JPH08257701A - Continuous casting method - Google Patents

Abstract

PURPOSE: To reduce a variation range of component and to uniformize a component concn. of an alloy by impressing brake magnetic field in the direction crossing the drawing direction of a cast slab to molten steel below an immersion nozzle, in a continuous casting of the different component of steel or the different component ratio of steel. CONSTITUTION: At the time of pouring the molten steel 4 having the constant component ratio into a mold 2 through the nozzle 11, the electric magnets 7 for electromagnetic brake is energized to form the static magnetic field 8, and the alloy component is supplied into the molten steel 4 above this magnetic field at the speed proportional to the cast speed. Since a pool is formed and mixed with the alloy component and the molten steel 4 by the static magnetic field 8 of the electric magnets 7, the alloy component concn. is uniformized for a short period of time, and the length of a transition part which changes from the initial component to the following component, becomes the shortest. In such a way, the component concn. in the cast slab 6 after elapsing a prescribed time from the addition of the alloy becomes the constant, and the length of the variation range of component is drastically shortened and also, the yield of the cast product can be improved.

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 a slab having a component or a component ratio different from that of molten steel from a part of the molten steel by adding an alloy component to the molten steel in a mold at one stage of continuous casting. .

[0002]

BACKGROUND OF THE INVENTION The use of steel materials has increased over time, and as a result, the types of steel materials have increased.
Therefore, in order to meet many demands of customers, steel materials of different materials are manufactured little by little. This is the production of so-called high-mix low-lot materials. In the production of high-mix low-lot materials, if it is not possible to create the required characteristics in the subsequent manufacturing process such as rolling, even if there is a slight difference in alloy composition or composition ratio, it will be treated as a different steel type. Must be manufactured. In that case, industrial production requires refining in a large-capacity converter, for example, 300 tons, so the originally required amount is at most 1.
Even if it is about 0 tons, 300 tons must be tapped. This is a great waste, and when stocking the remaining 290 tons as a slab until it is necessary, there is a problem that the inventory increases and storage space and interest rates are required. Further, in the case of remelting as scrap, there arises a problem that extra cost is required for scrapping. These problems will eventually raise the price of steel products.
Therefore, the production of high-mix low-lot materials has been a longstanding problem in the steel industry.

As a proposal of a technique for overcoming the problems of a large variety of small lots, for example, there is a wire addition method presented to Takashi Ito: 72nd and 73rd Nishiyama Memorial Technology Course, p143-p172, Japan Iron and Steel Institute. . The purpose here is Sol. Although it is in the control of the Al content, if this is expandedly interpreted, it is possible to manufacture a slab that can be used for the manufacture of a wide variety of small lot materials by adding alloy components that change other materials into molten steel. it can.

[0004]

However, in this method, it takes time from immediately after adding the alloy components until the drawn slab becomes a desired component, and the slab (transition part; component transition part) during this time is , The composition ratio of the added alloy is uncertain and non-uniform. That is, it means that the transition portion is long and its components are uncertain and non-uniform, so that it cannot be used, and the yield is poor.

According to the present invention, alloy components are added to molten steel in a mold at a time during continuous casting to produce a slab having a different component or a different component ratio from the molten steel from a part of the molten steel. The first purpose is to shorten the length (drawing direction) of the transitional part in which the content of the alloy component is uncertain and non-uniform, and to improve the yield of continuous casting of a wide variety of small lot materials. The purpose is 2.

[0006]

According to the present invention, a continuous casting mold is continuously supplied with molten steel having substantially the same composition from the outside of the mold through an immersion nozzle, while an alloy component is supplied to the molten steel in the mold. A continuous casting method for casting a component steel or a steel with a different composition ratio is characterized in that a braking magnetic field is applied to the molten steel below the immersion nozzle in a direction intersecting with the slab drawing direction.

In the first embodiment of the present invention, an electromagnetic brake for applying a unidirectional magnetic field having a uniform magnetic flux density across molten steel in a continuous casting mold or a slab that has left the mold is provided at the bottom of the mold or Using a continuous casting machine disposed below the mold, applying the magnetic field during the continuous casting, and at least one of alloying components Ti, Nb and V in the molten steel on the upstream side of the magnetic field, When added alone, Ti: 0.01% or more and Nb: 0.01% or more by weight,
It is a continuous casting method for precipitation-strengthened high-strength steel in which V: 0.01% or more, and when two or more kinds are added, the sum thereof is 0.01% or more.

