JPH01234514A - Submerged tube in molten steel - Google Patents

Abstract

PURPOSE:To prevent sticking of metal to free board in a ladle and to prevent pick-up of C and N in molten steel by submerging a molten steel submerged tube formed with a top plate having opening hole, cylindrical type iron plate and refractory and having the outer diameter smaller than inner diameter in a ladle, into molten steel in the ladle. CONSTITUTION:The molten steel 12 submerged tube 30 supported at the upper end of the ladle 2 is formed with the top plate 32 having opening hole, the cylindrical type iron plate 31 and the refractory 36 and the outer diameter thereof is smaller than the inner diameter of the ladle 2 and the lower part thereof has length to be possible to submerge into the molten steel 12. At the time of executing decarbonization by supplying oxygen in vacuum, as high pressure oxygen jet from tip part of oxygen lance 5 is blown on the surface of molten steel 12, splash is developed, but by inserting the submerged tube 30 into the ladle 2 and submerging it into the molten steel 12, the splash is stuck on the surface of the submerged tube 30. After completing the carbonization by supplying the oxygen, the lance 5 is taken out to out of the system, and the cover 4, etc., for the ladle 2 is retreated from the upper part of the ladle 2 to take out the submerged tube 30 sticking the metal in a ladle 2 to out of the system. Therefore, the stuck metal at the free board part 16 in the ladle 2 is eliminated and the pick up of C and N in the molten steel 12 can be eliminated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is directed to immersion of molten steel, which is used in a vacuum acid decarburization method with strong stirring, etc., in order to obtain a ferritic stainless steel with extremely low carbon and nitrogen. It is related to pipes.

[Prior Art] Ferritic stainless steel has the advantage of superior stress corrosion resistance compared to austenitic stainless steel, but has the disadvantage of poor toughness.

In order to improve this, it is known to lower the carbon and nitrogen contents in molten steel.

This method includes a vacuum oxygen decarburization method. However, since the Cr content of stainless steel significantly lowers the activity coefficients of C and N, it is difficult to obtain extremely low carbon and extremely low nitrogen stainless steel by the usual vacuum oxygen decarburization method. In order to obtain ultra-low carbon stainless steel, it is effective to blow a large amount of gas into a steel bath and perform strong stirring to promote the degassing reaction.

In addition, in order to obtain ultra-low nitrogen stainless steel, vacuum oxygen supply with strong stirring is necessary to increase the activity coefficient of N by C and to actively utilize CO gas generated during decarburization as a denitrification reaction interface. It is effective to carry out the decarburization treatment from [C] -1.0% or more.

FIG. 6 is a sectional view showing a conventional strong stirring vacuum acid feeding decarburization treatment apparatus. 1 is a vacuum acid decarburization treatment device with strong stirring, 2 is a ladle, 3 is a lid of the vacuum acid decarburization treatment device with strong stirring, 4 is a ladle lid, 5 is an oxygen lance, 6 is a gas blowing plug, 7 is a sliding plate, 8 is a vacuum exhaust duct, 9 is a trunnion shaft of a ladle, 10 is a trunnion bearing stand, 11 is an oxygen lance insertion hole, and 12 is molten steel.

Ferritic stainless steel is melted in a converter or electric furnace. Molten steel is tapped into a blow-stop ladle 2 with a carbon content of 1.0 to 2.0%.

The slag on the surface of the molten steel tapped into the ladle is removed.

