Metallurgy
ELHACHMI ESSADIQI , UIR
4th of Aerospace Engineering
2021/2022
CONTINUOUS
CASTING OF STEEL
Continuous Casting of Steel
• Introduction to the continuous casting of steel
• Continuous casting plant components
• Continuous casting operations
• Continuous casting metallurgy
• Cleanliness of liquid steel
• Solidification during CC
• Heat transfer
• Structure
• Segregation
• Product quality
• Mechanical properties
• Hot ductility and crack formation in the continuous casting of
steels
• Special processes :
• Thin slab casting
• Strip casting
Historical Developments of Continuous
Steel Casting
• Production of steel :
• 1963 – 73 : increasing rate about 30Mt/year
• 80’s : 700 Mt/year
• 2001 - 847 Mt/year
Continuous Casting
• Growth of CC at the expense of Ingot
• Introduced as a significant production process in the
early 1960’s
• Major advantages of continuous casting
• Increase in yield
• Reduced production cost
• Energy savings by elimination of soaking pits and
slabbing mill
• Possibility of direct charging or direct rolling
Historical development of Continuous
Casting
• 1840 : S.E. Sellers was the first to gain a patent
on a device for the CC of lead tubing
• 1843: J. Lang CC of lead tubing.
• 1846: H. Bessemer invented twin roll casting
covered by an English patent
• 1856: Bessemer applied twin roll casting to
malleable iron . The patent was granted
• 1887: R. M. Daelen : submit the first patent for
CC machine with an open-ended mould
Historical development of Continuous
Casting
• 1952
• The first production plant (single strand machine) for
small steel billets was put into operation at Barrow (GB).
Carbon steel was cast into billets of 50 to 100 mm and
stainless steel
• 1954, 1958 and 1960
• Commissioning of the 1st multi-strand caster in FRG, Italy
and France
• 1961
• Experiments with casting flux covering the mould in FRG
and France
• Mid 1964
• Introduction of automatic stopper control in Great Britain
Historical development of Continuous
Casting
• 1965
• Casting with submerged nozzle and casting flux in
France
• 1966
• First use of tubular shrouds to protect the ladle pouring
stream
• April 1968
• First technical paper published on sequence casting
Comparison of Continuous Casting
Yield with Ingot Casting Yield
Average Yield 1975 Continuous casting Ingot Casting
% %
Billet 95.57 81.29
Blooms 95.87 82.93
Slabs 94.74 84.45
Average 95.01 83.45
Process Stages in Ingot Casting and
Continuous Casting
Ingot Casting
Blooming/ Finish-rolled
Molten Casting Soaking Scarfing Inspection Reheating Finishing
Slabbing product
steel machine mill
mill
Continuous Casting
Continuously cast
slab/bloom/billet
Molten Finishing Finish-rolled
Casting Inspection Reheating
mill product
steel
Ingot Casting Production
• Size of steel pieces that can not be produced by
continuous casting – ( as-cast or as-forged)
• Nuclear Industry
• Mechanical industry
• Mould materials for plastics
• Thicker plates of 150 tons
• Super alloys, alloyed steels and tool steels
Ingot Casting Production
• 0.3% of total steel is produced by Ingot
• Continuous cast steel price ( rolled)
• 300 – 400 $/ton
• Forged ingot :
• Up to 3,000 $/t
Process Various types of stream-lining practice
Converter
Molten steel
Ingot casting
Ingot
Soaking furnace
Slab caster
Slabbing mill
Slab CC - HCR
Slab conditioning
Reheating furnace CC - HDR
Rougher mill
Thin slab caster
Sheet bar
Finisher mill
Hot strip product Strip Caster
Cold rolling
Thin strip caster
Cold strip product
Processing times Vs Technology Change
Definition of Billets Blooms and Slabs
• Billet refers to cross sections with a side
dimension of < approx. 150 mm
• Blooms refers to cross sections with a side
dimension > 150 mm and a thickness-to-width
ratio of < 1:1.3.
• Slabs are cross sections with a thickness >
100 mm and a thickness-to-width ratio of >
1:1.3
• Round strands are classified as either billets or
blooms depending on their diameter
Continuous Casting Components
17
Pouring shrouds from ladle to tundish to
mold. Source: Ref 12
Slide Gate
19
The Hazelett machine for continuous
casting of copper anode strip.
Ref: R.W. Hazelett and C.E. Schwartz,
"Continuous Casting Between Moving Flexible
Belts," Paper presented at the AIME Annual
Meeting, American Institute of Mining,
Metallurgical, and Petroleum Engineers, 1964
Mould Oscillation
Electromagnetic stirring
Spray systems for Secondary Cooling
Principle Types of Continuous Casting
Tundish and Mould for Horizontal Caster
25
Nonferrous Continuous Casting
Direct-Chill Casting
Twin Roll casting
TWIN ROLL CASTER at CANMET
TRC at CANMET – Magnesium Strip
casting
Setback – TRC
Microstructure of AZ31 (TRC)-Longitudinal
RD
Top to bottom
Casting direction
SDAS distribution
Longitudinal Direction Transverse Direction
12
10
Top to the centre
8
SDAS (μm)
0 Casting direction
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Distance from the top
(μm)
SDAS VS cooling rate
Relationship between SDAS
and cooling rate for cast
aluminum
SDAS VS cooling rate
The relation between SDAS
and cooling rate nickel-based
superalloy.
Microstructure of Hot rolled and annealed AZ31 Mg Sheet
Optical micrograph of AZ31 TRC strip after rolling and annealed
for two minute at 450°C
38
Imperfections in Solids
• What are the solidification mechanisms?
• What types of defects arise in solids?
• Can the number and type of defects be varied
and controlled?
• How do defects affect material properties?
• Are defects undesirable?
39
Imperfections in Solids
• Solidification- result of casting of molten material
• 2 steps
• Nuclei form
• Nuclei grow to form crystals – grain structure
• Start with a molten material – all liquid
nuclei crystals growing grain structure
liquid Adapted from Fig. 4.14(b), Callister & Rethwisch 8e.
• Crystals grow until they meet each other
40
Polycrystalline Materials
Grain Boundaries
• regions between crystals
• transition from lattice of one
region to that of the other
• slightly disordered
• low density in grain
boundaries
• high mobility
• high diffusivity
• high chemical reactivity
Adapted from Fig. 4.7,
Callister & Rethwisch 8e.
41
Solidification
Grains can be - equiaxed (roughly same size in all directions)
- columnar (elongated grains)
~ 8 cm
heat
flow
Shell of
Columnar in equiaxed grains
area with less due to rapid
undercooling cooling (greater
Adapted from Fig. 5.17, T) near wall
Callister & Rethwisch 3e.
Grain Refiner - added to make smaller, more uniform, equiaxed grains.