In a second embodiment of the present invention, an electromagnetic brake for applying a unidirectional magnetic field having a uniform magnetic flux density across molten steel in a continuous casting mold or a slab discharged from the mold is provided at the bottom of the mold or Using a continuous casting machine disposed below the mold and above the electromagnetic brake, an electromagnetic stirring device that stirs the molten steel in the mold is used, and the magnetic field is applied above the magnetic field. Alloying component T in molten steel
When adding at least one of i, Nb and V,
When added alone, Ti: 0.01% by weight
Or more, Nb: 0.01% or more, V: 0.01% or more,
In the case of adding two or more kinds, the sum of 0.01% or more is added and the molten steel in the mold, which is upstream of the magnetic field, is stirred by adding the electromagnetic stirrer. It is a continuous casting method.

In any of the embodiments, in order to further shorten the length of the transition portion (component transition portion) in the slab withdrawal direction, the molten steel in the mold is added when alloying components are added. A shield plate for preventing vertical mixing is inserted on the molten steel surface in the mold.

[0010]

When the supply of the alloy components is started and ended, the above-mentioned transition portion (component transition portion) can be formed into a slab.

According to the present invention, when a braking magnetic field in a direction intersecting the slab drawing direction is applied to the molten steel below the immersion nozzle when the supply of the alloy components is started, the nozzle is injected at the braking magnetic field. The molten steel flow, which tends to flow downward (in the slab withdrawal direction), is subjected to an electromagnetic force that attempts to return it upward, that is, a force that blocks the downward flow, which causes the molten steel flow to reach the braking magnetic field at the inner surface of the mold. The advancing direction bends in the direction toward, and tries to rise along the inner surface of the mold. That is, with respect to the braking magnetic field, the molten steel on the upper side (immersion nozzle side) is restrained from flowing downward, and as a result, a circulating flow is formed on the upper side (hereinafter, this region is referred to as a blocking pool). And The alloy component is supplied to the shut-off pool, which is efficiently dispersed in the molten steel in the pool by the circulating flow. That is, due to the braking magnetic field,
The blocking pool is separated (molten steel flow is blocked or suppressed) from the molten steel preceding the blocking pool, and stirring of the supplied alloy components is realized in the blocking pool. The diffusion of the alloy components supplied thereafter to the molten steel to which the alloy components are not supplied is small, and moreover, the convergence of the molten steel in the mold to the desired component ratio of the alloy components is quick after the supply of the alloy components is started. Transition part (component transition part)
However, the length in the slab withdrawal direction is significantly reduced. That is, the yield of the different steel type casting is significantly improved.

Next, according to the present invention, when the supply of alloy components is stopped, a braking magnetic field in a direction intersecting with the slab drawing direction is applied to the molten steel below the dipping nozzle by the braking magnetic field. Isolation pool is separated (molten steel flow is blocked or suppressed) from molten steel added with alloy components preceding
No alloying components are supplied to the shut-off pool. This allows
The diffusion of the molten steel not supplied with the alloy component to the preceding molten steel supplied with the alloy component is small, and therefore the length of the transition portion (component transition portion) in the slab drawing direction is significantly shortened. That is, the yield of the different steel type casting is significantly improved.

A more specific description will be given below. Figure 1
FIG. 2 is a vertical cross-sectional view of a mold 2 for carrying out the present invention in one aspect, taken along a plane perpendicular to a wide surface, and FIG. 2 is a vertical cross-sectional view taken along a plane parallel to the wide surface of the mold 2. An electromagnet 7 for electromagnetic braking is installed in the lower part of the mold 2, and an electromagnetic stirrer 9 is installed at a position slightly below the molten steel meniscus. The electromagnet 7 for the electromagnetic brake is configured to cross a molten steel 4 in the continuous casting mold 2 with a magnetic field in one direction which produces a magnetic flux having a uniform density in the width direction of the wide surface and orthogonal to the slab drawing direction 10. Then, it can be applied to the molten steel 4 in the mold.
Reference numeral 8 is a static magnetic field (static magnetic field) at this time. The electromagnet 7 of the electromagnetic brake may be arranged below the mold 2. However, it is above the lowest point f where the flow of molten steel injected into the mold 2 substantially extends.

The molten steel flow injected from the tundish into the mold 2 through the nozzle 11 reaches point f when the static magnetic field 8 is not applied. However, when the static magnetic field 8 is formed, the Lorentz force that blocks the molten steel injection flow passing through the static magnetic field 8 acts from the static magnetic field 8, and the penetration depth of the injection flow is approximately c / d (dashed line). Up to the level. In FIG. 2, the magnetic flux generated by the static magnetic field 8 flows from the back side of the paper to the front side.

