JPH1112640A - Manufacture of oxide dispersed steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacture of an oxide-dispersed steel, where the dispersion density of oxides including Al-Mn type oxides is controlled with high precision. SOLUTION: Si concentration and Mn concentration are regulated in a ladle, and a prescribed amount of oxygen is blown while adding a slagging agent and Si and heating is performed to form a CaO-SiO2 -Al2 O3 -MgO type slag having a composition in the range where the value of CaO/SiO2 is regulated to 0.8-4 and the amounts of Al2 O3 and MgO are regulated to 3-40 wt.% and 5-20 wt.% (where the weight percentage of each oxide means its concentration in the slag), respectively. Simultaneously, after control into a molten steel where the amounts of Al and total oxygen in the molten slag are regulated to 0.0001-0.003 wt.% and 0.002-0.01 wt.%, respectively, Si concentration is regulated again to 0.05-0.2 wt.% and gas bubbling and vacuum degassing treatments are performed. In this manufacturing method, Ti or/and Zr are added independently or in combination in the course of the vacuum degassing treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide-dispersed steel capable of dispersing an oxide containing an Al-Mn-based oxide at a predetermined density with high precision, which can ensure high toughness in a heat affected zone of welding. And a method for producing the same.

[0002]

2. Description of the Related Art The demand for high-strength steel materials used for large structures such as marine structures installed in ice waters, line pipes for cold regions, ships, LNG tanks and the like has been increasing at present while increasing the strength level. It has been made continuously. However, at the same time, the demand for improving the toughness in a welded part, particularly in a weld heat affected zone (hereinafter, referred to as “HAZ”) has become high, reflecting the severe use environment in an ice sea area and the like. This also means that there is a high demand for steel materials capable of obtaining high HAZ toughness even when performing high-efficiency welding using a larger welding heat input. As a method for meeting this demand, there is known a method of dispersing various oxide particles in a steel material to improve HAZ toughness.

As one of such improvement methods, after limiting the contents of Si and Al in steel, Ti is added and Ti-based oxides such as TiO and Ti ₂ O ₃ are solidified in the steel during solidification. A method for producing steel that secures high HAZ toughness by dispersing the steel into HAZ has been proposed (Japanese Patent Publication No. 5-1730).
No. 0). As a method of finely dispersing such a Ti-based oxide in a steel material in a solidification process, Si and Mn are used for deoxidation in a first step, and Ti or Z is used for deoxidation in a second step.
There has been proposed a method in which Ti-based or Zr-based oxides are precipitated individually or in a composite manner by adjusting the oxygen concentration to 50 ppm or less by weight using r (Japanese Patent Laid-Open No. 3-267311, JP-A-4-2713).

[0004] These methods are all methods for finely dispersing a Ti-based oxide in a solidification process, and only show that the main oxide is composed of a Ti-based oxide or a Zr-based oxide. there were. However, in a steel material in which an oxide mainly composed of a Ti-based oxide is dispersed, the toughness improvement margin is small in a subcoarse grain region where the austenite grain size heated to 1200 to 1350 ° C. is slightly larger in the HAZ region. , The effect was limited.

On the other hand, there is disclosed a method of improving the toughness of the entire HAZ including the above-described subcoarse grain region by dispersing an oxide containing an Al—Mn-based oxide in steel (see, for example, Japanese Patent Application Laid-Open No. H11-157556). JP-A-7-278736). This Al-M
As a method for producing steel in which an n-based oxide is uniformly dispersed,
A method for producing steel in which an oxide having a desired composition is dispersed by controlling the slag composition during smelting has been disclosed (JP-A-8-92629). In addition, S in the ladle
A method for producing an Al-Mn-based oxide-dispersed steel in which the heating of molten steel and the control of slag are simultaneously performed by performing i addition and oxygen spraying has been proposed (Japanese Patent Application No. 8-260965).
No.).

[0006] However, these methods cannot control the dispersion density of the Al-Mn-based oxide dispersed in the steel with high accuracy. In particular, when fluctuations such as a prolonged vacuum degassing for dehydrogenation or removal of large inclusions occur, the dispersion density of the Al—Mn-based oxide often varies. For this reason, Al-Mn
It has been desired to establish a method for accurately producing oxide-dispersed steel in which a system oxide is dispersed at a sufficient density.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is
An object of the present invention is to provide a method of manufacturing an oxide-dispersed steel capable of grasping and controlling the dispersion density of an oxide containing a Mn-based oxide with high accuracy.

