Thin-walled casting method

Abstract

To provide a manufacturing method for a thin cast piece that can stably manufacture a thin cast piece having uniform columnar crystal structures, without rupturing the piece.SOLUTION: In a manufacturing method for a thin cast piece, molten metal is supplied to a molten metal pool part formed of a pair of rotary cooling drums and a pair of side ingates and solidifying shells are made to be formed and grown on peripheral surfaces of the cooling drums so as to manufacture a thin cast piece, the amounts of heat extraction of the cooling drums are set to be 7.5 MW / m2 or more, the temperature t of the molten metal in the molten metal pool part is set to be in a range of t1+10°C≤t≤t1+30°C, with respect to a liquidus-line temperature t1 of the molten metal, and pressing force P per unit width length of the cooling drums is set to be in a range of 24 N / mm or more and 75 N / mm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a thin cast slab by supplying molten metal to a molten metal pool formed by a pair of rotating cooling drums and a pair of side weirs, forming and growing solidified shells on the circumferential surfaces of the cooling drums, and joining the solidified shells formed on the circumferential surfaces of the cooling drums at roll kiss points and rolling them down to produce a thin cast slab. [Background technology]

[0002] As a method for producing thin metal billets, for example, as disclosed in Patent Document 1, a twin-drum continuous casting machine is provided, which is equipped with cooling drums having an internal water-cooling structure, and which supplies molten metal from a tundish through an immersion nozzle to a molten metal pool formed between a pair of rotating cooling drums, causing solidified shells to form and grow on the circumferential surfaces of the cooling drums, and the solidified shells formed on the respective circumferential surfaces of the pair of cooling drums are joined at drum kiss points and then pressed down to produce thin billets of a predetermined thickness. Such production methods using twin-drum continuous casting machines are applied to various metals. The above-described twin-drum continuous casting apparatus can produce thin-walled cast strips having a shape similar to that of the final product, thereby reducing energy consumption and production costs.

[0003] Furthermore, in the above-mentioned twin-drum continuous casting apparatus, as shown in Patent Document 2, for example, a dummy sheet is sandwiched between the cooling drums, and the cooling drums are rotated while molten steel is supplied to a molten steel pool formed by the pair of cooling drums and the pair of side weirs, to form a thin cast piece connected to the dummy sheet, and the dummy sheet and the thin cast piece connected to this dummy sheet are then drawn out from between the cooling drums. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 239868 [Patent Document 2] Japanese Patent Application Publication No. 2019-098342 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, if the pressing force per unit width length of the cooling drum (hereinafter sometimes referred to as pressing force) is increased, the formed columnar crystal structure may be destroyed and the uniformity of the structure may be impaired. Therefore, in order to form a uniform columnar crystal structure, it is necessary to appropriately control the pressing force of the cooling drum. Furthermore, if the strength of the connection between the dummy sheet and the thin billet is not ensured at the start of casting, the thin billet will break during casting, causing the casting to stop. For this reason, it is necessary to ensure that the pressing force of the cooling drum is above a certain value to allow solidification to proceed sufficiently. As described above, it has been difficult to achieve both uniformity of the columnar crystal structure and stabilization of casting simply by controlling the pressing force of the cooling drum.

[0006] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing a thin-walled cast slab that can stably produce a thin-walled cast slab having a uniform columnar crystal structure without fracture. [Means for solving the problem]

[0007] As a result of extensive research conducted by the present inventors to solve the above-mentioned problems, it was discovered that by setting the temperature of the molten metal in the molten metal pool within an appropriate range, it is possible to suppress the destruction of columnar crystals even when the pressing force of the cooling drum is set high, and it is possible to stably produce thin-walled cast strips with a high columnar crystal ratio and uniformity.