In the first embodiment of the present invention, the electromagnetic brake is used during continuous casting of molten steel, that is, when molten steel having a substantially constant composition ratio is continuously injected into the mold 2 through the nozzle 11. The electromagnet 7 for use is energized, that is, the above-mentioned static magnetic field 8 is formed, and the alloy component is supplied into the molten steel above the static magnetic field 8. FIG. 2 shows a mode in which the steel wire 3 in which the alloy components are enclosed in a uniform density is fed into the molten steel in the mold at a rate proportional to the casting rate, so that the molten steel is quantitatively supplied.

Therefore, the alloy components are supplied to the molten steel in the mold at a predetermined ratio, but the static magnetic field 8 prevents the molten steel injection flow from the nozzle 11 from entering below the level of c / d.
As a result, the molten steel containing the supplied alloy components is a, b,
In the shut-off pool in the range of c ′, d ′, the molten steel flow is uniformly mixed and extruded downward from this pool at a constant speed (drawing speed). That is,
By the electromagnetic brake of the electromagnet 7, a small pool for mixing the supplied alloy components with the molten steel is formed in the mold 2, and the mixing is performed within the range, so that the time required for the concentration to be uniform is shortened. At the same time, the flow pushed downward from this pool is plug-flowed, and it is difficult to form convection, so that new mixing (mixing of the preceding molten steel and the following molten steel) is caused in the lower part of the static magnetic field 8. Absent. Therefore, the length of the seam, that is, the transition portion (component transition portion) where the first component changes to the second component becomes the shortest.

As described above, since the alloy components are sufficiently mixed in the pool having a constant volume above the electromagnetic brake, a predetermined time has elapsed after the addition of the alloy was started, and the alloy components were obtained at the time when the steady state was reached. The component concentration in the cast slab is stable,
It is constant in the cross section of the slab and the length direction of the slab. Therefore, by implementing the present invention, the length of the component change region caused by the addition of the alloy is significantly reduced, and the concentration of the alloy component is made uniform at any portion in the cast slab, and the yield of the cast product is greatly improved.

The elements added at this time are Ti, Ti, for the purpose of producing a precipitation-strengthened high-strength steel in a small lot.
And / or Nb and / or V are added. When they are added individually, the weight ratio is Ti: 0.01% or more, Nb: 0.01% or more, and V: 0.01% or more. Addition of each element below the above lower limits does not show the effect of precipitation strengthening. When two or more kinds are added at the same time, the total amount is 0.01% or more. Also, if the sum is less than 0.01%, the effect of precipitation strengthening does not appear. The upper limit is not particularly limited, but addition of an alloy causes an increase in cost.
% Or less is preferable.

In the second embodiment of the present invention, the electromagnetic stirrer 9 is used at least while the alloy components are being supplied to the molten steel of the mold 2.
Drive. The electromagnetic stirrer 9 is a linear motor that applies thrust to the molten steel in the mold, but other known devices may be used. The electromagnetic stirrer 9 is arranged above the electromagnet 7, preferably near the meniscus of the molten steel in the mold. According to this method, the strong stirring force F ′ generated by the molten steel injection flow is applied to the molten steel within the range of a, b, c ′, d ′ in FIG.
And the electromagnetic stirring force both act, and the molten steel mixes more significantly. Therefore, at the time of adding the alloy component, the rate of uniformizing the alloy component concentration in the molten steel is high, and the effect of uniformizing the alloy component concentration is high. At the start of the supply of the alloy components, the amount of the alloy components to bring the molten steel in the blocking pool to the desired component concentration is supplied at high speed, and after this supply, the alloy components are supplied at a rate proportional to the casting speed. By using the control together with the electromagnetic stirring, the length of the transition part (component transition part) is further shortened, and the yield of the cast product is further improved.

Immediately before adding the alloy components and immediately after stopping the addition of the alloy components, a shield plate for preventing vertical mixing of the molten steel in the mold is inserted into the molten steel surface of the molten steel in the mold. can do. This has a high effect of preventing the diffusion of the alloy components from the molten steel to which the alloy components have been added to the molten steel to which the alloy components have not been added when adding two or more alloys having different specific gravities. In this case, a known shield plate may be used.

