JPH08257702A - Method for continuous casting precipitation enhance type high strength steel - Google Patents

Abstract

PURPOSE: To enable a continuous casting of a precipitation enhancing type high strength steel of a small lot by adding the specific contents of at least one kind of Ti, Nb and V into molten steel at the upstream side of brake magnetic field and supplying only the molten steel in the other strands. CONSTITUTION: At the time of pouring the molten steel 4 having the constant component ratio into a mold 2 through a nozzle 11, the electromagnets 7 for electromagnetic brake is energized to form a magnetostatic field 8, and the alloy components are supplied into the molten steel 4 above this magnetic field at the speed proportional to the casting speed. Since a pool is formed and mixed with the alloy elements and the molten steel 4 by the electromagnetic brake, the alloy component concns. are uniformized, and the length of a transition part which changes to the following component, is drastically reduced and the yield of the cast product can be improved. In order to obtain the precipitation enhancing type high strength steel in the small lot, Ti, Nb or V is added, and in the case of one kind of the single element among these, the element is added to >=0.01%, and in the case of two or more kinds, the total thereof is added to >=0.01%, and then, the continuous casting supplying only the molten steel 4 in the other strands can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting machine composed of a plurality of strands, in which alloy components are added to molten steel in a mold at a time of continuous casting, and a portion or part of the molten steel becomes a component or a component with the molten steel. It relates to a method for producing slabs having different ratios.

[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 by Takashi Ito: 72th and 73rd Nishiyama Memorial Technology Lecture, 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.

The first object of the present invention is to realize continuous casting of a large variety of precipitation-strengthened high strength steels in continuous casting by a continuous casting machine having a plurality of strands. A second object is to improve the yield of reinforced high strength steel.

[0006]

In a first embodiment of the present invention, in one strand of a continuous casting machine consisting of a plurality of strands, molten steel is supplied to the continuous casting mold from the outside of the mold through a dipping nozzle, When a braking magnetic field is applied to the molten steel below the dipping nozzle in a direction intersecting with the slab drawing direction, and at least one of the alloying components Ti, Nb and V is added to the molten steel upstream of the magnetic field alone. Is T by weight
i: 0.01% or more, Nb: 0.01% or more, V: 0.
In the case of adding two or more kinds, 0.01% or more, the sum thereof is added by 0.01% or more, and in other strands, only molten steel from the outside of the mold is continuously cast.

In a second embodiment of the present invention, in one strand of a continuous casting machine composed of a plurality of strands, molten steel is supplied to the continuous casting mold from the outside of the mold through a dipping nozzle, and the molten steel below the dipping nozzle is supplied. A braking magnetic field in a direction intersecting the slab withdrawing direction is applied to the molten steel and the molten steel upstream of the magnetic field in the mold is electromagnetically stirred while at least one of alloying components Ti, Nb and V is contained in the molten steel upstream of the magnetic field. When added singly, Ti: 0.01% or more, Nb: 0.01% or more, V: 0.01% or more by weight ratio,
When adding two or more kinds, 0.01% or more of the sum is added, and in other strands, only molten steel from the outside of the mold is continuously cast.

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

[0009]

In one strand, the above-mentioned transition portion (component transition portion) can be formed into a slab when the supply of the alloy components is started and when the supply of the alloy components is completed.