[0008]

Means for Solving the Problems The present inventors have proposed Al-M
The results of investigating the dispersion density of Al-Mn-based oxide by adding Si to molten steel in a ladle, controlling slag composition, gas bubbling and vacuum degassing when smelting n-based oxide-dispersed steel The following items could be confirmed.

(A) After deoxidation with Si and Mn in a ladle, oxygen is sprayed while adding a slag-making agent and Si to adjust the basicity of the slag and the composition of Al ₂ O _{3 and the} like in the slag. By doing so, the Al concentration and the total O concentration in the molten steel can be controlled.

(B) When gas bubbling is performed in the molten steel adjusted as described above in a ladle, an oxide containing an Al—Mn-based oxide is determined at a rate determined in accordance with a gas flow rate per unit time and per unit amount of molten steel. (Hereinafter, referred to as “containing (Al—Mn-based) oxide”) ”. At this time, the initial value of the oxide dispersion density before gas bubbling is determined by “Si concentration in molten steel” (hereinafter, referred to as “[% Si]”). In addition, the degree of decrease in oxide density with the passage of gas bubbling strongly depends on [% Si] in addition to the gas flow rate. By adjusting the above (a), the oxide density can be quantitatively predicted by controlling the gas flow rates of (a) [% Si] and (b) gas bubbling.

(C) The density of the oxides containing (Al-Mn) oxides also decreases due to the floating of the oxides during the vacuum degassing of the molten steel. At this time, the degree of decrease in the density of the oxide containing (Al—Mn) oxide also depends on [% Si] at that time.

(D) When Ti or Zr is added,
l-Mn) The degree of reduction in oxide density is Ti or Zr
Greatly changes from the time of addition. However, also in this case, the degree of reduction of the oxide after the addition of Ti or Zr can be quantitatively grasped.

The present invention has been completed based on the above-mentioned matters through experiments on a laboratory scale and test production at a production site. The gist of the present invention is as follows: In the method of manufacturing steel.

(1) In a ladle, while adjusting the Si concentration and the Mn concentration, heating is performed by blowing oxygen while adding a slag-making agent and Si, and heating in the following range.
O-SiO ₂ -Al ₂ O ₃ to form a slag composition of -MgO system, and after controlling the composition of the molten steel in the following ranges, the Si concentration in the molten steel to 0.05 to 0.2 wt% Re Adjust,
A method for producing an oxide-dispersed steel containing an Al-Mn-based oxide, which is subjected to a gas bubbling treatment and a vacuum degassing treatment under predetermined conditions (referred to as [Invention 1]).

CaO (% by weight) / SiO ₂ (% by weight) = 0.8 to 4 Al ₂ O ₃ : _{3 to} 40% by weight MgO: 5 to 20% by weight Is the concentration at

: Al in molten steel: 0.0001 to 0.003% by weight Total oxygen in molten steel: 0.002 to 0.01% by weight (2) During the degassing process in the production method of the above [Invention 1] For producing oxide-dispersed steel in which Ti or Zr or a combination thereof is added to steel (referred to as [Invention 2]).

In the above [Invention 1] and [Invention 2], the oxide-containing steel refers to a steel containing an oxide containing an (Al-Mn-based) oxide. As described above, “containing (Al-M
“n-based) oxide” is an “oxide containing an Al—Mn-based oxide.” In this oxide, some of the plurality of oxides are Al—Mn-based oxides. "Al-Mn-based oxide" refers to both the case where one oxide is complexly formed of various oxides and one of them is an Al-Mn-based oxide. Represents an oxide composed of Al, Mn and O.
(Al-Mn-based) oxide "means that at least one of the oxides contained in two or more phases is an Al-Mn-based oxide, and (Al + Mn) has an atomic ratio of metal elements in the oxide of 40% or more, and (Al / Mn) in a range of 1 or more and less than 5.