[0008] The present invention has been made based on the above findings, and a method for producing a thin-walled cast slab according to the present invention comprises supplying molten metal to a molten metal pool formed by a pair of rotating cooling drums and a pair of side weirs, and forming and growing a solidified shell on the circumferential surface of the cooling drums. Plate thickness: 1.0mm to 2.4mmA method for producing thin-walled cast slabs, wherein the heat removal amount W of the cooling drum is 7.5 MW / m 2 or more, the temperature t of the molten metal in the molten metal pool is within the range of t1+10°C≦t≦t1+30°C relative to the liquidus temperature t1 of the molten metal, and the pressing force P per unit width length of the cooling drum is within the range of 24 N / mm to 75 N / mm.

[0009] According to this method for producing thin-walled cast slabs, the heat dissipation amount W of the cooling drum is 7.5 MW / m 2 Since the temperature t of the molten metal in the molten metal pool is set within the above-mentioned range, a columnar crystal structure is sufficiently formed and the strength of the thin-walled cast slab can be ensured. Furthermore, since the pressing force P per unit width of the cooling drum is set within the above-mentioned range, the destruction of the columnar crystal structure can be suppressed and the strength of the thin-walled cast slab can be ensured. Therefore, it becomes possible to stably produce thin-walled cast strips having a uniform columnar crystal structure without fracture. [Effects of the Invention]

[0010] As described above, according to the present invention, it is possible to provide a method for producing a thin-walled cast slab that can stably produce a thin-walled cast slab having a uniform columnar crystal structure without causing fracture. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is an explanatory diagram showing an example of a twin-drum continuous casting apparatus used in a method for producing a thin-walled cast strip according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged explanatory view of the vicinity of the cooling drum of the twin-drum continuous casting machine shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a method for producing a thin-walled cast slab according to an embodiment of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiment. In this embodiment, molten steel is used as the molten metal, and a thin cast 1 made of steel is produced. In this embodiment, the width of the produced thin cast 1 is within a range of 200 mm to 1800 mm, and the thickness is within a range of 1.0 mm to 2.4 mm.

[0013] First, a twin-drum continuous casting apparatus 10 used in the method for producing a thin-walled cast strip according to this embodiment will be described. The twin-drum continuous casting apparatus 10 shown in FIG. 1 includes a pair of cooling drums 11, 11, pinch rolls 12, 13 that support a thin-walled cast strip 1, side weirs 15 disposed at the widthwise ends of the pair of cooling drums 11, 11, a tundish 20 that holds molten steel 3 to be supplied to a molten steel pool 16 defined by the pair of cooling drums 11, 11 and the side weir 15, and an immersion nozzle 18 that supplies molten steel 3 from the tundish 20 to the molten steel pool 16. In this embodiment, as shown in FIG. 1, a thin-walled cast 1 is produced toward the vertically downward side of the cooling drum 11, and this thin-walled cast 1 is curved and transported horizontally by pinch rolls 13.

[0014] In this embodiment, the heat dissipation amount W of the cooling drum 11 is 7.5 MW / m 2 That is said to be the case. The cooling drum 11 is structured so that cooling water flows inside, and the amount of heat dissipation W of the cooling drum 11 can be adjusted by the material of the cooling drum 11, the flow conditions of the cooling water, etc.

[0015] Next, a method for producing the thin-walled cast strip 1 of this embodiment using the above-mentioned twin-drum continuous casting apparatus 10 will be described.

[0016] Molten steel 3 is supplied from a tundish 20 via an immersion nozzle 18 to a molten steel pool 16 formed by the pair of cooling drums 11, 11 and the side weirs 15, 15, and the pair of cooling drums 11, 11 are rotated in the rotation direction R, i.e., so that the area where the pair of cooling drums 11, 11 approach each other faces the drawing direction of the thin-walled cast slab 1 (downward in FIG. 1). At this time, the cooling drums 11, 11 are pressed against each other in the direction in which they approach each other.

[0017] As a result, a solidified shell 5 is formed on the circumferential surface of the cooling drum 11. The solidified shell 5 grows on the circumferential surface of the cooling drum 11, and the solidified shells 5, 5 formed on the pair of cooling drums 11, 11 are pressed together at the drum kiss points, thereby casting a thin-walled cast 1 having a predetermined thickness.

