JPS63203718A - Method for accelerating dehydrogenation of molten steel - Google Patents

Abstract

PURPOSE:To increase a gas-metal boundary area and to effectively accelerate dehydrogenation by putting a molten steel contg. a specific ratio of alloy components into a vessel in which an adequate reduced pressure is maintained and top blowing the powder of an oxidizing agent which is previously sufficiently dried by heating onto the surface of the molten steel. CONSTITUTION:The molten steel which contains >=1wt.% alloy components in total and is hardly dehydrogenatable is subjected to the dehydrogenation treatment after alloy component adjustment. The molten steel is put into the reduced pressure vessel in which <=200Torr is maintained in this dehydrogenation treatment. The powder of the oxidizing agent or powder for refining which is previously dried by heating at about >=400 deg.C to <=0.05wt.% moisture sticking thereto or contained therein is top-blown or blown to the surface or inside of such molten steel. The decarburization reaction is thereby accelerated and the gas-metal boundary area is increased, by which the dehydrogenation reaction of the molten steel is effectively accelerated and the hydrogen in the molten steel is decreased down to about <=1ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for promoting dehydrogenation reaction in molten steel.

(Prior art) The solubility of (H) in molten steel is 1600°C as shown in Figure 8.
The hydrogen content is as high as 26.8 ppm, and in order to reduce the hydrogen content,
The following two conditions are required.

■ Reduced pressure (vacuum) Hydrogen partial pressure on the gas side at the gas-metal interface (PHZ)
As shown in FIG. 9, when the value of tJm is lowered, the degree of (H)tJm in the molten steel that is in equilibrium with this decreases.

At this time, reach (H)t! degree can be lowered.

(2) Reaction interfacial area The dehydrogenation reaction occurs at the gas-metal interface, and the larger the interfacial area, the faster the dehydrogenation reaction rate.

Further, under reduced pressure (vacuum) conditions, the bubbles in the molten steel can be expanded, which is effective in promoting the deH reaction.

Therefore, in order to effectively reduce H, it is necessary to increase the gas-metal interface area as much as possible (improve the dehydrogenation rate) and perform high vacuum treatment (increase the stirring force of bubbles and lower the attained (H) value). is essential.

(Problems to be Solved by the Invention) However, since the free surface of molten steel in the gas-metal interfacial area is determined by equipment conditions, it is difficult to increase it. Therefore, a method of introducing gas into molten steel is generally adopted, but since introducing a large amount of gas deteriorates the degree of vacuum, the amount of introduced gas cannot be increased unconditionally. Additionally, equipment improvements such as increasing the evacuation capacity to ensure the degree of vacuum are also required (as an example of this, we will explain the equipment at RH).

When currently processing 2507ON molten steel, the amount of circulating Ar gas is approximately 160ON1/n+in, and the degree of vacuum is 0.3To.
Processing is performed using rr. In order to promote dehydrogenation, the amount of refluxed Ar gas was increased to 3,000 (~5,000 Nl), and a large amount of splash adhered to the side wall of the vacuum chamber near the top, sometimes interfering with the operation. Therefore, the degree of vacuum was set to the conventional level (0.3T).
Although the vacuum pumping capacity was increased to reduce the amount of water splash (orr), it was not possible to reduce the amount of splash.

The dehydrogenation rate at this time is approximately 10 x 10-' (see-
'), the reached H value was 1.5 ppn+, and by increasing the reflux Ar11, the dehydrogenation rate improved slightly (12X 10-
'C5ec-9), the achieved H value was 1.3 ppm. However, it is difficult to reduce the amount to 1 ppm or less on average.

In other words, the problem in this RH example is that when a large amount of Ar gas is introduced, (1) the degree of vacuum deteriorates, and (2)
Splash is increased by the locally introduced Ar gas. On the other hand, there is a countermeasure for the problem (■) by increasing equipment, but there is no countermeasure for the problem (■).

The present invention aims to provide a method for promoting dehydrogenation of molten steel that can solve these problems.

(Means for Solving the Problems) The present inventors conducted various studies and experiments in order to solve the above-mentioned problems, and as a result, they found the following improvements.

