JPH024652B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method and apparatus for producing ultra-low sulfur, ultra-low oxygen clean steel by vacuum induction melting. [Prior art and its problems] Vacuum induction melting is known as a method for producing clean steel with extremely low carbon and extremely low nitrogen content. In this method, an induction furnace is installed in a vacuum tank, the iron raw material charged into the induction furnace is heated by a coil buried in the wall of the induction furnace, and after melting and refining in a vacuum, It is made by casting in a vacuum. According to this method, the C-O reaction, degassing reaction, etc. of molten steel are promoted by vacuum refining, and clean steel with an extremely low content of carbon, nitrogen, etc. can be produced. However, the conventional method described above has the following problems. (1) Due to insufficient stirring of molten steel and slag in the induction furnace, the reaction progresses extremely slowly and refining takes a long time. (2) Molten metal in an induction furnace is heated by a coil buried in the furnace wall, but the surface of the molten metal is cooled by a water cooling coil installed in the furnace wall. It becomes difficult to keep the slag melted, the desulfurization reaction progresses slowly, and desulfurization cannot be carried out sufficiently. (3) Because it is difficult to separate molten steel and slag during casting, some of the slag gets caught up in the steel ingot.
Prevents cleaning of steel. (4) It is difficult to separate fine slag particles dispersed in molten steel, which hinders the cleaning of steel materials. (5) Due to slag adhering to the refractories of the induction furnace, during melting and casting after the next charge,
Contaminates molten steel. [Object of the Invention] Therefore, the object of the present invention is to provide a steel ingot in which the reaction is actively carried out, the desulfurization and deoxidation reactions are promoted, and the cleaning of the steel ingot is not hindered by the mixing of slag. We can produce clean steel with extremely low sulfur and oxygen content.
An object of the present invention is to provide a method and apparatus for producing clean steel. [Summary of the Invention] The method of the present invention is a method for manufacturing clean steel by vacuum induction melting, in which a refining reaction is promoted by blowing an inert gas into the molten metal in an induction furnace, and the molten metal is The slag floating on the surface is heated by a heating means installed in an induction furnace to maintain it in a molten state,
After primary refining, the molten metal is poured into a mold to prevent slag from getting mixed in to form a steel ingot.Then, the steel ingot is converted into a steel ingot under vacuum using an induction furnace with no slag attached to the furnace walls. The feature is that the molten metal that has been refined and secondary refined in this way is poured into a mold so that slag is not mixed in. [Structure of the Invention] Next, the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing one embodiment of the apparatus used in the method of the invention. A raw material charging device 2 is provided at the top of the vacuum tank 1, and an exhaust port 3 connected to a vacuum exhaust system is provided at one side wall. An induction furnace 4 is provided in the vacuum tank 1 below a raw material charging device 2 . The induction furnace 4 is placed on a table 5, and is moved in the direction of arrow a by winding or unwinding a wire 6, which is attached to one end of the table 5 and whose other end is wound around the main shaft 7 of the motor. It can be tilted. A tundish 8 and a mold 9 located below the tundish 8 are provided in the tilted position of the induction furnace 4 . Tundish 8 and mold 9
is placed on a truck 10, and can be moved in and out of the vacuum tank 1 by the truck 10. 1
Reference numeral 1 denotes a ferroalloy addition shooter which is provided in the vacuum tank 1 and is rotatable in the direction of arrow b; 12 is a molten steel temperature measuring and sampling mechanism provided at the upper part of the vacuum tank 1; and 13 is a member in the induction furnace 4. 14 is a viewing window provided at the top and side of the vacuum tank 1, and 26 is a weighing device. A heating coil 15 is embedded in the furnace wall of the induction furnace 4, and a heating element 16 as a slag heating means is further installed in the upper part of the furnace wall near the hot water surface to heat the slag in the furnace. It is buried. At the top of the vacuum tank 1, there is a lance 17, whose tip is immersed in the molten metal in the induction furnace 4 and serves as an inert gas blowing means for stirring the molten metal by blowing inert gas. It is set up so that it can move freely. 1
8 is a lance 17 provided outside the vacuum tank 1
19 is a gas control device. The above-mentioned inert gas blowing means has an inert gas blowing plug 20 provided at the bottom of the induction furnace 4 instead of stirring the molten metal in the induction furnace 4 from above with the lance 17, and A cylinder 1 provided outside the vacuum tank 1 is connected to the gas supply pipe 21 at one end.
8', an inert gas may be blown into the molten metal in the induction furnace 4 from the plug 20 by a gas control device 19'. As shown in the enlarged cross-sectional view in FIG. 2, the tundish 8 has a nozzle 22 provided at its bottom with a refractory part as a slag separating means to pass only molten steel and prevent the outflow of slag. A porous filter 23 is provided. 24 is a heating element embedded in the wall of the nozzle 22. Next, the operation of the above-described device will be explained.
A raw material is supplied by a raw material charging device 2 to an induction furnace 4 in a vacuum tank 1 maintained at a predetermined degree of vacuum,
