JPH07284896A - Steel continuous casting method and continuous casting mold - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent surface defects during continuous casting of hypoperitectic carbon steel or austenitic stainless steel and enable high speed casting. [Configuration] At least on the inner surface of the long side plate 1 of the copper plate mold,
Nickel plating 2 has a grid spacing a of 10 to 40 mm and a plating width b of 0.
2 a ≤ b ≤ 0.5 a (mm), plating thickness c is 0.5 mm or more, using a grid-shaped mold, melting point of 1100 ℃ or less, and 1300 ℃
Use a powder whose viscosity η at ° C satisfies the following formula in relation to the cast strip drawing speed Vc. η ≦ 0.3 Vc +1.5 (poise)

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention prevents vertical cracks and lateral cracks, which are found in hypoperitectic carbon steel and austenitic stainless steel, due to shell nonuniform solidification near the meniscus, and has excellent surface properties. The present invention relates to a continuous casting method capable of producing a slab and a continuous casting mold.

[0002]

2. Description of the Related Art In continuous casting, controlling the initial solidification in the vicinity of a meniscus is extremely important from the viewpoint of preventing surface defects. Longitudinal cracks occur in the mold, and one of the causes is uneven solidified shell thickness. As the factors involved in the non-uniform formation of the solidified shell thickness, the carbon concentration (alloy component) of steel and the heat removal amount in the mold are considered.

With regard to the above, it has been reported that the solidified shell thickness is likely to be nonuniform in hypoperitectic carbon steel and austenitic stainless steel in which contraction occurs due to the δ → γ transformation immediately after solidification (eg, Sugiya et al. "Iron and Steel," 65 (197
9), P.1702).

Regarding the above, many techniques have been reported for reducing the heat removal amount in the mold by using a slow cooling powder. For example, a method is disclosed in which the solidification temperature of the powder is increased, the fixing layer formed between the mold and the shell is thickened, and the thermal resistance is increased to achieve slow cooling to improve the uneven solidification of the shell (mountainous land). Et al .: “Materials and Processes”, vol.6
, No. 1 (1993) -287). It has also been reported that the use of powder with low thermal conductivity without using a high melting point reduces the depletion rate of hypoperitectic carbon steel (Ansai et al .: “Materials and Processes”, vol. 6,
No. 1 (1993) -282). There is also a report that the uneven copper solidification was improved by forming 0.9 mm pitch grooves on the copper mold plate in the vertical direction (drawing direction of the slab) and creating an air gap between the mold and the solidified shell (Nakai et al. : "Iron and Steel", 73 (1987), P. 498). In addition, it is assumed that the solidified shell thickness can be made uniform by providing grooves of 5 to 10 mm interval, width of 0.5 to 1 mm, and depth of 0.5 to 1 mm in a grid pattern on the copper mold plate and filling the grooves with dissimilar metals or ceramics. There is also a report (Japanese Patent Laid-Open No. 2-20645). These slightly delay the initial solidification of the shell in the groove, which is the weak cooling part, to leave a thin part of the shell at regular intervals and absorb the strain at the time of shrinkage, and as a result, the mold and the solidified shell do not separate and are uniform. This is the amount of heat removed, and the aim is to uniformly grow the solidified shell thickness.

[0005]

In the conventional slow cooling method,
The high melting point powder was used to obtain the effect of improving the uneven solidification of the shell. However, if a high melting point powder is used, a thick layer of powder is created between the mold and the shell near the meniscus, which is advantageous for slow cooling, but high-speed casting consumes less powder, so there is a risk of breakout. Therefore, casting is difficult.

In the method of providing the vertical groove on the inner surface of the mold, the life of the mold is shortened, and the molten steel enters the groove at the start of casting and while pouring the molten steel, which causes seizure or breakout. There is.

In the method of using a mold in which lattice-shaped grooves are provided on the inner surface of the mold and different kinds of metals or ceramics are filled in the grooves, the groove width is in the range of 0.5 to 1 mm, which is a problem. As is clear from the comparison of the results of the actual machine test to be described later, it was found that the temperature difference between the groove portion filled with metal and the non-groove portion was small, and the effect on the partial heat removal amount difference was small. ing. From the above points, there are problems in each of the conventional techniques, and they cannot be said to be perfect measures.

