JPH07100813B2 - Method for promoting dehydrogenation of molten steel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for promoting a dehydrogenation reaction in molten steel.

(Prior Art) The solubility of [H] in molten steel is 2 at 1600 ° C as shown in Fig. 8.
It is as high as 6.8 ppm, and the following two conditions are necessary to reduce it.

Reduced pressure (vacuum) When the hydrogen partial pressure (P _H2 ) on the gas side at the gas-metal interface is lowered, the [H] concentration in the molten steel that equilibrates with this decreases as shown in FIG.

At this time, the reached [H] concentration can be reduced.

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, bubbles in the molten steel can be expanded, which is effective in promoting the dehydrogenation reaction. Therefore, in order to effectively reduce H, gas-
Increase the metal boundary area as much as possible (improve the H removal rate)
It is important to carry out high vacuum treatment (increasing the stirring power of bubbles and lowering the reaching [H] value).

(Problems to be Solved by the Invention) However, it is difficult to increase the free surface of the molten steel in the gas metal boundary area because it is determined by the equipment conditions. Therefore, a method of introducing gas into the molten steel is generally adopted, but if a large amount of gas is introduced, the degree of vacuum is deteriorated, and therefore the amount of introduced gas cannot be unconditionally increased. It is also necessary to improve equipment such as enhancing the vacuum pumping capacity to secure the degree of vacuum. An example of this in RH will be described.

Currently, the amount of circulating Ar gas is about 16 when processing 250 tons of molten steel.
Processing is performed at 0 Nl / min and a vacuum degree of 0.3 Torr. In order to promote dehydrogenation, the amount of refluxing Ar gas should be 3000 (~ 5000) Nl / min.
The degree of vacuum deteriorated to 0.6 to 0.8 Torr. As the circulating flow rate increased, a large amount of splash adhered to the side wall of the vacuum chamber immediately above the riser pipe, sometimes hindering the operation. Therefore, in order to bring the degree of vacuum to the conventional level (0.3 Torr), the evacuation capacity was increased, but the splash could not be reduced.

At this time, the H removal rate is about 10 × 10 ^-4 (sec ^-1 ) and the reached H value is
When the amount of reflux Ar was increased at 1.5 ppm, the dehydrogenation rate was slightly improved (12 × 10 ⁻⁴ (sec ⁻¹ )), and the reached H value was 1.3 ppm. However, it is difficult to reduce the average to 1 ppm or less.

That is, the problem in this RH example is that when a large amount of Ar gas is introduced, the degree of vacuum is deteriorated and the splash is increased by the Ar gas introduced locally. On the other hand, there is a measure to increase the equipment for the problem of, but there is no measure for the problem of.

The present invention is intended to provide a method for promoting dehydrogenation of molten steel which can solve such problems.

(Means for Solving Problems) As a result of various researches and experiments for solving the above problems, the inventors found the following points to be improved.

A gas amount smaller than the Ar gas increase amount (for example, 1400 Nl / min) is generated from inside the molten steel. The diameter of gas bubbles generated from inside the molten steel is made small. The bubbles generated from inside the molten steel are uniformly generated inside the molten steel and from the entire surface of the molten steel.

However, if improvements in (1) to (3) can be made, the deterioration of the degree of vacuum can be reduced, and
The metal interfacial area can be increased, and further the localized molten steel splash is reduced, resulting in extremely stable operation.

Therefore, in the present invention, when performing dehydrogenation treatment after adjusting the alloy composition on molten steel containing a total of 1% by weight or more of the alloy composition, it is heated and dried in advance at a temperature of 400 ° C. or more to have a content of 0.05 wt. % Or less of oxidizer powder or refining powder is blown onto the surface of molten steel placed in a decompression container of 200 Torr or less or into the inside of the molten steel to accelerate the decarburization reaction and promote the gas-metal interface area. The point is to increase.

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

1) Addition method For example, oxidizer powder such as iron and / or Mn oxide or refining powder containing metal carbonate is added so that it penetrates and disperses in the molten steel and becomes a CO generation nucleus. The feature is to let. In particular, immediately below the molten steel free surface, the static iron pressure is lower than that in the molten steel, so _PCO (CO partial pressure) can be lowered in the C removal reaction C + O = CO to promote the reaction.

Therefore, as a method of addition, it is preferable that the powder is blown upward from above the surface of the molten steel to penetrate and disperse.

However, in the case of the powder injection into the molten steel, the CO formation nucleation effect can be exhibited even if the static iron pressure is large if the powder is sufficiently dispersed.