■Increased amount of Ar gas (e.g. 1400Nil/akin)
) is generated from inside the molten steel.

■Reducing the diameter of gas bubbles generated from within molten steel into fine bubbles. ■Bubbles generated from inside the molten steel are generated uniformly from within the molten steel and from the entire surface of the molten steel.

Therefore, if these improvements can be made, the deterioration of the degree of vacuum can be reduced due to ■, and the gas per unit amount of gas can be reduced due to ■.
The metal interfacial area can be increased, and local molten steel splash is reduced due to (1), making the operation extremely stable.

Therefore, in the present invention, when dehydrogenating molten steel containing 1% by weight or more of alloy components in total after adjusting the alloy components, the molten steel is heated and dried at a temperature of 400° C. or higher in advance to reduce adhesion or water content to 0. The decarburization reaction is promoted by blowing oxidizer powder or refining powder containing 0.05% by weight or less onto the surface of molten steel placed in a vacuum vessel at 200 Torr or less or into the molten steel, thereby promoting the decarburization reaction. The gist of this is to increase the metal interfacial area.

Next, the method of the present invention will be explained in detail.

l) Addition method: For example, the addition of oxidizer powders such as iron and/or Mn oxides or refining powders containing metal carbonates may penetrate into the molten steel.
The feature is that it is added in a dispersed manner so that the color of CO is produced. In particular, directly below the free surface of molten steel, the static iron pressure is lower than in the molten steel, so PCO
(Co partial pressure) can be lowered to promote the reaction.

Therefore, it is preferable to add the powder by blowing the powder from above the surface of the molten steel to penetrate and disperse it.

However, in the case of powder injection into molten steel, if the powder can be sufficiently dispersed even in areas where static iron pressure is large, COO
A nucleation effect can be exerted.

2) Top blowing of the powder allows the decarbonization reaction to be promoted directly below the surface of the molten steel where the static iron pressure is low, allowing the setting of the lowest PCO and Pl (!) conditions. Dispersal after infiltration becomes easier.

The lance used for top blowing is not limited to (a) a single-hole lance with a straight nozzle;
Although any lance having a special four-hole nozzle described in Japanese Patent No. 35615 may be used, it is not enough for the powder to just reach the surface of the molten steel, and it is desirable that the powder penetrate into the molten steel and be dispersed.

3) In the powder blowing method, the effect of the above-mentioned top blowing is slightly inferior. This is due to the powder being trapped in the blown gas and mutual agglomeration of the powder, but compared to split charging, the effect of coloring CO production in molten steel and the formation of fine CO bubbles are higher. .

The nozzle used for blowing has a structure in which (a) only gas flows at all times, and (b) powder can be supplied as needed. It is not sufficient to simply add powder into the molten steel; it is desirable to have the powder dispersed within the WI steel.

4) Moisture in the Powder The oxidizer powder or refining powder absorbs or deposits atmospheric moisture or other sources of moisture under normal conditions of use. Therefore, it is preferable that the amount of water attached to and contained in the powder be as small as possible when used for the purpose of dehydrogenation, but it is extremely difficult to completely eliminate this amount. The allowable amount varies depending on the decarbonization method, but in the top blowing method, if it is 0.1% by weight or less, (H)≦
1 ppm can be achieved, but the blowing method can achieve (H)≦1 ppm at 0.5% by weight or less.

Therefore, in the present invention, the content is set to 0.05% by weight or less.

By the way, the reason why the heating and drying temperature was set at 400°C or higher in order to reduce the moisture content in the powder to 0.05% by weight or less was to remove not only the attached moisture but also the contained moisture (hydrate). be.

Note that at temperatures below 400°C, it takes a considerable amount of drying time to reduce the water content to 0.05% by weight or less.

5) Particle Size of Powder It is desirable that the number of particles of the powder is large in order to cause CO to form and color in molten steel, and it is preferable to disperse it in the molten steel. The larger the amount of CO-generated color, the more opportunities for COO formation will increase, and the finer the CO-generated color, the finer the bubbles of CO gas will be.

