JP2017087230A - Tundish construction method, tundish before heated, and steel manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tundish construction method for reducing the hydrogen pickup stably from a tundish at the time of performing a steel continuous casting by using the tundish.SOLUTION: On the inner face of a tundish 1 used for continuous casting of steel, there is mounted a coating material 5 having a moisture content of 5.5 L/mor less per construction area of the tundish 1, and the tundish 1 equipped with the coating material 5 is heated.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a tundish construction method, a tundish before heating, and a method for producing steel.

  The inner surface of the tundish used in continuous casting of steel is provided with a refractory coating material by spraying or troweling in order to repair the base refractory and prevent contamination of the molten steel. Such a coating material contains moisture and hydrogen. For this reason, when molten steel is accommodated in the tundish, hydrogen concentration in the molten steel may increase due to absorption of hydrogen in the coating material by the molten steel (hydrogen pickup). Hydrogen in molten steel solidifies into molten steel and forms a slab, and then accumulates in segregation and cracks inside the slab, causing cracking (hydrogen-induced delayed fracture). Such cracks occur after several days after rolling. In particular, in the case of high carbon steel having a high C (carbon) content, segregation and cracks are likely to occur inside the slab, so how to reduce the hydrogen pickup becomes an issue.

For example, Patent Document 1 discloses a method for preventing a hydrogen pick-up of molten steel during continuous casting by providing a coating material on a tundish and drying the coating material at a back surface temperature of 800 ° C. or higher. Has been.
Patent Document 2 discloses a method of adding a metasilicate hydrate to a binder of a coating material.

Japanese Patent Laid-Open No. 7-251247 JP 2000-176612 A

However, in the method described in Patent Document 1, the hydrogen pickup can be reduced by managing the back surface temperature of the coating material, but depending on the conditions, the occurrence of the hydrogen pickup may not be suppressed. It was a problem. In particular, high carbon steel, which is prone to hydrogen-induced delayed fracture, may crack even when the amount of hydrogen pick-up is small, resulting in a reduction in product quality.
Moreover, in the method described in Patent Document 2, since it is necessary to use a raw material of a special component for the binding material of the coating material, there is a problem that the cost for the construction of the tundish increases.

  Therefore, the present invention has been made paying attention to the above-mentioned problem, and stably performing hydrogen pickup from the tundish by an inexpensive method when performing continuous casting of steel using the tundish. An object of the present invention is to provide a tundish construction method, a tundish before heating, and a steel production method.

According to one aspect of the present invention, a coating material having a moisture amount per tundish construction area of 5.5 L / m ² or less is provided on the inner surface of a tundish used for continuous casting of steel, and the coating material There is provided a tundish construction method characterized by heating the tundish provided with.

According to one aspect of the present invention, a tundish used for continuous casting of steel, the coating material having a water content per construction area of the tundish of 5.5 L / m ² or less is provided on the inner surface. A tundish before heating is provided.

According to one aspect of the present invention, a coating material having a moisture amount per tundish construction area of 5.5 L / m ² or less is provided on the inner surface of a tundish used for continuous casting of steel, and the coating material The tundish is provided by heating the tundish, and the steel is continuously cast using the applied tundish.

  According to one embodiment of the present invention, when steel is continuously cast using a tundish, hydrogen pickup from the tundish can be stably reduced by an inexpensive method.

It is sectional drawing which shows the tundish which concerns on one Embodiment of this invention. It is a graph which shows the relationship between the moisture content of a coating material, and UT abnormality occurrence rate in an Example. It is a graph which shows the relationship between the moisture content of a coating material, and the amount of hydrogen in steel in an Example.

