JP2013086131A - Continuous casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous casting method capable of casting slabs in a plurality of shapes differing in thickness using a common long side by replacement with short sides having widths corresponding to thicknesses of the slabs.SOLUTION: There is provided the continuous casting method of casting slabs having N kinds of thicknesses by arranging N kinds of short sides 13 and 14, 13a and 14a, and 13b and 14b having widths corresponding to the thicknesses of the slabs to be cast in replaceable states between long sides 11 and 12 arranged opposite each other, and pouring molten steel in a mold space part V formed in a vertically through state, wherein N division gradient regions L, L, and Lcommunicating with the opposite sides 11 and 12 except top parts are formed more in conformity with coagulation shrinkage profiles on coagulation start sides of the slabs determined by the widths of the short sides 13b and 14b, 13a and 14a, and 13 and 14 made narrower in width in order respectively, and molten steel surface height positions of the molten steel are set in the division gradient regions L, L, and Laccording to the widths of the slabs determined by the selected short sides 13 and 14, 13a and 14a, and 13b and 14b.

Description

The present invention relates to a continuous casting method for casting a slab having a plurality of thicknesses.

When casting molten steel into a continuous casting mold and casting a slab, solidification shrinkage occurs during the solidification process of the molten steel, so the solidified shell (slab) formed on the mold contact surface side of the molten steel and the mold inner surface A gap is formed between the two. In the solidified shell, the cooling efficiency of the portion facing the gap is reduced, so that there is a problem that solidification delay (portion where the shell thickness is thin) occurs and the slab breaks. Furthermore, if the solidified shell breaks during casting, there is a risk of accidents in which molten steel leaks from the inside. Therefore, there is a continuous casting mold in which a multitaper approximating the solidification shrinkage profile of the solidified shell (simply referred to as a shrinkage profile) is formed on the inner surface of the mold so that a gap is not generated between the solidified shell and the inner surface of the mold. It has been proposed (see, for example, Patent Document 1).
On the other hand, when casting slabs with multiple thicknesses, instead of preparing multiple continuous casting molds, the long sides of continuous casting molds prepared for casting slabs with a certain thickness are shared and placed facing each other. The short sides opposed to each other between the long sides are replaced with short sides having a width corresponding to the thickness of the cast slab to be cast, thereby casting slabs having different thicknesses.

JP 2010-201450 A

Produced for casting a slab of thickness T _A , having a long side A arranged oppositely and a short side A arranged opposed between the long sides A, and a multitaper was provided on the inner surface of the mold in the continuous casting mold a, the short side a, to replace the short side B having a possible width casting of slab thickness T _a larger thickness T _B, using a long side a and the short side B continuous when performing casting slab casting mold B configuration with a thickness of T _B, and the inner surface of the long side a is multitaper approximating the solidification shrinkage profile of the solidified shell a to form a slab of thickness T _a Therefore, the inner width between the long sides A is gradually reduced as it goes downward reflecting the vertical distribution of the amount of solidification shrinkage of the solidified shell A. On the other hand, the solidification shrinkage of the solidified shell B to form a slab of thickness T _B is greater than the solidification shrinkage of the solidified shell A to form a slab having a thickness of T _A.
For this reason, a gap is generated between the solidified shell B formed in the continuous casting mold B and the inner surface of the long side A, and the gap is accompanied with the progress of solidification (as the solidified shell B moves downward). Therefore, there is a problem that solidification delay occurs in the solidified shell B and the slab breaks. Furthermore, when the solidification delay increases, there is a possibility of an accident that the solidified shell B breaks during casting and the molten steel leaks from the inside.

The present invention has been made in view of such circumstances, and N types of short sides having a width corresponding to the thickness of a cast piece to be cast are arranged opposite to each other between the long sides opposed to each other, It is an object of the present invention to provide a continuous casting method capable of casting cast pieces of N types of thickness by putting molten steel in a mold space portion formed in a vertically penetrating state.