A ladle 2 containing molten steel 12 is transported by a crane to a vacuum acid feeding decarburization treatment apparatus 1 with strong stirring. The trunnion shaft 9 of the ladle is attached to the trunnion bearing stand 1 of the vacuum acid feeding decarburization treatment equipment 1 with strong stirring.
Put it on 0. Then, ladle N4 is placed on ladle 2. Then, the lid 3 of the vacuum acid feeding decarburization treatment equipment with strong stirring is in the retracted position (
(indicated by a dotted line in the figure) is moved onto the strongly agitating, vacuum acid-supplying, decarburizing, and decarburizing treatment apparatus 1 and set therein. Vacuum exhaust device (not shown)
is activated to lower the degree of vacuum of the strong stirring vacuum acid feeding decarburization treatment apparatus 1. The air and gas present in W1 during the strong agitation vacuum oxygen decarburization process pass through the vacuum exhaust duct 8 and are exhausted to the atmosphere via the vacuum exhaust device. For example, in the case of a 50T ladle 2, the pressure is reduced to 100 Torr or less for 5 to 10 minutes. Then, the oxygen lance 5 is inserted into the oxygen lance insertion hole 11 of the ladle lid 4 and the M3 of the vacuum oxygen feeding decarburization treatment apparatus with strong stirring. At this time, the oxygen supply conditions of the oxygen lance 5 are 10 atm and 20 to 60 n (
/min, and the acid feeding time is 30 to 50 minutes.

Since stirring of the molten steel 12 is insufficient using only the oxygen lance 5, a gas blowing plug 6 (bowl plug or multi-hole plug) is attached to the bottom of the ladle 2, and argon gas is blown into the molten steel 12. The argon gas blowing conditions are 3.
During the vacuum acid feeding decarburization process with strong stirring at ~4 atmospheres and 03 to 0.4 rrf/min, 10 kg/ch of a slag-forming agent is introduced so as to dilute the chromia generated during the acid feeding decarburization process. The carbon content in the molten steel at the end of oxidative decarburization is 0.02 to 0.05%. After oxidation decarburization, 1 to lower the carbon in the molten steel.
Vacuum decarburization treatment is performed at a high degree of vacuum below torr.

After the vacuum decarburization is completed, a slag-forming reducing agent such as Ca○, Si, Aρ, etc. is added to perform Cr reduction and final refining.

After Cr reduction and final refining, the ladle is transported to a continuous casting machine or an ingot, and poured into a tundish or mold by opening and closing the sliding plate 7.

Table 1 shows changes in the composition of molten steel during the refining process. The timing is when steel is tapped in a melting furnace, oxidation decarburization is completed, vacuum decarburization is completed,
This was done after finishing scouring. As is clear from this table, there was an increase in C and N in the components after final scouring.

Table 1 [Problems to be Solved by the Invention] FIG. 7 is a cross-sectional view of a ladle in a vacuum oxygen feeding decarburization treatment apparatus with strong stirring. 13 is the iron skin of the ladle, 14 is the permanent brick of the ladle, 15 is the work brick of the ladle, 616 is the freeboard part of the ladle, 17 is the splash, 18 is the oxygen jet,
One is the attached metal. The other figure numbers are the same as those explained in FIG. Ladle 2 is made of iron shell 13 and permanent brick 14
and a work brick 15. The ladle 2, permanent brick 14, and work brick 15 are generally M
g-Cr bricks are used. The portion above the surface of the molten steel 12 is called a freeboard portion 16 of the ladle.

However, since the decarburization treatment using vacuum oxygen feeding with strong stirring is carried out from decarburization treatment to final refining with the molten steel 12 placed in the ladle 2, the decarburization treatment from the high carbon region is as shown in Figure 7. As the high-pressure oxygen jet 18 is sprayed onto the surface of the molten steel 12 from the tip of the oxygen lance 5, a splash 17 is generated from the surface of the molten steel 12 that the high-pressure oxygen jets 1 to 18 collide with, and the work bricks 1- in the ladle are It is attached to the freeboard section 16 of No.5. This is called the attached base metal 19. This deposited metal 19 contains about 1% carbon. Then, vacuum decarburization, reduction, and final refining are performed. In particular, Sj, Affl and Cab are used as reducing agents in reduction and finishing refining.

Since a slag-forming agent such as CaF2 is added, the atmospheric temperature inside the ladle 2 rises to 300 to 400°C compared to the conventional one, and the adhered metal 19 attached to the free hoard portion 16 of the ladle melts and is dissolved in the molten steel 12. This causes carbon and nitrogen in the molten steel 12 to be picked up, making it difficult to obtain ferritic stainless steel with extremely low carbon and extremely low nitrogen. The present invention has been made in view of the above circumstances, and aims to solve the above-mentioned problems and provide a molten steel immersion tube for producing extremely low carbon and extremely low nitrogen ferritic stainless steel.