In view of the above points, the present invention is applied to a hypoperitectic carbon steel and an austenitic stainless steel to prevent surface defects of the slab and realize high speed casting, and a continuous casting mold. Is intended to provide.

[0009]

The continuous casting method for steel according to the present invention is to solve the above-mentioned problems by the following method. (1) Use a copper plate mold in which at least the inner surface of the long side is nickel-plated in a grid pattern. (2) Melting point below 1100 ° C and viscosity η at 1300 ° C is
Use a powder having a viscosity that satisfies the following formula in relation to the slab drawing speed Vc (m / min). η ≦ 0.3Vc +1.5 (poise)

In the grid-shaped nickel plating, the grid spacing a is 10 to 40 mm, and the plating width b is 0.2a≤b≤0.5a.
(Mm), thickness shall be 0.5 mm or more.

The mold powder contains CaO, A
l ₂ O ₃ and SiO ₂ as main components, containing one or more kinds of metal oxides, carbonates and fluorides, and the crystallization temperature is 1100 ° C.
It is characterized by using the following.

The continuous casting mold used in the present invention is a copper plate continuous casting mold in which the lattice spacing a is formed on the inner surface of the mold.
10 to 40 mm, plating width b 0.2a ≦ b ≦ 0.5a
(Mm), having a thickness of 0.5 mm or more, and having a long side plate formed by nickel plating in a grid pattern.

[0013]

FIG. 1 shows the outline of a long side plate which is a constituent element of the continuous casting mold of the present invention. (A) is a front view and (b) is a sectional view. In the figure, 1 is a long side plate of a copper plate, 2 is a nickel-plated portion formed on the inner surface of the long side plate 1 in a lattice shape (lattice spacing a (mm), plating width b (mm), thickness c (mm)). Is. The entire inner surface of the long side plate 1 having the nickel plated portion 2 is made smooth.
Although the short side plate is not shown here, the short side plate may be provided with a grid-like nickel plated portion similar to the long side plate 1.

When a continuous casting mold in which at least the inner surface of the long side plate is plated with nickel in a lattice (hereinafter referred to as "lattice-plated mold") is used, a continuous casting mold made of a conventional flat plate (hereinafter referred to as " Compared to the "flat mold"),
A solidified shell of uniform thickness is obtained. The reason is as follows.

FIG. 2A shows how a non-uniform solidified shell is formed when a flat plate mold is used. In the figure, 3 is a solidified shell, and 4 is a long side copper plate of a flat mold. The solidified shell 3 is deformed by the large solidification shrinkage caused by the δ → γ transformation that occurs immediately after the solidification of the molten steel in contact with the flat plate mold, but the solidified shell 3 is pushed back by the static pressure of the molten steel, so that a warp of a certain interval L occurs. At this time, a part of the solidification shell 3 separates from the flat mold, and the heat removal amount decreases at that portion, and the solidification is delayed. As a result, the solidified shell 3 has severe irregularities.

On the other hand, in the case of the lattice-shaped plating mold, as shown in FIG. 2B, the lattice spacing a (provided that a <L).
Since nickel plating is applied in a grid pattern to form a portion where the amount of heat removed is forcibly and regularly, the nickel plating part 2 has a delay in solidification, and solidification occurs due to solidification shrinkage accompanying the δ → γ transformation. The deformation of the shell 3 occurs at intervals of a. Therefore, the warp of the solidification shell 3 is reduced and the shrinkage strain is concentrated on the solidification delay portion. As a result, a large amount of deformation does not occur in the entire solidification shell 3, so that solidification with a uniform thickness is promoted.

As shown in Japanese Patent Laid-Open No. 2-20645,
A comparison is made between the conventional method using a lattice groove mold in which a lattice-shaped groove is provided on the inner surface of the mold, and the groove is filled with a dissimilar metal or ceramics, and the method of the present invention using a lattice-shaped plating mold. There are features and differences.

(1) In the conventional method, the width of the lattice groove is 0.5 to 1.
0mm is good. On the other hand, in the method of the present invention, the grid spacing a is 10 to 40 mm and the plating width b is 0.2 a ≦ b ≦ 0.
5a, that is, 2 to 20 mm is good. Therefore, the temperature at the time of casting was measured for the metal-filled groove portion of the lattice groove mold and the portion having no groove, and for the plated portion and the portion having no plating portion of the lattice-shaped plating mold, and the average temperature difference was determined. As a result, it was found that the conventional method had a significantly smaller temperature difference. That is, in the conventional method, the effect of the metal-filled groove portion on the partial difference in the heat removal amount is not sufficient, and the above-mentioned effect of improving the uneven solidification cannot be expected so much.