The alloy is supplied by powder, particles,
The alloy component wire or the like can be continuously fed, but a method in which a steel wire having an alloy component enclosed therein is supplied into molten steel is preferable. According to this method, the alloy components are not oxidized or contaminated until they are supplied to the molten steel, the alloy components to be added can be easily dissolved in the molten steel, and the alloy components can be evenly distributed in the slab.

In both the first embodiment and the second embodiment described above, when the continuous casting of precipitation-strengthened high-strength steel is completed, that is, when the supply of alloy components is completed, the alloy components are supplied. After the stop, the amount of molten steel in the shut-off pool at that time passes through the lowest point f, where the flow of molten steel injected into the mold 2 substantially when the static magnetic field 8 is not applied, is followed by the electromagnet. Turn off the power supply of 7. Even during the supply of the alloy components, the component concentration in the slab is stabilized after the alloy addition is started, and the electromagnet 7 may be de-energized after the stable region passes the point f. When the supply of the alloy components is terminated after the interruption in this way, the supply of the alloy components is stopped, the electromagnet 7 is energized to apply the static magnetic field 8 to the molten steel, and the molten steel present at the interruption pool at that time is applied. After the quantity has passed the lowest point f, where the flow of the molten steel injected into the mold 2 substantially extends when the static magnetic field 8 is not applied, the energization of the electromagnet 7 is cut off. In addition, when the application of the static magnetic field 8 does not hinder or burden the operation in particular, the electromagnetic field 8 may be constantly applied.

[0023]

【Example】

Example 1 300 tons of molten steel of steel A having the composition ratio (% by weight) shown in Table 1 was obtained by ordinary refining, 250 tons of steel A was first cast in a continuous casting machine, and then steel A in the mold. By adding Ti with a wire from the meniscus of molten steel, the steel is added 50% so that Ti becomes 0.08% from the middle.
Ton cast. The slab has a thickness of 230 mm and a width of 1250.
It was mm. The electromagnet 7 for the electromagnetic brake is installed at a position 500 to 700 mm below the meniscus in the mold, and the two conditions of the case where the magnetic field is applied and the case where the magnetic field is not applied are changed during the casting of 50 tons described above. Carried out.

[0024]

[Table 1]

The amount of Ti in the steel with and without application of a magnetic field was 0.08% after the wire was added.
Table 2 shows the length of the cast slab and the variation in Ti after the Ti content was 0.08%.

[0026]

[Table 2]

As can be seen from Table 2, the length of the slab until the amount of Ti in the slab reaches a predetermined value can be greatly reduced by the method of the present invention, and the variation in the concentration thereafter is small.

[Example 2] Component ratios (% by weight) shown in Table 1
A molten steel having substantially the same composition as that of Steel A in Example 1 is obtained by an ordinary refining method, and when an alloy component is added to the molten steel from a meniscus in a mold by a wire in a continuous casting machine, the type of alloy in the wire and the feeding of the wire By changing the speed, Steel B to Steel H in Table 3 were obtained as cast pieces in this order. At that time, the magnetic field was continuously applied after the wire feeding was started. Moreover, when the type of alloy in the wire of each steel type and the wire feed speed were changed, the seam of each steel type was clarified by inserting a shielding plate into the meniscus.

[0029]

[Table 3]

For these slabs, the slab extraction temperature:
1250 ° C, finish rolling finish temperature: 920 ° C, winding temperature:
Hot rolling was performed under the condition of 600 ° C. to obtain a hot rolled steel sheet having a plate thickness of 3 mm. This hot rolled sheet was subjected to a reheating test that maximizes the characteristics of the precipitation strengthened high strength steel sheet, and the difference in strength between the as-rolled sheet and after the reheating test was determined. For the reheating test, 80
It was immersed in a 0 ° C. salt bath for 10 minutes and then air-cooled. The strength characteristics were evaluated by a tensile test. The tensile test is J
Using the No. 5 test piece described in ISZ2201, the same Z2241
According to the method described, the tensile strength TS was measured. The longitudinal direction of the test piece was the rolling direction of the product. In addition, as the evaluation of economic efficiency, the weight of the steel pieces from Steel B to Steel H according to this method was taken as the required amount, and the difference when each steel was melted by 300 tons, which is the usual method, was evaluated as the unnecessary amount. . Table 4 shows the difference (ΔTS) in TS between the as-rolled and after reheating tests, the unnecessary amount, and the ratio to 300 tons.