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. However, it will be apparent that one or more embodiments may be practiced without such specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.
<Configuration and construction method of tundish>
With reference to FIG. 1, the structure and construction method of the tundish 1 which concerns on one Embodiment of this invention are demonstrated. The tundish 1 is an intermediate container provided in a continuous casting facility, accommodates molten steel poured from a ladle, and further supplies the molten steel to a mold (mold). As shown in FIG. 1, the tundish 1 includes an iron skin 2, a permanent brick 3, an irregular refractory 4, a coating material 5, a pair of nozzle receiving bricks 6, and a pair of upper nozzles 7. Prepare. In addition, a sliding nozzle, an immersion nozzle, and the like (not shown) are provided at the outer end of the tundish 1 of the upper nozzle 7.

The iron skin 2 has a substantially box-like shape with an upper surface opened, and has a pair of openings in which a pair of upper nozzles 7 are respectively provided on a lower surface (bottom surface) facing the upper surface. The permanent brick 3 is a regular refractory and is provided on the inner surface of the iron skin 2. The amorphous refractory 4 is provided on the inner surface side of the iron skin 2 so as to cover the surface of the permanent brick 3. The coating material 5 is provided on the inner surface side of the iron shell 2 so as to cover the surface of the irregular refractory 4. That is, on the inner surface of the iron skin 2, the permanent brick 3, the irregular refractory 4 and the coating material 5 are lined in order. The permanent brick 3 and the irregular refractory 4 are made of Al ₂ O ₃ —SiO ₂ refractory, and the coating material 5 is made of MgO refractory. The pair of nozzle receiving bricks 6 are provided in a lining layer formed of the permanent brick 3, the irregular refractory 4 and the coating material 5 in accordance with the pair of openings of the iron skin 2. The pair of upper nozzles 7 are regular refractories, and are fitted and provided inside the pair of nozzle receiving bricks 6, respectively.

In the tundish 1 having the above-described configuration, the permanent brick 3 is first provided on the inner surface of the iron skin 2. Next, the irregular refractory 4, the pair of nozzle receiving bricks 6, and the upper nozzle 7 are provided on the inner surface of the permanent brick 3. Furthermore, after the amorphous refractory 4 is dried, the coating material 5 is provided on the surface of the amorphous refractory 4 that is the inner surface of the tundish 1. At this time, the coating material 5 is used in which the water content [L / m ² ] per construction area of the tundish 1 is adjusted to 5.5 L / m ² or less. The construction area of the tundish 1 is the area [m ² ] where the coating material 5 on the inner surface of the tundish 1 is lined, and the amount of water per construction area of the tundish 1 is in the coating material 5 used for construction. Is the value obtained by dividing the amount of water [L] by the construction area of the tundish 1. The tundish 1 before heating which concerns on this embodiment is constructed by said process. At this time, the lower limit of the amount of water [L / m ² ] per construction area of the tundish 1 of the coating material 5 is preferably 4.5 L / m ² . When the lower limit value of the moisture amount [L / m ² ] per construction area of the tundish 1 of the coating material 5 is smaller than 4.5 L / m ² , the coating material 5 has too little water added. There is a possibility that it will not be adsorbed on the inner surface of the tundish 1. Thereafter, the tundish 1 provided with the coating material 5 is heated by a burner or the like for a predetermined temperature and time, whereby the coating material 5 is dried and moisture is removed to complete the construction. For example, for a tundish having a capacity (molten steel capacity) of 30 t capable of accommodating molten steel, when heated using a coke oven gas (calorific value = 4500 kcal / Nm ³ ), the tundish for a period of 300 min to 360 min It is preferable to heat until the temperature of the inner wall of 1 becomes 1000 ° C. or higher and 1200 ° C. or lower.

