JPH0813024A - Production of oxide dispersed steel - Google Patents

Abstract

PURPOSE:To stably produce an Al-Mn based oxide dispersed steel having high welding toughness by performing preliminary deoxidation by the use of Si and Mn, regulating total oxygen content to a prescribed value or below, and then adding Al and oxide or Al-containing oxide. CONSTITUTION:At the time of steelmaking, a molten steel is preliminarily deoxidized with Si and Mn and total oxygen content is regulated to 0.0020-0.0100% and then an Al alloy and an oxide capable of controlling oxygen potential in the molten steel or an Al-containing oxide capable of controlling oxygen potential in the molten steel is added, by which Al content in the molten steel is regulated to 0.0001-0.0O30%. Moreover, in the case where a converter or an electric furnace is used, carbon content in the molten steel is regulated and then preliminary deoxidation is performed by the use of Si and Mn during tapping or in a ladle and also slag modification is done, and, after total oxygen content is regulated to 0.0020-0.0100% by ladle refining, an Al-containing alloy and an oxide capable of controlling oxygen potential in the molten steel or an Al-containing oxide capable of controlling oxygen potential is added during ladle refining, by which Al content is regulated to 0.0001-0.0030%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide-dispersed steel, which is a steel grade for thick plates that requires high weld heat affected zone toughness.

[0002]

2. Description of the Related Art Recently, in order to rationalize the welding process, a large amount of heat input welding of steel materials such as thick steel plates has been aimed. Generally, in large heat input welding, the heat affected zone of the base material (hereinafter HAZ
It is known that the toughness is significantly reduced due to the coarsening of the crystal grains in the HAZ part. We must try to solve the problem of commutation.

By the way, it has been conventionally known that by dispersing fine particles of an appropriate oxide or nitride in a steel material, the structure is refined and the toughness of the HAZ part is remarkably improved.

As a method of utilizing such finely dispersed particles, Japanese Examined Patent Publication No. 5-17300 discloses a method in which the amount of Si and the amount of Al in steel are specified, and Ti is added so that Ti is added during the solidification process.
A method for producing a steel having a high toughness in the HAZ part, in which fine Ti-based oxides such as O and Ti ₂ O ₃ are precipitated and dispersed, has been proposed.

As a method for finely depositing and dispersing such a Ti oxide in the steel material during the solidification process, as disclosed in JP-A-3-267311 and JP-A-4-2713, other methods are known. Si and Mn are used as the first deoxidizing element, and Ti, Zr, and Ca are added as the second deoxidizing element, and the oxygen concentration is 50 pp in weight ratio.
There is a method of precipitating Ti-Zr-based oxide particles containing Ti and Zr as the main components to m or less.

Further, in Japanese Unexamined Patent Publication (Kokai) No. 4-191314, in order to finely precipitate Ti-based oxides during solidification, undeoxidized molten steel is vacuum-treated to obtain a dissolved oxygen concentration of 0.002 by weight.
A method is disclosed in which Ti is added after adjustment to ˜0.015%.

Further, in order to make such precipitated particles of Ti-based oxide finer, Japanese Patent Publication No. 3-67467 discloses a method of controlling the cooling rate after casting, and Japanese Patent Laid-Open No. 4-6243 discloses a method. A method has been proposed for defining the time until tapping after adding Ti.

Further, in JP-B-5-25580 and JP-A-3-177535, it is effective to further add Zr, Y or the like to finely disperse the particles precipitated in the solidification process. It is stated.

By the way, each of these methods is a method of finely depositing and dispersing a Ti-based oxide in the solidification process,
The oxide composition was only shown for those with Ti-based oxides.

Further, as far as the inventors of the present invention are aware, the improvement in the toughness of the HAZ portion obtained by depositing and dispersing particles mainly composed of a Ti-based oxide is not sufficient as the actual effect and is more effective. Further, it has been desired to develop a material containing dispersed particles for making the HAZ portion highly tough and a method for stably and easily manufacturing the material.

[0011]

By the way, the applicant of the present invention has proposed, in Japanese Patent Application No. 6-77057, an Al-Mn-based oxide phase as a steel for thick plates that stably toughens the HAZ portion. We have proposed an oxide-dispersed steel in which the oxides with are dispersed in the steel. That is, dispersed particles having a diameter of 0.2 to 20 μm are dispersed at 4 or more and less than 1000 per 1 mm ^{2 of the} steel material cross section, and (Al + Mn) is 40% in the atomic ratio of the metal element as the oxide phase constituting the dispersed particles. Above, Al: Mn ratio is 1: 1
It is an oxide-dispersed steel in which an oxide having an Al-Mn oxide phase having a characteristic of not less than 5: 1 is dispersed in the steel.

However, since a method for stably producing such oxide-dispersed steel has not yet been established, industrially sufficient characteristics cannot be exhibited, and further improvement in the production method is required.

Therefore, the object of the present invention is to disperse in the steel an oxide containing an Al-Mn-based oxide phase, which has high performance as a steel for thick plates which requires high toughness in the heat-affected zone of welding. An object of the present invention is to provide a more stable production method of oxide-dispersed steel.