(2) In the conventional method, the mold powder is not specified, but in the method of the present invention, the viscosity at 1300 ° C. is 0.3 Vc +1.1 against the drawing speed Vc (m / min).
Use powder not exceeding 5 (poise), Ca
O, Al ₂ O ₃ and SiO ₂ as main components, metal oxides,
Contains at least one of carbonate and fluoride, and has a crystallization temperature of 11
It is stipulated that powder below 00 ℃ should be used. The mold powder fills the space between the mold and the shell,
The above-mentioned mechanism for improving the heterogeneous solidification by the mold actually actually progresses indirectly through the powder. If the powder has a high melting point, a thick fixed layer is formed between the molten powder and the mold, creating voids, which dominate the heat transfer. Therefore, in order to fully exhibit the characteristics of the grid-plated mold, the space between the mold and the shell should be filled with a uniform molten powder, the fixing layer on the mold side should be thin, and a powder that does not easily generate voids should be used. Is essential. The use of low-viscosity powder ensures a uniform inflow between the mold and the shell, and the use of powder with a low crystallization temperature suppresses the formation of the fixed layer on the mold side. The difference can be fully introduced.

[0020]

【Example】

(Example 1) ... Comparison with a flat plate mold made of a copper plate A first strand of a continuous casting machine is provided with a grid plating mold of the present invention (however, a copper plate on a long side is plated with nickel plating b = 5 m).
m, grid spacing a = 10 mm, plating thickness c = 0.5 mm), and a flat plate mold made of copper plate with no plating on the second strand for comparison, 0.08-0.18%
A casting test was conducted by changing the drawing speed of carbon steel within the range of 1 to 3 m / min. Both strands have a viscosity of 13
1.8 poise of powder was used at 00 ° C. FIG. 3 shows the result. This is a comparison of the relationship between the drawing speed and the incidence of vertical cracking.

As can be seen from this figure, the lattice-plated mold has an effect of suppressing vertical cracking as compared with a flat plate mold made of a copper plate, and the effect is remarkable in a high speed range of 1.5 m / min or more.

(Embodiment 2) Comparison with a conventional lattice groove mold A lattice-plated mold similar to that used in Embodiment 1 was mounted on the first strand of a continuous casting machine, and the second strand was used for comparison as a conventional method (special feature). Lattice groove molds (grating width 0.
5mm, grid spacing 10mm, depth 0.5mm), 0.10 to 0.
A test was conducted to cast 12% carbon steel at a drawing speed of 1.8 m / min. Both strands were powders with a viscosity of 1300 ° C and 2.0 poise. In this test, in order to investigate the influence of the lattice portions of the two molds A and B, as shown in FIG. 4, the nickel plating portion 2 or the metal (nickel) filling portion 5 and the thermocouple 6 are attached to the portions where they do not exist, respectively. The temperature during casting was measured in a steady state. There are two measurement positions for each mold, and a thermocouple 6 is embedded from the rear surface so that the distance from the surface is 1 mm near the meniscus at the center of the long side of the mold.

Measured values at each position (T1, T2 in FIG. 4)
, T3, T4), the average value of the temperature difference is ΔT = T2 −
T1 (Example) and .DELTA.T '= T4-T3 (Conventional example) were determined. FIG. 5 shows the result. That is, in the conventional method, the effect of the metal-filled portion on the partial difference in the heat removal amount is not sufficient, and the effect of improving the above-mentioned nonuniform solidification cannot be expected.

(Embodiment 3) -Influence of powder viscosity and crystallization temperature In the action section, in the case of the lattice-plated mold of the present invention, the effect is easily exhibited when a low-viscosity mold powder is used together. As mentioned above, since the shell-side temperature between the mold and the shell increases as the drawing speed increases, even if powders having the same viscosity at 1300 ° C. are used, the higher the drawing speed, the smaller the practical viscosity of the powder. Therefore, when the drawing speed is high, the viscosity at 1300 ° C may be higher than when the drawing speed is low.