In the present description, "dispersion density of oxide" refers to the dispersion density of molten steel. The dispersion density of the oxide in the molten steel is reflected in the dispersion density of the oxide when it becomes a steel material. As will be described later, the measurement of the oxide dispersion density in molten steel is performed by microscopic examination of a bomb sample. Therefore, the oxide density as referred to herein is a value obtained by polishing a quenched sample or a cast sample obtained by collecting molten steel with a mold bomb, and polishing the polished surface with a scanning electron microscope at a magnification of 1000 to 2000 times at 50 times.
It shows the average number of oxides per unit area when 100 visual fields are observed from the visual field.

[0019]

Next, the reason why the present invention is limited as described above will be described. In the following description, “%” for alloy elements and oxides indicates “% by weight”.

1. In order to disperse the oxide containing (Al-Mn) in the steel,
Deoxidation by Si and Mn is performed at the time of tapping the smelting furnace to control the primary deoxidation product to have a MnO—SiO ₂ composition. Si and Mn in the molten steel after deoxidation are respectively [% Si]: 0.05 to 0.2%, and [% Mn]:
It is desirable to be in the range of 0.8 to 2%. [% Si]
Is less than 0.05% and more than 0.2%, the total oxygen content and the Al concentration in the molten steel cannot be set to the predetermined ranges described below when a treatment such as addition of a slag-making agent is performed. There are cases. When [% Mn] is less than 0.8%,
Of the oxides containing (Al-Mn), the Al-Mn-based oxide may not be generated to the extent that the HAZ toughness can be improved.
On the other hand, when [% Mn] exceeds 2%, there is a tendency that it is difficult to form a slag having a desired composition by adding a slag-making agent or the like described later.

2. Production of Al-Mn-based oxide-containing steel by controlling slag composition, etc. Next, in order to achieve both slag composition adjustment and ladle heating in ladle refining, a predetermined amount of Si and slag-making agent are placed in the ladle. While oxidizing Si, a predetermined amount of oxygen is blown into the molten steel. Si to be charged
May be a commonly used ferro-alloy such as ferrosilicon.
In addition, oxygen blown upward, a CaO source added as a slag-making agent,
The Al ₂ O ₃ source, SiO ₂ source, and MgO source may be general ones such as quicklime and dolomite, and are not particularly limited. The oxygen blowing method may be a method generally used for ladle refining. For example, it may be sprayed from a refractory lance at an acid feed rate of about 20 to 100 Nm ³ / min.

By this treatment, after blowing over oxygen, CaO
Forming a slag consisting of -SiO ₂ -Al ₂ O ₃ -MgO system. At this time, the weight concentration in the slag is (% CaO) /
(% SiO ₂ ) is 0.8-4, and Al ₂ O ₃ concentration is 3-40.
% And the MgO concentration must be 5 to 20%. Since then
The weight% of the concentration of oxides such as CaO in slag
O) is displayed. (% CaO) / (% SiO ₂ ) is 0.1%.
If less than 8, the total oxygen concentration exceeds 0.01%, while
If it exceeds 4, the total oxygen concentration will be less than 0.002%. When the Al ₂ O ₃ concentration is less than 3%, the Al concentration in the molten steel is less than 0.0001%, and when it exceeds 40%, the Al concentration in the molten steel exceeds 0.003%. In addition, MgO
If the concentration is less than 5%, the slag having the above composition has poor slagging properties and poor controllability.

[% Si] and [% M] before adding the slag-forming agent
n] and the slag composition are in the above range, the Al concentration in the molten steel is in the range of 0.0001 to 0.003%,
Further, the total oxygen concentration in the molten steel is 0.002 to 0.01%.

When the Al concentration in the molten steel is less than 0.0001%, it is not possible to obtain a sufficient Al-Mn-based oxide density for improving the HAZ toughness. On the other hand, 0.003
%, The generated oxides agglomerate, and it is impossible to obtain an Al-Mn-based oxide dispersion density sufficient for improving the HAZ toughness. In addition, the total oxygen concentration in the molten steel is 0.002%
If less than, the amount of dispersed oxides in the steel is insufficient,
On the other hand, if the content exceeds 0.01%, the size of the dispersed oxide increases and the cleanliness of the steel deteriorates significantly.

The amount of Si and the amount of oxygen sprayed at this time are determined from the temperature before heating and the temperature after heating in consideration of securing the temperature of the molten steel in the subsequent process. Further, the amount of the slag-making agent added is the amount of
It is determined to control O ₂ to the target concentration. Each relationship is described by the following equations (1) to (6), and the amount of each addition can be determined.

