JP3033002B2 - Low cost method of adding Mg to molten steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently adding Mg to molten steel, whereby the size of oxides in the molten steel is reduced at low cost and the quality of the steel material is excellent. Supply becomes possible.

[0002]

2. Description of the Related Art In recent years, the quality required for steel materials has become increasingly intense and diversified, and there is a strong demand for the development of technology for producing cleaner and more functional steel. Oxide-based inclusions in steel materials have been required to be further reduced in order to reduce the degree of adverse effects in steel materials. That is, oxide-based inclusions, particularly alumina (Al ₂ O ₃ ) -based inclusions, cause disconnection of the tire cord and the like, cause deterioration of the rolling contact fatigue characteristics of bar steel such as bearing steel, and further cause the thinning of DI cans and the like. Steel plates are known to cause cracking during can-making, and reduction thereof has been strongly demanded. For this reason, T.P. Various techniques have been developed or studied to reduce the O content. They are for removing alumina in the secondary refining stage of molten steel, preventing foreign oxides from being mixed, and the like.

[0003] However, T.A. It is true that the reduction of the O content has reached technical limits. That is, for example, in high carbon chromium bearing steel, T.V. It is difficult to reduce the O content to 5 ppm or less, while T.O. O content is 5ppm
Oxidation may cause fatigue fracture due to oxides.
Therefore, the problem was technically a major barrier.

[0004] The present inventors have established a drastic measure against such a situation by a new concept. These are Japanese Patent Application No. 3-337922, Japanese Patent Application No. 4-14498, and Japanese Patent Application No. 5-59333. The alumina (Al ₂ O ₃ ) in the molten steel is changed to MgO.Al ₂ O ₃ or M
Basically, the composition is converted to gO and the size of the oxide is reduced. That is, in Japanese Patent Application No. 3-337922, M
Fe-Si-Mg, Fe-Mn-Mg, Fe
-Si-Mn-Mg, a method using a Si-Mg alloy,
In Japanese Patent Application No. 4-14498, Al-M is used as a Mg source.
A method using g alloy was proposed. Furthermore, Japanese Patent Application No. 5-59
No. 333 proposed an efficient composition conversion method in which the S content in molten steel before the addition of the Mg alloy was 0.005% by weight or less. As a result, the quality of the obtained steel material has been dramatically improved.

[0005]

However, as a result of repeating experiments on the above method, it was found that the above method had a disadvantage that the production cost was increased because Mg was added as an alloy. That is, for alloying, it is necessary to heat and melt the raw material, which requires a great deal of electric energy.

The present invention has been made in view of the above circumstances, and provides a low-cost manufacturing method by improving an Mg source.

[0007]

The gist of the present invention is to add Si, Mn and Al to molten steel containing 1.2% by weight or less of C when adding Mg to molten steel.
Mg is mixed with at least one of Mn, Al, Fe-Si, Fe-Mn, and C, and the Mg content in the mixture is 0.5 to
15 wt%, and further, the particle size of Mg is 0.01 to 3.0.
A method of adding low-cost Mg to molten steel, characterized by being added as mm.

Here, the addition rate of Mg is set to 0.002 to 0.
Control at 050 kg / t-molten steel / min, MgO: 3 to 15%, FeO + F
_{e 2 O 3 + MnO: CaO} -SiO containing 5% or less
It is also characterized by adding Mg in the presence of _2- Al ₂ O ₃ -based slag. Further, the Mg mixture is added at one or more points of a ladle, a continuous casting tundish and a continuous casting mold, the Mg mixture is blown into molten steel by an inert gas, the Mg mixture is filled into an iron wire, and the molten steel is filled. It is also characterized by feeding into molten steel while stirring.

[0009]

The purpose of the addition of Mg is to reduce the size of the oxide present in the molten steel and to avoid the adverse effect of the oxide on the quality of the steel material. That is, as the size of the inclusions in the steel material is larger, the stress is more likely to be concentrated on that portion, which is likely to cause a defect. Based on this idea,
The present inventors have found that Al ₂ O ₃
Various refinement methods were studied. As a result, by modifying Al ₂ O ₃ by adding Mg and changing the composition to Al ₂ O ₃ .MgO or MgO, the interfacial energy between the oxide and the molten steel is reduced, and thus the oxide is refined. Found to be.

As is well known, Mg is a high vapor pressure element, and even if it is added to molten steel, evaporation loss is liable to occur. Also, it has a strong affinity with oxygen and is easily oxidized at the molten steel-air interface. If the Mg loss is large, the progress of the Al ₂ O ₃ reforming reaction is undesirably hindered. As a measure for preventing Mg loss, a method of alloying Mg to reduce the reactivity of Mg is generally used. However, since alloying causes a great increase in cost as described above, the present inventors have developed a preferable method using a mixture without using an Mg alloy.