2) When the powder on spray on spray can facilitate de C reaction just below a lower surface of molten steel of static iron pressure, setting the lowest condition P _CO and P _H2. In addition, the upper blowing facilitates the dispersion of the powder after it has entered the molten steel.

The lance used for the upward blowing is not limited to (a) a single-hole lance having a straight nozzle, but (b) for example, Japanese Patent Laid-Open No. 59-
Any of a lance having a special 4-hole nozzle described in Japanese Patent No. 35615 may be used, but it is not enough that the powder reaches the surface of the molten steel, and it is desirable that the powder penetrates into the molten steel and is dispersed.

3) Powder blowing The blowing method is slightly inferior in the effect of the above blowing. This is because the powder is trapped in the blown gas and the powder particles agglomerate with each other, but when compared with the split charging, the effect as CO-generating nuclei in molten steel and the effect of forming fine CO bubbles are high.

The nozzle used for blowing has a structure in which (a) only gas always flows and (b) powder can be supplied as needed. It is not enough to add the powder to the molten steel, and it is desirable that the powder be dispersed in the molten steel.

4) Water in powder Oxidizer powder or refining powder absorbs or attaches water in the air or other water sources under normal use conditions. Therefore, the amount of water adhered and contained in the powder is preferably as small as possible when used for the purpose of dehydrogenation, but it is extremely difficult to eliminate it. The allowable amount depends on the method of decarbonization, but if it is 0.1% by weight or less in the top blowing method, [H] ≦ 1 pp
m can be achieved, but with the blowing method, 0.5% by weight or less [H] ≦
1ppm is possible.

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

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

At 400 ° C or lower, a considerable amount of drying time is required to reduce the water content to 0.05% by weight or lower.

5) Particle size of powder It is desirable that the particle size of the powder is large in order to act as CO generation nuclei in the molten steel, and it is preferable to disperse it in the molten steel. When a large amount of CO-producing nuclei are present, that much CO
The chances of production increase, and the finer the CO-producing nuclei, the finer the bubbles of CO gas produced.

Then, the dehydrogenation reaction occurs at this gas-molten steel interface,
If the amount of CO generated is the same, the smaller the generated bubbles, the larger the boundary area. Therefore, the formation of fine CO bubbles can increase the dehydrogenation rate accordingly.

When the particle size of the powder is large, the generated CO bubbles are large and 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 small, it becomes easy for them to come into contact with each other when entering the molten steel to form an aggregate, and the absolute amount of kinetic energy of the powder decreases, making it difficult for the particles to enter the molten steel. As a result, the effect of increasing the gas-metal interface area decreases. Therefore, there is an optimum particle size range depending on the addition method and conditions.

In the case of powder top spraying, it is desirable to use within a range of 1 mm at maximum and 0.05 mm at minimum. Also, in the case of powder injection, it is difficult to use because it aggregates in the finer area.
About 1 mm, at least about 0.2 mm was necessary.

6) Degree of vacuum Even if the powder penetrates into the molten steel and is sufficiently dispersed, the better the degree of vacuum, the more promoted the decarbonization. That is, the lower the pressure, the more advantageous the promotion of decarbonization.

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

However, when it deteriorated to more than 200 Torr, the top-blown powder stalled and scattered before and after reaching the molten steel, and also in the case of the blown powder, the carrier gas blown at the same time did not expand sufficiently and aggregated the powder. Therefore, in the present invention, it is preferable to use it under a reduced pressure condition of 200 Torr or less, and of course, a higher vacuum is preferable.

7) The total amount of alloying components is specified to be 1% by weight or more, because the [H] pickup is made from the ferroalloy at the time of adjusting the components, and it is particularly limited to the steel types that are difficult to reduce in H content. Is.

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

Part 1) Example using ladle Molten steel (2TON, C = 0. 0) put in ladle 3 as shown in FIG.
1% by weight, Mn = 1.5% by weight, 1600 ° C) and height of molten metal 400 mm
From there, the iron ore powder was top-blown using the top-blown lance 1 (invention 1). The pressure in the vacuum tank 2 is 20 Torr and the ladle 3
Molten steel 4 was stirred with Ar gas from the bottom. The iron ore supply rate is approximately 0.2 kg / min · t, and the bottom blown Ar gas amount is approximately 1 to 3
l / min · t. However, the decarburization amount in about 20 minutes after blowing on the iron ore powder was about 0.05% by weight.

At this time, the dehydrogenating behavior of the initial [H] = 2.8 ppm reached to 0.32 ppm after 20 minutes.

The results of the present invention 1 are shown in Tables 1 and 2 below together with the results of a comparative experiment in which oxygen gas was blown upward to remove C using the same apparatus and iron ore grains were dividedly added from above.
It is shown in FIG.

