Cardset

1. cold dri

   1. also called sponge iron, is the direct product of the Midrex. It preserves the shape of the iron ore but because it has been reduced it is very porous (from there its name). It is also easily oxidized and corroded, therefore it is not safe to transport since when it is stored the heat generated by the oxidation, if in contact with moisture, could cause an explosion

2. hbi : briquettes

   1. DRI that was compared right after reduction in order to reduce the porosity facilitate transportation and reduce reactivity. This iron cane

      safely stored and transported overseas.

3. hot dri

   1. DRI that is immediately transported to the EAF for steel production. This is done to preserve some of the heat and facilitate melting.

cold dri, hot dri, bricks > EAF

bricks > BF and BOF

scrap preheating uses hot gas to heat scrap in the bucket before charging

AD:

• no wet charge so no explosion

• reduced electrical consumption and increased productivity

• less pollution

DIS:

• need post combustion of co and co2

CONSTEELL

• continuous feeding of EAF by the scrap, pre-heated and conveyed through a conveyor moving in a pre-heating tunnel, in which the exhaust gas from EAF, flowing counter current of metallic charge is combusted by injected air.

1. for chemical and thermal homogenization

2. to favor the inclusions floation and removal from the bath

3. in increase the kinetics of the reactions at the slag metal interface

The removal of Sulfur is favored by low Oxygen levels and in the ladle deoxidation operations are carried out, which means that levels of Oxygen as low as 10 ppm can be achieved. If deoxidation is done with Aluminum, the content that remained in

equilibrium alongside CaO will aid desulfurization.

Stirring will also play a crucial role, specially if the process is done under high vacuum

levels. Both will favor the kinetics of the process.

MgO present in dolomite and lime (flux) is used to saturate the slag with MgO. Furnace refactories are made of MGo and the slag without MgO would be very corrosive to it.

by saturating the slag with Mgo its a simple way to reduce the dissoltion potential of the major lining compoent, reduce its wear, and thus prolong the life of the structure.

To counteract for the solidification contraction metal goes through inside of the mould.

If the taper would not exist, an air gap would form between the mould and the strand,

causing geometric defects such as rhomboidity, which could them lead to internal

cracking.

The production cost of a single cast piece is calculated considering the cost of materials, tools and equipment, and labor required for each step of the process,

For materials, it needs to be considered that some fraction of the initial input will go to waste, therefore the cost of material needs to account for not only the material that is in the piece at the end but the material that was input at the beginning of the process.

For tools, the total cost needs to be divided by the number of parts that can be produced using that/those tools.

For equipment, similar to tools, it needs to be considered how many pieces can be produced with the equipment but also the energy they consume needs to be accounted for.

For labor, the number of hours invested in the production of the piece needs to be considered.

The full analysis is done for each stage of the process and at the end the sum of the cost of all stages is summed to obtain the total cost.

they are difficult to prodcue since the critical straind depends on the steel composition , depth of ocsillation marks, and surface tension.

HSLA steels are very prone to surface crack formation

essential for the stability of countinous casting process

it is a synthetic slag used as a lubricant between the product and the mould, but also used to improve heat trasnfer between them, provide thermal insulation, protect from oxidation, and help trap imuprities and inclsuions.

improves the surface quality

1. Iron ore:

   1. in the form of lump, pellets and/or sinters. Usually about 90% of the charge is sinters because they are auto fluxing and have a better size distribution.

2. Fluxing agents:

   1. limestone and/or dolomite to form as slag with the silica coming from the iron ore.

3. coke

   • to deoxidize the iron ore and provide chemical energy for the process. As a replacement (total or partial) for coke, fuel oils and pulverized coal can be injected

     in the Tuyeres.

4. oxygen

   1. to control the temperature of the process

1. Shaft furnace:

   1. vessel where the reduction takes place. It has 4 main zones:

      1. the feed zone, Through the feed zone the charge enters the furnace and is preheated by the off gases

      2. the reduction zone, the reduction takes place

      3. the transition zone ransition zone natural gas is introduces to help cool down the DRI

      4. cooling zone. ; twhich is not always present, the DRI is cooled down to produce cold DRI.