[0014]

Means for Solving the Problems The present inventors have added Si and Mn during pre-deoxidation to change the composition of inclusions consisting of primary deoxidation products to the MnO-SiO ₂ system, thereby forming inclusions. With a diameter of more than 10 μm is easily floated and removed, and effective pre-deoxidation is possible, and the remaining inclusions become small-diameter inclusions of 5 μm or less. Also, when Al is added in the next step. By adding together an oxide that can control the oxygen potential,
Knowing that it serves as a nucleus for the formation of system inclusions, it is possible to finely disperse Al-Mn-based oxides in steel by simultaneously controlling the oxygen potential in molten steel and the trace Al concentration in molten steel. They have found the present invention and completed the present invention.

Thus, the gist of the present invention is as follows.
In producing an oxide-dispersed steel having an Al-Mn oxide phase and an unavoidably coexisting oxide phase as dispersed particles,
Pre-deoxidation of molten steel with Si and Mn to obtain a total oxygen concentration of 0.0020%
After adjusting to not less than 0.0100%, either an Al-containing alloy and an oxide capable of controlling the oxygen potential in molten steel, or an oxide containing Al capable of controlling the oxygen potential in molten steel, By adding Al to the molten steel, the Al concentration in the molten steel is 0.0001% to 0.0030% in terms of polymerization rate.
This is a method for producing an Al-Mn-based oxide-dispersed steel, which is controlled as follows.

From another aspect, the present invention provides dispersed particles.
When smelting an oxide-dispersed steel having an Al-Mn oxide phase and an unavoidably coexisting oxide phase, the carbon concentration was adjusted in a converter or an electric furnace, and Si was added during tapping or ladle.
And Mn to pre-deoxidize molten steel and slag reforming, and adjust the total oxygen concentration to 0.0020% or more and 0.0100% or less in the ladle refining equipment of the ladle furnace, and then control the Al-containing alloy and oxygen potential in the molten steel. It is possible to control the oxygen potential or the oxide containing Al, by adding the Al-containing oxide to the molten steel during ladle refining, the Al concentration in the molten steel to a weight ratio. 0.0001% or more 0.
It is a method for producing an Al-Mn-based oxide-dispersed steel, which is characterized by controlling the content to be not more than 30%.

According to a preferred embodiment of the present invention, the above Al-containing alloy and the oxide or the oxide containing Al are added to molten steel, and then Ti is added to the molten steel in an amount of 0.050% or less by weight. You may

According to another preferred embodiment of the present invention, after pre-deoxidizing with Si and Mn in the tapping or ladle and performing slag modification, the ladle refining equipment of the ladle furnace is further installed. May be desulfurized to a sulfur concentration of 0.002% or less.

Thus, according to the present invention, an oxide having an Al-Mn-based oxide phase and an unavoidable oxide phase, more specifically, having a diameter of 0.2 to 20 μm, An oxide in which an oxide containing an Al-Mn-based oxide phase is dispersed, in which (Al + Mn) is 40% or more as a mole fraction of a metal element, and the Al: Mn ratio is 1.0 or more and less than 5.0. Dispersed steel is manufactured stably.

[0020]

Next, the operation of the present invention will be described more specifically. The molten steel used in the present invention may be any molten steel that has been melted with the required composition that can achieve the target final steel composition, for example, simply melted in an appropriate melting furnace. Alternatively, it may be decarburized and smelted in a converter or an electric furnace.

The carbon content is preferably 0.05 to 0.08% and the oxygen content is 0.04 to 0.07%. Especially when preparing molten steel by converter or electric furnace, C: 0.01
It is preferably adjusted to 0.25%.

Pre-deoxidation : First, Al as dispersed particles in steel
-In order to produce an oxide-dispersed steel having an Mn-based oxide phase and an unavoidably coexisting oxide phase, in the early stage of the production of the molten steel prepared as described above, the affinity for oxygen in the molten steel is high. Pre-deoxidation is carried out with Si and Mn which have the oxygen content, and the total oxygen concentration is adjusted to fall within a predetermined range. Si and Mn may be added to molten steel in the form of ferroalloy (Fe-Si, Fe-Mn), Mn ore, etc., as in ordinary deoxidation, and there is no particular limitation.

Here, the amount of Si and Mn added during the preliminary deoxidation is not particularly limited as long as the total oxygen concentration is 20 to 100 ppm, but preferably the molten steel concentration is Si: 0.05 to 0.
60% and Mn: 0.3-3.0%. The reason is that the primary deoxidation product formed in the preliminary deoxidation is easily aggregated and effective deoxidation is performed in the MnO-SiO ₂ system, and the total oxygen concentration is 0.0020 to 0.0100% by this preliminary deoxidation. To form nuclei of dispersed oxide.

