JP5428780B2 - Steel continuous casting method - Google Patents

Description

The present invention relates to a method for continuous casting of steel the non-solidified portions of the cast piece while electromagnetic 攪拌.

  When continuously casting a slab for an electromagnetic steel sheet from a molten steel containing a large amount of silicon, generally, as shown in FIG. In the solidification structure in which the columnar crystal has developed, the columnar crystal falls down without breaking during rolling and remains in the rolled structure. In particular, when rolling to a thickness of 3 mm or less, fine irregularities are generated on the surface. This fine unevenness is called ridging.

  In the case of an electromagnetic steel sheet that exhibits an effect by overlapping a plurality of sheets, when a plate having ridging is used, a gap is generated on the crimping surface of each plate, and the performance of the product is deteriorated.

Therefore, when continuously casting slabs for electrical steel sheets from molten steel containing a large amount of silicon, in order to suppress the formation of columnar crystals, unsolidified molten metal remaining inside the slab drawn from the mold and by the action of electromagnetic 攪拌力respect (hereinafter, referred to as non-solidified portion.).

  In the slab manufactured by the above method, the generation of columnar crystals is suppressed and the ratio of equiaxed crystals precipitated from the molten metal increases (see FIG. 8). Since equiaxed crystals are excellent in workability unlike columnar crystals, they do not remain when rolled, and ridging or the like does not occur when rolled into a thin plate.

For example, in Patent Document 1, the thickness of the equiaxed crystal in the vicinity of the center of the thickness of the slab is 40% or more of the thickness of the slab so that it remains in the slab drawn from the mold. continuous casting method of reacting an electromagnetic 攪拌力by the electromagnetic stirring device of the 2 groups with respect to the coagulation section is disclosed.

  However, because the equiaxed crystal ratio of the slab to be produced varies due to variations in operating conditions, the method disclosed in Patent Document 1 may not avoid the occurrence of ridging. Moreover, since two electromagnetic stirrers are used, the capital investment cost becomes high.

Japanese Patent Laid-Open No. 2-192853

Problems which the invention is to provide, if the action of electromagnetic 攪拌力the unsolidified portion remaining inside the cast piece is withdrawn from the mold, due to variations in operating conditions, of the slab to produce equiaxed The rate varies and the occurrence of ridging may not be avoided.

The steel continuous casting method of the present invention is
In order to prevent the occurrence of ridging by avoiding the occurrence of ridging so that the slab to be produced has the target equiaxed crystal ratio even if there are variations in operating conditions,
3.5 wt% or less Si content in the component, Ti content of 50ppm or less, N content of not more than 80 ppm, and, for continuous casting of molten steel for silicon steel you satisfy the following formula (b) A method,
When stirring the molten steel in the unsolidified part using the electromagnetic stirrer disposed at the slab position including the unsolidified part, the electromagnetic stirring intensity satisfying the following formula (a) including the casting speed Vc (m / min) The molten steel in the unsolidified portion is stirred with G (T: Tesla), and the equiaxed crystal formation ratio (e / D), which is the ratio of the equiaxed crystal thickness e (mm) to the total thickness D (mm) of the cast slab ) Is 0.3 or more.
G ≧ (1.08 × Vc + 0.14) × 0.05 (a)
Ti × N ≧ 350 (b)
Here, Ti: component Ti content (ppm), N: component N content (ppm).

According to the continuous casting method of the present invention, even when the casting speed is variously changed by the operation mode, in the electromagnetic 攪拌apparatus 1 groups, it is possible to obtain a equiaxed Akiraritsu a target, the occurrence of ridging No slab can be obtained. Further, if the concentration product of Ti and N in the molten steel is optimally adjusted to prevent the equiaxed crystal ratio from decreasing, the generation of ridging can be further prevented.

It is the schematic diagram which showed the cross section of slab. It is the figure which showed the relationship between the casting speed Vc when changing an electromagnetic stirring intensity | strength, and equiaxed crystal thickness. It is the figure which showed the relationship between casting speed Vc, electromagnetic stirring intensity | strength, and the presence or absence of ridging generation | occurrence | production. It is a schematic diagram of the continuous casting apparatus used for the experiment of this invention. It is the figure which showed the relationship between casting speed, equiaxed crystal ratio, and the presence or absence of ridging. It is the figure which showed the relationship between the concentration product of Ti and N, and an equiaxed crystal. It is a figure explaining the cross-sectional structure of the slab which consists of columnar crystal structure. It is a schematic diagram of the cross-sectional structure | tissue of the slab in which the equiaxed crystal was produced | generated by electromagnetic stirring.