First, the temperature rise of the molten steel caused by the oxidation of Si (hereinafter referred to as "Si heat-up") is determined by equation (1).

Te−Ts = {WSi + Wsteel · ([% Si] s − [% Si] e) · 10} × ΔTSi−Σ (Wi · ΔTi) −ΔTH · t (1) where The symbols in the equation (1) are as follows. Ts: molten steel temperature before heating (° C), Te: target molten steel temperature after heating (° C), Wsteel: weight of molten steel (steel-t), WSi: Si
Addition amount (kg / steel-t), [% Si] s: Si concentration in molten steel before heating (%), [% Si] e: Target weight concentration of Si in molten steel after heating (%), ΔTSi: Temperature rise of molten steel per kg / steel-t of Si (° C / (kg / steel-t)), Wi: input weight of slagging agent i (kg / steel-t), i is slagging agent such as CaO, ΔTi: Temperature drop of molten steel per unit weight of slag-making agent (° C / (kg / T)), ΔTH: Temperature drop rate of molten steel due to heat dissipated outside the system (° C / min), t: Heating time (min) The mass balance of CaO inside is determined by the following equation (2).

[Wslag + {WSi + Wsteel · ([% Si] s − [% Si] e) × 10} · 2.14 + ΣWi] · (% CaO) / 100 = WCaO + W′CaO + W ″ CaO (2) where, W'i: weight of i component in slag before heating (kg / st)
eel-t), W''i: weight of the i component generated during heating (kg /
steel-t), Wslag: Slag amount before heating (kg / steel-
t), (% i): Target weight concentration of i component in slag after heating (%) Similarly, the following formula (3) is a basic formula for mass balance of SiO ₂ in slag.

[Wslag + {WSi + Wsteel · ([% Si] s − [% Si] e) × 10} · 2.14 + ΣWi] · (% SiO ₂ ) / 100 = WSiO ₂ + W′SiO ₂ + W ″ SiO ₂ (3) The basicity of slag is determined by the following equation (4).

C / S = (WCaO + W′CaO + W ″ CaO) / (WSiO ₂ + W′SiO ₂ + W ″ SiO ₂ ) (4) where C / S is after heating. Slag target basicity in ladle (= (%
CaO) / (% SiO ₂ )).

The mass balance of Al ₂ O _{3 in} the slag is as follows:
It is described by equation (5).

[Wslag + {WSi + Wsteel · ([% Si] s − [% Si] e) × 10} · 2.14 + ΣWi] · (% Al ₂ O ₃ ) / 100 = W Al ₂ O ₃ + W'Al ₂ O ₃ + W ″ Al ₂ O ₃ (5) The following equation (6) is a basic equation for determining the amount of oxygen necessary for the above reaction. Q = {WSi + Wsteel · ([% Si] s − [% Si] e) × 10} /28·22.4/β (6) Here, Q is the acid supply amount (m ³ / steel-t), and β is the acid deposition efficiency.

As described above, after the deoxidation with Si and Mn, if the molten steel is heated while adding oxygen and blowing oxygen upward, and the slag-making agent is added, it is possible to obtain an Al-Mn-containing material.
The oxide-dispersed steel can be melted. But,
The steel material obtained by the above method is an oxide-containing steel in which the dispersion of the (Al-Mn-based) oxide-containing density is not a problem.

3. Control of Density of Containing (Al-Mn) Oxide Next, a method of controlling the dispersion density of the containing (Al-Mn) oxide will be described. As described above, containing (Al-Mn-based)
The oxide dispersion density refers to the dispersion density of oxide-based inclusions containing an Al-Mn-based oxide phase, but in the following description, "oxide" includes (Al-Mn-based) unless otherwise specified.
Oxide shall be referred to.

3.1. Control in Ladle When the above-described deoxidation method, Si heat-up, and slag composition control method are adopted, the dispersion density of the oxide having a diameter of 0.4 to 20 μm immediately after the Si heat-up is changed by the molten steel after the Si heat-up. It was found that the concentration was determined by the Si concentration in the inside, that is, [% Si]. That is, S
i Inclusion in molten steel caused by oxygen overblowing for heating
The dispersion density of the (Al-Mn) oxide can be related to the [% Si] value. This is because the oxide formation mechanism is
This is because the mechanism of formation of the primary deoxidation product in deoxidation is similar.