That is, in the above preferred embodiment, when the Si concentration is larger than 0.60%, the inclusions are mostly SiO ₂ -based and the total oxygen concentration is 20% even if the Mn concentration is 3.0% or less.
This is because the amount of the primary deoxidation product, which becomes the nucleus of the oxide to be dispersed, becomes insufficient because it may be less than ppm. On the other hand, when the Si concentration is less than 0.05%, the Mn concentration is 0.3%
Even if it is more than the above, the inclusions become FeO-MnO-based and are not suitable for the nuclei of Al-Mn-based oxides, and the total oxygen concentration is 100 pp.
Since it exceeds m, the oxygen supply source near the undeoxidized state becomes excessive and the cleanliness of molten steel becomes insufficient.

The same applies to the Mn concentration. When the Mn concentration is less than 0.3%, the Si deoxidized region is formed and the inclusions are SiO ₂ -based.
It is not suitable for the production of oxides. On the other hand, if the Mn concentration exceeds 3.0%, the oxygen concentration will be less than 20 ppm even if the Si concentration is 0.60% or less, and it will not be possible to leave MnO-SiO ₂ inclusions that will become the core of the dispersed oxide. There is.

By the way, generally, when the Si concentration in steel is increased, Si deoxidation becomes strong, and the total oxygen concentration is largely reduced before the addition of Al in the subsequent step, and as a result, it is necessary to disperse in the steel before the addition of Al. Since the amount of minute MnO—SiO ₂ inclusions decreases, it is desirable that the Si content be low. Furthermore, the Si concentration in the steel
It is known that if it exceeds 0.20%, the low temperature toughness is deteriorated. Therefore, it is desirable that the Si content is low. From these facts, the Si amount is preferably Si: 0.20% or less.

Therefore, taking these points into consideration, in the preferred embodiment of the present invention, the Si concentration is 0.05 to 0.20% and the Mn concentration is 0.8.
It is controlled to ~ 2.0%. In this concentration range, inclusions are more stably converted to MnO-SiO ₂ system, and the total oxygen concentration is 0.0020.
It can be ~ 0.0100%.

By the way, the reason why the inclusions are of the MnO-SiO ₂ system is that the inclusions larger than 10 μm are not only easily floated and removed but also effective preliminary deoxidation is possible.
This is because the remaining inclusions become small-diameter inclusions of 10 μm or less, and serve as nuclei for forming minute Al—Mn-based inclusions in the next step together with dissolved oxygen. The total oxygen concentration is 0.0020
〜0.0100% is MnO- which becomes the nucleus of dispersed oxide.
This is because the SiO ₂ system is allowed to remain and sufficient cleanliness is ensured.

Addition of Al + oxide or Al-containing oxide : According to the present invention, after adding Si and Mn to perform pre-deoxidation to control the total oxygen concentration as described above, the oxygen potential in the molten steel and the molten steel are controlled. The Al-Mn-based oxide can be finely dispersed in the steel by controlling the medium-trace Al concentration at the same time.

According to the present invention, therefore, either an Al-containing alloy and an oxide capable of controlling the oxygen potential in molten steel, or an oxide containing Al capable of controlling the oxygen potential in molten steel. It is added to the molten steel.

As means for controlling the oxygen potential in the molten steel and the trace Al concentration in the molten steel, an oxide having an oxygen potential similar to that of an Al-Mn-based oxide is added to the molten steel together with Al addition. , Simultaneously control the oxygen potential in molten steel and the Al concentration in molten steel.

At this time, in order to control the Al concentration in the molten steel, the amount of Al contained in the ferroalloy is controlled, or the oxide containing Al is used as the above oxide. is there.

FIG. 1 is a graph showing changes in free energy of formation per mol of oxygen of various oxides at the steelmaking temperature. Here, among the Al-Mn-based oxides that are now targeted,
Considering Al ₂ O ₃ .MnO as the most representative complex oxide, it is as follows.

First, the target free energy of formation of Al ₂ O ₃ .MnO is smaller than that of SiO ₂ which is a typical steelmaking oxide and larger than Al ₂ O ₃ . In general, SiO ₂ is known to be a weak deoxidizing molten steel such as Si-Mn deoxidized steel resulting molten steel contamination resulting reduction of SiO ₂ is. On the other hand, Al ₂ O ₃ is Al ₂
It is more stable than O ₃ · MnO and does not affect molten steel in weakly deoxidized steel.

Therefore, in order to produce an Al-Mn-based oxide with MnO.SiO ₂ as the nucleus in the molten steel, firstly SiO ₂ and
An oxide having an oxygen potential between Al ₂ O ₃ and
It is considered desirable to use an oxide having an oxygen potential similar to that of Al ₂ O ₃ .MnO.

[0036] Therefore, the spirit and "can be controlled oxygen potential in the molten steel" in the present invention are, for example free energy of FIG. 1 is smaller than SiO _2, Al ₂ O ₃
It can be said that it is bigger.

Secondly, it is desirable that the oxide be an oxide that slightly reacts with the molten steel and supplies a trace amount of Al into the molten steel. The former of such oxides is ZrO ₂ · SiO ₂ , M
_{gO · SiO 2, 2MgO · SiO} 2, MgO · 2TiO 2, MgO · TiO 2, Ti
O ₂ , CaO · MgO · 2SiO ₂ , Ce ₂ O ₃ · Cr ₂ O ₃ etc. are considered.