The coil 15 of the induction furnace 4 is energized to heat and melt the raw material. In the refining stage, a predetermined amount of ferroalloy is put into the induction furnace 4 from the shooter 11 so as to have a predetermined composition, and the lance 17 is lowered and its tip is immersed in the molten metal 25 of the induction furnace 4, and the lance 17 is passed through. The molten metal 25 is stirred by blowing inert gas. The molten metal 25 may be stirred by blowing an inert gas into the molten metal 25 through a plug 20 provided at the bottom of the induction furnace 4 . During such heating and refining, the slag floating on the surface of the molten metal is turned into a molten state by heating the slag on the surface of the molten metal using a heating element 16 buried in the upper part of the furnace wall near the surface of the induction furnace 4. Retained. As the heating element 16 as the slag heating means, a substance capable of induction heat generation by high frequency may be used, or heating means such as arc or gas plasma may be used. After the primary refining is completed as described above, the motor is operated to tilt the induction furnace 4, and the molten steel in the induction furnace 4 is injected into the mold 9 through the tundish 8. At this time, since a filter 23 as a slag separating means is attached to the nozzle 22 of the tundish 8, most of the slag is separated by the filter 23. Note that the filter 2 is used as the slag separation means.
Instead of 3, a baffle plate made of refractory may be attached to the upper part of the induction furnace 4 or the upper part of the tundish 8, and the baffle plate may prevent the outflow of slag, or the slag may be discharged from the induction furnace 4. Since the beginning of the molten metal is mostly molten steel, it may be poured into the tundish 8, and the molten metal near the end mixed with slag may be discharged into another container. Next, the steel ingot is removed from the mold 9, and is melted again under vacuum in an induction furnace lined with a refractory not contaminated by slag to perform secondary refining. Clean steel is manufactured by injecting the molten steel from which the fine slag dispersed in the steel ingot has been separated into a mold and casting it. Furthermore, once used induction furnace refractories have slag attached to the top, and even if the amount of metal is increased by cleaning and melting to remove this, it is impossible to completely remove the slag. It is. Therefore, since the refractory cannot be used as it is for melting clean steel after the next charge, it is necessary to replace the refractory as soon as possible. For this purpose, it is desirable to prepare in advance several induction furnaces lined with new refractories. [Examples of the Invention] Next, the present invention will be further explained with reference to Examples.
Using the apparatus shown in FIGS. 1 and 2, an electrolytic iron 14
4 kg was charged in three parts and melted and refined while maintaining the degree of vacuum in the vacuum tank 1 at 2 x 10 ^-2 Torr. After vacuum deoxidation, graphite 170g, metal silicon 390g, metal manganese 2.500g, metal nickel 750g, metal chromium 380g, metal molybdenum
305 g and 135 g of metallic aluminum were added to the molten metal in the induction furnace 4 by the shooter 11.
Five minutes after the addition, the temperature of the molten metal was measured and sampled by the temperature measurement/sampling mechanism 12, and thereafter the load voltage of the induction furnace 4 was adjusted so that the temperature of the molten metal was about 1600°C. Next, as a desulfurizing agent, 60wt.
% CaF ₂ :30 wt.% and Al ₂ O ₃ :10 wt.%, 1.2 kg of flux was added into the molten metal. The flux melted 3 minutes after it was added, so a lance 17 made of magnesia with an outer diameter of 45 mm and a nozzle diameter of 2 mm was lowered, the tip nozzle of the lance 17 was immersed in the molten metal, and argon gas was added at a rate of 5 Nl/min. Molten metal 2
5 and stirred the molten metal 25. During this time, the slag was maintained in a molten state by the heating of the heating element 16 buried in the upper part of the furnace wall of the induction furnace 4, and the amount of slag scattered and attached to the furnace wall above the molten metal surface was also small. After performing such refining for 15 minutes, the temperature of the molten metal was measured and sampled by the temperature measuring sampling mechanism 12, and then the blowing of argon by the lance 17 was stopped and the lance 17 was raised. The induction furnace 4 was tilted by winding up a wire 6 that was wound around the main shaft 7 of the motor, and the molten steel 25 in the induction furnace 4 was injected into the mold 9 through the tundish 8. At this time, nozzle 2 of tundish tray 8
Most of the slag remained in the tundish 8 and did not flow into the mold 9 due to the filter 23 provided at the tundish 8. Through such primary refining, a steel ingot with a diameter of 180 mm and a height of 280 mm was prepared. Next, the furnace body of the induction furnace 4 is replaced, a new furnace body with no slag attached is installed, and this induction furnace 4
The above-mentioned steel ingot was charged and melted, and secondary refining was performed in the same manner as above. To adjust the composition, 30 g of graphite, 80 g of metal manganese, and 52 g of metal aluminum were added to the molten metal, and the mixture was refined for 5 minutes.
Next, temperature measurement and sampling were performed, and after 1 minute the steel was tapped, and the molten steel was poured into the mold 9 through the tundish 8, thus producing clean steel. Table 1 shows the temperature and composition of the molten steel in the above primary refining and secondary refining.