From the above viewpoints, 0.10 to 0.20% carbon steel was subjected to a casting test by changing the powder viscosity and the drawing speed.
In the test, the same grid-shaped plating mold as in Example 1 was used. Casting speed is 1.0-3.0m / min, viscosity at 1300 ℃ is 1.0-3.0p
The test was conducted by changing the range of oise. FIG. 6 shows the relationship between the viscosity η at a drawing speed of 2.0 m / min and the rate of occurrence of vertical cracks when a lattice-shaped plating mold was used. Here, ∘ indicates that the slab was acceptable (the vertical crack occurrence rate was 0), and ● indicates that it was a rejected slab (with vertical cracks).

From FIG. 6, when η exceeds 2.0 poise, it fails. Therefore, when casting at a casting speed of 2.0 m / min, it is understood that powder with a viscosity of 2.0 poise or less should be used. Similarly, for other drawing speeds, the relationship between the casting speed and the viscosity was obtained. The result is shown in FIG. 7. FIG. 7 is a diagram showing the relationship between the viscosity η at 1300 ° C. and the casting speed Vc, where ◯ is a pass slab and ● is a slab that is not pass. Of the two slabs at each casting speed, the one with the highest viscosity is almost on a straight line, and when the straight line is obtained by linear regression, η = 0.3 Vc +1.5 Therefore, the area indicated by the diagonal lines in the graph of FIG. It was found that a good slab can be obtained by using a powder having a viscosity satisfying η ≦ 0.3 Vc +1.5.

Further, in the action section, in the case of a grid-shaped plating mold, by using a powder having a low crystallization temperature, the fixing layer on the mold side is thinned, and the generation of the fixing layer is suppressed, so that It was stated that the effect of the flat plating mold is easy to be exhibited. 0.10
~ 0.20% carbon steel powder viscosity is η ≦ 0.3 Vc +1.5
8 is satisfied, the crystallization temperature is in the range of 900 to 1200 ° C., the drawing speed is 2.5 and the result is 3.0 m / min. ○ in the figure
Indicates a pass, and ● indicates a failure. When the crystallization temperature is 1100 ° C or lower, it is good, but when it exceeds 1100 ° C, it fails. Therefore, when the drawing speed is high, the influence of the crystallization temperature is significant, and it is necessary to consider the crystallization temperature. The threshold temperature was found to be 1100 ° C.

(Embodiment 4) Relation between lattice spacing and plating width In order to determine an appropriate lattice spacing a and plating width b, 0.10 to 0.
A test for casting 12% carbon steel at a casting speed of 2.0 m / min was conducted as follows. At this time, the viscosity at 1300 ℃ is 2.0 po
I used ise powder.

First, a test was conducted by changing the lattice spacing a. The plating thickness is all 0.5 mm, and the lattice spacing a is 1 mm ~
The mold changed in the range of 60 mm was used. However, the plating width was all b = a / 2. The test results are shown in FIG. From this result, it is understood that the lattice spacing a is preferably 10 to 40 mm.

Next, the plating width b was changed with the lattice spacing a set to 10 mm or 20 mm. The plating thickness was 0.5 mm.
The result is shown in FIG. From this result, it is understood that 2 to 5 mm is preferable when a = 10 mm and 4 to 10 mm is preferable when a = 20 mm. Therefore, the relationship between the lattice spacing a and the plating width b is optimally within the range of 0.2 a ≦ b ≦ 0.5 a.

(Embodiment 5) Relationship with plating thickness FIG. 11 shows the test results when the thickness of the grid plating was changed.
Plating width is 5 mm, lattice spacing is 10 mm, and plating thickness is 0.2 to 1.5 m
Using a grid-type plating mold varied in the range of m, 0.10 ~ 0.
A test was conducted in which 12% carbon steel was cast at a casting speed of 2.0 m / min using a powder having a viscosity of 1300 ° C and 2.0 poise. From this figure, it can be seen that the appropriate plating thickness is 0.5 mm or more. If the thickness is less than 0.5 mm, the thickness is not sufficient and the heat insulating effect does not appear.