The latter compound which can also be supplied with Al includes
Al ₂ O ₃ · TiO ₂ in addition to Al ₂ O ₃ · MnO is itself, 3Al ₂ O
_{3 · 2SiO 2, CaO · Al} 2 O 3 · 2SiO 2, FeO · Al 2 O 3 was found to be applicable.

When the first oxide is used as an additive, it is necessary to provide another supply source capable of supplying a trace amount of Al content to the molten steel. In addition to Fe-Si used as ferroalloy, Fe-Nb, Fe-V, Fe-Mo, Fe-B, etc. used as components for thick plates can be used to supply a trace amount of Al to molten steel. .

Here, the reason why the ferroalloy is used for supplying a trace amount of Al instead of the metallic Al is that Si is used because this steel type is for thick plates.
Not only is there an opportunity to add Nb, V, and Mo, but the amount of Al contained in these ferroalloys is at most about 1-5% by weight, reducing the possibility of forming Al ₂ O ₃ -based inclusions. As a result, the added Al becomes a dissolved component and gradually
It is possible to react with Mn0-SiO ₂ inclusions and dissolved oxygen to form dispersed Al-Mn oxides, and depending on the required amount of steel species, the amount added as ferroalloy increases and trace amounts Al
It is easy to adjust the ingredients.

On the other hand, with respect to the second oxide, the oxide itself acts as an Al supply source. That is, the oxide itself can be partially decomposed to supply a trace amount of Al into the molten steel, or it reacts with the suspended MnO-SiO ₂ -based oxide to form an Al-Mn-based oxide as a dispersed oxide in the steel. Can be formed.

It is sufficient for all the oxides to be added to contain the oxides in an amount of 90% or more by weight, and the particle size is not particularly limited, but considering the handling at the time of addition, the average particle size is not limited. 0.05 mm to 0.5 mm is considered appropriate.

Since the main purpose of the method of adding the oxide is to bring the oxide into contact with molten steel to react with it, any method such as batch addition and powder blowing may be used. Next, the reason for defining the amount of dissolved Al is as follows. In the present invention, an Al-Mn-based oxide is dispersed and produced in molten steel while consuming dissolved oxygen with MnO-SiO ₂ inclusions as nuclei in the temporary deoxidation process.

Here, in the steelmaking temperature range from 1527 ° C to 1723 ° C
The oxygen potential of the Al-Mn-based oxide is roughly like the sloped portion in FIG. In addition, the figure also shows that the oxygen potential region at the dissolved oxygen concentration [% O] = 0.002 to 0.01% and the Al ₂ O ₃ oxide (activity Al ₂ O) at the time of adding [% Al] = 0.001%
The oxygen potential when ₃ = 0.1) is also shown.

The upper limit of Al--Mn oxide is [% Mn] = 0.3
%, When [% Al] = 0.0001%, the lower limit is [% Mn] = 3%,
When [% Al] = 0.003%, the Al-Mn-based oxide formation region shown during this is approximately 0.002 to 0.01% dissolved oxygen concentration.
Overlap with the oxygen potential region of.

Therefore, [% Mn] = 0.3%, [% Al] = 0.
If it is less than 0001%, the oxygen concentration becomes too high and deoxidation becomes insufficient. If it exceeds [% Mn] = 3% and [% Al] = 0.003%, Al ₂ O
_It can be seen that the possibility of formation of ₃ type oxides increases rapidly.

For refining processes using converters or electric furnaces
Regarding : Next, a description will be given according to a specific processing operation when the oxide-dispersed steel in which the Al-Mn oxide is dispersed according to the present invention is melted using a converter or an electric furnace. Of course, the present invention can be carried out by using a melting furnace such as a high frequency melting furnace.

For example, molten steel smelted in a converter or an electric furnace by a conventional method has a carbon concentration of preferably 0.01
Adjust to ~ 0.25%. The reason for this is that the steel type targeted by the present invention is used as a thick plate material, so that the carbon concentration usually has an upper limit, and it is necessary to be 0.25% or less. On the other hand, if the carbon content is limited to 0.01% or more, the molten steel and the slag do not become in a peroxidized state, and the pre-deoxidation step and slag reforming step with Si and Mn, which are the post-steps, can be easily performed.

Next, Si and Mn are added and adjusted during tapping or in a ladle. The reason for the composition range at this time has been described above, but in the actual operating process, it is difficult to control the preliminary deoxidation due to the slag that is inevitably brought in during tapping from the converter or the electric furnace. Therefore, while suppressing the outflow of slag as much as possible, it is desirable to reduce the oxygen potential of the slag by reforming the slag.

Further, in the actual operation process, the amount of molten steel is large, and it takes time to adjust the oxygen concentration by preliminary deoxidation. For example, the RH degasser refluxes to promote the floatation of the deoxidized product, the LF heating device gives sufficient time to float the product while heating the molten steel, or the VOD furnace is used to stir the gas for large-scale deoxidation. It is effective to promote the floating of the product and control the oxygen concentration.