<Method of manufacturing steel>
Next, the steel manufacturing method according to this embodiment will be described. In this embodiment, first, the tundish 1 before heating is constructed by providing the coating material 5 on the inner surface of the tundish 1 as described above. And the tundish 1 is finally constructed by heating the tundish 1 before a heating.
Next, continuous casting of steel is performed using the applied tundish 1. In continuous casting, first, molten steel that has been refined in advance is poured into a tundish 1 from a ladle (not shown). At this time, since the moisture content of the coating material 5 before heating lined to the tundish 1 is regulated, it is possible to suppress hydrogen pickup from the coating material 5 after heating to the molten steel. In the present embodiment, the steel (molten steel) is 0.70 mass% or more and 0.85 mass% or less C, 0.20 mass% or more and 1.00 mass% or less silicon (Si), and 0.50 mass% or more and 1.30 mass% or less. It is a high carbon steel containing not more than% manganese (Mn). After the molten steel is poured into the tundish 1, the molten steel accommodated in the tundish 1 is respectively injected into two molds (not shown) through a pair of upper nozzles 7 and an immersion nozzle. The molten steel injected into the mold forms solidified shells at the boundary between the two molds by cooling with the mold. Thereafter, the formed solidified shell is further cooled by a secondary cooling device (not shown) while being drawn, whereby a slab in which all molten steel is finally solidified is manufactured. The manufactured slab is covered with a heat-insulating cover and cooled. As a result, the slab is cooled (slowly cooled) at a lower cooling rate than other cooling methods such as normal air cooling without a cover, and hydrogen in the slab becomes easier to diffuse, thereby removing the slab from the slab. Dehydrogenation is promoted.

<Modification>
Although the present invention has been described above with reference to specific embodiments, it is not intended that the present invention be limited by these descriptions. From the description of the invention, other embodiments of the invention will be apparent to persons skilled in the art, along with various variations of the disclosed embodiments. Therefore, it is to be understood that the claims encompass these modifications and embodiments that fall within the scope and spirit of the present invention.

  For example, in the above embodiment, the steel to be manufactured is made from 0.70 mass% to 0.85 mass% C, 0.20 mass% to 1.00 mass% Si, and 0.50 mass% to 1.30 mass% Mn. However, the present invention is not limited to such an example. The hydrogen pickup can be reduced by applying in the same manner to steel types having component compositions other than those described above.

In the above embodiment, the slab obtained by continuous casting is gradually cooled in a state where it is covered with a heat-insulating cover, but the present invention is not limited to such an example. For example, if the amount of hydrogen contained in the slab obtained by continuous casting satisfies the required quality, special cooling such as slow cooling may not be performed.
Further, in the above embodiment, the tundish 1 is constructed by providing the permanent tension brick 3, the irregular refractory material 4, the coating material 5, the nozzle receiving brick 6 and the upper nozzle 7 inside the iron skin 2. The present invention is not limited to such an example. For example, the present invention can also be applied when the coating material 5 is provided as a repair after the tundish 1 once constructed is used for continuous casting.

<Effect of embodiment>
(1) The construction method of the tundish 1 according to one aspect of the present invention is such that the water content per construction area of the tundish 1 is 5.5 L / m ² or less on the inner surface of the tundish 1 used for continuous casting of steel. The coating material 5 is provided, and the tundish 1 provided with the coating material 5 is heated.

Here, for example, in the method of managing the back surface temperature of the coating material as in Patent Document 1, hydrogen pickup may occur depending on the coating material and construction conditions. In contrast, the present inventors have found that the amount of hydrogen picked up into molten steel during continuous casting is greatly affected by the amount of water per construction area of tundish 1. The amount of moisture per construction area of the tundish 1 is a value obtained from the amount of moisture in the coating material 5 used and the construction area of the tundish 1, and considering this, the amount of moisture in the coating material 5 and The influence of the thickness of the coating material 5 can be considered. That is, according to the said structure, compared with the case where other conditions, such as the back surface temperature of a coating material, are considered like patent document 1 by adjusting the moisture content of the coating material 5 per construction area of the tundish 1, In addition, hydrogen pickup to the molten steel during continuous casting can be stably reduced. In addition, the amount of hydrogen pick-up can be suppressed by making the water amount per construction area of the tundish 1 not more than 5.5 L / m ² , and hydrogen-induced delayed fracture can be prevented. On the other hand, when the amount of water per construction area of tundish 1 exceeds 5.5 L / m ² , the amount of hydrogen pick-up increases and hydrogen-induced delayed fracture is likely to occur, so that the internal quality of the product deteriorates. It becomes.
Moreover, according to the said structure, the reduction effect of a hydrogen pick-up can be acquired only by adjusting the moisture content of the coating material 5 per construction area of the tundish 1. For this reason, it is not necessary to use a special raw material for the coating material unlike the method described in Patent Document 2, and the cost required for the construction of the tundish 1 can be reduced.

