JPS60184618A - Production of low-nitrogen steel - Google Patents

Abstract

PURPOSE:To obtain low-nitrogen steel which is improved in (r) value and is decreased in concn. of N in the molten steel in order to prevent strain aging by subjecting the crude high-carbon molten steel produced in a steel making furnace to top blowing of oxidizing agent powder under the reduced pressure and accelerating the denitrification arising in this stage. CONSTITUTION:Two immersion pipes 3a, 3b of a cylindrical reflux degassing device 3 are immersed into a crude molten steel 1 contg. <=0.1% (C) which is produced in a steel making furnace and is charged into a ladle 2. Gaseous Ar is supplied 7 to the pipe 3a and the inside of the device 3 is evacuated 6 to a reduced pressure to suck up the steel 1 in the ladle 2 by the reflux gas from the pipe 3 into the device 3 and to return the same from the other pipe 3b into the ladle 2, thereby circulating the molten steel. Oxidizing agent powder 5 such as iron oxide or the like is blown from a top blowing lance 4 provided to the peripheral wall of the device 3 so as to be inclined to the molten steel surface by a carrier gas such as gaseous Ar. As a result, the powder 5 is penetrated and dispersed deeply into the steel 1, by which the decarburization and denitrification reaction is progressed uniformly. The molten steel is subjected to continuous casting in the next stage and is fed to a rolling stage, by which the casting steel is made into a sheet material. The final product is obtd. by annealing continuously the sheet material.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method of manufacturing low nitrogen steel. [Prior art] Generally, nitrogen in carbon steel is A7! , T'i, and other nitrides, which have a large effect on the refinement of crystal grains and other properties. For example, there is cold-rolled Al-killed 1ζ steel sheet material that is annealed by producing a certain amount of A6N, and there is also cold-rolled 81IJ sheet material that is continuously annealed by reducing (N) in the molten steel as much as possible. Nitrogen addition methods for these carbon steels include addition of nitrogen-containing ferroalloys, CaCN2, etc., or N2
There is also the bubbling method. However, degassing treatment for the purpose of denitrifying molten steel is not actively carried out, and vacuum degassing is performed using RII equipment, VOI) equipment, etc. for the purpose of decarburizing crude molten steel melted in steelmaking furnaces. It would be great if gas treatment was carried out and denitrification was confirmed as a side effect. That is, conventional low carbon A
For β-killed steel, it is degassed under reduced pressure using B air processing equipment such as R [1 equipment] in order to reduce the (C) content in the steel. Nitrogen is used during box annealing of cold-rolled steel sheets in the subsequent process. It is necessary to promote fine N precipitation, and the concentration was controlled within a certain range. However, due to advances in rolling technology, a continuous annealing method has recently been adopted, which involves rapid heating. Because of the rapid cooling process, it was difficult for AIVN to precipitate, and no improvement in the Lankford value (r value), which is an indicator of workability, could be expected, and as a result, the amount of residual solid solution nitrogen increased, making strain aging more likely. In order to improve this, it is necessary to increase the nitrogen concentration in the rolled product by 20%.
It is effective to reduce the nitrogen content to below ppm, and for this purpose, (N) is added at the end of the RII process in anticipation of the pickup of nitrogen into the molten steel during continuous casting or ingot making, which is about 2 times the rolling process. It was necessary to stably keep each charge below 10 ppm.This varies depending on the degree of sealing between the ladle and Lande 4221 during continuous casting, for example, but even if the seal is well sealed by 1 m, This is because the pick-up of nitrogen is at least about 2 to 311 ρm. [Objective] The present invention was made in view of the above circumstances, and its purpose is to improve the r value and reduce strain aging. In order to prevent this, the present invention provides a method for manufacturing a low nitrogen steel that can reduce (N) by 91 degrees in /8 steel. [Structure] The method for manufacturing a low nitrogen steel according to the present invention includes (C) ≧0.1% crude molten steel, oxidized + AH under reduced pressure
It is characterized by top-blowing the A body to decarburize it and promoting the denitrification that occurs. Melt&m? n
It is characterized by being performed diagonally above the surface. [Example] The present invention will be specifically described below based on the drawings. FIG. 1 is a schematic diagram showing the implementation state of the present invention, and in the figure 1
was refined in a steelmaking furnace such as a converter, electric furnace, or AOD furnace and charged into ladle 2.