First, Si, Mn, Al, Fe-Si, F
e-Mn, at least one kind of C is mixed with Mg, and the Mg content in the mixture is adjusted to 0.5 to 15% by weight.
The reason for adding the particles having a particle size of 0.01 to 3.0 mm is described. The purpose of setting these conditions is to prevent evaporation and oxidation loss by reducing the reactivity when adding Mg. That is, if the reactivity of Mg is relaxed, the evaporation rate is slowed down, severe bumping is avoided, and oxidation loss can be prevented. Si, Mn, Al, Fe-Si, Fe-M
The reason why Mg is mixed with at least one of n and C is that the reactivity of Mg is reduced by coexisting an element having a strong affinity for Mg in the vicinity of the added Mg in the molten steel. Also, by setting the Mg content in the mixture to 15% by weight or less, the reactivity of Mg can be reduced to a practical level. If it exceeds 15% by weight, Mg loss and scattering of molten steel increase, which is not preferable. If it is less than 0.5% by weight, the supply of Mg becomes slow and the reforming reaction does not proceed. Further, when the particle size of Mg is 0.01 to 3.0 mm, appropriate Mg reactivity can be secured. If the thickness is less than 0.01 mm, the reactivity of Mg becomes severe due to the grain refinement, so that it is not preferable. If the thickness exceeds 3.0 mm, a local Mg concentration region is generated in the molten steel, and the reactivity of Mg becomes extremely large.

Next, the addition rate of Mg in the Mg mixture is
Control to 0.002 to 0.050 kg / t-molten steel / minute
State the reason for the Mg is very reactive
Therefore, if added at a certain speed or more,
Fire erosion and the like occur, which is not preferable. In this regard, M
g at a rate of 0.050 kg / t-molten steel / min or less.
Can prevent intense smoke and refractory erosion.
I understood. The addition rate is 0.002 kg / t-
If the rate is less than steel / minute, evaporation loss of Mg occurs, and Al _TwoO_Three
Does not proceed sufficiently, which is not preferable. The rate of this addition is M
g is smaller than that of the alloy, and the reactivity is higher in the case of a mixture.
The addition speed must be reduced by the amount of intensification
Means

On the surface of molten steel, MgO:
3-15%, FeO + Fe_TwoO_Three+ MnO: 5% or less
CaO-SiO contained_Two-Al_TwoO_ThreeSystem slag exists
This also reduces Mg evaporation and oxidation loss.
Wear. Here, the reason for setting MgO to 3 to 15% is that
The solubility of MgO in the molten steel to below a certain value
To prevent migration into the slag when it becomes MgO
The effect appears when the content of MgO is 3% or more.
Is more than 15%, the effect is slowed down. Ma
FeO + Fe_TwoO_Three+ MnO to 5% or less
, Significantly suppresses Mg oxidation at the molten steel-slag interface
Thus, Mg oxidation loss can be prevented. Further slag basics
The component system is CaO-SiO_Two-Al_TwoO_ThreeReason
Is the most common and low cost form of this slag system
This is because it is possible to do so. Compositionally, three components
Assuming 100% in total, CaO: 25 to 60% by weight, S
iO _Two: 15 to 50% by weight, Al_TwoO_Three： 10-45 layers
Amount% is an appropriate range. Other, CaF_Two, Na_TwoO etc.
May be combined.

The reasons for defining the molten steel composition before adding the Mg alloy are as follows. C forms MgC in the solidification process together with the added Mg, thereby inhibiting the object of the present invention.
It needs to be 2% by weight or less. In this range, almost no MgC is generated. If C is less than 0.2% by weight, the molten oxygen in the molten steel increases, and the added Mg reacts violently with the oxygen, causing the molten steel to be scattered. As a measure against this, A
It is effective to add a deoxidizing agent such as 1 to make molten oxygen in molten steel 50 ppm or less. This is not the case when the C content is 0.2% by weight or more. Note that Si and Mn are replaced by Mg
If it is added after the addition, the time required from the addition of Mg to the casting becomes long, and therefore, Mg loss is undesirably increased. For this reason, it is better to add Mg to molten steel containing predetermined amounts of Si and Mn. Further, the object of the present invention is achieved even if Al is contained in the molten steel before Mg addition.
In addition, Si, Mn added as a mixture with Mg,
Since a considerable amount (% by weight) of Al and C increases with the addition of Al and C, the concentration before addition needs to be reduced correspondingly.

The S content of molten steel before Mg addition is 0.00
It is desirable that the content be 5% by weight or less. Thereby, Mg
The generation of S is suppressed, and coarsening due to the attachment of MgS to the oxide can be prevented. In order to ensure the machinability of steel materials, Mg
After the addition, S may be added as necessary. Next, Mg
The conditions for adding the mixture will be described. Ladle with Mg mixture,
The reason for the addition in at least one of the continuous casting tundish and the continuous casting mold is to prevent evaporation loss of Mg. Since Mg is a high vapor pressure element, it should be added at a lower temperature place. Specifically, addition in a continuous casting tundish and / or a continuous casting mold is desirable. However, in the present invention, since the evaporation loss of Mg can be remarkably prevented, it is also possible to add Mg in a molten steel ladle.