(2) The tundish 1 before heating which concerns on 1 aspect of this invention is the tundish 1 used for continuous casting of steel, Comprising: The moisture content per construction area of the tundish 1 is 5.5 L / m < ² > or less The coating material 5 is provided on the inner surface.
(3) In the method for producing steel according to one aspect of the present invention, the amount of moisture per construction area of the tundish 1 is 5.5 L / m ² or less on the inner surface of the tundish 1 used for continuous casting of steel. The coating material 5 is provided, and the tundish 1 provided with the coating material 5 is heated to construct the tundish 1, and the applied tundish 1 is used to continuously cast steel.
According to the configurations (2) and (3), the same effect as the configuration (1) can be obtained.

(4) When the steel is continuously cast in the configuration of (3) above, C of 0.70 mass% or more and 0.85 mass% or less, Si of 0.20 mass% or more and 1.00 mass% or less, and 0.50 mass% or more 1. A steel containing Mn of 1.30 mass% or less is continuously cast.
According to the said structure, segregation and a crack are easy to produce inside a slab, and in a high carbon steel in which hydrogenous delayed fracture is easy to generate | occur | produce, hydrogenous delayed fracture can be suppressed. For this reason, the internal quality in the product after a rolling process can be improved, and the yield of a product can be improved significantly.
(5) In the configuration of (3) or (4), the slab, which is steel obtained by continuous casting, is cooled in a state of being covered with a cover having heat insulating properties.
According to the said structure, since dehydrogenation from a slab can be accelerated | stimulated, generation | occurrence | production of hydrogenous delayed fracture can further be suppressed.

Next, examples performed by the present inventors will be described. In the examples, in the continuous casting method according to the above-described embodiment, the water content of the coating material 5 per construction area of the tundish 1 was changed to investigate the influence on the hydrogen-induced delayed fracture.
In the examples, first, a tundish 1 having a molten steel capacity of 30 t was applied by the same method as in the above embodiment. At this time, in providing the coating material 5 to the inner surface of the tundish 1, by changing the water content of the coating material 5 per construction area of the tundish 1 in the range of 5.3L / m ² of 7.6 L / m ² The tundish 1 under a plurality of conditions was constructed. The component composition of the coating material 5 was MgO = 85 mass%, SiO ₂ = 4 mass%, and Al ₂ O ₃ = 1.6 mass%. The construction area of the tundish 1 was 18.45 m ² . The thickness range of the coating material 5 is 12 mm or more in the slag line of the tundish 5 (wall part in contact with the slag layer on the steel bath), 8 mm or more in the metal line of the tundish 5 (wall part in contact with the steel bath), The tundish 5 laying portion (inner bottom portion) was set to 20 mm or more. The upper limit value of the thickness of the coating material 5 is a value that is naturally determined by the upper limit value of the moisture amount per unit construction area of the coating material 5. Further, when the coating material 5 was heated, heating was performed using a coke oven gas until the temperature of the inner wall of the tundish 1 became 1000 ° C. or more and 1200 ° C. or less for a time of 300 min or more and 360 min or less.