[Means for Solving the Problems] A molten steel immersion tube according to the present invention is a molten steel vacuum processing apparatus that includes a ladle storing molten steel, a molten steel immersion tube supported at the upper end of the ladle, and a molten steel immersion tube supported at an upper end of the ladle. A ladle lid that covers the top,
The ladle has an oxygen lance inserted into the ladle through the ladle lid, an inlet at the bottom of the ladle through which inert gas is blown into the ladle, and is supported at the upper end of the ladle. The lower part of the molten steel immersion tube has a length immersed in molten steel, and the molten steel immersion tube is composed of a perforated top plate, a cylindrical iron plate, and a refractory, and the outer diameter of the molten steel immersion tube is smaller than the inner diameter of the ladle. has been done.

[Function] According to the present invention, the molten steel immersion pipe is supported at the upper end of the molten steel ladle and is composed of a cylindrical iron plate and a castable, and is smaller than the inner diameter of the molten steel ladle, so that the molten steel immersion pipe is not inserted into the ladle. Can be inserted. When performing vacuum acid film acidification, a high-pressure oxygen jet is sprayed onto the surface of the molten steel from the tip of the oxygen lance, so splash is generated from the surface of the molten steel that the high-pressure oxygen jet collides with. It sticks to this surface. After the completion of oxygen supply and deoxidation, the oxygen lance is taken out of the system, and the lid of the vacuum oxygen supply decarburization treatment apparatus with strong stirring and the ladle lid are evacuated from the ladle. Then, the molten steel immersion tube with metal attached inside the ladle is taken out of the system. After that, in order to perform vacuum decarburization, the lid of the vacuum oxygen decarburization processing equipment with strong stirring and the ladle lid are set on the ladle, and vacuum decarburization, reduction, and final refining are performed, so the Since there is no gold adhesion, there is no pick-up of carbon or nitrogen in the molten steel.

[Examples] Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a strong stirring vacuum acid feeding decarburization treatment apparatus showing one embodiment of the present invention. FIG. 2 is a sectional view of a ladle in a vacuum acid feeding decarburization treatment apparatus with strong stirring, showing an embodiment of the present invention. Figure 3 is a diagram showing a molten steel immersion pipe.
(a) is a plan view, and (b) is the line AA' in Fig. 3 (a).
FIG. 30 is a molten steel immersion tube, 31 is a cylindrical iron plate, 32 is a perforated top plate, 33 is a hanging fitting for the molten steel immersion tube, 34 is a reinforcing member, 35 is a stud, and 36 is a castable.

The other figure numbers are the same as those explained in FIGS. 6 and 7. The molten steel immersion pipe 30 has a cylindrical iron plate 31 and a perforated top plate 32
It consists of a hanging fitting 33 for a molten steel immersion pipe, a reinforcing member 34, a stud 35, and a castable 36. The perforated top plate 32 is welded to the cylindrical iron plate 31, the suspension fitting 33 of the molten steel immersion pipe, and the reinforcing member 34. The other end of the reinforcing member 34 is welded to the cylindrical iron plate 31. A V stud 35 is welded to the cylindrical iron plate 31. Castable was applied between the V studs 35, heated to 1000°C at 50°C/H, and held for 6 hours.

Ferritic stainless steel is melted in a converter or electric furnace. Molten steel is tapped into a blow-stop ladle 2 with a carbon content of 1.0 to 1.5%.

The slag on the surface of the molten steel tapped into the ladle is removed.

A ladle 2 containing molten steel 12 is transported by a crane to a vacuum acid feeding decarburization treatment device 1 with strong stirring.

The trunnion shaft 9 of the ladle is placed on the trunnion bearing stand 10 of the vacuum acid feeding decarburization treatment apparatus 1 with strong stirring. Then, the molten steel immersion pipe 3o is inserted into the ladle 2 containing molten steel. The inner diameter of the ladle 2 is 2300 mm, the outer diameter of the molten steel immersion tube 30 is 1860 mmΦ, and the inner diameter of the molten steel immersion tube 30 is 1600 mm.
mmΦ, the inner diameter of the perforated top plate 32 is 1760 mmΦ, the outer diameter of the perforated top plate 32 is 2500 mmΦ, the perforated top plate 32
The thickness of is 16 mm, and the thickness of the cylindrical iron plate 31 is 9 mm.
■Stud welding is performed on the front and back surfaces of the cylindrical iron plate 31.