Here, if a braking magnetic field is present while the alloy components are being supplied, the molten steel flow injected from the nozzle at the braking magnetic field and trying to flow downward (in the slab drawing direction),
An electromagnetic force that tries to return upward is applied, that is, a force that blocks the downward flow is applied, so that at the position where the braking magnetic field is reached, the molten steel flow bends in the direction toward the inner surface of the mold and then rises along the inner surface of the mold. And 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, the braking magnetic field separates the blocking pool from the molten steel preceding the blocking pool (blocks or suppresses the molten steel flow), and stirring of the supplied alloy components is realized in the blocking pool. , Thereby, the diffusion of the alloy component supplied to the preceding molten steel to which the alloy component is not supplied is small, and moreover, after the alloy component is started to be supplied to the desired component ratio of the alloy component of the molten steel in the mold. Convergence is fast, and therefore, the length of the above-mentioned transition portion (component transition portion) in the slab drawing direction is significantly reduced. That is, the casting yield of precipitation-strengthened high-strength steel in a large variety of small lots with one strand is significantly improved. In the other strand, continuous casting of only the molten steel that enters the mold is performed, which is a conventional large-scale continuous casting of the same type of ingot, and the casting yield is as high as the conventional one.

A more specific description will be given below. Figure 1
One strand continuous casting mold 2 assigned to casting multiple lots of a small lot of precipitation-strengthened high-strength steel in a multiple-strand continuous casting machine for carrying out the present invention in one aspect
2 is a vertical cross-sectional view taken along a plane perpendicular to the wide-width surface, and FIG. 2 is a vertical cross-sectional view taken along a plane parallel to the wide-width surface of the mold 2.

An electromagnet 7 for electromagnetic braking is installed in the lower part of the mold 2, and an electromagnetic stirring device 9 is installed at a position slightly below the molten steel meniscus. Electromagnetic blur
The electromagnet 7 for g is a mold in such a manner that a magnetic field in one direction that produces a magnetic flux having a uniform density in the width direction of the wide surface and that is orthogonal to the slab drawing direction 10 traverses the molten steel 4 in the continuous casting mold 2. It can be applied to the inner molten steel 4. Reference numeral 8 is a static magnetic field (static magnetic field) at this time. The electromagnet 7 of the electromagnetic brake
May be disposed 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 the continuous casting of the molten steel, that is, when the 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 component was obtained 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 stirring device 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 metal 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 the composition 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 the precipitation-strengthened high-strength steel is completed, that is, when the supply of the 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.

[0022]

【Example】

[Example 1] 300 tons of molten steel of Steel A having the composition (component ratio: wt%) shown in Table 1 was obtained by ordinary refining, and in a continuous casting machine having two strands, a mold for one strand (hereinafter referred to as small Steel A first with a lot casting mold)
50 tons of steel is cast so that Nb becomes 0.05% by adding 00 tons of molten steel in the small lot casting mold from the meniscus to the molten steel in the middle, and then the other strand is usually Steel A of 150 tons was cast by the above method. The shape of the slab in the width direction of the mold was 230 mm in thickness and 1250 mm in width. The electromagnet 7 for the electromagnetic brake is 500 m from the meniscus in the mold.
It was installed at a position of m to 700 mm, and during 50 ton casting with Nb added, there were two conditions, that is, when the braking magnetic field by the electromagnet 7 was applied and when it was not applied.

[0023]

[Table 1]

The amount of Nb in the steel when the braking magnetic field was applied and when it was not applied was 0.05 after the wire feeding was started.
Table 2 shows the variation in the length of the cast slab until the content of Nb and the concentration of Nb after the Nb content became 0.05%.

[0025]

[Table 2]

As can be seen from Table 2, when a braking magnetic field is applied, the length of the slab until the Nb amount of the slab reaches a predetermined value is greatly shortened, and the variation in Nb concentration thereafter is also small. .

Example 2 Molten steel having substantially the same composition as steel A having the composition shown in Table 1 was obtained by a conventional refining method, and an alloy was added to the molten steel from a meniscus in a small lot casting mold by a wire. At that time, steels B to H having the compositions shown in Table 3 were obtained as cast pieces in this order by changing the type of alloy in the wire and the feed rate of the wire. At that time, the braking magnetic field was continuously applied after the wire feeding to the molten steel in the mold was started. In addition, the seam of each steel was clarified by inserting a shielding plate when the type of alloy in the wire of each steel type and the wire feed speed were changed.