Next, continuous casting was performed using tundish 1 having different construction conditions, and a plurality of cast pieces were produced for each construction condition. Steel for continuous casting is high carbon steel containing C of 0.70 mass% to 0.85 mass%, Si of 0.20 mass% to 1.00 mass%, and Mn of 0.50 mass% to 1.30 mass%. It was.
Furthermore, the slab obtained by continuous casting was gradually cooled using the cover in the same manner as in the above embodiment, and the cooled slab was heated and rolled to produce a product rail. Thereafter, the processed product was subjected to UT inspection and measurement of the amount of hydrogen in steel, and the internal quality was investigated.

FIG. 2 shows the relationship between the construction conditions of the tundish 1 and the UT abnormality occurrence rate of the manufactured product. In FIG. 2, the horizontal axis represents the moisture content of the coating material 5 per construction area of the tundish 1 (tundish 1 construction conditions), and the vertical axis represents a plurality of products manufactured for each tundish 1 construction condition. It is an abnormality occurrence rate (UT abnormality occurrence rate) in the UT inspection. The UT abnormality occurrence rate indicates a ratio of products in which internal defects are detected by UT inspection among the inspected products. In the embodiment, the main cause of the internal defect detected by the UT inspection is hydrogen delayed fracture. As shown in FIG. 2, it was confirmed that as the moisture content of the coating material 5 per construction area of the tundish 1 increased, the UT abnormality occurrence rate also increased. Moreover, it confirmed that it could reduce significantly by making the moisture content of the coating material 5 per construction area of the tundish 1 into 5.5 L / m < ² > or less.

FIG. 3 shows the relationship between the construction conditions of the tundish 1 and the amount of hydrogen in the steel of the manufactured product. In FIG. 3, the horizontal axis represents the moisture content of the coating material 5 per construction area of the tundish 1 (the construction condition of the tundish 1), and the vertical axis represents a plurality of products manufactured for each construction condition of the tundish 1. It is a measurement result of the amount of hydrogen in steel. As shown in FIG. 3, as the moisture content of the coating material 5 per construction area of the tundish 1 increases, the amount of hydrogen pick-up from the tundish 1 increases and the amount of hydrogen in the steel of the product increases. confirmed. Since such a result shows the same tendency as the UT abnormality occurrence rate shown in FIG. 2, it is considered that the UT abnormality occurrence rate increased due to an increase in the amount of hydrogen in steel.
From the above, by making the moisture content of the coating material 5 per construction area of the tundish 1 within the range of the above embodiment, the amount of hydrogen picked up from the tundish 1 can be stably reduced by an inexpensive method. It was confirmed that the amount of hydrogen in the steel of the product can be reduced. As a result, the UT abnormality occurrence rate is reduced, and the yield of products can be greatly improved.

DESCRIPTION OF SYMBOLS 1 Tundish 2 Iron skin 3 Permanent brick 4 Indeterminate refractory 5 Coating material 6 Nozzle receiving brick 7 Upper nozzle

Claims (5)

The inner surface of the tundish used for continuous casting of steel is provided with a coating material having a water content per construction area of the tundish of 5.5 L / m ² or less,
A tundish construction method, wherein the tundish provided with the coating material is heated. A tundish used for continuous casting of steel,
A tundish before heating, wherein a coating material having a moisture content per construction area of the tundish of 5.5 L / m ² or less is provided on the inner surface. The inner surface of the tundish used in the continuous casting of steel, the amount of water per construction area of the tundish provided with the coating material is 5.5 L / m ² or less, heating the tundish which the coating material is provided To construct the tundish,
A method for producing steel, characterized in that steel is continuously cast using the tundish applied.   When continuously casting the steel, C contains 0.70 mass% or more and 0.85 mass% or less, Si contains 0.20 mass% or more and 1.00 mass% or less, and Mn contains 0.50 mass% or more and 1.30 mass% or less. The method for producing steel according to claim 3, wherein the steel is continuously cast.   The method for producing steel according to claim 3 or 4, wherein the steel slab obtained by the continuous casting is cooled in a state of being covered with a cover having heat insulating properties.

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