The length of the cylindrical iron plate 31 is 1600 mm, the diameter of the cylindrical iron plate 31 is 1760 mmΦ, and the inside and outside thereof are coated with castable. The inside of the cylindrical iron plate 31 is coated with 80mm castable, and the outside of the cylindrical iron plate 31 is coated with 50m.
It is coated with m castable. The reason why the thickness of the castable is different between the inside and outside of the cylindrical iron plate 31 is that the thickness of the castable is thicker on the inside of the cylindrical iron plate 31 because the stirring of slag and molten steel is more intense and the castable is more likely to be damaged by melting.

The ladle 2 containing the molten fi[12] is transported by crane to the vacuum acid feeding decarburization treatment equipment 1 with strong stirring. The trunnion shaft 9 of the ladle is placed on the trunnion bearing stand 10 of the vacuum acid feeding decarburization treatment apparatus 1 with strong stirring. Then, ladle M4 is placed on ladle 2. Then, the lid 3 (not shown by the dotted line in the figure) of the strong stirring vacuum acid decarburization treatment apparatus which is in the retracted position is moved onto the strong stirring vacuum acid decarburization treatment apparatus 1 and set. A vacuum evacuation device (not shown) is operated to lower the degree of vacuum in the strong stirring vacuum oxygen feeding decarburization treatment device 1. Vacuum acid feeding decarburization treatment equipment with strong stirring 1
The air and gas present in the vacuum exhaust duct 8 are exhausted to the atmosphere via a vacuum exhaust device. For example, in the case of a 50T ladle 2, the temperature is reduced to 100 Torr or less for 5 to 10 minutes. Then, the oxygen lance 5 is inserted into the oxygen lance insertion hole 11 of the lid 3 and the ladle lid 4 of the strong stirring vacuum acid feeding decarburization treatment apparatus.

At this time, the oxygen supply conditions of the oxygen lance 5 are 10 atm, 20 to 6
At 0 m1/min, the oxygen supply time is 30 to 50 minutes.

Since stirring of the molten steel 12 is insufficient with only the oxygen lance 5, a dregs blowing plug 6 (a bowlus plug or a multi-hole plug) is attached to the bottom of the ladle 2, and argon gas is blown into the molten steel 12. The argon gas blowing conditions are 3.
During the vacuum oxygen decarburization treatment with strong stirring at ~4 atmospheres and 0.3 to 0.4 rrr/min, 10 kg/ch of slag forming agent is added to dilute the chromia generated during the acid decarburization process. . The carbon content in the molten steel at the end of oxidative decarburization is 0.02 to 0.05%. To lower the carbon in molten steel after oxidative decarburization]
The vacuum decarburization process is performed at a high vacuum degree of , torr or less.

FIG. 4 is a schematic diagram of the acid decarburization treatment method according to an embodiment of the present invention, (a) is a diagram during the acid decarburization treatment, and (b) is a molten steel immersion pipe after the acid decarburization treatment. This is a diagram when taken out of the system.

As shown in FIG. 4, since a high-pressure oxygen jet 18 is sprayed onto the surface of the molten steel 12 from the tip of the oxygen lance 5, a splash 17 is generated from the surface of the molten steel 12 that the high-pressure oxygen jet 18 collides with, and the molten steel is immersed. It is attached to the castable inside the pipe 3o. This is called the attached base metal 19.