The initial oxide density No immediately after the Si heating and the [% Si] value in the molten steel are quantitatively related by the following equation (7).

No = α / [% Si] (7) where [% Si] is 0.05% or more. 0.2%, [% M
n] is 0.8% to 2%, and (% CaO) / (% Si
When O ₂ ) is in the range of 0.8 to 4, 200 can be adopted as the initial value coefficient α determined empirically.

The generated oxides are agglomerated and float in the same manner as the primary deoxidized product by stirring the molten steel such as gas bubbling in a ladle, and the number thereof is reduced. Therefore, the initial oxide density No
(1 / mm ² ) and the oxide density N (1 / m ² ) after time t seconds.
m ² ) is related by the following equation (8).

N / No = exp (kt) (8) Here, the oxide reduction rate k (1 / s) is, of course, It fluctuates according to the degree of stirring of bubbling. Bubbling is introduced into the molten steel in the ladle through a porous plug or nozzle.
And the like. The degree of agitation is represented by agitation energy density ε (W / m ³ ), and the gas flow rate for molten steel in one smelting (about 220 to 300 t) is represented by Q (Nm ³ / s). The relations of equations (9) and (10) hold.

K ∞ ε (9) ε Ｑ Q (10) Therefore, the relationship between k and Q can be expressed by equation (11).

K = γ · Q (11) where the reduction rate coefficient γ is an oxidation It depends on [% Si] because it is related to the initial value of the material density and the aggregation and floating of the oxide,
The amount of molten steel to be processed at one time is 220 to 300 tons, and the gas flow rate in one bubbling is 0.01 to 0.1 (Nm ³ /
In the range of s), if the [% Si] value is within a certain range, it is almost constant.

Table 1 shows the value of the reduction rate coefficient γ according to the [% Si] value under the conditions of the single molten steel processing amount and the stirring gas flow rate.

[0043]

[Table 1]

That is, equations (7), (8) and (11), initial value coefficient α, reduction rate coefficient γ and reduction rate k,
Using the value of [i] makes it possible to control the oxide dispersion density by adjusting the gas flow rate and the processing time accordingly.

FIG. 1 shows molten steel in ladle 220-
Treatment time and oxide dispersion density ratio N / No when stirring at 300 t for Ar gas flow rate Q = 0.1 Nm ³ / s
FIG. Where N is the oxide dispersion density,
No is the initial value of the oxide dispersion density. In FIG.
Curves showing changes in the oxide dispersion density ratio for four levels of [% Si] values of 0.05, 0.10, 0.15, and 0.20% are shown. This is a value calculated by the above equation based on the value of the reduction rate coefficient γ in Table 1.

FIG. 2 shows the relationship between the processing time t and the oxide dispersion density (mm ⁻² ) under the same conditions. These figures 1
Alternatively, it can be seen from FIG. 2 that if the processing time t is determined according to the [% Si] value after heating the Si, a molten steel having a target oxide dispersion density can be obtained.

3.2. Next, the relationship between the vacuum degassing time and the oxide dispersion density will be described. Vacuum degassing is performed by RH process or VOD
A general molten steel processing method represented by a process or the like may be used. Vacuum degassing is performed mainly for dehydrogenation in the case of molten steel for thick steel plates, which is one of the target steels to which the method of the present invention is applied. It is also known as a method of reducing oxides together with degassing because of the vigorous stirring of molten steel. In the method of the present invention, it is necessary to leave a predetermined amount of oxide in the molten steel. Therefore, it is essential for the method of the present invention to quantitatively grasp the relationship between the vacuum degassing time and the oxide dispersion density. Is an important matter.

In the present invention, the composition of molten steel, particularly [% Si], the composition of slag, and the like are determined as described above by prior processing before vacuum degassing, and the predetermined oxide dispersion density is determined by bubbling with a ladle. Is controlled. The degree of vacuum for the molten steel that has been subjected to such a preliminary treatment is 10 to.
In the processing at rr or less, the relationship of the equation (12) having the same form as the equation (8) is established between the oxide dispersion density ratio and the vacuum degassing time.

N / No = exp (mt) (12) Here, the reduction rate m during the vacuum degassing process is 10 to
Below rr, it can be determined according to the [% Si] value in the molten steel.