[0018] In this embodiment, when the thickness of the thin-walled cast 1 is within the range of 1.0 mm or more and 2.4 mm or less, it is preferable that the contact time T between the cooling drum 11 and the molten steel 3 is within the range of 0.1 seconds or more and 0.5 seconds or less. The contact time T between the cooling drum 11 and the molten steel 3 is more preferably 0.12 seconds or more, and even more preferably 0.15 seconds or more. The contact time T between the cooling drum 11 and the molten steel 3 is more preferably 0.4 seconds or less, and even more preferably 0.35 seconds or less.

[0019] The contact time T between the cooling drum 11 and the molten steel 3 is calculated from the contact length L (m) between the cooling drum 11 and the molten steel 3 and the casting speed v (m / min) by the following formula. T(sec)=L / v×60 As shown in FIG. 2, the contact length L (m) between the cooling drum 11 and the molten steel 3 is calculated from the casting arc angle θ (°) and the diameter D (m) of the cooling drum 11 by the following formula: L(m)=D×π×(θ / 360) Therefore, the contact time T between the cooling drum 11 and the molten steel 3 can be set within the above range by adjusting the casting speed v and the casting arc angle θ according to the diameter D of the cooling drum 11.

[0020] In this embodiment, the temperature t of the molten steel 3 in the molten steel pool portion 16 is set within the range of t1+10°C≦t≦t1+30°C relative to the liquidus temperature t1 of the molten steel 3. The temperature t of the molten steel 3 in the molten steel pool portion 16 can be set within the above-mentioned range by adjusting the temperature of the molten steel 3 in the tundish 20. The liquidus temperature can be determined by a method of actually measuring by differential thermal analysis, a method of calculating the experimentally determined liquidus temperature using an equation expressed as a function of the steel composition, a method of calculating an equilibrium phase diagram, or the like. The temperature t of the molten steel 3 in the molten steel pool portion 16 is preferably t1+11°C or higher, and more preferably t1+24°C or higher. The temperature t of the molten steel 3 in the molten steel pool portion 16 is preferably t1+29°C or lower, and more preferably t1+26°C or lower.

[0021] Furthermore, in this embodiment, the pressing force P per unit width of the cooling drum 11 is set to be within the range of 24 N / mm to 75 N / mm. The pressing force P per unit width of the cooling drum 11 is preferably 70 N / mm or less, and more preferably 50 N / mm or less.

[0022] According to the method for producing the thin-walled cast 1 of this embodiment configured as described above, the heat dissipation amount W of the cooling drum 11 is 7.5 MW / m 2 Since the temperature t of the molten steel 3 in the molten steel pool 16 is set within the above range, a columnar crystal structure is sufficiently generated and the strength of the thin cast slab 1 can be ensured. Furthermore, since the pressing force P per unit width of the cooling drum 11 is set within the above range, destruction of the columnar crystal structure can be suppressed and the strength of the thin cast slab 1 can be ensured. Therefore, it becomes possible to stably produce the thin-walled cast 1 having a uniform columnar crystal structure without fracture.

[0023] The above describes in detail the method for producing a thin-walled cast slab according to an embodiment of the present invention, but the present invention is not limited to this and can be modified as appropriate within the scope of the technical concept of the invention. In this embodiment, the twin-drum continuous casting apparatus shown in Figures 1 and 2 has been described as an example, but the present invention is not limited to this, and twin-drum continuous casting apparatuses with other structures may also be used. [Example]

[0024] The results of experiments carried out to confirm the effects of the present invention will be described below. Thin-walled slabs were produced from molten steel containing 0.02 mass% C, 3.5 mass% Si, 0.6 mass% Al, and 0.2 mass% Mn using the twin-drum continuous casting machine shown in Figure 1. The liquidus temperature t1 of this steel type was calculated to be 1490°C using Hirai's equation (Iron and Steel Institute of Japan, 3rd Edition, Iron and Steel Handbook I, Basics, Maruzen, 1981, p. 205), which is one of the equations that expresses the experimentally determined liquidus temperature as a function of the steel's composition. The diameter of the cooling drum was 600 mm (0.6 m), and the width of the cooling drum was 400 mm (0.4 m). As shown in Tables 1 and 2, the thickness of the thin-walled cast slab was 1.0 mm in Inventive Examples 1 to 4 and Comparative Examples 1 to 5, 1.9 mm in Inventive Example 5, and 2.4 mm in Inventive Example 6.

