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Simple diagram of the processing steps that are followed to produce continuously cast steel. Ingot casting is still used for
low volume specialized applications. Electric furnaces are extensively used in place of the BOF. They can run with as
little as 0% molten steel. This eliminates the expense of operating the supply stream of the Blast furnace. The burden of
securing scrap and paying for electricity is added when using a EAF.
low volume specialized applications. Electric furnaces are extensively used in place of the BOF. They can run with as
little as 0% molten steel. This eliminates the expense of operating the supply stream of the Blast furnace. The burden of
securing scrap and paying for electricity is added when using a EAF.
Oxygen – Lime/Flux – Scrap Coal – Limestone – Iron ore
BOF – Basic Oxygen Furnace Coke oven – Crusher – Sinter – Pelletizer
EAF – Electric Arc Furnace
Coal provides the power to produce the molten steel. Virgin ore reduction allows a better control of metal
chemistry. There is a build up of tramp elements that can not be removed during remelting in an EAF.
chemistry. There is a build up of tramp elements that can not be removed during remelting in an EAF.
Speed, is the biggest benefit. The rapid turn around time is typically 30 minutes tap to tap. A normal charge
is 30% scrap and 70% molten pig iron. The molten charge is stirred by the flow of Oxygen from the lance.
Argon / Nitrogen is added to help mix the liquid metal and drive the refining reactions to completion.
is 30% scrap and 70% molten pig iron. The molten charge is stirred by the flow of Oxygen from the lance.
Argon / Nitrogen is added to help mix the liquid metal and drive the refining reactions to completion.
The major elements found in the BOF charged scrap or liquid pig iron are C – Carbon, Mn – Manganese, P –
Phosphorous, S – Sulfur, and Si – Silicon. The C serves as a fuel source to drive the reactions needed to refine the
metal composition. Waste products are typically complex oxides, sulfides, and silicates. They are absorbed into the
slag and taken out of solution.
Phosphorous, S – Sulfur, and Si – Silicon. The C serves as a fuel source to drive the reactions needed to refine the
metal composition. Waste products are typically complex oxides, sulfides, and silicates. They are absorbed into the
slag and taken out of solution.
Two furnace types used to refine steel.
Continued steel treatment is carried out in the transfer ladle. The treatment could be as simple as
re-heating or as complex as refining and detailed alloy additions to make the targeted grade.
re-heating or as complex as refining and detailed alloy additions to make the targeted grade.
Over view of a Cast house. This method is used world wide.
Entry end of a caster.
Detail of the entry end of a caster.
Flow diagram of coil production.
The additional heat costs money. Saving these dollars feed the development of production units that
feed hot slabs directly from the caster into the hot roll furnaces.
feed hot slabs directly from the caster into the hot roll furnaces.
This simple application of water defines the strip properties. Steels under go an internal structural
transformation that is defined by the rate of quenching.
transformation that is defined by the rate of quenching.
Wet and dry looping pits are not the latest design. Accumulating towers are the norm today. A temper mill in
line would produce the best quality. Do not confuse the scale breaker for a temper mill.
line would produce the best quality. Do not confuse the scale breaker for a temper mill.
Single stand reversing mills, two, three, four, five, and as many as six tandem reduction stands are in
use today. Thinner gages and flatter strip can be produced with larger numbers of reduction stands.
use today. Thinner gages and flatter strip can be produced with larger numbers of reduction stands.
Single stack, multiple stack (as shown), and continuous anneal lines are all in operation. The volume of
similar material produced would determine which method was used. A protective atmosphere is introduced
inside the can shaped covers to protect the steel during heating. HNX gas (nitrogen with 3% to 15%
hydrogen) or 100% hydrogen atmospheres are typically used.
similar material produced would determine which method was used. A protective atmosphere is introduced
inside the can shaped covers to protect the steel during heating. HNX gas (nitrogen with 3% to 15%
hydrogen) or 100% hydrogen atmospheres are typically used.
Small diameter work rolls are needed to process thinner or stronger materials (tin plate or stainless
steel). Four high rolling mills use a large diameter stiffening backup roll to the support the small
diameter work roll. Shape correction is also possible if the mill has hydraulic jacks that can flex or
bend the work rolls during rolling.
steel). Four high rolling mills use a large diameter stiffening backup roll to the support the small
diameter work roll. Shape correction is also possible if the mill has hydraulic jacks that can flex or
bend the work rolls during rolling.