[0]≧0.1% crude steel. Above the ladle 2, there are two dipping tubes 3a at the bottom thereof,
A cylindrical recirculation type degassing device (RH device) 3 is provided, and its two immersion tubes 3a and 3b are provided.
is immersed in molten steel. 'ζA I-gas is supplied to the inside of the base IN pipe 3d via the Canova supply pipe 7. The R11 device 3 is evacuated from the direct air exhaust duct 1-6 to evacuate the inside of the I71! J.I.
When the inside of each device 3 is depressurized, the 11th molten steel in the ladle 2 is removed from the immersion layer 3d based on the principle of a gas lift pump using the circulating gas from one immersion pipe 3d. 1 is sucked up and enters the R11 device 3, and the entered crude molten steel 1 is immersed in the other immersion Tri', 't l+
Inside the ladle 2... it returns, that is, it circulates. The degree of vacuum inside the RH device 3 is preferably close to vacuum;
The molten steel 11 at the bottom of the RH device 3 in the reflux is adjusted so that it is at least 200 mm or more.
This is to prevent the refractory material at the bottom of the device 3 from being easily worn out, and to prevent the process from becoming too shallow, which would result in less /8 steel processing p per hour (which would result in a longer processing time). A top blow lance 4 is installed at an appropriate height on the peripheral wall of the RH device 3 so that the blow angle is oblique to the /8614 m plane.Top blow lance 4
Karaba iron oxide, Mn oxide, Ca CO3. The oxidizing agent powder 5 is blown into the crude molten steel 1 using a carrier gas such as argon gas so that it sufficiently penetrates into the crude molten steel 1. Note that the blowing angle is 20' to 80° from the molten steel scene. If it is less than 20 degrees, it will be disturbed and scattered by the scene,
The oxidizer powder 5 does not sufficiently enter the crude molten steel 1. On the other hand, if the angle exceeds 80°, the lance becomes long and uneconomical.
The splash also gets bigger. Regarding the lance height, it is preferable that the height from the molten steel surface to the blowing hole at the tip of the top blowing lance 4 is 300 mm to 900 mm. If it is less than 300 mm, it will cause severe splash, which is unfavorable for operation.
This is because if it exceeds 0 mm, the penetration of the powder becomes shallow, which is unfavorable in terms of reaction efficiency. As for the oxidizing agent powder 5, it is preferable to use one having an appropriately small particle size. If the same amount of fine oxidant powder is used, the number of particles that become CO nuclei will increase, and each time a large amount of fine CO bubbles are generated, the reaction area where the denitrification reaction occurs can be increased. It is possible to speed up the decarburization reaction rate, but if the particle size is too small, the particles will sinter with each other and become coarse, so this is to prevent the powder from becoming dispersible in the molten steel. . As the carrier gas, CO gas or CO2 gas may be used, and as the blown powder, spider powder, Mn powder, Cr powder, Al12
0. It is also possible to use powder, CaO powder, etc. In this case, an oxygen source is required and oxygen gas is blown into the powder. However, iron powder + M
When injecting n-powder or the like, Ar gas or the like is used as a carrier gas, and in addition to this, oxygen gas is injected to prevent the explosion of iron powder or the like. In addition, denitrification effects can also be obtained by blowing Fe powder or the like with Ar gas. This is thought to be due to the fact that the N2 partial pressure is lowered by the Ar gas and the Fe powder becomes the reaction nucleus, as will be described later. As the oxidizing agent powder 5, Cr oxide, Mn oxide, etc. may be injected also for the purpose of component adjustment. The oxidizing agent powder top-blown as described above penetrates deeply into the crude molten steel l and is dispersed, so that the decarburization and denitrification reaction described below proceeds uniformly. After the denitrification treatment is carried out in this way until the required components are reduced to jη, /8&VI is continuously cast, then subjected to a rolling process to be made into a plate material, and further continuously annealed to become a final product. Of course, the denitrification treatment/8 steel may be made into a steel ingot by the ingot forming method instead of the continuous spinning method. Furthermore, the present invention is not limited to an RH device, but is applicable to a VOD device. Of course, a DH device or the like may also be used. In the case of a VOD device, since the height of the canopy is low, the oxidizer powder may not be blown obliquely upwards, but rather the lance may be oriented vertically and blown directly above. In this case, the denitrification efficiency can be further improved by using a porous brick at the bottom of the ladle and stirring the II molten steel by blowing Ar gas into it. Next, the reaction caused by injecting the oxidizing agent powder will be explained. Figure 2 shows RI (with device 3, the temperature is 1610°C.
The rough/8 steel 1 was depressurized to 6 torr, and the top-blown lance 4 was
The changes in (C), (N), and (Mn) when iron oxide is injected at a rate of 17.0 kg per ton of crude molten steel are 1, and the processing time (minutes) is plotted on the horizontal axis. Also, on the vertical axis [Ca
(%), [N) (ppm), and (Mn) (%). In the case of the treatment of the present invention, the EC) ranges from 0.30% to 0.30%.
By 0.04%, (N) decreased from 20 ppm to 7 ppm. And (Mn) remained unchanged. In the case of this reaction, it can be seen that (N) decreases as (C) decreases. The reason is as follows. Since iron oxide serves as an oxygen supply source, this iron oxide has co/1. It becomes nucleated, 1;
The co reaction shown in formula (1) is '4-LS. C+)=CO(g)...fil However, 1: Carbon in molten steel p, 1: Oxygen CO [1 Ni oxidized carbon] N2 on the gas side at the gas-metal interface of this CO dregs Pressure +
, l: Due to CO bubbles, the temperature is extremely low, and (0) on the metal side is considered to be approximately constant, as the work constant K of the CO reaction, shown in the following equation, is determined by temperature. Also, because the melt &[4 is under reduced pressure, CO
The gas partial pressure (Pco) decreases and the concentration product of carbon and oxygen becomes smaller, promoting the decarburization reaction.