[0025] Then, thin billets were cast under the conditions shown in the table. The presence or absence of plate breakage during continuous casting using 450 kg of molten steel and the columnar crystal ratio of the obtained thin billets were evaluated. The columnar crystal ratio was determined by sampling the entire width of the thin slab every 10 rotations of the cooling drum, observing the metal structure in the width direction excluding 20 mm at both ends of the width, and the minimum value of the ratio of columnar crystals to the thickness of the thin slab is shown in the table.

[0026] [Table 1]

[0027] [Table 2]

[0028] In Comparative Example 1, the molten steel temperature t in the molten steel pool was set to t = t + 40°C, where t is the liquidus temperature of the molten steel, and the slab fractured during casting. This is presumably because the molten steel temperature was too high and the strength of the thin-walled slab was insufficient. In Comparative Example 2, the pressing force P per unit width length of the cooling drum was set to 80 N / mm, and the columnar crystal ratio was low at 50%, presumably because the columnar crystals were destroyed by the pressure of the cooling drum. In Comparative Example 3, the pressing force P per unit width length of the cooling drum was set to 20 N / mm, and the slab fractured during casting. This is presumably because solidification did not proceed sufficiently, resulting in insufficient strength of the thin-walled slab.

[0029] In Comparative Example 4, the molten steel temperature t in the molten steel pool was set to t=t1+9°C where t1 is the liquidus temperature of the molten steel, and the columnar crystal ratio was low at 60%. This is presumably because the molten steel temperature was low and the columnar crystals did not grow sufficiently. In Comparative Example 5, the heat dissipation amount W of the cooling drum was 7.4 MW / m 2 The pressing force P per unit width length of the cooling drum was set to 15 N / mm, which resulted in slab fractures during casting and a low columnar crystal ratio of 60%. This is presumably because solidification did not progress sufficiently, the strength of the thin-walled slab was insufficient, and the columnar crystals did not grow sufficiently.

[0030] In contrast, in Inventive Examples 1-6, which satisfied the conditions specified in the present invention, no breakage occurred in the slab during casting, and stable casting was possible. In addition, the columnar crystal ratio was 95% or more, and a thin slab with a high columnar crystal ratio was obtained.

[0031] From the above results, it was confirmed that the method for producing a thin-walled cast slab according to the present invention can provide a method for producing a thin-walled cast slab having a uniform columnar crystal structure in a stable manner without fracture. [Explanation of symbols]

[0032] 1 Thin-walled cast billets 3 Molten steel (molten metal) 5 Solidified shell 10. Twin drum continuous casting equipment 11 Cooling drum 15 Side Weir 16 Molten steel pool section (molten metal pool section) 18 Submerged Entry Nozzle 20 Tundish

Claims

[Claim 1] A method for producing thin cast slabs having a thickness of 1.0 mm to 2.4 mm, comprising the steps of: supplying molten metal to a molten metal pool formed by a pair of rotating cooling drums and a pair of side weirs; and forming and growing a solidified shell on a peripheral surface of the cooling drums, the method comprising the steps of: The heat dissipation amount W of the cooling drum is 7.5 MW / m ２ That is all, a temperature t of the molten metal in the molten metal pool is set within a range of t1+10°C≦t≦t1+30°C relative to a liquidus temperature t1 of the molten metal; A method for producing a thin-walled cast slab, wherein the pressing force P per unit width length of the cooling drum is set within a range of 24 N / mm to 75 N / mm.

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