These so-called secondary refining facilities are not only effective in promoting preliminary deoxidation including slag reforming and controlling the total oxygen concentration, but also have the effect of degassing and heat application, and as a whole, Help optimize the process.

Slag reforming : The slag reforming method and the slag reforming agent at this time are not particularly limited, but, for example, Al—CaCO ₃ agent, Al ash, Si-based modifying agent and the like can be used. In order to facilitate the preliminary deoxidation by this slag modification, it is preferable that the (T.Fe +% MnO) concentration in the slag is 2% or less in weight ratio.

Ti addition : Next, the reason for limiting the Ti addition amount will be described. After adjusting the total oxygen concentration to [% O]: 0.002 to 0.010%, add an alloy containing Al by the action as described above and add an oxide that controls the oxygen potential in the molten steel, or The Al concentration in molten steel is made to be a weight ratio by adding an oxide containing Al capable of controlling Al in the ladle refining [% Al]: 0.0001% or more 0.
The Al-Mn-based oxide is adjusted to be not more than 30% to disperse it in the steel.

Here, if Ti is added so as to have a weight ratio of 0.050% or less after the Al concentration is adjusted, the Al-Mn-based oxide is absorbed and disappeared due to the influence of the refractory or the atmosphere, and other intervening substances are present. There is an effect that it is possible to suppress a change in the material composition. As a result, the Al-Mn-based oxide is more easily dispersed as fine inclusions, and the Al-Mn-based oxide is finely dispersed more effectively.

On the other hand, Ti contributes to the refinement of the dispersed oxide, and is preferably added in an amount of 0.005% or more, and is preferably 0.02% or less in order not to affect deoxidation.
Further, when Ti is added in an amount of more than 0.050%, deoxidation by Ti becomes predominant, which hinders the generation and dispersion of Al-Mn-based oxides.

By the way, by adding Ti, Al-Mn
Some of the system inclusions may inevitably combine with the Ti oxide and the Ti-Mn system oxide, but in the present invention, Al-Mn is contained in the steel.
Since the main purpose is to disperse an oxide containing a system oxide, there is no problem even if such an oxide coexists.

Desulfurization : According to the present invention, in a process of performing appropriate slag reforming, preliminary deoxidation and addition of Al + oxide, even a weak deoxidized steel such as the present steel type is subjected to desulfurization agent such as quick lime. Sulfur can be removed by adding it together with the slag modifier. Therefore, if the weight ratio of sulfur is 0.002% or less, the Al-Mn-based oxide can exist more stably. The reason for this is that even if a large amount of Mn is contained, it is difficult for MnS-based inclusions to form in steel types that suppress sulfur to 20 ppm or less. Further, it is well known that this MnS causes stress corrosion cracking in terms of steel quality, and it can be expected to improve steel quality concomitantly.

The type of steel targeted by the present invention is not particularly limited, but if it is shown as a typical example, it has the following composition. C: 0.05 to 0.20%, Si: 0.05 to 0.02
%, Mn: 0.8 to 2.0%, S: 0.005% or less, P: 0.03%
Below, Cu: 0.2-1.0%, Ni: 0.1-1.0%, Nb: 0.01
~ 0.15%, V: 0.01-0.2%, B: 0.00005-0.0004
%, Ti: 0.005-0.02%, N: 0.0005-0.0100%, balance
Fe and inevitable impurities. However, Cu, Nb, V, B
, Ti should be contained at least one kind.

[0059]

EXAMPLES Next, the operation of the present invention will be described more specifically by way of examples. (Example 1) In order to confirm the effect of the present invention, a test showing an example and a comparative example of the present invention was conducted using a 150 kg high frequency heating furnace.

Carbon concentration: 0.05 to 0.08%, initial oxygen concentration:
0.04 to 0.07% molten steel was melted in MgO stamped refractories at 1550 ° C to 1650 ° C. Using this molten steel, Si in metallic form,
Preliminary deoxidation was carried out by adjusting the Si and Mn concentrations by adding Mn, and the total oxygen concentration was confirmed.

Next, when adjusting the Al concentration as the oxide powder by the Al content in the iron alloy, etc., ZrO ₂ .SiO ₂ and 2MgO.Si
O ₂ , MgO ・ 2TiO ₂ , MgO ・ TiO ₂ , TiO ₂ , CaO ・ MgO ・ 2Si
If oxide powders such as O ₂ and Ce ₂ O ₃ · Cr ₂ O ₃ are used and the Al concentration is not adjusted (the upper limit is not exceeded considering the Al content in the ferroalloy), Al ₂ O ₃・ MnO, Al ₂ O ₃・ TiO ₂ , 3Al ₂ O ₃・
Oxides such as 2SiO ₂ , CaO · Al ₂ O ₃ · 2SiO ₂ , and FeO · Al ₂ O ₃ were used.