Further, using the same apparatus, iron ore powder was blown out to remove C at a depth of 150 mm from the surface of the molten steel 4 as shown by the chain line in FIG. 1 (Invention 2). At this time, as shown in Table 1 above, although the dehydrogenating effect is slightly inferior to that of the present invention 1, it is clear that the dehydrogenating effect is higher than in Comparative Examples 1 and 2.

Therefore, as described in the detailed description of the present invention, when an oxygen source is added to the molten steel to forcibly cause the de-C reaction and promote the de-H removal, the oxidizer powder is blown or blown as in the present invention. The blowing method is particularly effective in removing H. Moreover, it is also clear that the present invention [H] ≤ 1 ppm can be easily obtained in the present invention in a situation where it is difficult to obtain, and it is 1600 ° C shown in Fig. 9.
It was possible to obtain about 1/10 of the hydrogen solubility of about 4 ppm.

Part 2) Example of using RH Molten steel (250TON, C =
0.07% by weight, Mn = 1.4% by weight, 1600 ° C) at the time of RH treatment, the height between the lance and the molten metal surface is 600 mm in the vacuum chamber 2 '.
From there, the iron ore powder was top-blown using the top-blown lance 1 (invention 3). The pressure in the vacuum chamber 2'is about 0.8 Torr and R
The H-reflux Rr gas was kept constant at 1600 Nl / min, and the decarbonization amount when the RH treatment was carried out for 20 minutes was about 0.06% by weight. H removal at this time
The behavior of the initial [H] = 4.2 ppm reached 0.8 ppm.

The results of Invention 3 are shown in Table 2 below together with a comparative experiment in which oxygen gas was blown obliquely upward from the side wall of the vacuum chamber using the same RH and when an iron ore lump was dividedly charged from above.

Using the same RH, iron ore powder was blown out through the blown tuyere 5 of FIG. 4 at a depth of about 200 mm from the surface of the molten steel to remove C (invention 4). As shown in Table 2 above, the dehydrogenating effect at this time was almost the same as that of the present invention 3, and compared to Comparative 3 and Comparative 4, all exhibited a high dehydrogenating effect.

As described above, the present invention is not limited to the promotion of H removal of molten steel in a ladle.
H removal in a vacuum chamber when circulating molten steel such as RH
It is also very effective for promotion, and is an extremely excellent dehydrogenation method capable of easily producing [H] ≦ 1 ppm.

Further, also in Example 2), the invention 3 and the invention 4 are extremely characteristic of breaking the barrier of [H] concentration of 1 ppm as compared with the result of promoting dehydrogenation obtained when oxygen gas or a solid oxidant is simply added. It turns out that it is a C-free method.

Part 3) Water content of powder Using molten steel (2TON, C = 0.1% by weight, Mn = 1.7% by weight, 1600 ° C) in a ladle 3 shown in Fig. 1, the water content in the solid oxidant is removed. An experiment was conducted to show the effect on behavior.

The result is shown in FIG. When the top blowing method or blowing method of the present invention was used, when the water content in the oxidizing agent was 0.05% by weight or less, the reaching [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 the solid oxidant is added (supplied), it can be said that the oxidant powder top-blowing method and the powder blasting method of the present invention have loose restrictions on the water content in the oxidant. The reason for this is that in the case of the method of the present invention, each fine particle of the oxidant powder blown up or blown serves as an oxygen supply source and a generation nucleus for the formation of fine CO bubbles, so that the adhered water is efficiently mixed with the fine CO bubbles. I think it will be removed.

However, it is preferable that the amount of the attached or contained water is small as shown in FIG.

Part 4) Degree of vacuum Dehydration rate when using a solid oxidizer using molten steel (2TON, C = 0.1% by weight, Mn = 1.5% by weight, 1600 ° C) placed in the ladle 3 shown in Fig. 1. Experiments were conducted to show the effect of the degree of vacuum on the. The result is shown in FIG.

The present invention 1 ^{_{k H ≒ 30 × 10 -4 (}} sec -1) at the largest, then k _H ≒ 19 × 10 ^-4 of the present invention 3 (sec ^-1), further divided pitching k _H ≒ comparison 2 The order was 2.8 × 10 ^-4 (sec ^-1 ).

As is clear from this example, it is understood that the top blowing method of the present invention can maintain a high H removal rate under a vacuum condition of 200 Torr or less.

From this, it is clear that the oxidant powder top blowing method or the blowing method described in the present invention is an excellent dehydrogenation promoting method.