[0]
Since a large amount of nitrogen is consumed, the value remains low, creating conditions that make it easy for denitrification reactions to occur. Therefore, both decarburization and denitrification reactions occur simultaneously at this reaction interface. log K = P co/αc'αo =116+1
/ T +2.00=f2) However, 1. clc: Carbon activity α0: Oxygen activity '1゛: Temperature (°K) The equilibrium constant in equation (2) is determined by the temperature of molten steel, and based on this K, Pco and Pco during treatment are determined by the temperature of the molten steel. αC・(
Since there is a certain relationship with lo, that is, the concentration product of carbon and nitrogen, there is equilibrium when [C) a degree is less than o, 1%.

[0] As the concentration increases, the decarburization reaction slows down and denitrification becomes difficult to proceed. Therefore, in the present invention, (C) of crude molten steel is (C)≧0.1%
That's all. Here, the changes in (C)' and (N) in Figure 2 are used as an index using the well-known formula (3) below (published in 1980, "Iron and 1i
'J J 6th fi year S, 234) denitrification efficiency Cr is introduced and expressed. α-Δ(1/[%N))/Δ[%C]...(3) However, Δ(I/[%N)): Change in reciprocal of weight base 1- of (N) in steel Absolute value Δ [%C]: weight percent 1 - absolute value of change in CC in steel In the conventional technology when only vacuum decarburization is performed using device 3, α is at most about 800, and the difference compared to this is the decarburization in the case of the present invention;
It can be seen that the denitrification efficiency with respect to iI is separated by 1 and 2. As a result, the denitrification treatment time can be shortened and the amount of refractory/8 refractory can be reduced. Furthermore, the relationship between the amount of decarburization and denitrification in the case of denitrification according to the present invention is shown in FIG. In Figure 3, the horizontal axis shows the processing value (1iijO) CN) (ppm
) is taken and (N) (100 m) after treatment is plotted on the vertical axis, and the amount of decarburization is changed in 0.1% C increments to perform 1ζ denitrification. As can be understood from this figure, when performing denitrification treatment according to the present invention, the ('N) value of crude molten steel melted in a steelmaking furnace is set in a denitrification possible range based on the purpose and product composition. ), once the amount of decarburization is determined, the amount of denitrification is controlled accordingly. The rate of decarburization and denitrification and the nitrogen concentration reached are affected by the degree of vacuum. In other words, the higher the degree of vacuum, the lower the equilibrium nitrogen concentration (dissolved IW degree), and the higher the vacuum, the lower the equilibrium oxygen concentration for the same carbon concentration, according to equation (2) above, and historically A vacuum The denitrification reaction is promoted because the culm CO bubbles expand further and increase the gas-metal interface area. Furthermore, since the Ar gas bubbles supplied from the immersion tube 3a become larger as the degree of vacuum increases, the N2 partial pressure is reduced. Therefore, a high degree of vacuum is more effective. The higher the degree of vacuum, the lower the solubility of (N), so the attained nitrogen concentration becomes lower, and the higher the degree of vacuum, the lower the amount of molten steel splash when injecting the oxidizer powder. In the present invention, the blown oxidizer powder can be deeply dispersed in the molten steel, and these dispersed particles act as the nucleus of the decarburization reaction.
Evokes a more active reaction. Therefore, in the case of Rf (treatment only), the present invention can very effectively promote the decarburization and denitrification rate in crude molten steel. From this point of view, in carrying out the present invention, it is necessary to use the equivalent iron oxide. Blow out Fe45) and 02 gas twice. In this case, the Fe powder acts as a nucleus for the decarburization reaction, and the 02 gas causes an oxidation reaction between the Fe powder and the 02 gas, and the heat of the reaction is generated locally around the Fe powder, so the decarburization reaction itself does not occur. This will be promoted. In addition, Fe12)
When using a porous lance, the ζFe powder is blown into one hole using a gas other than oxygen gas, such as Ar gas, as a carrier gas, and the 02 gas is blown into the other hole. This prevents explosions. Note that, like Fe powder, Cr powder and Mn powder can also be blown with 02 gas. Also, if A/'201 and CaO are added, ○
2 gas or C02 gas may be used. Next, examples under various conditions will be described. 2.5 ton VOD device for experimental use as a vacuum degassing device,
Denitrification was carried out according to the present invention using an actual 250-ton RH device and changing the degree of vacuum, the type of oxidizer powder, the supply rate, the molten steel temperature, the lance height, etc. Table 1 is a table summarizing the implementation conditions and results, and Examples 1, 2, 3, 4, 5.6.7 are 2.51-
In the case of a digital VOD device, Examples 8, 9 and 10 are 25
This is the case of the 01-n RH device. For comparison, RH
Comparative Examples 1.2, 3, 4.5 where only the depressurization treatment was performed
The cases are shown in Table 2. As can be understood from this table (in the case of the present invention, 10 pp.
The denitrification amount of the present invention is significantly larger than the denitrification amount of the comparative example of 2 to 5 ppm. In addition, in the case of the present invention, the denitrification 'AJ rate is about 1800 or more, which is significantly higher than that of Comparative Example 3, which obtains a high Ji denitrification rate of 1η784, indicating that the denitrification rate is fast. Recognize. Therefore, a decrease in molten steel temperature due to treatment can be suppressed. In the case of Example 7 above, (Mn) in the molten steel before treatment is 2