2. Reformer:

   1. engine room where the reducing gas is produced. The top gas is mixed with natural gas and is converted in a mix of hydrogen and carbon monoxide by suing nickel on alumina foam as catalyzer.

3. Scrubber:

   1. it recovers the gas and cleans it before it is recirculated to the reformer.

the mould gives the shape of the product.

provide rapid and uniform cooling of the molten steel, promote the rapid and uniform growth of the billet shell, and form a billet shell with good quality.

The mould has two main roles: give the shape to the strand and help cool down the liquid so that a solidified skin can be formed before exiting the mould. The solidified shell needs to be thick enough to then bare the ferrostatic pressure exerted by the remaining liquid. Because of this, moulds are made of copper due to its thermal conductivity and have internal water cooling channels.

it describes the ability of the slab to remove sulpor and non metal inclusions from steel

Eutectic alloys or alloys with a close to eutectic composition have a higher fluidity than

other alloys because:

- Their solidification range is smaller

- They have a lower melting temperature therefore at a given temperature, eutectic

alloys will have a higher superheat in comparison to non-eutectic alloys and thus will

have a higher fluidity.

The formation of bubbles is favored by solute enrichment in the interdendritic liquid,

which in turn favors the nucleation of molecular Nitrogen, Hydrogen and Oxygen that

reacts with carbon to form carbon monoxide. Bubbles are formed when the total

pressure in the bath reaches the external pressure, which is usually considered as 1

atm.

EMS is electromagnetic stirring where SEMS is electromagnetic stirrying below the mould.

The stirring movement breaks the birrtle dendrites tips and thus encourages the transition to centre equaxial soldidification

it can help improve internal cracks, columnor structure, centre line segreagtion, and centre prosotity

homogenizes the liq and reduces the indendritic segregation

the circular motion causes a more constant shell thickness and reudces thermal deformations

1. Charging and melting

- the metallic charge and the fluxing agents are placed on the furnace. Usually the

total charge is divided into different charging steps due to volumetric limitations of

the furnace. Usually 2 to 3 baskets are required for a batch, and the following

basket is dumped once the previous one is completely melted.

- When starting melting, the arc should be short to avoid excessive damage on the

vessel and the cover due to thermal charge and as the charge melts the arc length

is increased for a better distribution of the heat.

1. Refining and heating

- Refining refers to removing impurities, mainly Sulfur at this stage, and making

additions. However, the EAF is not used for this purpose anymore and refining is

usually done in the ladle.

1. Sampling

- A small sample of the liquid is extracted via the working door to confirm

temperature and composition. If either one of those is not right, adjustments are

made.

1. slagging off and tapping

The furnace is tilted backwards and the steel is poured in the ladle and slag is

poured in the slag pots. The turbulence induced by the pouring alongside a noncontrolled

atmosphere is usually the cause of gas absorption that needs to

eventually be removed by degassing operations.

The usual temperature in which the Furnace of the Midrex plant is operated is between

800 and 900°C, and usually 800°C while the production of the gas in the reformer takes

place at around 1000°C.

- Oscillation marks are produced when there’s a protective slag in the mould, thus the interaction of the protective slag and the metal may produce a slag rim in the corners the piece, leaving a metal gap. As the piece goes down, liquid coming from above will

fill the gap but it will form again, forming the oscillation marks.

- The spacing between the marks is related to the oscillation rate of the oscillation system of the tundish.

- These can be critical if they act as nucleation site for cracks because they may favor the formation of transversal cracks.

Factors

- Type and magnitude of the current

- Time the current is on

- Diameter of the electrode

- Length of the arc

Electrode wear

- Tip sublimation

- Erosion of the tip due to AC

- Corrosion of the tip due to the contact with the slag and the liquid steel.

- Sidewall oxidation

- Tip breakage due to thermal stresses

- Electrode breakage due to the excessive mechanical stress