Table 2 shows the reduction rate of the oxide during the vacuum degassing process according to each [% Si] value.

[0051]

[Table 2]

When [% Si] in the molten steel and the desired oxide dispersion density are determined from the above, the vacuum degassing time can be set in accordance with Table 2, equation (12) and the like.

FIG. 3 shows the relationship between the vacuum degassing time and the oxide dispersion density ratio N / No when [% Si] is 0.05%. Here, since the reduction rate m depends on the Ar gas flow rate for gas bubbling, Q (Nm ³ /s)=0.0
N / No was shown for four levels of 1, 0.02, 0.05 and 0.10%. From these N / No curves, the Ar gas flow rate Q and the processing time t corresponding to the target oxide dispersion density are obtained.
Can be determined.

FIG. 4 is a diagram showing the relationship between the processing time of the vacuum degassing process and the oxide dispersion density ratio N / No. Even during the vacuum degassing treatment, the initial dispersion density of oxides and the floating of oxides are strongly affected by [% Si] as in the ladle, so that [% Si] = 0.05, 0.10, 0 N / No curves are shown for four levels of .15 and 0.20%. Based on these N / No curves, it is possible to determine the vacuum degassing time t that matches the target oxide density.

3.3. Effect of Addition of Ti or Zr (in the case of [Invention 2]) Next, the effect of addition of Ti or Zr or combined addition of Ti and Zr in the vacuum degassing process will be described. Si
In order to control the dispersion density of oxides generated by oxygen deoxidation by oxygen and Mn and oxygen overblowing for heating of Si, T
Addition of i or addition of Zr or composite addition of Ti and Zr. At the time of this vacuum degassing process, a predetermined amount of Ti or Zr
And [% Ti] value in molten steel is 0.005 to 0.0
It is desirable to make adjustments so as to be 2% and 0.002 to 0.01% in [% Zr] value in molten steel. If [% Ti] or [% Zr] is less than the above range, the effect is not sufficiently exhibited and the oxide density tends to vary, while if it exceeds the above range, the mechanical properties of both Ti and Zr, particularly toughness, deteriorate. It becomes remarkable. Ti or Zr is contained as a small amount of Ti-based oxide or Zr-based oxide in the Al-Mn-based oxide, and has an effect of stabilizing the Al-Mn-based oxide phase. In the following description, an Al—Mn-based oxide containing a Ti-based oxide or a Zr-based oxide is also referred to as “containing (Al-Mn).
The term "system) oxide" is used, and is handled in the same manner as when referring to an oxide including other oxides.

The effect of the addition of Ti or Zr on the rate of oxide reduction was investigated.
It has been found that the rate of oxide reduction is significantly reduced.
The rate of reduction is such that the reduction rate m is 0.5 m for Ti and 0.2 m for Zr in the above concentration range.

FIG. 5 shows that 120 seconds after the start of the vacuum degassing process,
[% Ti] 0.01% after 300 seconds and 600 seconds
Oxide dispersion density ratio N / No when Ti is added so that
FIG. 4 is a diagram showing the change of the comparison with the case where no additive is added. As shown in the figure, the oxide reduction rate changes due to the addition of Ti, which is quantitatively grasped, so that the Ti addition time and the vacuum degassing time can be determined so as to obtain a desired oxide dispersion density. . FIG. 6 shows the start of vacuum degassing process 12
After 0 seconds, the change of the oxide dispersion density ratio N / N _o when after 300 seconds and 600 seconds [% Zr] was added Zr to be 0.005%, in comparison with the case of no addition FIG. As shown in the figure, the rate of reduction of the oxide dispersion density changes with the addition of Zr, so that the Zr addition timing and the vacuum degassing time can be determined so as to obtain a desired oxide dispersion density.

4. Next, an example in which the method of the present invention is applied to a method for producing a weldable thick steel plate will be specifically described. In the production of molten steel,
For example, it is desirable to adjust the carbon concentration to 0.01 to 0.25% in a smelting furnace such as a converter or an electric furnace. This is because if the carbon concentration is less than 0.01%, since the molten steel is in a peroxidized state, it is difficult to perform preliminary deoxidation and control of the slag composition by using Si and Mn in the subsequent steps. On the other hand, if the carbon concentration exceeds 0.25%, welding cracks are likely to occur. The oxygen concentration is 0.04 to 0.07% in total oxygen concentration.
It is desirable that The reason is that the total oxygen concentration is 0.0
If it is less than 4%, MnO is preliminarily deoxidized by Si and Mn.
This is because -SiO ₂ -based oxides are not easily generated sufficiently, while if it exceeds 0.07%, both molten steel and slag are in a peroxide state.