Each of the powders contained the above oxide in an amount of 90 mass% or more, and the particle size was an oxide mainly having a diameter of 0.05 to 0.5 mm, and the addition amount was 10 g to 100 g. Steel was cast and cast in 5 to 30 minutes after the oxide was added.

The number and composition of dispersed oxides in the steel ingot were examined by an optical microscope and an energy dispersive X-ray microanalyzer. In addition, Cu: 0.
2 to 0.5%, Ni: 0.2 to 0.8%, Nb: 0.02 to 0.8%,
V: 0.03-0.09%, and B: 0.0001-0.0016% were contained. The sulfur concentration is 0.0001 to 0.004%, Ti
The concentration was 0.005-0.05%. Table 1 shows a summary of the processing conditions of the examples of the present example and the comparative examples and the observation results of the morphology of inclusions.

[0064]

[Table 1]

Table 1 shows the examination results of the treatment conditions and inclusion morphology of this example. In the table, the form of inclusions is 0 diameter.
Al-Mn oxide-based inclusions of 2 μm or more and 20 μm or less,
Molten steel or 10 in the steel ingot / mm ² or more 1000 / mm ² below a certain thing ◎, was four / mm ² or more to 10 / mm ² below a certain ○ ones.

As shown in Tables 1 to 7 of the present invention,
In both cases, the total oxygen concentration was adjusted by adjusting the [% Si] and [% Mn] amounts, and the Al concentration was controlled in consideration of the Al content in the ferroalloy, and the oxide was added. Then, it can be seen that the Al-Mn-based oxide is dispersed in the steel ingot.

Further, as shown in Examples 8 to 12 of the present invention, [%
If the total oxygen concentration is adjusted by adjusting the [Si] and [% Mn] amounts, and the Al-containing oxide is added while considering the Al content contained in the iron alloy, the oxygen potential can be controlled. It becomes possible to control the Al concentration, and as a result,
It can be seen that the Al-Mn-based oxide is dispersed in the steel ingot.

On the other hand, as shown in Table 1 as Comparative Examples 13 and 14, when the oxide is not added, it is difficult to control the Al concentration even if the oxygen concentration is adjusted by the complex deoxidation of Si and Mn. It can be seen that the Al-Mn-based oxide is not dispersed in the steel ingot without controlling the concentration.

As shown in Comparative Examples 15, 16 and 17, even when the oxide (in this case, Al-free ZrO ₂ .SiO ₂ oxide or 2MgO.SiO ₂ oxide) was added, It can be seen that the Al-Mn-based oxide is not dispersed in the steel ingot when the concentration cannot be controlled or exceeds the upper limit.

Even when the oxide containing Al and capable of controlling the oxygen potential was added, the Si content and Mn
It is understood that when the amount control is inappropriate and the total oxygen concentration is below the lower limit or above the upper limit, the Al-Mn-based oxide is not dispersed in the steel ingot.

Example 2 In this example, the present invention was carried out by using a 250t converter, an LF heating device and an RH degassing vacuum device.

P: <0.03 in weight ratio by pretreatment
% Was used for decarburization in a converter. After reducing the carbon concentration to 0.01% or more and 0.25% or less by the converter, suppress the converter slag outflow, and add a modifier such as Al-CaCO ₃ agent or Al ash to the slag that flows out during tapping. Slag modification was performed. Further, at the time of tapping, Si and Mn were added for the main purpose of preliminary deoxidation to adjust the concentration to a predetermined value.

After that, the ladle furnace heating device is used for 15 to 30
After the heat treatment for 1 minute, the total oxygen concentration was adjusted by the RH degasser by the reflux treatment for 20 to 40 minutes while maintaining the degree of vacuum at 1 to 5 torr by RH. At this time, a sample was taken during the process to check the total oxygen concentration, and Fe-Si, Fe-Nb, Fe-V and Fe were placed in the vacuum chamber.
The Al concentration was adjusted with an iron alloy such as -B.

Next, after adjusting the total oxygen concentration, ZrO ₂ .Si
O ₂ , 2MgO ・ SiO ₂ , Al ₂ O ₃・ MnO or 3Al ₂ O ₃・ 2SiO ₂
Each of the above oxides was added to the molten steel in an amount of 1 to 12 kg / t in a vacuum chamber, and further refluxed for 5 to 20 minutes. When Ti was added, it was added together with iron alloy in a vacuum chamber.

After the refining was completed, a sample was taken in a ladle, and the number and composition of dispersed oxides were measured by an optical microscope and energy dispersive X-ray.
It was examined with a line microanalyzer. The number and composition of oxides dispersed in the slab sample after casting into a slab shape by continuous casting were also investigated by the same method.

The molten steel composition at this time was Cu: 0.2 to 0.4%, Ni: 0.2 to 0.7%, Nb: 0.02, except for the above components.
~ 0.5%, V: 0.03-0.09%, and B: 0.0001-0.00
16%. Table 2 shows a list of the processing conditions and the morphological observation results of inclusions in the examples and comparative examples of this example.