．． Although the denitrification efficiency was 78%, which was higher than that of other examples, no difference was observed compared to the denitrification efficiency of other examples. In other words, Mn has a strong affinity for oxygen and is easily oxidized, but when top-blowing powder is decarburized, the supplied oxygen source preferentially reacts with (C) rather than (Mn), resulting in decarburization. It is thought to promote and eliminate nitrification. Examples 2 and 3 are cases in which Mn-0re and Mn-02 were used as oxidant powder in a 2.5-ton VOD device, respectively, and were top-blown with Ar gas. As understood from FIG. 5, as [C] decreases, (N) decreases and (N) decreases to below xoppm. On the contrary, (Mn) is increasing. Therefore, regarding (Mn), as understood from Figure 2←
While decarburization and denitrification progress over time,
There is almost no change, and therefore, in the case of Mn-containing steel, the composition may be adjusted at the end of refining in the steelmaking furnace. Also, Figure 4,
As understood from FIG. 5, in the vacuum treatment according to the present invention (
Mn) can be made to perform the pyokuasop, so this process allows (
When adjusting the component (Mn), Mn oxide, Mn powder, or oxides of other metals containing Mn may be used. Next, Fe-0 was used as oxidizer powder in a 2.5 ton VOD device.
When this was top-blown with Ar gas using RE (Examples 1, 4, 5.7), and when the same was carried out using a 250-ton RH device (Example 8), the denitrification efficiency α was 230.
It is about 0 to 2800, and the attained (N) value is 7 to lOpp.
decreased to m. When the present invention was carried out by blowing Fe powder and 02 gas instead of iron oxide using a porous lance (Example 6)
The denitrification efficiency was about 1800, which is slightly lower than that of iron oxide, but it is significantly higher than the highest value of 784 in the comparative example. Even in this case, the reached (N) value is +opp
m or later and auto are possible. Note that even when the F and e powders are top-blown with Ar gas, the Ar gas lowers the N2 partial pressure and a sufficient denitrification effect is observed, allowing the (N) content to be reduced to 10 ppm or less. Fe
The same applies when Ca CO3 is used instead of (w). Furthermore, using a porous lance in a 250 ton RH device, Fe-0
In the case of top blowing Mn-0re and spraying 02 gas (Example 9 and Example 10), Fe-0r
The same denitrification efficiency as in Example 8, in which e was top-blown with Ar gas, was obtained, and it was possible to achieve an attained (N) value of 10 ρpi or less in I minutes. In this way, in the present invention, N is l (j p p
It is possible to produce low nitrogen steel of m. Regarding the loss of ii + fires/8 in the RH tank when such denitrification treatment is carried out, 1liJ fires/8
ti1i is 1 (, it is difficult to clearly understand the amount of erosion for each h,
Therefore, Fig. 6 shows the amount of erosion loss when the operation including the denitrification treatment of the present invention is carried out. Figure 6 is a graph showing the relationship between the ratio (%) when denitrification is performed during the entire operation on the horizontal axis and the lifespan (times) of the lower tank of the RH equipment on the vertical axis. , In the figure, the 0 mark indicates that the processing temperature is less than 1650℃, and the * mark indicates that the pre-processing temperature is 16
The cases where the temperature is 50° C. or higher are respectively shown, and the short horizontal lines and arrows at 0% indicate the range of variation in life when the denitrification treatment according to the present invention is not performed at all. As understood from this figure, in the case of the present invention, 1650
Even at relatively low temperatures below ℃, the supplied oxygen efficiently contributed to the decarburization reaction, making it possible to reduce the refractory erosion rate (average erosion rate). Regarding the amount of melting loss, as shown in Table 3 for RH filling equipment, when the average melting thickness of the refractory is 1650°C or higher, it is 0.
．． 85~1,05+nm, whereas 1650°
Below C, it is 0.6 to 0.8 mm, which is about 20 to 30%/
8, the lower tank life of the RH packing equipment can be reduced from about 380 times to about 420 times, and the number of furnace repairs can be reduced, so the operating rate of the RH packing equipment can be improved. It becomes possible. Table 3 [Effects] When the denitrification treatment is performed according to the present invention, the achieved (N) value is
It can be lowered to 109 ρm or less. For this reason, it is easy to continuously cast the molten steel according to the present invention, and even though the sealing condition is somewhat tUt <, it is easy to suppress the pink amplifier of N to 1 opp = or less, and for this reason, even if the (N) value increases, it is possible to It is possible to stabilize the charge and reduce the charge to 2 oppm or less in slabs. After cold rolling the spun J1 obtained in this way (q), the cold rolling phase obtained by continuous annealing was N (p
As can be seen from FIG. 7, which shows the relationship between pm ) and r 4ji, the r value was high, making it possible to improve the force-old J duality and suppress the occurrence of strain aging. As described below, in the case of the present invention, reaching (N)
It is possible to lower the carbon value, so it can be annealed continuously, improves the T value, has excellent deep drawability, and is a low-carbon quilt steel with suppressed strain aging. Nitrogen steel, etc. can be kneaded stably, and the denitrification efficiency is high, so the processing time is short. g #14 Temperature drop is small. Therefore, even if the processing temperature is increased to compensate for this temperature drop, processing can be performed at a relatively low temperature range, and since the processing time is short, the amount of erosion of refractories such as RH equipment and ladles is small. The present invention has excellent effects.

