. Transverse cut billet/slab slices are ground finish (mirror finish) to 18
mm thickness with parallel faces on which backscattered signals from the
globular macro-inclusion are measured by an ultrasonic C-scan immersion
system and analyzed using an image analyzing software.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 shows the photographs of ultrasonic "C" Scan Image Analysis System
showing (a) Multi-axis (X,Y and Z) scanner, (b) Pulser Receiver Model 5800, (c)
Computer display of "A" scan signals and "C" scan coloured image.
Fig.2 shows a typical ultrasonic C-scan image showing the inclusion band and
axial porousity of the CC billet sample with cast no.A.
Fig.3 shows a typical ultrasonic C-scan image showing the inclusion band and
axial porousity of the CC billet sample with cast no.B.
Fig.4 shows C-scan image analysis of CC billet with cast no.A. Inclusions/mm2 :
0.186 (Gate-5); 0.064 (Gate-2)
Fig.5 shows C-scan image analysis of CC billet with cast no.B. Inclusions/mm2:
0.138 (Gate-5); 0.051 (Gate-2)
Fig.6 shows variations in amplitudes of back wall echoes along the mid-line AB as
shown in Fig.2 in arbitrary scale (A.U) during ultrasonic scanning in the CC billets
with cast no.A.
Fig.7 shows variations in amplitudes of back wall echoes along the mid-line AB as
shown in Fig.2 in arbitrary scale (A.U) during ultrasonic scanning in the CC billets
with cast no.B.

Fig.8 shows typical globular macro-inclusions revealed in optical microscope after
paper polishing in sample with billet cast no.B
Fig.9 - Typical globular macro-inclusions revealed after paper polishing in sample
with billet cast no.A
Fig. 10 - Typical globular indications observed in the ultrasonically examined
inclusion band in microscope in the CC Billet with cast no.A.
Fig. 11 - Typical globular macro-inclusions observed in the ultrasonically
examined inclusion band in a microscope in CC Billet with cast no.B.
Fig. 12 - Size distribution of globular indications in the CC billet samples with cast
no.A and B.
Fig. 13 - Histogram of the different sizes of globular indications observed in
microscope in the CC billets with cast no A and B.
Fig. 14 - Typical globular non-metallic inclusion in cast no. B of size 192 urn.
Composition at location
1. SiO2=47.65%, CaO=1.27%, MnO=47.46%, S=0.69%, FeO=2.94%
2. SiO2=15.09o/O/ CaO=41.83%, MnO=14.88%, S=25.80%, FeO=2.31%
3. SiO2=48.77%, CaO=2.71%, MnO=46.80%, S=1.22%

Fig. 15- SEM/EDS of typical globular non-metallic inclusion in cast no. B of size
192 µm. At location 2.
Fig. 16- SEM/EDS of typical globular non-metallic inclusion in cast no. B of size
192 µm. At location 3.
Fig. 17- Typical globular non-metallic inclusion in cast no. A of size 334 µm.
Composition at location
1. SiO2=54.75%, CaO=3.84%, MnO=38.73%, FeO=2.68%
2. SiO2=57.23%, CaO=3.91%, MnO=36.85%, FeO=2.01%
Fig. 18- SEM/EDS of typical globular non-metallic inclusion in cast no. A of size
334 µm. At location 1.
Fig.19- SEM/EDS of typical globular non-metallic inclusion in cast no. A of size
334 µm. At location 2.
Fig.20- Ultrasonically measured inclusions/mm2 in Gate-5 and Gate-2 in cast no.
A and B in locations with inclusion band.
BRIEF DESCRIPTION OF PREFERRED EMBODIMENT OF THE
INVENTION
The steel billet material was taken from the soaked continuously cast billets at
1260°C in a reheating furnace. From fully soaked Cc billets, 20 mm thick

transverse cut slices of continuously cast steel billets of thermo-mechanically
treated (TMT) grade with cross section 130X130 mm were selected. The
chemical composition and casting details of these billets have been shown in
Table 1. these billet slices were ground with mirror finish to thickness 18 mm on
which ultrasonic measurements were conducted using an ultrasonic C-scan
image system as shown in Fig 1. The ultrasonically detected and measured
inclusion bands were cut for making samples microscopic observations.