[0077]

[Table 2]

Table 2 shows the results of the investigation of the conditions and inclusion morphology of this example. In the table, the classification of the form of inclusions is the same as in Table 1. Regarding the dispersed oxide, the state in the molten steel at the end of melting and in the slab after continuous casting was investigated. Although there were some differences in the composition form, number and diameter distribution of the dispersed oxides between the end-of-melting sample and the continuous cast slab, no essential difference affecting the present invention was observed.

Of the results shown in Table 2, Examples 1 and 2 of the present invention
As shown in 3 and 3, after adjusting the [% Si] and [% Mn] amounts to control the total oxygen concentration to 0.002 to 0.01%, the Al concentration was adjusted and each oxide was added. Medium Al concentration
It was found that the content was controlled to 0.0001 to 0.003%, and as a result, the Al-Mn-based oxide was dispersed in the steel ingot.

Among the results shown in Table 2, the total oxygen concentration was controlled to 0.002 to 0.01% by controlling the amounts of [% Si] and [% Mn] as shown in Examples 4 and 5 of the present invention. After that, as a result of adding each oxide containing Al, the Al concentration in the molten steel is 0.0001.
It is understood that the content of Al-Mn-based oxide is dispersed in the steel ingot as a result of being controlled to ~ 0.003%.

Further, as shown in Examples 6 to 9 of the present invention, the total oxygen concentration is adjusted by controlling the [% Si] and [% Mn] amounts, the Al concentration is adjusted, and an oxide is added, or Al
Al oxide concentration in molten steel is 0.0001 ~ by adding each oxide containing
It can be seen that the Al-Mn-based oxide was dispersed in the steel ingot by adding Ti in an amount of 0.05% or less after controlling the content to 0.003%.

On the other hand, as shown in Comparative Examples 10 and 11,
If the total oxygen concentration is less than 0.002% or more than 0.01% after preliminary deoxidation with Si and Mn, the Al-Mn-based oxide remains in the steel even if each oxide is added by adjusting the Al concentration. The required amount was not dispersed.

Further, as shown in Comparative Examples 12 and 13, Si
When the total oxygen concentration is less than 0.002% or more than 0.01% after preliminary deoxidation with Mn and Mn, the Al concentration in the molten steel exceeds 0.0030% or 0.0001% even if each oxide containing Al is added. %, And the required amount of Al-Mn oxide was not dispersed in the steel.

Next, as shown in Comparative Examples 14 and 15,
Oxygen concentration of 0.002 to 0.
Even if controlled to 01%, the required amount of Al-Mn oxide was not generated by the addition of the oxide containing no Al unless the Al concentration was adjusted to 0.0001 to 0.003%.

Comparative Examples 16 and 17 show the cases where the Ti concentration was added in excess of 0.05%, but in this case as well, the required amount of Al-Mn-based oxide was not formed in the steel. Furthermore, Comparative Example 18
As shown in 19 and 19, even if the oxygen concentration is controlled to 0.002 to 0.01% by preliminary deoxidation with Si and Mn, it is difficult to adjust the Al concentration when the oxide containing Al is not added, As a result, the required amount of Al-Mn-based oxide was not formed.

Comparative Examples 20 and 21 are cases where slag reforming was not carried out at the time of tapping the converter, but the predeoxidation concentration by Si and Mn tended to be high, and the Al concentration was controlled. Moreover, even when the oxide was added or the oxide containing Al was added, the required amount of Al-Mn-based oxide was not formed in the steel.

FIG. 3 shows the relationship between the average sulfur concentration in the dispersed oxide and the sulfur concentration in the molten steel in the weight ratio in this example. Since the sulfur in the dispersion inclusions forms oxysulfide containing MnS or Mn, as shown in the figure, the lower the sulfur concentration in the molten steel and the lower the average sulfur concentration in the dispersed oxide, the more the Al- The proportion of Mn-based oxides increased, and when desulfurization progressed, Al-
It is an Mn oxide.

(Example 3) Next, the present invention was carried out using a 30t electric furnace and a VOD apparatus. Use an electric furnace to reduce the carbon concentration to 0.
After adjusting to 01 to 0.25%, while suppressing the slag outflow from the electric furnace, Al-CaCO
_Three modifiers were added for slag modification. At the time of tapping, Si and Mn were added for the purpose of preliminary deoxidation to adjust the concentration to a predetermined value.

After that, the total oxygen concentration was adjusted by stirring the Ar gas under reduced pressure with a VOD device. In this case,
The treatment was performed for 10 to 40 minutes while maintaining the degree of vacuum at about 1 to 50 torr. At this time, while collecting the sample during the process to examine the total oxygen concentration, Fe-Si, Fe-Nb,
The Al concentration was adjusted with Al-containing alloy iron such as Fe-V and Fe-B, and an oxide was added or an oxide containing Al was added. When Ti was added, it was added together with iron alloy in a vacuum chamber.

After the refining was completed, a sample was taken in a ladle, and the number and composition of dispersed oxides were measured by an optical microscope and energy dispersive X-ray.
It was examined with a line microanalyzer. The number and composition of oxides dispersed in the slab sample after casting into a slab shape by continuous casting were also investigated by the same method.

