process variations in esr

7/28/2019 Process Variations in ESR

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Pranesh Rao K M

12PM07F


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Introducion

Electro slag Remelting is a Secondary steel refining

process

ESR products are well known for limited content of

undesirable elements such as Sulphur, Oxygen,Nitrogen, etc

But in order to meet customized product compositions

three process variations in ESR are developed

Pressurized ESR

Vacuum ESR

Inert gas atmosphere ESR


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ESR process

Electric current is passed between the

electrode(raw matarial) and a water-

cooled base-plate as shown in figure

Due to resistance offered by slag for

flow of current temperature of slagraises above melting point of metal

Hence molten metal droplets fall from

the tip of metal electrode to metallic

pool through slag bathWhen drop passes through slag it loses

its content of inclusions and

undesirable elements such as Sulphur,

Oxygen, Nitrogen, etc.

Refined metal solidifies on base plate


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Need for Pressurized ESR

Nitrogen has become increasingly attractive as an inexpensive

alloying element for enhancing the properties of steel

In austenitic steel, Nitrogen increases yield strength by forming a

super-saturated solid solution

Hence it is essential that a sufficiently high amount of nitrogen i.e.

above the solubility limit under normal pressure is introduced into the

molten steel

Also nitrogen loss is to be prevented during solidification

ESR process is carried at atmospheric pressure hence it is difficult to

achieve such high Nitrogen concentration


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Pressurized ESR

According to Sieverts law Solubility of a gas in asolution proportional to the square root of partial

pressure of gas

Since time of existence of molten metal droplet is for

very small ,Nitrogen pickup from gas phase is veryless

Solid Nitrogen-bearing additives are added to increase

nitrogen content of steel High pressure helps in retaining Nitrogen content of

Steel

Pressure level is decided by the required Nitrogen

content of alloy


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Vacuum ESR

Remelting is carried out under vacuum as in VAR, butslag is used

Problems of oxidation of the melt do not arise.

Dissolved gases such as Hydrogen and Nitrogen, canbe removed and the danger of white spots, as

encountered during VAR

Thus advantages of both ESR and VAR are combined

in one process.

This process is useful in Remelting of super alloys


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PESR furnace with stationary

mold

1 Ram drive system,

2 Electrode ram,

3 X-Y adjustment,

4 Load cell system,5 Sliding contact,

6 Pivoting drive,

7 Electrode,

8 Water jacket,

9 Base plate


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Need for inert gas atmosphere

ESR

Following problems are encountered in previous

process variations of ESR

Oxidation of electrodeHydrogen pickup

Oxidation loss of alloying elements(Ti ,Al ,Si)

These problems are attributed to the fact that ESR iscarried out in atmosphere of air(N,O,H)

Thus to overcome these problems atmospheric air is

replaced by inert gas maintained at atmospheric

pressure


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IESR

By using argon as the inert gas, pick-up of

nitrogen and hydrogen is avoided

By using nitrogen as the inert gas some pick-up

of nitrogen is possible

This process can be used for alloys containing

high amount of Al and Ti like super alloys

reason being prevention of oxidation


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IESR furnace

1 Electrode feed drive system

2 Ball screw

3 Pilotable furnace support gantry

4 Load cell system

5 Electrode ram

6 Electrode stub

7 Protective gas chamber

8 Slag pool

9 Ingot10 Mold assembly

11 High current contact assembly

12 Power cables

13 Ram guiding system


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Conclusions

ESR process which was previously used for obtaininglow S and N content in product can be now used to

process various alloys by implementing process

variation

ESR finds wide application in remelting of tool steel

,die steel ,ball bearing steel, because of process

variations in ESR

ESR which was considered to be economicallyunviable for desulphurization due to large quantity of

electricity consumption has regained importance due

to advent process variations


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Reference

Electro slag Remelting Processes and Furnaces by ALD

Vacuum Technologies


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Thank You

process variations in esr

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