Corrosion protection, heat resistance, or cosmetic function drives the need to process the steel through
subsequent operations. Continuous coating with: zinc, aluminum, zinc-aluminum, zinc-nickel, Galfan, tin, chromium,
paint, or some combination of several of these materials. A batch – post coating can also be called into action. In
each case the original triad of corrosion protection, heat resistance, or cosmetic function drives the steps selected.
subsequent operations. Continuous coating with: zinc, aluminum, zinc-aluminum, zinc-nickel, Galfan, tin, chromium,
paint, or some combination of several of these materials. A batch – post coating can also be called into action. In
each case the original triad of corrosion protection, heat resistance, or cosmetic function drives the steps selected.
Generic continuous coating shape.
Summary of the types of mills producing steel
An integrated mill (IM) with these four types of equipment has an easy time producing any
composition in any quantity : Blast furnace (BF)-smelting, Basic Oxygen furnace (BOF)-refining,
Electric furnace (EF)-refining, and Continuous Caster (CC)-production.
composition in any quantity : Blast furnace (BF)-smelting, Basic Oxygen furnace (BOF)-refining,
Electric furnace (EF)-refining, and Continuous Caster (CC)-production.
A mimi mill (MM) with these two types of equipment has a harder time producing any composition in
any quantity : Electric furnace (EF)-refining and Continuous Caster (CC)-production. The issue of
quantities is the availability of high quality scrap to feed the refining process.
any quantity : Electric furnace (EF)-refining and Continuous Caster (CC)-production. The issue of
quantities is the availability of high quality scrap to feed the refining process.
The smelting capabilities of a BF provides a steady supply of feed stock that is mixed with the scrap
stream on hand. The issue of composition is the limitation of refining in an EF. The heating mechanism in
a BOF is the released heats of reaction when Oxygen is blown at the molten metal. This is the driving
force to complete the refining process. The blown Oxygen of the BOF process drives these reactions :
decarburization, dephosphorization, desulfurization, and desiliconization. An EF uses the heating action
of an electric arc placed across the metal in the furnace. Additional refining must be completed by using
an Oxygen stream similar to the BOF process. Or adding slags to drive reactions to completion. Some
reactions, like the reduction of Nitrogen in the steel, could not be simulated by the EF procedures.
stream on hand. The issue of composition is the limitation of refining in an EF. The heating mechanism in
a BOF is the released heats of reaction when Oxygen is blown at the molten metal. This is the driving
force to complete the refining process. The blown Oxygen of the BOF process drives these reactions :
decarburization, dephosphorization, desulfurization, and desiliconization. An EF uses the heating action
of an electric arc placed across the metal in the furnace. Additional refining must be completed by using
an Oxygen stream similar to the BOF process. Or adding slags to drive reactions to completion. Some
reactions, like the reduction of Nitrogen in the steel, could not be simulated by the EF procedures.
MM product was characterized by the high levels of Nitrogen found in the metal because an EF can not
remove Nitrogen. This summary was correct until the demand for low residual compositions exceeded
the capabilities of most IM s. To answer that demand two more types of equipment were added :
Hotmetal Treatment (HT)-ladle refining of the material coming from the BF and Secondary Ladle
Treatment (SMT)-ladle refining and degassing of the metal coming from the BOF or EF. Most MM s
added the Secondary ladle Treatment (SMT)-ladle refining and degassing of the metal coming from the
EF. Now the range of compositions from IM s and MM s were the same. The residual and trace tramp
element levels were the same.
remove Nitrogen. This summary was correct until the demand for low residual compositions exceeded
the capabilities of most IM s. To answer that demand two more types of equipment were added :
Hotmetal Treatment (HT)-ladle refining of the material coming from the BF and Secondary Ladle
Treatment (SMT)-ladle refining and degassing of the metal coming from the BOF or EF. Most MM s
added the Secondary ladle Treatment (SMT)-ladle refining and degassing of the metal coming from the
EF. Now the range of compositions from IM s and MM s were the same. The residual and trace tramp
element levels were the same.
| Kieh Co. Metallurgical Savants |