important for steel making

1. Soumyabrata Basak-14MS06005
James Mathew -14MS06006

2. Continuous casting of steel is entering a new era of
development, not only with respect to its increasing
application in the production process, but also in its
own evolution as a process and its interaction with
other processes in steel manufacture. Continuous
casting output has shown an accelerating growth
curve. More than 50% of current world steel
production is continuously cast, and continuous
casting in Japan exceeds 80%.

3.  The purpose of continuous casting is to bypass conventional
ingot casting and to cast to a form that is directly rollable on
finishing mills. The use of this process should result in
improvement in yield, surface condition, and internal quality of
product when compared to ingot-made material.
 Continuous casting involves the following sequence of
operations:
1. Delivery of liquid metal to the casting strand
2. Flow of metal through a distributor into the casting mold.
3. Formation of the cast section in a water-cooled copper mold.
4. Continuous withdrawal of the casting from the mold.
5. Further heat removal to solidify the liquid core from the casting
by water spraying beyond the mold.
6. Cutting to length and removing the cast sections.
22-08-2014 3

4. The defect can be defined as any deviation from the
appearance, form, size, macrostructure or chemical properties
provided in the technical standards or other normative
documents in force.
Defects are detected at the billets reception, by
checking their surface quality on the inspection beds, or by
checking the macrostructure of the test samples.
A defect is not always the result of a single case.
Often, the defect is the result of multiple interacting causes,
depending on a variable number of parameters.
Defects in continuous casting originate from several
factors like mould oscillation, mould flux, segregation coefficient
of solute elements; phase transformation etc.
22-08-2014 4

5. DEFECTS
INTERNAL SURFACE SHAPE
• Midway cracks
• Triple point cracks
• Center line cracks
• Diagonal cracks
• Centre segregation
and porosity
• Casting flux
inclusion
• Blow holes
• Pipes
• Longitudinal mid
face cracks
• Transverse mid face
cracks.
• Star cracks
• Longitudinal
depression
• Transverse
depression
• Rhomboidity
22-08-2014 5

6.  Cracks are originated in the cast product due to
mechanical and thermal stresses
 Mechanical stresses are created by friction, ferro static
pressure, roll pressure , bending and straightening
operation.
It can be reduced by improving control of powder
feed rate, resonance in mold, more accurate
guidance..
 Thermal stresses are created by non-uniform cooling
in secondary zone
It can be controlled by Controlling water flux
impinging the surface of the strand and minimizing
reheating of strand, also air & water mist spray
provides more uniform cooling.
22-08-2014 6

7.  Blowholes are cavities in the outer surface or in the
subsurface zone of the billet , caused by
o Insufficient deoxidation (presence of gases:-hydrogen,
nitrogen, oxygen);
o Humidity of the casting powder.
 Non-metallic inclusions arise because of many
physical-chemical effects that occur in molten and
consolidated metal during production.
 Segregation refers to non-uniformity of chemical
composition. A high degree of positive segregation in
the central region is known as centreline segregation.
 As a result of segregation liquid is not able to flow
freely and compensate for shrinkage, results in porosity
 Pipes are shrinkage cavity formed during solidification
of fully deoxidized steel.These are normally open.
22-08-2014 7

8. Blow holes Triple point cracks
Midway Cracks Inclusio
n
Centre segregation
22-08-2014 8

9.  The unevenly removal of the heat in the mould and,
therefore, the uneven increase of the strand crust,
causing transverse tensions that lead to the strand
cracking if the crust is not strong enough (uneven
primary cooling);
 Turbulent flow of metal and a meniscus level variation
in the mould;
 Secondary cooling too intense or uneven;
 Unequal, advanced wear of the mould that leads to a
different thermal conductivity coefficient;
 High casting temperature
22-08-2014 9

10. Transverse cracks Longitudinal cracks
Star cracks 22-08-2014 10

11.  Transverse depressions are due to much larger
contractions occurred during solidification.
 Longitudinal depressions are due to uneven heat
transfer in the mould which caused due to-
o The steel level fluctuation in the mould.
o The uneven and advanced wear of the mould.
 Billet Rhomboidity (difference in opposite diagonals)
starts with non-uniform shell solidification in the mould
which is due to inconsistent mould cooling causing
irregular heat transfer.
22-08-2014 11

12. Transverse depression
Longitudinal depression
Rhomboidity 22-08-2014 12

13.  ASM Handbook vol 15
 Wikipedia
 Defect in steel by Octa Journal
 www.aws.org_itrends_2004_07_it0704-33
22-08-2014 13

14. 22-08-2014 14