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04 Mar 2014
INFLUENCE OF ARGON GAS WITH NONMETALLIC INCLUSION IN STEEL MELTING |
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The injection of argon gas into the molten metal especially in steel will influence to the cleanliness and better mechanical properties. The biggest cause of the decreasing in steel quality is nonmetallic inclusions and entrapment of the gases. The nonmetallic inclusions are formed mostly in the liquid steel during the deoxidation phase in a furnace or ladle, when these particles are not captured by the slag, they are found in solidified steel, deteriorate its mechanical properties as well as the entrapment of gases in which will create the pinhole defect in the steel casting. The injection of inert gases into molten metal is a procedure that is usually done to make the metal’s composition and temperature uniform over the volume of the induction furnace and to remove nonmetallic inclusions and dissolved of gas and impurities. Nonmetallic particles that are poorly wetted by the melt may be captured by the surface of gas bubbles and rise along with the bubbles to the free surface. Solid inclusions of alumina and silicon that are poorly wetted by liquid steel can be affectively removed together with gas bubbles. The rate of removal of nonmetallic inclusions of different sizes from a melt is significantly influenced their flotation by bubbles of the inert gas.
The experiment was conducted by the university in Slovakia on the injection of the argon gas through Gas Diffuser in the one tone capacity induction furnace in order to find the relationship between volume of argon gas and reduction of the nonmetallic inclusion. The melting time in the induction furnace is 45 minute, then samples were collected in different conditions for metallographic analysis.
| Sample No. |
Period of melt
|
Area fraction of the NI, % |
Ar flow rate, l/min |
Duration of Ar blowing, min.. |
Volume of Ar blowing, l |
| A0 |
after melting down of steel |
0.19 |
- |
- |
- |
| A5 |
5 minutes after melting down |
0.44 |
- |
- |
- |
| A7 |
7 minutes after melting down |
0.37 |
- |
- |
- |
| AL |
from the ladle |
0.23 |
- |
- |
- |
| B0 |
after melting down |
0.19 |
- |
- |
- |
| BE |
end of the melt |
0.24 |
6 |
2 |
12 |
| C0 |
after melting down |
0.21 |
- |
- |
- |
| CE |
end of the melt |
0.47 |
10 |
2 |
20 |
| D0 |
after melting down |
0.20 |
- |
- |
- |
| DE |
end of the melt |
0.43 |
10 |
4 |
40 |
| E0 |
after melting down |
0.19 |
- |
- |
- |
| EE |
end of the melt |
0.31 |
10 |
6 |
60 |
| F0 |
after melting down |
0.18 |
- |
- |
- |
| FE |
end of the melt |
0.15 |
10 |
8 |
80 |
| G0 |
after melting down |
0.16 |
- |
- |
- |
| GE |
end of the melt |
0.14 |
10 |
10 |
100 |
| H0 |
after melting down |
0.19 |
- |
- |
0 |
| HE |
end of the melt |
0.12 |
10 |
10 |
100 |
| J0 |
after melting down |
0.13 |
- |
- |
- |
| J2 |
2 minutes after melting down |
0.25 |
4 |
2 |
8 |
| J4 |
4 minutes after melting down |
0.65 |
4 |
4 |
16 |
| J6 |
6 minutes after melting down |
0.21 |
10 |
6 |
36 |
| J8 |
end of the melt |
0.18 |
10 |
8 |
56 |
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The sample A were taken without purging the argon gas in different time interval, samples B-H were taken before and after purging the argon gas. The sample J were taken in different purging time interval as well as different volume of argon gas.
The following table shows the comparison between sample A vs. sample J. In the both cases after 4th and 5th minute after melting down the content of nonmetallic inclusions has increased very expressively. It is caused of metallurgical processes in the molten metal. After then the content of non-metallic inclusions fell down. At the end of melt without argon blowing the content of nonmetallic inclusions increased about 17.3% and with argon blowing (argon was blowing for 8 minutes and volume of argon was 56 litters) the content of non-metallic inclusions dropped about 5.5%. Duration of argon blowing has a very important role for content of non-metallic inclusions.
The result from sample B – E in which purging argon gas between 2-6 minute together with different volume of gas flow (12-60 l) in comparable to the result from sample G & H in which purging time in 10 minute and volume of gas is 100 litre. The nonmetallic inclusion in the table shows that the sample G & H is less in which derived from the optimum of purging time and volume of gas.
A curve on the Fig.3 was created from samples A0, CE, DE, EE, FE and HE. All samples were taken from the melts with flow rate of argon 10 l per minute. The curve shows that in the minute of 2th – 4th the inclusion raise up in which caused from the reaction of the argon bubble but after purging longer for 10 minute the nonmetallic inclusion had already taken out by argon gas and drop down drastically
CONCLUSION The first period of melting, the content of nonmetallic inclusions has increased, after then the content of nonmetallic inclusions has dropped very clearly after purging the argon gas. Duration of argon blowing into the steel has had a very significant influence on the final content of non-metallic inclusions. A short time of argon blowing or small volume of can cause that final content of inclusions can be higher than on the beginning of melting in which because of the bubble gas need time for reaction. Minimum time of argon blowing necessary for reducing of content of non-metallic inclusion in one tonne electric induction furnace was 7 minutes and recommended argon flow rate is 10 litters per minute.
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