Lecture 26 Deg assing Practice
Cont ents:
Degassing processes
Ladle degassing
Stream degass ing
Recirculation de gassin g
Key words: dega ssing, hydrog en and nitrogen in steel, ladle degassing, reci rculat ion degass ing
Degassing processes
There are 3 methods of degassing which are in practice
i) Lad le degassing
ii) Stream de gassing
iii) Circulation degass ing
All these processes are carried out in ladles.
Ladle degass ing
Ladle containing molten steel is placed in a cha mber which is then evacuated. After a det ermine d time
ladle is remove d from the cha mber a nd is teem ed for casting. Figure 26.1 shows ladl e degassing unit.
Fig ure 26 .1 Arr angeme nt of ladle w ith porou s plug a nd hopper for d egassing
Ladle is provided with a porous plug at its bottom to purge argon gas as shown in the figure. In a v acuum
cham ber th e ladle is placed. The vacuum chamb er is equi pped with a hopper so as to make ad dition s of
elem ents as a nd when it is nee ded. For effective degassing of fully killed steel, it is necessary to purge
argo n thro ugh the bottom of the ladle. Stirring the b ath enh ances rate of gas removal. Vigorous removal
of gases causes metal splashi ng too. Therefore ladle is not fille d compl etely and abo ut 25% of its height
is kept as freeboar d to ac commodate the splashed met al dro p l et s . P ressure is maintained in betwe en
1mm Hg t o 10 mm Hg fo r effective degassi ng. During de gassing additions a re made for deoxidatio n and
alloying. In certain cases ladle is heated to compensate for the loss of heat during degassing. F o r t h e
effectiveness of degassing , it is necessary that carry-over slag either from BOF or EAF should be as low
as possible. Carry-over slag contains Fe O and since oxygen content o f steel is in eq uilibrium with FeO
content of slag, oxygen content of steel increases.
Stir ring gas is intro duced either from top through the r oof by a subm erged refract ory tube or through
the porous plug fitted at the botto m of the ladle.
Docsity.com