Therefore, the dehydrogenation reaction occurs at this gas-molten steel interface,
For the same amount of COO, the finer the bubbles are, the larger the interfacial area becomes. Therefore, the more fine CO bubbles are formed, the higher the dehydrogenation rate can be.

When the particle size of the powder is large, the co bubbles generated are large;
The effect of increasing the gas-molten steel interface area is small. On the other hand, if the particle size of the powder is too fine, it will be easier to contact each other and form aggregates when entering the molten steel, and the absolute amount of kinetic energy of the powder will decrease, making it difficult for the powder to penetrate into the molten steel. As a result, the effect of increasing the gas-metal interface area is reduced.

Therefore, there is an optimum particle size range depending on the adding method and conditions.

In the case of powder top blowing, the maximum is approximately 1 am, and the minimum is 0.
It is desirable to use it within a range of about 0.05 mm.

In addition, in the case of powder injection, it is difficult to use because it collects in small areas, and the maximum is about 1111, and the minimum is 0.2 m.
The degree was necessary.

6) Degree of Vacuum Even if the penetration and dispersion of the powder into the molten steel is sufficient, the better the degree of vacuum, the more the decarbonization will be promoted. In other words, the lower the pressure, the more advantageous it is to promote decarbonization.

In practice, when using powder, a carrier gas is required, and care must be taken as the gas deteriorates the degree of vacuum in the reaction system. However, in the case of the present invention, the penetration and dispersion effect of powder into molten steel does not change much even if the vacuum degree of the system deteriorates, and the promotion of C and H removal can be maintained.

However, when the temperature deteriorated to 200 Torr or more, the top-blown powder stalled and scattered before and after reaching the molten steel, and in the case of blown powder, the carrier gas blown at the same time did not expand sufficiently and caused the powder to aggregate.

Therefore, in the present invention, it is preferable to use the pressure reduction condition of 200 Torr or less, and of course, the higher the vacuum, the better.

7) Specifying that the total amount of alloy components is 1% by weight or more is when adjusting the components from ferroalloy to (H
) This is because it is limited to steel types that are particularly difficult to lower H among the steel types that should be lowered.

(Example) Examples of the method of the present invention will be described below.

Part 1) Example using a ladle As shown in Figure 1, molten steel (2TON, C
= 0.1% by weight, Mn = 1.5% by weight, 1600° C.), iron ore powder was top-blown from a height of 400 m using top-blowing lance 1 (invention 1). The pressure inside the vacuum chamber 2 is 20 Torr, and the molten steel 4 is heated with Ar gas from the bottom of the ladle 3.
was stirred. The iron ore supply rate is approximately 0.2 kg/5i
When n- is constant, the amount of bottom-blown Ar gas is approximately 1 to 31/ak.
It was set as in-t. The amount of decarburization approximately 20 minutes after top blowing of the iron ore powder was approximately 0.05% by weight.

The dehydration behavior at this time was that the initial (H) = 2.8 ppm reached Q, 32 pp+w after 20 minutes.

The results of the present invention 1 are shown in Table 1 and Figure 2 below, together with the results of a comparative experiment in which decarbonization was performed by blowing oxygen gas upward using the same device, and in which iron ore grains were added in portions from above.
It is shown in Figure 3.

Further, using the same device, iron ore powder was blown into the molten steel 4 at a depth of 150 mm from the surface as shown by the dashed line in Fig. 1 to decarbonize it (Invention 2). As shown in the table, although the dehydrogenation effect is slightly inferior to Invention 1, it is clear that the dehydrogenation effect is higher than Comparison 1 and Comparison 2.

Therefore, as described in the detailed description of the present invention, even when an oxygen source is added to molten steel to forcibly cause a decarbonization reaction to promote dehydrogenation, the oxidizer powder is top-blown or The blowing method has a particularly high dehydrogenation effect. Moreover, the conventional attainment (
It is also clear that the present invention can easily obtain H)≦1 ppm in situations where it is difficult to obtain H)≦1 ppm, as shown in FIG.
Approximately 1/10 of the hydrogen solubility of approximately 4 ppm at 600°C
was able to obtain.