During or after tapping from a smelting furnace to a ladle, deoxidation is performed by adding Si and Mn to the inside of the ladle. Simultaneously with or subsequent to the deoxidation by Si and Mn, a slag forming agent and Si for controlling the composition of the slag are added, and the slag composition is controlled while blowing oxygen to heat the Si. Thereafter, if the bubbling is performed by the above-described method using bottom blowing or a lance, the oxide dispersion density can be controlled. The gas used at this time is not particularly limited, but Ar gas usually used in steelmaking is preferable.

Next, as for the vacuum degassing process, the RH vacuum degassing method with less slag agitation is suitable as the vacuum processing method, and it is easy to control the target oxide dispersion density. Also, when adding Ti or Zr, the above-mentioned vacuum processing method can be used.

In the case of a steel plate which is one of the steels to be subjected to the method of the present invention, Cu:
0.2-0.5%, Ni: 0.2-0.8%, Nb:
0.02-0.8%, V: 0.03-0.09%, S:
0.0004-0.0040%, P: 0.006-0.
018% and B: 0.0001 to 0.0016% of 1
Examples include steels containing one or more species.

[0062]

EXAMPLES Next, the results of tests conducted to confirm the effects of the method of the present invention using a 250-ton converter, a ladle refining facility, and an RH vacuum degassing apparatus will be described.

First, a carbon concentration of 0.05 to 0.1 was set in a converter.
0%, molten steel 250 with initial oxygen concentration of 0.04 to 0.07%
t was melted. Next, molten steel at a temperature of 1650 to 1700 ° C. was tapped into a ladle, and ferrosilicon (Fe—Si) and ferromanganese (Fe—Mn) were added for deoxidation with Si and Mn. Yet at the same time Zokasu agent, a predetermined amount of quicklime, calcium carbonate, Al ₂ O ₃ containing Zokasu agent, silica sand, was added fluorite or the like. Further, while adding a predetermined amount of Si, oxygen was blown upward to raise the temperature and adjust the slag composition. Then, [% Si] is reduced to approximately 0.1%.
%, And the molten steel in the ladle was stirred with Ar gas.
Thereafter, molten steel processing was further performed by an RH vacuum degassing apparatus. In some tests, Ti addition or Zr addition was performed at a predetermined timing during RH vacuum degassing.
The amount of Ti or Zr added is [% Ti] = 0.
005 to 0.02%, or [% Zr] = 0.002
The addition amount was adjusted to be 0.01%. For comparison, a test was performed in which the Ar bubbling time and the RH vacuum degassing time in the ladle were not particularly limited. In each test, the test of the repetition number n was repeated for each test. In the above comparative test, the conditions for the addition of Ar bubbling time, RH vacuum degassing treatment time, Ti, etc. are not particularly limited, and therefore, the conditions are not the same between the repetitions within the same test number. This directly reflects the conventional method in which the oxide dispersion density could not be controlled.
Immediately after the end of the RH degassing treatment for each test number, a steel bomb sample was taken from the molten steel, and the cross section of the sample was mirror-polished. Diameter in 100 fields of view.
The number of oxides of 2 to 20 μm was measured.

Table 3 shows ladle stirring, vacuum degassing, Ti,
It shows the conditions such as Zr addition and the test results under those conditions, that is, the oxide dispersion density.

[0065]

[Table 3]

In Test No. 1, which is an embodiment of the present invention, the flow rate of Ar gas for stirring the ladle Q = 0.10 Nm ³ / s, the stirring time of the ladle was 600 seconds, and the RH degassing time was 90.
This is a result of n = 8 after the RH degassing treatment when the operation was performed for 0 seconds. Test No. 2, which is a comparative example, is a result of n = 11 when the ladle stirring time, the stirring gas amount and the RH degassing time are not limited. In test number 1,
The oxide dispersion density was close to the target obtained by calculation, and a result with little variation was obtained. On the other hand, in test number 2, [%
Although Si] was adjusted, the oxide dispersion density varied greatly, and the oxide dispersion density itself was small due to excessive stirring and degassing. This is because, as described above, the Ar bubbling time and the RH vacuum processing time were different between the repetition number n, and the result reflected the conventional method.