  In the present invention, even if there are variations in operating conditions, the objective is to obtain the target equiaxed crystal ratio for the cast slab to be manufactured. This was achieved by stirring the molten steel in the unsolidified part with stirring strength.

The present invention will be described below.
In the continuous casting method, the slab drawn from the mold is secondarily cooled from the surface, and a solidified shell grows.

Therefore, when continuous casting of molten steel for the silicon steel sheet containing 3.5 mass% of Si, the unsolidified molten steel region 攪拌by an electromagnetic stirrer arranged in the slab position including the unsolidified portion, etc. When increasing the amount of axial crystals generated, the relationship between the thickness of the solidified shell, which varies depending on the casting speed, and the thickness of the unsolidified portion cannot be ignored.

Therefore, quantitative slab produced is, in order to ensure that it has a certain level of equiaxed generation amount (equal JikuAkiraritsu) a variety varying factors (solidified shell thickness, between 攪拌時) by casting speed Must be evaluated and reflected.

The electromagnetic 攪拌, when 攪拌molten steel unsolidified portion, (1) the interfacial area unsolidified portion of 攪拌, (2) 攪拌時between, to be taken into consideration the effects of (3) 攪拌強degree Don't be. The contents of the influence will be described below.

(1) 攪拌thickness d of the solidified shell at the position when the unsolidified portion in the electromagnetic stirring device arranged in the slab position including the interfacial area unsolidified portion of the unsolidified portion is 攪拌that is generally below It is defined by Equation 1. From Equation 1, it can be seen that when the casting speed Vc decreases, the solidified shell thickness d at the stirring position increases, and when the casting speed Vc increases, the solidified shell thickness d (see FIG. 1) at the stirring position decreases.

On the other hand, the interfacial area A per unit length of the unsolidified portion is 攪拌by the electromagnetic stirring device can be calculated from Equation 2 below.

That is, the casting speed is slower, if the solidified shell thickness at 攪拌located is thickened by electromagnetic stirring apparatus, since the interfacial area A of the unsolidified molten steel 攪拌decreases, only smaller amount equal The amount of axial crystals produced will decrease.

(2) 攪 range拌時between stirring force acts is only unsolidified portion of the range of the electromagnetic coil of the electromagnetic stirring apparatus is installed. Thus, in the continuous casting, as shown in the following equation 3, the equiaxed 攪拌力is unsolidified portion by a time t the effective length S portion of the target slab passes to act is stirred unsolidified portion Generated.

That is, since 攪拌時between t unsolidified portion is inversely proportional to the casting speed Vc, the casting speed Vc is slow 攪拌時between t is the amount of equiaxed longer is increased, the casting speed Vc is high 攪拌時between t is the amount of equiaxed decreases becomes shorter.

(3) 攪拌強degree such axed crystal is produced by 攪拌the molten steel unsolidified portion. Therefore, it is impossible to obtain a 攪拌力required to generate the 攪拌強small degree of equiaxed. That is, it can be said that in order to generate an equiaxed inside a slab continuous casting, it is necessary a certain value or more 攪拌力.

  Considering the above, it is considered that the relationship between the equiaxed crystal ratio and the above-mentioned (1), (2), and (3) is expressed by the following mathematical formula 4.

That is, Equation 4, equiaxed Akiraritsu is, the interfacial area A per unit length of the unsolidified portion is 攪拌by the electromagnetic stirring device, a stirring time of unsolidified portion t, stirring force by electromagnetic stirring device It is proportional to the product of G.

  Of these, the interfacial area A is proportional to the casting speed Vc from Equations 1 and 2, and the stirring time t is apparent from the Equation 3 to be inversely proportional to the casting speed Vc. The crystallinity is related to the casting speed Vc and the stirring strength.

  Accordingly, in order to clarify these relationships, the inventors conducted a casting test and a simulation analysis on a slab having a thickness of 250 mm. As a result, the ratio between the equiaxed crystal ratio, the casting speed Vc, and the electromagnetic stirring strength G was determined. Was found to have the relationship shown in FIG.

  From the results shown in FIG. 2, the casting speed Vc and electromagnetic stirring strength G for the equiaxed crystal thickness with no ridging to be 75 mm (the equiaxed crystal ratio is 75 mm / 250 mm = 0.3 = 30%) or more. When the relationship was obtained, the result shown in FIG. 3 was obtained, and the following formula 5 was obtained.

In other words, by performing continuous casting that satisfies Equation 5, it is possible to stably generate equiaxed crystals and to obtain a slab that does not generate ridging even during rolling. This is the main configuration of the invention according to claim 1 of the present application.

  In addition, when Ti is added to the molten steel, it combines with N present in the molten steel to form heterogeneous solidification nuclei, forming TiN that forms the nuclei of equiaxed crystals. It was found that when the concentration product of Ti and N that can be calculated is small, the equiaxed crystal ratio of the manufactured slab decreases.