Part 2) Example using RH As shown in Figure 4, molten steel (250 TON) was placed in a ladle 3.
5C = 0.07% by weight, M n = 1.4% by weight,
1600℃), the vacuum chamber 2'
The iron ore powder was top-blown using a top-blowing lance (3) from a height of 600 Io between the lance and the scene (invention 3). The pressure inside the vacuum chamber 2° is approximately 0°8 Torr, and the RH reflux Ar
Gas is 160 ONI! /n+in was constant and the R)l treatment was carried out for 20 minutes, and the amount of Cl removed was about 0.06% by weight. The dehydrogenation behavior at this time is initial [H) = 4.2 p
pts reached 0.8 ppHl.

The results of Invention 3 are shown in Table 2 below, together with comparative experiments in which oxygen gas was blown obliquely upward from the side wall of the vacuum chamber using the same RH and in which iron ore lumps were charged in portions from above.

Further, using the same RH, iron ore powder was decarbonized by blowing through the blowing tuyere 5 shown in FIG. 4 at a depth of about 200 mm from the surface of the molten steel (Invention 4). The dehydrogenation effect at this time is the second
As shown in the table, it is almost the same as Invention 3, and Comparative 3
, Comparison 4, and Comparison 4, all exhibited higher dehydrogenation effects.

As described above, the present invention is very effective not only for promoting the dehydrogenation of solid solution steel in a ladle, but also for promoting the dehydrogenation in a vacuum chamber when circulating molten steel such as RH, and easily converts (H) ≦1p
This is an extremely excellent dehydrogenation method that can produce pII+.

Furthermore, in Example No. 2), the present invention 3 and the present invention 4 have (H) It can be seen that this is a very unique C removal method that breaks the 1 ppm barrier.

Part 3) Moisture of powder Molten steel (2TON,,C=
An experiment was conducted to show the effect of water in a solid oxidant on the dehydrogenation behavior.

The results are shown in FIG. When the top blowing method or the blowing method of the present invention was used, if the water content in the oxidizing agent was 0.05% by weight or less, H≦1 ppm was obtained.

The water content in the oxidizing agent used in Invention 1 was about 0.02% by weight, and the water content in the oxidizing agent used in Invention 2 was also about 0.02% by weight.

Therefore, even when a solid oxidizing agent is added (introduced), it can be said that the oxidizing agent powder top blowing method and the powder blowing method of the present invention have less restrictive conditions on the moisture contained in the oxidizing agent. The reason for this is that in the case of the method of the present invention, each fine particle of the top-blown or blown oxidizing agent powder becomes an oxygen supply source and a generation nucleus for the formation of fine CO bubbles, so that the attached moisture is removed efficiently (fine CO bubbles). It is assumed that it will be removed along with the

However, as shown in FIG. 5, it is preferable that this attached or contained moisture be small.

Part 4) Vacuum degree Molten steel (2TON, C=
An experiment was conducted to show the influence of the degree of vacuum on the dehydrogenation rate when using a solid oxidizing agent (Mn = 1.5 wt%, 1600° C.). The results are shown in FIG.

Invention 1 is the largest in kg # 30
(sec-'), and further comparison 2 separation method kH''42.8X
The order was 10-' (sec).

As is clear from this example, the top-blowing method of the present invention provides high dehydrogenation under vacuum conditions of 200 Torr or less.
It turns out that the speed can be maintained.

From this, it is clear that the oxidizing agent powder top-blowing method or blowing method described in the present invention is an excellent method for promoting deH removal.

Part 5) Bottom-blown Ar gas Molten steel (2TON, C=0.
1% by weight, Mn = 0.8% by weight, Cr-0.7% by weight, 1600°C) was overblown with iron ore powder. The implementation conditions at this time are the same as those of the present invention 1 in Part 1), but ArPi
The results obtained without stirring are shown by the * mark in FIG. 7 (Invention 5).

Note that the conditions for the cases marked with * in FIG. 7 are as shown in Table 3 below.

The dehydrogenation behavior at this time was initially (H) = 2.5 ppm, which decreased to 0.78 ppa+ after 20 minutes.