In the continuous casting method according to the present invention for the above purpose, N types of short sides having a width corresponding to the thickness of a cast piece to be cast are arranged so as to be exchanged between the long sides arranged opposite to each other. It is a continuous casting method capable of casting slabs of N types of thickness by putting molten steel into a mold space portion formed in a through state in a direction,
Solidification shrinkage on the solidification start side of the slab determined by the widths of the short sides of N divided gradient regions communicating from the top to the bottom except for the uppermost portion on the long sides facing each other. The molten steel surface height position of the molten steel is set in the divided gradient region corresponding to the width of the slab determined by the selected short side.

In the continuous casting method according to the present invention, the molten steel surface height position of the molten steel is preferably matched with the upper end portion of the divided gradient region corresponding to the width of the slab determined by the selected short side.

In the continuous casting method according to the present invention, it is preferable that the lowermost divided gradient region is formed by a plurality of straight lines approximated to a solidification shrinkage profile of the slab formed by the short side having the minimum width.

In the continuous casting method according to the present invention, the division gradient region formed at the upper position of the lowermost division gradient region is one straight line approximated to the solidification shrinkage profile on the solidification start side or two or more connected. It is preferable to form the straight line.

In the continuous casting method according to the present invention, it is preferable that the shape of the contour line of the side edge of the short side is matched with the shape of the inner contour line of the long side.

In the continuous casting method according to the present invention, when casting slabs of N types of thickness, N divided gradient regions communicating from the top to the bottom except for the uppermost portion are sequentially formed on the opposing long sides. When casting a slab with the minimum thickness (thinnest) when casting the slab with the minimum thickness, it is formed by approximating the solidification shrinkage profile on the solidification start side of the slab determined by the narrow side width. Select the short side with the width corresponding to the piece, replace it with the selected short side to configure the continuous casting mold, and cast the molten steel surface height position in the mold space when casting the slab of minimum thickness Is set in the division gradient region corresponding to the width of the slab determined by the selected short side, i.e., the division gradient region formed at the bottom of the long side. A gap may form between the solidified shell and the inner surface of the lowermost gradient zone. It is braking, it is possible to sufficiently perform the cooling of the solidified shell. As a result, no solidification delay occurs in the solidified shell, and cracking of the solidified shell can be prevented to produce a high-quality slab.

In addition, the division gradient region that is sequentially formed above the lowest division gradient region is formed stepwise by approximating the solidification shrinkage profile on the solidification start side of the slab formed by the wide short side. Therefore, for example, when casting the K (K = 2, 3,..., N) th thin slab K, a short side having a width corresponding to the slab K is selected, and the selected short side is selected. Replaced to form a continuous casting mold, and the molten steel surface height position in the mold space when casting the Kth thin slab K corresponds to the width of the slab determined by the selected short side Is set in the Kth divided gradient region from the bottom of the long side, so that there is a gap between the solidified shell formed in the Kth divided gradient region and the inner surface of the Kth divided gradient region. Occurrence is suppressed, and the solidified shell is sufficiently cooled at the solidification start stage. It can be grown to a thickness of the solidified shell.

The solidified shell formed in the Kth division gradient region from the bottom enters the K-1th division gradient region immediately below, but the K-1th division gradient region is the K-1th thinnest slab K. -1 (the solidified shell that forms the K-1 thinnest slab K-1) based on the solidification shrinkage profile on the solidification initiation side, the solidification that enters the K-1th division gradient region The surface of the shell does not adhere to the inner surface of the (K-1) th division gradient region. However, since the solidification shrinkage amount of the solidified shell in the (K-1) th division gradient region is smaller than the solidification shrinkage amount of the solidification shell in the Kth division gradient region, the surface of the solidification shell and the inner surface of the long side The distance between the gaps does not increase greatly. For this reason, the solidified shell can be continuously cooled even in the (K-1) th divided gradient region, and the occurrence of a solidification delay in the solidified shell can be avoided.

Then, the solidified shell that has passed through the second division gradient region from the bottom enters the lowest division gradient region. Even in the lowermost divided gradient region, the surface of the solidified shell does not adhere to the inner surface of the lowermost divided gradient region, but the amount of solidification shrinkage of the solidified shell is further reduced, so the surface of the solidified shell and the lowermost divided gradient region The distance of the gap between the inner surface of the film does not increase much. For this reason, the solidified shell can be continuously cooled even in the lowermost divided gradient region, and the occurrence of a solidification delay in the solidified shell can be avoided. As a result, cracking of the solidified shell can be prevented and a high quality slab can be produced.