  Therefore, although it is not an essential element, the concentration product of Ti and N (Ti: 50 ppm or less, N: 80 ppm or less) that can be contained within a range that does not impair the performance of the electrical steel sheet is set to a certain amount or more, etc. It was found that the reduction of the amount of axial crystals can be prevented.

Hereinafter, confirmation of the effect of the main configuration of the invention according to claim 1 and a test performed to obtain an optimum concentration product of Ti and N added to the molten steel will be described.

As shown in FIG. 4, the meniscus 3 of the molten steel 2 injected into the mold 1 by using a continuous casting apparatus which is disposed a strand electromagnetic 攪拌device 4 to the position of 7m, the thickness D is 250 mm, the width W 1100 to A 1300 mm slab 5 was produced. Molten steel 2 used for continuous casting contains C: 0.003% by mass, Si: 2.0% by mass, and for silicon steel sheets having a ΔT (difference between molten steel temperature and liquidus temperature) of 20 to 40 ° C. Molten steel.

In the above conditions, the casting speed Vc is cast while varying between 0.70m / min~1.4m / min, casting when imparted with electromagnetic 攪拌強value G corresponding to the casting speed (the present invention) The cross-sectional structure of the piece and the ridging occurrence state in the plate made by rolling the slab were investigated. For comparison, a similar study was conducted even when imparted with electromagnetic 攪拌強value G at 0.05 (T) constant.

  From the cross-sectional structure of the slab as shown in FIG. 1, the formation thickness of equiaxed crystals was measured, and the equiaxed crystal ratio was calculated. The investigation on the board was classified by the presence or absence of ridging.

  The casting conditions and the casting results are shown in Table 1 below. FIG. 5 shows the relationship between the casting speed and the equiaxed crystal ratio.

In conditions were constant at the electromagnetic 攪拌強degree G 0.05 (T) to be applied to the unsolidified portion (○ mark), etc. JikuAkiraritsu E decreases according improve casting speed Vc, etc JikuAkiraritsu E Ridging was confirmed when the casting speed Vc was 1.1 m / min or more.

On the other hand, in the case of the present invention imparted with electromagnetic 攪拌強value G corresponding to the casting speed Vc (■ marks), even if the casting speed Vc is increased, ensuring the stable 30% or more equal JikuAkiraritsu E The generation of ridging was not confirmed even after rolling into a thin plate.

Further, the inventors found that in the continuous casting described above, the casting speed Vc and the electromagnetic 攪拌強degree G of 1.0 m / min, in 0.070T certain conditions, the concentration product of by adding Ti Ti and N Various changes of molten steel were continuously cast, and the relationship with the slab structure was investigated. The results are shown in Table 2 below and FIG.

  As shown in Table 2 and FIG. 6, the equiaxed crystal ratio E could be stably generated by securing a concentration product of N and Ti of 350 or more. On the other hand, in the region where the concentration product of N and Ti is less than 350, it has been confirmed that the equiaxed crystal ratio E decreases as the concentration product of N and Ti decreases.

The invention according to claim 1 of the present application was made based on the above experimental results, and as a molten steel used when carrying out the main configuration of the invention according to claim 1 of the present application, in mass%, A component having a Ti content of 50 ppm or less, an N content of 80 ppm or less, and a concentration product of N and Ti of 350 or more is used.

The present invention is not limited to the above example, if the scope of the technical spirit as set forth in 請 Motomeko, it may of course be changed as appropriate embodiment.

  For example, the molten steel to be used is not limited to the above experimental example as long as it does not impair the performance of the electromagnetic steel sheet, and may further contain Si, Mn, Al, or the like.

1 Mold 2 Molten Steel 4 Electromagnetic Stirrer 5 Cast

Claims (1)

3.5 wt% or less Si content in the component, Ti content of 50ppm or less, N content of not more than 80 ppm, and, for continuous casting of molten steel for silicon steel you satisfy the following formula (b) A method,
When stirring the molten steel in the unsolidified part using the electromagnetic stirrer disposed at the slab position including the unsolidified part, the electromagnetic stirring intensity satisfying the following formula (a) including the casting speed Vc (m / min) The molten steel in the unsolidified portion is stirred with G (T: Tesla), and the equiaxed crystal formation ratio (e / D), which is the ratio of the equiaxed crystal thickness e (mm) to the total thickness D (mm) of the cast slab ) Is set to 0.3 or more.
G ≧ (1.08 × Vc + 0.14) × 0.05 (a)
Ti × N ≧ 350 (b)
Here, Ti: component Ti content (ppm), N: component N content (ppm).

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