5) Bottom blown Ar gas Iron ore powder was placed on the molten steel (2TON, C = 0.1% by weight, Mn = 0.8% by weight, Cr = 0.7% by weight, 1600 ° C) in the ladle 3 shown in Fig. 1. Blew. The conditions for carrying out at this time are the same as those in Invention 1 of 1), but the results when Ar stirring is not carried out are shown by the ● marks in FIG. 7 (Invention 5).

The conditions in the case of the ● marks and the like shown in FIG. 7 are as shown in Table 3 below.

At this time, the dehydrogenation behavior was initially [H] = 2.5 ppm, but decreased to 0.78 ppm after 20 minutes.

That is, it has been clarified that [H] ≦ 1 ppm can be achieved by using the top blowing method of the present invention even without bottom blowing Ar stirring. However, when bottom blowing Ar gas stirring is also used, dehydrogenation is further promoted. The effect is enhanced.

In addition, the results of the implementation described in the second aspect of the present invention 1) show that the effect of stirring the Ar gas by the method of blowing iron ore powder is a residual effect. Under the conditions of the present invention 2, bottom blowing Ar
When the gas stirring is stopped (Invention 6), the initial [H]
= 2.8ppm reached 1.0ppm.

6) CaCO ₃ top blowing Molten steel (2TON, C = 0.
1% by weight, Mn = 1.2% by weight, Cr = 0.7% by weight, 1600 ° C.), the CaCO ₃ powder was top-blown using the top-blown lance 1 from the height of the lance-melt level of 400 mm (the present invention 7). ). The pressure in the vacuum chamber 2 was 20 Torr, and the molten steel 4 was stirred with Ar gas from the bottom of the ladle.

Feeding rate of CaCO ₃ powder is constant at about 0.2 kg / min ・ t, bottom blowing
The amount of Ar gas was set to about 1 to 3 Nl / min · t. The amount of decarburization about 20 minutes after the CaCO ₃ powder was blown was about 0.02% by weight.

At this time, the dehydrogenating behavior was 1.1 ppm after 20 minutes for the initial [H] = 3.1 ppm, and was 1 ppm or less after 25 minutes. Although this is slightly inferior to Invention 2 of Table 1 above, it occurs due to the thermal decomposition of the powder without significantly lowering [C] in the molten steel.
CO ₂ bubbles act effectively to promote dehydrogenation and CO ₂ + C = 2C
CO ₂ due to O causes decarbonization of molten steel.

CaCO ₃ powder does not easily adsorb (absorb) moisture in the air, and since the water content of the powder used is easy to manage, it has a high effect of promoting dehydrogenation.

(Effects of the Invention) As described above, the present invention heats and dries in advance at a temperature of 400 ° C. or higher when performing dehydrogenation treatment on molten steel containing a total of 1 wt% or more of alloying components after adjusting the alloying components. Decarburization reaction by spraying or blowing oxidizer powder or refining powder with water content of 0.05 wt% or less onto the surface of molten steel placed in a decompression container of 200 Torr or less or into the molten steel. Is a method of increasing the area of the gas-metal interface by accelerating the reaction, all the problems in the conventional method can be solved, and dehydrogenation can be effectively promoted.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a first embodiment of the method of the present invention, and FIG.
FIG. 3, FIG. 3 and FIG. 7 are diagrams showing the relationship between refining time and hydrogen concentration value, FIG. 4 is an explanatory diagram showing a second embodiment of the method of the present invention, and FIG. Relationship diagram with hydrogen concentration value,
FIG. 6 is a diagram showing the relationship between the degree of vacuum and the dehydrogenation rate coefficient, FIG. 8 is a drawing showing the solubility of hydrogen in pure iron, and FIG. 9 is a drawing showing the solubility of hydrogen at 1600 ° C. 1 is a lance, 2'is a vacuum tank, 4 is molten steel.

Claims (2)

[Claims] 1. When performing dehydrogenation treatment on a molten steel containing a total of 1% by weight or more of alloy components after adjusting the alloy components,
200 T of oxidizer powder or refining powder that has been previously dried by heating to a content of 0.05% by weight or less
Gas is generated by accelerating the decarburization reaction by blowing on or into the surface of molten steel placed in a decompression container at orr or below.
A method for accelerating dehydrogenation of molten steel, which is characterized by increasing a metal boundary area. 2. When the powder is sprayed onto the surface of the molten steel, the powder is sprayed onto the surface of the molten steel while introducing an inert gas or by aiming at the gas boiled out on the surface of the molten steel. The method for promoting dehydrogenation of molten steel according to claim 1.