The ultrasonic scanning using 5 MHz focused beam probe (with 38.1 mm focal
length in water) was done on the mirror finish face with incremental distances
AX = AY = 0.4mm. Water path for testing the sample was calculated using
relation:


Where,
Sw = Water Path,
Sf = Focal distance in water,
Sm = Sound path in test material,
Cw = Sound velocity in water,
Cm = Sound velocity in test material
The through thickness ultrasonic travel path in the sample is equally divided into
5 parts appearing as 5 different gates on the A scan computer display. Gate-1
includes the sample/water interface echo whereas Gate-5 includes the back wall
echo of the sample. The ultrasonic signals close to the entry surface appear in
the Gate-2 whereas those close to the back wall appear in the Gate-4. Gate-3
represents the central thickness part of the sample.
The A- scan signal plots in Gate-2 and Gate-5 on the C-Scan image have been
considered for the analysis of the inclusion band using an image analysis
software. The variations in back wall echo amplitudes in Gate-5 are shown as
different colours in the C-scan image as shown in Fig.2 and 3.
The inclusions were indicated as back scattered signal spots with specific
amplitudes in the Gate-2 and also as low amplitude spots in the Gate-5 as shown
in Fig.4 and 5. Using the image analysis software the concentration of the
inclusions i.e nos./area can also be measured.

The inclusion band includes low back wall echo amplitude zone due to high
ultrasonic scattering losses from the non-metallic inclusions. These zones have
been clearly identified as shown in Fig.6 and 7 in which the images were formed
from the variation in the amplitudes of Gate-5.
The Presence of macro-inclusion in the inclusion bands in two different heats A
and B revealed on the polished sample cut from such locations and observed
under microscope as shown in Fig. 8 and 9. Fig. 10 and 11 show the absence of
cast columnar coarse dendritic structure in the fully homogenized samples which
avoids the high microstructural noise and favours good transmission of
ultrasound in the steel medium.
Fig. 12 and 13 show typical distribution of the macro-inclusion in the
ultrasonically examined sample from two different heats A and B. Fig.14 - 19
show SEM/EDS analysis present in the inclusion bands. Si,Mn,Ca and S speaks
were observed in the EDS spectrums.

WE CLAIM
1. A method to detect, measure and analyze inclusion bands in continuously
cast steel billets using ultrasonic Immersion C-scan image analysis
comprising:-
- a heat treated (1260°C) sample of size 130 mm X 130 mm X 18
mm having mirror finished surface taken out from the billet of
continuous casting;
- the said sample is immersed in liquid medium;
- conducting ultrasonic testing by using 5 MGZ focused beam probe
and a multi Scan Computerized immersion system with an image
analysis software;
- characterized in that,
- Concentration of inclusion in inclusion band is measured by the
variation in back wall echo characteristic from the front surface and
rear surface of the immersed sample and
- conducting SEM/EDS analysis of macro inclusion present in the
inclusion bands of the said sample to find out the presence of Si,
Mn, Ca and S from the peaks of EDS spectrums.

2. The method as claimed in claim 1 where in mirror finish surface of the
sample is made by grinding or fine polishing.
3. The method as claimed in claim 1 wherein the sample is immersed in
water.
4. The method as claimed in claim 1 wherein the through thickness
ultrasonic travel path in the sample is equally divided into 5 parts to
locate inclusion band.
5. The apparatus engaged in performing the method as claimed in claim 1
comprising :-

- an ultrasonic "C" scan image Analysiser having at least one multi
axis (X,Y and Z) scanner.
- at least one computer display of "A" scan signals and "C" scan
colour image.
- at least one pulse receiver.

- at least one optical Microscope.
- at least one Electron Scanning Microscope.
6. The method to detect, measure and analyze inclusion bands in continuous
cast steel billets using ultrasonic immersion C-scan images analysis as
substantially illustrated and describe herewith along with accompanying
drawings.

ABSTRACT

A NOVEL METHOD TO DETECT, MEASURE AND ANALYZE INCLUSION
BANDS IN CONTINUOUSLY CAST STEEL BILLETS USING ULTRASONIC
C-SCAN IMAGE ANALYSIS
A novel method is disclosed to detect, measure and analyze inclusion bands in
continuous cast steel billets using immersion C-scan image analysis. This method
comprises a heat treated (1260°C) sample of size 130 mm X 130 mm X 18 mm
having mirror finished surface taken out from the billet of continuous casting and
the sample is immersed in liquid medium when ultrasonic testing is conducted by
using 5 MGZ focused beam probe and a multi scam computerized immersion
system with an image analysis software when it reveals the inclusion band and
concentration are measured from inclusion band by the variation in back wall
echo characteristic from the front surface and rear surface of the immersed
sample and scanning electron microscope (SEM) / energy dispersive X-ray
detector (EDS) analysis of macro inclusion present in the inclusion bands are
conducted of the said sample to find out the presence of Si, Mn, Ca and S from
the peaks of EDS spectrums.