Lutsenko Pavel Sergeyevich
Theme of master's work:
"Research
of technology factors that influence upon the nitrogen contents
in metal during steelmaking in EAF".
The research supervisor: Korzun E. L.
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The nitrogen concerns
to harmful impurity in steel. The large contents of nitrogen in
steel, which is made in electric arc furnaces (EAF), is
explained to that melting in EAF conducts at the large meanings of
temperatures (which both in open hearth furnaces, and in BOFs are
not reached) at the expense of use of heat of electrical arches.
Demand for steel recently has increased, in this connection the
capacity EAF, hence, has increased contents of nitrogen in steel
also has increased. Presently to steel the very rigid requirements
are showed, as it is one of the most important materials of a modern
industry. For this reason to removal of nitrogen from steel give a
lot of attention, forces and time. All it is made to improve
properties of steel.
At the given stage of
my master's work considered influence decarbonisation of steel upon
the
removal of nitrogen from metal. Speed of removal of nitrogen from
melt at first was theoretically designed by it mass transfer in gas
bubbles, which are formed as a result of oxidation of carbon
contained in metal. This account was carried out with the help of
the following equation:
,
(1)
where
-quantity
of the removed carbon (speed of decarbonisation), %/min;
-molecular
weight of carbon (=12), g/mole;
-
molecular weight of nitrogen
(=28),
g/mole;
-
pressure above metal, atm;
-
constant of balance of reaction of dissolution of nitrogen in liquid
metal;
-
the current contents of nitrogen in metal in one minute, %;
-
the initial contents of nitrogen in metal, %.
The
conditions, at which the given account was carried out, were the
following: temperature - 1600
оС;
pressure - 1 atm; the initial contents of nitrogen in metal - 0,01
%; speed of decarbonisation - from 0,01 up to 0,15 %/min.
The received results of calculations
are given in the table 1.
The table 1
- Results of theoretical calculations
VC,
%/min |
0,01 |
0,04 |
0,08 |
0,12 |
0,15 |
,
%/min |
1,09 |
3,28 |
4,93 |
5,94 |
6,46 |
Then the analysis of
the practical data was made which were taken on done melts in
electric steelmaking shops on the Moldavian Metallurgical Plant
(first half-year of 2000) and Byelorussian Metallurgical Plant
(July, 2000). On this practical data the changes of concentration of
carbon and nitrogen in metal, speed of removal of carbon and
nitrogen from melt were calculated. The graphic dependence of speed
denitrogation from speed of removal of carbon is represented in a
fig. 1.
Fig. 1 - Dependence of
speed of removal of nitrogen on change of speed of removal of carbon
Visually to observe, as
far as the theoretical accounts differ from the practical data, we
shall construct graphic dependences of speeds of removal of nitrogen
on change of speeds of removal of nitrogen of the fixed sizes and
results of theoretical calculations.
Fig. 2 - Dependence of
the decimal logarithm of speed of removal of nitrogen on speed of
removal of carbon
Having analysed results
of calculations and given figures it is possible to make the
following conclusions:
1. The
change of concentration of carbon does not render essential
influence on change of concentration of nitrogen;
2. The
change of speed of decarbonisation does not render essential
influence on changes of speed of denitrogation of metal;
3.
Theoretical given, designed proceeding from the equation (1) on the
order differ from practical.
It is possible to
explain a difference between theoretical and practical meanings by
influence on the contents of nitrogen in metal of other factors,
such for example, as: "pumping effect ", purge of melt by inert gas,
low contents of nitrogen in raw materials, higher temperature of
melting (in comparison with what took for theoretical accounts),
lower partial pressure of nitrogen in an environmental atmosphere
etc.
As the result can be told, that the removal of nitrogen from steel
with bubbles of oxid of carbon has shown low efficiency. But the
given divergence between the theoretical and practical data causes
of the further study of a question of efficiency of removal of
nitrogen by taking away it with bubbles of gas.
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