(Example 6) Casting of SUS304 steel All the above tests were performed on hypoperitectic carbon steel (0.12% C), but the same test was performed on austenitic stainless steel (SUS304) with δ → γ transformation. A comparative test with the case of using a flat plate mold was conducted. That is, the same grid-shaped plating mold as in Example 1 was used for the first strand of the continuous casting machine,
As a comparison with the strand, a conventional flat plate-shaped mold on which nickel plating was applied was mounted, austenitic stainless steel (SUS304) was cast at a casting speed of 2.0 m / min, and a test for checking the number of depletions was conducted. At this time, a powder having a viscosity of 1300 ° C and 2.0 poise was used for both strands. The result is shown in FIG.

As shown in this figure, good results were also obtained with SUS304 steel. In addition, it is confirmed that the grid-shaped plating mold of the present invention is more effective in the same test with SUS316 steel.

The limits of each range for the carbon steels obtained in Examples 1 to 5 are also applicable to the austenitic stainless steel.

[0035]

As described above, according to the present invention, when a hypoperitectic carbon steel or an austenitic stainless steel is continuously cast, a long-side inner surface is coated with a grid-like nickel plating and a grid-shaped plating mold By using the viscous powder together, it was possible to obtain a slab having excellent surface properties even during high speed casting. As a result, the hypoperitectic carbon steel was directly rolled and the austenitic stainless steel was slab-free.

[Brief description of drawings]

FIG. 1 is a schematic view showing a long side plate of a continuous casting mold of the present invention.

FIG. 2 is a schematic diagram comparing the growth of a solidified shell between a grid-shaped plating mold of the present invention and a conventional flat plate-shaped mold.

FIG. 3 is a graph comparing the relationship between the drawing speed and the occurrence rate of vertical cracks in an actual machine test between the grid-plated mold of the present invention and the case of using a conventional flat plate mold.

FIG. 4 is a diagram showing respective temperature measurement positions for a grid-shaped plating mold of the present invention and a conventional grid groove mold.

FIG. 5 is a graph showing the results of measuring the temperature difference in FIG.

FIG. 6 is a graph showing the relationship between powder viscosity and vertical crack occurrence rate at a casting speed of 2.0 m / min.

FIG. 7 is a graph showing the relationship between casting speed and powder viscosity.

FIG. 8 is a graph showing a relationship between a crystallization temperature and a vertical crack occurrence rate.

FIG. 9 is a graph showing the relationship between the lattice spacing and the vertical crack occurrence rate in an actual machine test.

FIG. 10 is a graph showing a relationship between a plating width and a vertical crack occurrence rate in an actual machine test.

FIG. 11 is a graph showing a relationship between a plating thickness and a vertical crack occurrence rate in an actual machine test.

FIG. 12 is a graph comparing the number of depletions generated during casting of SUS304 steel in an actual machine test between the case of using the grid plating mold of the present invention and the case of using a conventional flat plate mold.

[Explanation of symbols]

 1 Long side plate 2 Nickel plated part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Suzuki Marunouchi 1-2-2, Chiyoda-ku, Tokyo Nihon Steel Tube Co., Ltd. (72) Yasuto Miyata 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Kentaro Mori 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd. (72) Inventor Ryuzo Nishimachi 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Inside Steel Pipe Co., Ltd.

Claims (4)

[Claims] 1. In continuous casting of steel, at least a melting point of 1100 ° C. or less and a viscosity η at 1300 ° C. is used to draw out a slab by using a copper plate mold in which at least the inner surface of the long side is grid-plated with nickel plating. A continuous casting method for steel, characterized in that a powder satisfying the following formula in relation to the speed Vc (m / min) is used. η ≦ 0.3Vc +1.5 (poise) 2. The lattice-shaped nickel plating has a lattice spacing a of 10 to 40 mm and a plating width b of 0.2a ≦ b ≦ 0.5a (m
The continuous casting method for steel according to claim 1, wherein m) and the thickness is 0.5 mm or more. 3. A mold powder containing CaO, Al ₂ O ₃ and SiO ₂ as main components, containing at least one of metal oxides, carbonates and fluorides and having a crystallization temperature of 1100 ° C. or lower. The continuous casting method for steel according to claim 1, which is characterized in that. 4. A continuous casting mold made of a copper plate, having a lattice spacing a of 10 to 40 mm and a plating width b of 0.2 on the inner surface of the mold.
A mold for continuous casting of steel, characterized in that it has a long side plate a ≦ b ≦ 0.5a (mm) and a thickness of 0.5 mm or more and is plated with nickel in a grid pattern.