[0031]

[Table 4]

As ΔTS is smaller, the strength before and after reheating does not change, and the characteristic of precipitation strength steel appears. The results are shown for steels C, E, F and G. In each case, the composition ratio of the precipitation strengthening element is within the range defined in the first embodiment and the second embodiment (hereinafter, defined range). On the other hand, steel A, which is the original steel material, shows the characteristics that precipitation strengthening elements are not included although it is not the object of evaluation, and steels B, D, and H whose contents are out of the defined range show the characteristics as precipitation strengthening steels. There wasn't.

Further, the unnecessary rate of each steel produced by the ordinary method shown as a guideline for evaluating the economical efficiency is 85% or more, showing that this method is an economical method with a good casting yield. There is.

[0034]

According to the present invention, an alloy is added to molten steel in the course of continuous casting, and a slab containing this alloy is made from a part of the molten steel to have a uniform alloy component content and transfer thereof. It can be manufactured to have fewer parts. Furthermore, precipitation-strengthened high-strength steel that exhibits important properties although the required amount is small can be manufactured extremely economically.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a long piece of a continuous casting mold that embodies the present invention in one aspect.

FIG. 2 is a vertical cross-sectional view of a short piece of the mold shown in FIG.

[Explanation of symbols]

2: Mold 3: Wire 4: Molten steel in mold 5: Solidified shell 6: Molten steel in cast piece 7: Electromagnet for electromagnetic brake 8: Static magnetic field 9: Electromagnetic stirrer 10: Extraction direction of cast piece 11: Immersion nozzle

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Claims (7)

[Claims] 1. A different component steel or a different component ratio steel is obtained by continuously supplying molten steel having substantially the same composition from the outside of the mold to a continuous casting mold through an immersion nozzle while supplying an alloy component to the molten steel in the mold. In the continuous casting method for casting, a braking magnetic field is applied to the molten steel below the dipping nozzle in a direction intersecting with the slab withdrawal direction, a continuous casting method for different component steel or different component ratio steel. 2. A braking magnetic field in a direction intersecting with a casting product drawing direction is applied to the molten steel below the immersion nozzle at least at the start and end of the supply of the alloy components. The continuous casting method of different composition steel or different composition ratio steel. 3. A braking magnetic field is applied at the start of the supply of alloy components, and then a braking magnetic field is applied after the molten steel having a substantially constant weight ratio of the composite components in the slab drawing direction has passed a predetermined position. Stopping, applying a braking magnetic field when the supply of the alloy component is stopped, and then stopping the application of the braking magnetic field after the molten steel substantially free of the synthetic component has passed a predetermined position,
The continuous casting method according to claim 2, wherein the different component steel or the different component ratio steel is cast. 4. The heterogeneous steel according to claim 2 or 3, wherein the molten steel upstream of the braking magnetic field is electromagnetically stirred at least while supplying the alloying components to the molten steel and applying the braking magnetic field. Alternatively, a continuous casting method for steel with a different composition ratio. 5. An electromagnetic brake for applying a unidirectional magnetic field having a uniform magnetic flux density across the molten steel in the continuous casting mold or the slab leaving the mold is disposed below the mold or below the mold. In the case where the magnetic field is applied during the continuous casting and at least one of the alloy components Ti, Nb and V is added to the molten steel on the upstream side of the magnetic field by using the continuous casting machine described above, By weight ratio, Ti: 0.01% or more, Nb: 0.01% or more, V: 0.01% or more,
A continuous casting method for precipitation-strengthened high-strength steel, which comprises adding 0.01% or more of the sum when two or more kinds are added. 6. An electromagnetic brake for applying a magnetic field in one direction having a uniform magnetic flux density across the molten steel in the continuous casting mold or the slab leaving the mold is disposed below the mold or below the mold. And, using a continuous casting machine provided with an electromagnetic stirring device for stirring the molten steel in the mold above the electromagnetic brake, the alloy component Ti in the molten steel above the magnetic field with the magnetic field applied, When adding at least one of Nb and V, when added alone, Ti: 0.01% or more and Nb: 0.01% or more by weight ratio,
V: 0.01% or more, and in the case of adding two or more kinds, the sum of 0.01% or more is added and the molten steel in the mold upstream of the magnetic field is stirred by the electromagnetic stirring device. , A continuous casting method for precipitation strengthened high strength steel. 7. The method according to claim 5, wherein a shield plate for preventing the molten steel in the mold from being mixed in the vertical direction when the alloy component is added is inserted into the molten steel surface of the molten metal in the mold. Alternatively, the continuous casting method for precipitation-strengthened high-strength steel according to claim 6.