In other words, it became clear that (H)≦1 pp+s can be achieved by using the top blowing method of the present invention even without bottom blowing Ar gas stirring, but when combined with bottom blowing Ar gas stirring, H can be further removed. The promotion effect is enhanced.

In addition, the implementation results described in the present invention 2 of 1) show that the effect of Ar gas stirring by the method of injecting iron ore powder appears as a complementary effect. Among the conditions of present invention 2, when the bottom-blown Ar gas stirring is stopped (present invention 6), the initial (
H) = 2.8 ppm is 1. It reached Oppra.

Part 6) CaCOz top blowing As shown in Figure 1, molten steel (2TON,
C=0.1% by weight, Mn=1.2% by weight, Cr=0.
7% by weight, 1600° C.) using a top blowing lance from a lance-to-scene height of 400 mm (Invention 7). The pressure inside the vacuum chamber 2 is 2QTorr
The molten steel 4 was stirred with Ar gas from the bottom of the ladle.

The feeding rate of CaCO3 powder is approximately 0.2 kg/m1n-
is constant, and the bottom-blown Ar gas amount is approximately 1 to 3Nβ/m1n-
It was set as t. The amount of CaCO5 powder topblown powder was about 20% by weight.

The dehydrogenation behavior at this time is that the initial (H) = 3:1 ppm becomes 1.1 ppm after 20 minutes, and 1 p after 25 minutes.
It became below pm. Although this is slightly inferior to Invention 2 in Table 1 above, the CO□ bubbles generated by thermal decomposition of the powder act effectively to promote deH without significantly reducing the (C) in the molten steel. CO with +C=2GO
□ causes decarbonization of molten steel.

CaC0, powder is difficult to adsorb (absorb) moisture in the atmosphere,
Since the moisture content of the powder used is easy to control, the effect of promoting dehydrogenation is also high.

(Effects of the Invention) As explained above, the present invention provides a method for dehydrogenating molten steel containing 1% by weight or more of alloy components in advance by heating and drying the steel at a temperature of 400° C. or higher after adjusting the alloy components. Oxidizer powder or refining powder with a water content of 0.05% by weight or less is heated to 200 Torr.
This method increases the gas-metal interface area by promoting the decarburization reaction by blowing onto the surface of the molten steel placed in a reduced pressure vessel below r or into the molten steel, so it has problems with conventional methods. All of these problems can be solved and dehydrogenation can be effectively promoted.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the first embodiment of the method of the present invention, FIGS. 2, 3, and 7 are relationship diagrams between refining time and hydrogen concentration value, and FIG. 4 is a diagram showing the second embodiment of the method of the present invention. Explanatory diagram showing the example, No. 5
The figure shows the relationship between the amount of water in the oxidizing agent and the hydrogen concentration reached, Figure 6 shows the relationship between the degree of vacuum and the dehydrogenation rate coefficient, Figure 8 shows the hydrogen solubility in pure iron, and Figure 9 shows the relationship between the degree of vacuum and the dehydrogenation rate coefficient. The figure shows the solubility of hydrogen at 1600°C. 1 is a lance, 2.2 is a vacuum chamber, and 4 is a molten steel. Figure H1 Figure 2 Figure 3 Figure 7 Figure 8 jfft 11tIi41i (min) Figure 9 CPH,) cm%)

Claims (2)

[Claims] (1) When dehydrogenating molten steel containing 1% by weight or more of alloy components in total after adjusting the alloy components, an oxidizing agent that is heated and dried in advance to reduce the adhesion or water content to 0.05% by weight or less Powder or refining powder, 200
A method for promoting dehydrogenation of molten steel, which comprises blowing onto the surface of molten steel placed in a reduced pressure vessel of Torr or less or blowing into the interior of the molten steel to promote decarburization reaction and increase the gas-metal interface area. (2) When top-blowing the powder onto the surface of the molten steel, the powder is top-blown while introducing an inert gas into the molten steel or toward the gas boiling up on the surface of the molten steel. A method for promoting dehydrogenation of molten steel according to claim 1.