The composition of the molten steel at this time was Cu: 0.2 to 0.4%, Ni: 0.2 to 0.7%, Nb: 0.02, except for the above components.
~ 0.5%, V: 0.03-0.09%, and B: 0.0001-0.00
16%.

[0092]

[Table 3]

As shown in Examples 1 and 2 of the present invention in Table 3, after tapping in an electric furnace, preliminary deoxidation with Si and Mn was performed in a VOD apparatus to adjust the oxygen concentration to 0.002 to 0.01%, and then If ZrO ₂ · SiO ₂ is added while adjusting the Al concentration, the Al-Mn-based oxide can be dispersed in the steel ingot.

Further, as shown in Example 3 of the present invention in Table 3, after the steel was discharged from the electric furnace, preliminary deoxidation with Si and Mn was performed in the VOD device to adjust the oxygen concentration to 0.002 to 0.01%, and then the Al concentration was further increased.
If you add Al ₂ O ₃ · TiO ₂ oxide containing
It is controlled to 0.0001 to 0.003%, resulting in Al-Mn in steel.
A system oxide can be dispersed.

Further, as shown in Examples 4 and 5 of the present invention in Table 3, even if each oxide was added after the preliminary deoxidation with Si and Mn and Ti was further added, the Al--Mn system was added to the steel ingot. The oxide can be dispersed.

On the other hand, as shown in Comparative Examples 6 and 7 in Table 3, when the oxygen concentration could not be adjusted to 0.002 to 0.01% by predeoxidation with Si and Mn in the VOD apparatus after tapping in the electric furnace In addition, even if ZrO ₂ · SiO ₂ is added while adjusting the Al concentration, or Al ₂ O ₃ · TiO ₂ oxide containing Al is added, the Al-Mn oxide is dispersed in the steel ingot. I couldn't.

As shown in Comparative Example 8, even after the predeoxidation with Si and Mn, the oxide containing no Al was added without adjusting the Al concentration, the Al-Mn-based oxide was added to the steel ingot. The material could not be dispersed.

Further, as shown in Comparative Example 9, Si and
Even if each oxide is added while adjusting the Al concentration after preliminary deoxidation with Mn, if the Ti concentration exceeds 0.05% by weight,
The Al-Mn-based oxide could not be dispersed in the steel ingot.

Further, as shown in Comparative Examples 10 and 11,
Even if oxygen concentration is adjusted by preliminary deoxidation with Si and Mn, if each oxide is not added, the Al concentration will not be adjusted to the prescribed concentration, or the required dissolved Al concentration will not be achieved, resulting in steel The Al-Mn-based oxide could not be dispersed in the mass.

[0100]

As described above, according to the present invention, an oxide having an Al-Mn oxide phase is finely dispersed in the steel as a steel for thick plates which requires high weld heat affected zone toughness. When melting the dispersed Al-Mn oxide dispersed steel, Al
-Al in which oxide containing Mn oxide phase is finely dispersed in steel-
It is possible to stably produce Mn-based oxide-dispersed steel.

[Brief description of drawings]

FIG. 1 is a graph comparing the oxygen potentials formed by various oxides at steelmaking temperatures.

FIG. 2 is a graph showing a region in which Al-Mn-based oxide is stably present in molten steel at a steelmaking temperature.

FIG. 3 is a graph showing the effect of sulfur concentration in molten steel on sulfur concentration in dispersed oxide.

Claims (3)

[Claims] 1. When melting an oxide-dispersed steel having an Al-Mn oxide phase and an unavoidably coexisting oxide phase as dispersed particles, the molten steel is pre-deoxidized with Si and Mn to reduce the total oxygen concentration. After adjusting to 0.0020% or more and 0.0100% or less, either an Al-containing alloy and an oxide capable of controlling the oxygen potential in molten steel, or an oxide containing Al capable of controlling the oxygen potential in molten steel. By adding or to the above molten steel, the Al concentration in the molten steel is 0.0001 by weight.
% -0.0030% or less Al-Mn characterized by controlling
Of manufacturing oxide-based dispersed steel. 2. When melting an oxide-dispersed steel having an Al-Mn oxide phase and an unavoidably coexisting oxide phase as dispersed particles, the carbon concentration is adjusted in a converter or an electric furnace, and the steel is tapped. The molten steel is pre-deoxidized with Si and Mn in the middle or ladle, and slag is reformed, and the total oxygen concentration is adjusted to 0.0020% or more and 0.0100% or less in the ladle refining equipment of the ladle furnace. And an oxide capable of controlling the oxygen potential in molten steel, or an oxide containing Al capable of controlling the oxygen potential, by adding to the molten steel during ladle refining A method for producing an Al-Mn-based oxide-dispersed steel, characterized in that the medium Al concentration is controlled to be 0.0001% to 0.0030% by weight. 3. The Al-containing alloy and the oxide or the oxide containing Al are added to the molten steel, and then Ti is added to the molten steel in an amount of 0.050% or less by weight.
A method for producing an Al-Mn-based oxide-dispersed steel as described.