In Test No. 3 which is an embodiment of the present invention, the flow rate of the Ar gas for stirring the ladle Q = 0.10 Nm ³ / s, the stirring time of the ladle was 600 seconds, and the RH degassing time was 6 times.
00 seconds, and 300 seconds after the start of the RH degassing process, T
The result of n is 5 when i was added so that [% Ti] = 0.01%. Test number 4, which is a comparative example,
In particular, the ladle stirring time, the stirring gas amount, the RH degassing treatment time, and the Ti addition timing are results of n = 6 when not determined. In Test No. 3, a result was obtained in which the oxide dispersion density was close to the target value obtained by calculation and the dispersion was small. On the other hand, in Test No. 4, which is a comparative example, the oxide dispersion density had a large variation, and the results were smaller due to excessive stirring and degassing. This result is also due to the fact that these conditions differed between the repetitions without grasping each processing time and addition time.

Test No. 5 was prepared according to the method of the present invention.
Ar gas flow rate for stirring the ladle Q = 0.10Nm ³ / s,
The ladle stirring time was 600 seconds, and the RH degassing time was 600 seconds in total.
This is the result of n = 3 when r is added so that [% Zr] = 0.005%. Test No. 6 is the result of n = 4 when the ladle stirring time, stirring gas amount, RH degassing time and Zr addition timing are not limited. In Test No. 5 which is an example of the present invention, a result close to the target obtained by calculation of the oxide dispersion density was obtained. On the other hand, in Test No. 6, which is a comparative example, the oxide dispersion density had a large variation, and a small result was obtained due to excessive stirring and degassing.

[0069]

According to the method of the present invention, it has been impossible to control the oxide dispersion density with high accuracy.
It has become possible to stably produce a system oxide-containing steel with good reproducibility. As a result, even if high efficiency welding is performed, a high HAZ is obtained.
It will be possible to supply inexpensive and large quantities of steel materials that can secure toughness, which will have a beneficial effect not only on steel manufacturers but also on steel material-related industries.

[Brief description of the drawings]

FIG. 1 is a view showing the influence of [% Si] in molten steel and Ar gas stirring time on oxide dispersion density ratio N / No in a ladle.

FIG. 2 shows the effect of [% S on oxide dispersion density N in a ladle.
FIG. 7 is a diagram showing the influence of i] and Ar gas stirring time.

FIG. 3. Effect of A on oxide dispersion density ratio N / No in ladle
It is a figure which shows the influence of r gas flow rate and Ar gas stirring processing time.

FIG. 4 is a diagram showing the influence of [% Si] and the RH vacuum degassing time on the oxide dispersion density ratio N / No in the RH vacuum degassing apparatus.

FIG. 5 is a diagram showing the effect of Ti addition on the oxide dispersion density ratio N / No in the RH vacuum degassing apparatus.

FIG. 6 is a diagram showing the effect of Zr addition on the oxide dispersion density ratio N / No in the RH vacuum degassing apparatus.

Claims (2)

[Claims] In a ladle, the Si concentration and the Mn concentration are adjusted, and heating is performed by blowing oxygen while adding a slag-making agent and Si, thereby heating CaO-S in the following range.
forming a slag having a composition of iO ₂ —Al ₂ O ₃ —MgO system,
And, after controlling the composition of the molten steel to the following range, the Si concentration in the molten steel is readjusted to 0.05 to 0.2% by weight, and gas bubbling and vacuum degassing are performed under predetermined conditions. A method for producing an oxide-dispersed steel containing an Al-Mn-based oxide, characterized in that: : CaO (% by weight) / SiO ₂ (% by weight) = 0.8 to
4 Al ₂ O ₃ : _{3 to} 40% by weight MgO: 5 to 20% by weight However, the weight% of the oxide is the concentration in the slag. : Al in molten steel: 0.0001 to 0.003% by weight Total oxygen in molten steel: 0.002 to 0.01% by weight 2. A method for producing an oxide-dispersed steel according to claim 1, wherein Ti or Zr or a combination thereof is added during the vacuum degassing process.