[Table] As is clear from Table 1, desulfurization treatment during primary refining reduces S in molten steel to 1 ppm.
The S content in the final steel ingot after secondary refining was 2 ppm.
Furthermore, the TO content in the steel ingot after primary refining was 31 ppm, but the TO content in the final finished steel ingot after secondary refining decreased to 12 ppm. Table 2 is a comparison of the final S and TO amounts between the above examples of the present invention and comparative examples. Comparative Example 1 is a case where secondary refining is not performed, Comparative Example 2 is a case where slag separation is not performed when pouring molten steel into the mold, Comparative Example 3 is a case where slag heating in the induction furnace is not performed, Comparative Example 4 This is the case when the molten metal in the induction furnace was not stirred.

〔Effect of the invention〕

As detailed above, according to the method and apparatus of the present invention, when producing clean steel by vacuum induction melting, the refining reaction is promoted, desulfurization and dephosphorization are sufficiently performed, and slag The cleaning of the steel ingot is not hindered by the contamination of
This provides an industrially excellent effect in that ultra-low oxygen clean steel can be produced.

[Brief explanation of drawings]

Figure 1 shows one of the apparatuses used in the method of this invention.
FIG. 2 is an enlarged sectional view of the tundish portion. In the drawings, 1...vacuum tank, 2...raw material charging device, 3...exhaust port, 4...induction furnace, 5...stand, 6...wire, 7...main spindle, 8...tundish, 9...mold, 10...cart, 11 ...Shooter, 12...Temperature measurement/sampling mechanism, 13...Punching rod, 14...Peep window, 15...Heating coil, 16...Heating element, 17...Lance, 1
8, 18'... Bonpe, 19, 19'... Gas control device, 20... Plug, 21... Gas supply pipe, 2
2... Nozzle, 23... Filter, 24... Heating element,
25... Molten metal, 26... Weighing device.

Claims (1)

[Claims] 1. Melting and refining iron raw materials under vacuum in an induction furnace installed in a vacuum tank, and injecting the thus refined molten steel into a mold installed in the vacuum tank. A method for producing clean steel that produces a clean steel ingot by blowing an inert gas into the molten metal in the induction furnace in order to promote the refining reaction in the induction furnace. , the molten metal is stirred, and the slag floating on the surface of the molten metal in the induction furnace is heated by a heating means provided in the induction furnace to maintain it in a molten state, and in this way, the primary refining is completed. The molten metal is separated to prevent slag from getting mixed in and poured into the mold to form a steel ingot.Then, the steel ingot is heated in an induction furnace with no slag attached to the furnace walls. , the molten metal is melted under the vacuum and subjected to secondary refining, and the molten metal that has undergone the secondary refining is separated and poured into the mold to prevent slag from being mixed in, thereby making it clean. A method for producing clean steel, which comprises producing a steel ingot. 2. A vacuum tank for maintaining the interior at a predetermined degree of vacuum, an induction furnace installed in the vacuum tank for melting and refining iron raw materials under vacuum, and iron materials refined by the induction furnace. A clean steel manufacturing apparatus comprising a mold for casting molten steel, the induction furnace having an inert gas injection means for stirring the molten metal in the furnace by blowing an inert gas, and a mold for casting molten steel. and a slag heating means for heating slag floating on the surface of the molten metal to maintain it in a molten state, and a tundish provided at the upper part of the mold for injecting refined molten steel into the mold, An apparatus for manufacturing clean steel, comprising a slag separating means for preventing slag from flowing into the mold.