Desoxidacion Acero Liquido

5

©2001 CRC Press LLC

Deoxidation of Liquid Steel

Steelmaking is a process of selective oxidation of impurities in molten iron. During this, however,

the molten steel also dissolves some oxygen. Solubility of oxygen in solid steel is negligibly small.

Therefore, during solidification of steel in ingot or continuous casting, the excess oxygen is rejected

by the solidifying metal. This excess oxygen causes defects such as blowholes and nonmetallic

inclusions in castings. It also has significant influence on the structure of the cast metal.

Therefore, it is necessary to control the oxygen content in molten steel before it is teemed.

Actually, the oxygen content of the bath in the furnace is high, and it is necessary to bring it down

by carrying out deoxidation after primary steelmaking and before teeming the molten metal into

an ingot or continuous casting mold. This chapter is concerned with thermodynamics and kinetics

of deoxidation, and finally on industrial deoxidation.

5.1 THERMODYNAMICS OF DEOXIDATION OF MOLTEN STEEL

The dissolution of oxygen in molten steel may be represented by the equation

(5.1)

where [O] denotes oxygen dissolved in the metal as atomic oxygen. For the above reaction,

(5.2)

where KO is equilibrium constant for Reaction (5.1), denotes partial pressure of oxygen in the

gas phase in atmosphere, and hO is the activity of dissolved oxygen in liquid steel with reference

to the 1 wt.% standard state. KO is related to temperature as1

(5.3)

Again,

(5.4)

where WO denotes the concentration of dissolved oxygen in weight percent, and fO is the activity

coefficient of dissolved oxygen in steel in 1 wt.% standard state. In pure liquid iron,

1

2

--O2(g) = [O]

KO

hO

pO2

1 ⁄ 2 ---------

 

 

 

equilibrium

=

pO2

logKO

6120

T

= ----------- + 0.15

hO = [ f O][WO]

...