After the oxygen decarburization treatment, the lance 5 is taken out of the system, and the degree of vacuum in the vacuum oxygen decarburization treatment apparatus 1 with strong stirring is lowered. Then, the lid 3 of the vacuum acid feeding decarburization treatment apparatus with strong stirring is evacuated from above the ladle 2, and the ladle lid 4 is taken out of the system. Thereafter, the molten steel immersion tube 30 with the metal adhered to its inner surface is taken out of the system using a colander or the like. Then, set the ladle lid 4 on the ladle 2 again, and then set the ladle lid 3 on the ladle 2 of the vacuum acid feeding decarburization treatment equipment with strong stirring.
set on top. The next step is vacuum decarburization →
Performs reduction and final refining. Since the molten steel immersion tube 30 with metal adhered to the inner surface is taken out from the ladle 2 to the outside of the system before vacuum decarburization, the freeboard portion 16 of the ladle is free of adhered metal, so vacuum decarburization is possible. Since there is no pick-up of carphone in the molten steel even after treatment, reduction, and final refining, it is possible to produce ferritic stainless steel with extremely low carbon and extremely low nitrogen. FIG. 5 is a graph showing the amount of carbon picked up in molten steel before strong stirring vacuum acid feeding decarburization treatment and the pickup amount of carbon in molten steel before strong stirring vacuum acid feeding decarburization treatment.

In this figure, the ○ marks are for the method of the present invention, and the * marks are for the conventional method. As is clear from this figure, the conventional method picks up about 30 ppm of carbon in molten steel, but the method of the present invention hardly picks up carbon in molten steel. Although this figure describes carphone in molten steel, the same tendency applies to nitrogen in molten steel. In this embodiment, the lid 3 of the vacuum acid decarburization treatment apparatus with strong stirring is moved, but the lid 3 of the vacuum acid decarburization treatment apparatus with strong stirring is fixed.
The ladle can also be moved using a ladle cart system.

[Effects of the Invention] Since the present invention is configured as described above, there is no base metal adhering to the freeboard portion of the ladle, so carbon in the molten steel,
There is no nitrogen pickup.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing a vacuum acid decarburization treatment apparatus with strong stirring, which is an embodiment of the present invention, and Fig. 2 is a sectional view showing the inside of a vacuum acid decarburization treatment apparatus with strong stirring, which is an embodiment of the present invention. A cross-sectional view of the ladle part of
FIG. 3(a) is a plan view of a molten steel immersion tube, FIG. 3(b) is a sectional view taken along line A-A' in FIG. 3(a), and FIG. 4 is a plan view of a molten steel immersion tube. A schematic diagram of the acid decarburization treatment method, Figure 5 shows the relationship between carbon in molten steel before vacuum acid decarburization treatment with strong stirring and carbon in molten steel after vacuum acid decarburization treatment with strong stirring. FIG. 6 is a sectional view showing a conventional vacuum oxygen decarburization treatment apparatus with strong agitation, and FIG. 7 is a sectional view of a ladle in the vacuum acid decarburization treatment apparatus with strong agitation. 1...Vacuum acid feeding decarburization treatment equipment with strong stirring, 2...Ladle, 3...Lid of the vacuum oxygen feeding decarburization treatment equipment with strong stirring, 4...Ladle lid, 5...Oxygen lance , 6... Gas blowing plug, 7... Slip ink plate, 8... Vacuum exhaust vent, 9... Ladle trunnion shaft, 10... Trunnion bearing stand, 11... Oxygen lance Insertion hole, 12... Molten steel, 30 ・
Molten steel immersion pipe, 31. Cylindrical iron plate, 32. Iron plate with holes, 33. Hanging fitting for molten steel immersion pipe, 34. Reinforcement member, 35. V stud, 36. Castable.

Claims (1)

[Claims] In a vacuum processing device for molten steel, a ladle that stores molten steel,
A molten steel immersion tube supported at the upper end of the ladle, a ladle lid covering the top of the molten steel immersion tube, an oxygen lance inserted into the ladle through the ladle lid, and a bottom portion of the ladle. The molten steel immersion tube has a blow port through which inert gas is blown into the ladle, the lower part of the molten steel immersion tube supported at the upper end of the ladle has a length to be immersed in the molten steel, and the molten steel immersion tube has a hole. A molten steel immersion tube comprising a top plate, a cylindrical iron plate, and a refractory, and characterized in that the outer diameter of the molten steel immersion tube is smaller than the inner diameter of a ladle.