Further, in a system in which a granular Mg mixture is blown into molten steel with an inert gas, or in a system in which the mixture is fed into molten steel and supplied into molten steel, contact between Mg and oxygen in the atmosphere is suppressed, and Oxidation loss is greatly reduced. In addition,
In the method of filling the steel wire and supplying it to the molten steel, a lance made of refractory with an iron pipe interior is immersed in the molten steel from above,
It is desirable to supply an iron wire to the vicinity where the inert gas is blown. As a result, Mg is supplied and immediately dispersed in the molten steel, so that the reactivity of Mg is reduced and the reforming efficiency is increased, which is preferable.

As described above, the effect of adding Mg is further enhanced, and the material properties are dramatically improved. Hereinafter, examples of the present invention will be described, and effects of the present invention will be described.

[0018]

EXAMPLE A thin steel sheet (thickness: 2 m) having the composition shown in Table 1 was obtained by a 120 ton converter-RH-Mg addition-continuous casting-rolling method.
m), spring steel (diameter 6 mmφ), bearing steel (diameter 65 mm)
φ) was manufactured at 110 to 120 tons. At that time, as shown in Table 2 for the thin steel sheet, Table 3 for the spring steel, and Table 4 for the bearing steel,
The g addition conditions and slag conditions were set as appropriate conditions in the present invention. As a result, as shown in Tables 2 to 4, the obtained raw materials and the material test results were almost the same as Comparative Example-1 using the Mg alloy, and were extremely good. Also the inclusions in the material are comparative examples-
Al ₂ O ₃ · MgO and M
gO, and its size was extremely fine, 4 to 10 μm for a thin steel plate, 2 to 7 μm for a spring steel, and 1 to 5 μm for a bearing steel. Further, the Mg addition cost is 20 to more than Comparative Example-1.
It remained at 30% lower level.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

[0022]

[Table 4]

Comparative Example 1 A thin steel plate (with a thickness of 2 m) shown in Table 1 was prepared in the same manner as in Example.
m), spring steel (diameter 6 mmφ), bearing steel (diameter 65 mm)
φ) was manufactured. In this case, unlike the examples, an Mg alloy was used as the Mg source, and as shown in Table 2 for the thin steel plate, Table 3 for the spring steel, and Table 4 for the bearing steel, the addition conditions were in the appropriate range for the Mg alloy. As shown in Tables 2 to 4, the material test results of the obtained material were almost equivalent to those of the examples. The composition and size of the inclusions in the material were almost the same as in the examples.

Comparative Example 2 A thin steel plate (2 m thick) shown in Table 1 was prepared in the same manner as in Example.
m), spring steel (diameter 6 mmφ), bearing steel (diameter 65 mm)
φ) was manufactured. In this case, unlike the embodiment, as shown in Table 2 for the thin steel plate, Table 3 for the spring steel, and Table 4 for the bearing steel,
The g addition conditions and slag conditions were outside the range of the proper conditions of the present invention. As shown in Tables 2 to 4, the material test results of the obtained material were at an unfavorable level as compared with the examples.
The inclusion composition is mostly unmodified alumina, and its size is 10 to 25 μm for thin steel plate and 6 to 18 μm for spring steel.
m, the bearing steel was 4 to 15 μm, which was an unfavorable level as compared with the examples.

[0025]

As is apparent from the above, according to the present invention, it has become possible to efficiently add an inexpensive Mg mixture of Mg. As a result, a reduction in the manufacturing cost of the Mg-added steel is achieved, and a technology capable of deriving the effect of miniaturizing inclusions by the addition of Mg at a lower cost is established, which is extremely useful for the industry.

Claims (6)

(57) [Claims] 1. When Mg is added to molten steel containing Si, Mn, and Al and further containing 1.2% by weight or less of C, one of Si, Mn, Al, Fe—Si, Fe—Mn, and C is added. More than one kind is mixed with Mg, the Mg content in the mixture is set to 0.5 to 15% by weight, and the particle size of Mg is set to 0.0
A method for adding low-cost Mg to molten steel, characterized in that it is added as 1 to 3.0 mm. 2. The addition rate of Mg is 0.002 to 0.05.
2. The method for adding low-cost Mg to molten steel according to claim 1, wherein the control is performed at 0 kg / t-molten steel / minute. 3. On the surface of molten steel, MgO: 3% by weight%
_{15%, FeO + Fe 2 O} 3 + MnO: 5% in the presence of a CaO-SiO ₂ -Al ₂ O ₃ slag containing the following, according to claim 1 or 2, characterized in that the addition of Mg
A method for adding low-cost Mg to molten steel as described. 4. The method for adding low-cost Mg to molten steel according to claim 1, wherein the Mg mixture is added at one or more of a ladle, a continuous casting tundish, and a continuous casting mold. . 5. The method for adding low-cost Mg to molten steel according to claim 1, wherein the Mg mixture is blown into the molten steel with an inert gas. 6. Filling the Mg mixture into an iron wire,
The low-cost M for molten steel according to any one of claims 1 to 4, wherein the molten steel is supplied into the molten steel while stirring.
g Addition method.