[0028]

[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. In the reheating test, the hot-rolled sheet was immersed in a salt bath at 800 ° C. for 10 minutes and then air-cooled. The strength characteristics were evaluated by a tensile test. For the tensile test, a No. 5 test piece described in JIS Z2201 was used and the same Z2
According to the method described in 241, the tensile strength TS was measured. The longitudinal direction of the test piece was the rolling direction of the product. Also,
In order to evaluate the economic efficiency, the weight of the slabs of Steel B to Steel H according to this method was used as the required amount, and each steel was measured by the usual method to obtain 300
The difference in the case of continuous ton casting was evaluated as an unnecessary amount.
Table 4 shows the difference between the as-rolled and TS after the reheating test (ΔT
S), unnecessary amount, and ratio to 300 tons (unnecessary rate) are shown.

[0030]

[Table 4]

As ΔTS is smaller, the strength before and after reheating does not change, and the characteristic of precipitation strengthened steel appears. The results are shown for steels C, E, F and G. In each case, the alloy component, that is, the precipitation strengthening element is within the range of the above-described first embodiment and second embodiment. On the other hand, although steel A, which is the original steel material, is not a target of evaluation, it shows characteristics that precipitation strengthening elements are not included, and the content of steel B is outside the range of the above-mentioned first embodiment and second embodiment, D and H are
It did not show the properties as a precipitation strengthened steel. 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, and the precipitation-strengthened high-strength steel casting according to the present invention has good yield and is economical. Is shown.

[0032]

EFFECTS OF THE INVENTION According to the present invention, alloy components are added to molten steel in the course of continuous casting, and from a part of the molten steel, a slab of precipitation-strengthened high-strength steel of a large variety of small lots is formed. Can be manufactured so as to have a uniform content and to reduce the transition portion thereof. That is, a precipitation-strengthened high-strength steel that exhibits important properties, although the required amount is small, is extremely economical and has a relatively high degree of freedom, without significantly lowering the casting capacity and efficiency of a multi-strand continuous casting machine. It can be manufactured with a high casting schedule.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a long piece of a mold for casting multiple types of small lots of precipitation-strengthened high-strength steel in a multi-strand continuous casting machine that embodies the present invention in one embodiment.

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

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B22D 11/00 B22D 11/00 P 11/08 11/08 A

Claims (3)

[Claims] 1. A continuous casting machine comprising a plurality of strands.
In one strand, molten steel is supplied to the continuous casting mold from the outside of the mold through a dipping nozzle, and a damping magnetic field in a direction intersecting with the slab drawing direction is applied to the molten steel below the dipping nozzle, and the molten steel upstream of the magnetic field is applied. When at least one of the alloy components Ti, Nb and V is added alone, the weight ratio of Ti: 0.01% or more and Nb: 0.01% or more,
V: 0.01% or more, when adding two or more kinds, the sum of 0.01% or more is added, and in other strands, only molten steel from the outside of the mold is continuously cast. Continuous casting method for high strength steel. 2. A continuous casting machine comprising a plurality of strands.
In one strand, molten steel is supplied to the continuous casting mold from the outside of the mold through a dipping nozzle, and a braking magnetic field in a direction intersecting the slab drawing direction is applied to the molten steel below the dipping nozzle and When at least one of the alloy components Ti, Nb and V is added to the molten steel upstream of the magnetic field while electromagnetically stirring the molten steel upstream, Ti: 0.01% or more by weight ratio, Nb, : 0.01% or more,
V: 0.01% or more, when adding two or more kinds, the sum of 0.01% or more is added, and in other strands, only molten steel from the outside of the mold is continuously cast. Continuous casting method for high strength steel. 3. When adding an alloy component, a shield plate for preventing vertical mixing of molten steel in the mold is inserted into the molten metal surface of the molten steel in the mold. Alternatively, the continuous casting method for precipitation-strengthened high-strength steel according to claim 2.