[Brief explanation of the drawing]

Fig. 1 is an inspection diagram showing the implementation state of the present invention, Fig. 2 is a graph showing the composition change according to the present invention when iron oxide is injected, and Fig. 3 explains the reaction content of the present invention. Graphs used for this purpose, Figures 4 and 5 are graphs showing the composition changes according to the present invention when Mn oxide is injected, and Figure 6 is a graph showing the amount of refractory corrosion when according to the present invention. , FIG. 7 is a graph used to explain the present invention in detail. 1... Crude molten steel 3... RH device 4... Top blowing lance 5... Oxidizing agent F1) body patent Applicant Sumitomo Metal Industries Co., Ltd. agent Patent attorney Ali IF 98 years of experience ( Minute) Fue 2 illustration J Ko Yoitori [Nko (rr') Yu J1 Kei Roji Ma (Iri) 4th - Diagram Yura Ri 81 Ma (Ko) OIO20 Kobun body 10 ＾ De-7 peel processing country J (%) Atsushi 6 Figure o 10 2 o J (140 So c.

Claims (1)

[Claims] 1. The 20.1% (C) crude molten steel produced in a steelmaking furnace is top-blown with oxidizer powder under reduced pressure to decarburize and solidify it, and the decarburization that occurs at this time is A method for manufacturing low-nitrogen steel, which is characterized by promoting and removing nitrogen. 2. A 20.1% roughened steel (C) made with 18 v steel weight was brought to a reduced pressure F in a recirculation degassing device, and this reduced pressure 11
A method for manufacturing low-nitrogen steel, which comprises top-blowing oxidizer powder to decarburize the steel and promote denitrification that occurs at this time. 3. The method for producing low nitrogen steel according to claim 2, wherein the oxidizing agent powder is blown diagonally above the crude molten steel.