In the continuous casting method according to the present invention, when the molten steel surface height position is matched with the upper end portion of the divided gradient region corresponding to the width of the slab determined by the selected short side, the molten steel is formed in the divided gradient region. The surface of the solidified shell that comes into contact with the inner surface of the divided gradient region can reliably cool the solidified shell at the solidification start stage, and the thickness of the solidified shell can be efficiently grown.

In the continuous casting method according to the present invention, when the lowermost divided gradient region is formed by a plurality of straight lines approximated to the solidification shrinkage profile of the slab formed by the short side of the minimum width, the lowermost divided gradient region The shape of the mold can be made close to the shape corresponding to the solidification shrinkage profile of the slab with the minimum thickness, and the shape can be made simple, making it easy to process the bottom gradient zone of the longest side, making a continuous casting mold Since the manufacturing cost of the slab is reduced, the manufacturing cost of the slab can be reduced.

In the continuous casting method according to the present invention, the divided gradient region formed at the upper position of the lowermost divided gradient region is represented by one straight line approximated to the solidification shrinkage profile on the solidification start side or two or more connected straight lines. When forming, the shape of the divided gradient region formed sequentially above the lowermost divided gradient region is made to correspond to the solidification shrinkage profile on the solidification start side of the slab formed by the successively wider short sides. As it gets closer, it can be made into a simple shape. Thereby, the process of the division | segmentation gradient area | region above a lowermost part of a long side becomes easy, the manufacturing cost of a continuous casting mold reduces, and the manufacturing cost of a slab can be reduced.

In the continuous casting method according to the present invention, when the shape of the contour of the side edge of the short side is matched with the shape of the inner contour of the long side, the short side is replaced according to the thickness of the cast slab. However, it is possible to prevent a gap from being generated between the end surface of the short side and the inner side surface of the long side.

It is a perspective view of the continuous casting mold applied to the continuous casting method which concerns on one embodiment of this invention. It is a longitudinal cross-sectional view of the long side of the continuous casting mold. It is explanatory drawing which shows the relationship between the taper of the inner surface of the long side which concerns on an Example, and the amount of solidification shrinkage | contraction. It is explanatory drawing of the calculation result of distribution of the shell thickness in the corner part of the solidification shell formed by the continuous casting method of an Example. It is explanatory drawing of distribution of the shell thickness of the corner part of a solidification shell. It is explanatory drawing which shows the relationship between the taper of the inner surface of the long side which concerns on a comparative example, and the amount of solidification shrinkage. It is explanatory drawing of the calculation result of distribution of the shell thickness in the corner part of the solidification shell formed by the continuous casting method of a comparative example.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
As shown in FIGS. 1 and 2, a continuous casting mold 10 according to an embodiment of the present invention has three types (an example of N types) of short sides 13 between long sides 11 and 12 arranged to face each other. 14, 13 a, 14 a, 13 b, 14 b are arranged so as to be exchangeable, and molten steel is put into a mold space V formed in a vertically penetrating state so that slabs of three types of thickness (the width of the slab is Casting). In addition, inside the long sides 11 and 12 and inside the short sides 13 and 14 (the same applies to the short sides 13a and 14a, the short sides 13b and 14b), a wear-resistant reinforcing film (not shown) (for example, plating) Layer, sprayed layer). In addition, although the amount of reduction of the inner width between the long sides 11 and 12 is slight, for convenience of explanation, it is exaggerated in FIGS. Details will be described below.

On the outer surfaces of the long sides 11 and 12 and the short sides 13 and 14 (the surface surrounding the mold space V, that is, the surface opposite to the surface in contact with the molten steel), they are arranged side by side in the vertical direction (casting direction). A back plate (not shown) is attached via a fastening means group composed of a plurality of bolts (not shown). Thereby, the cooling water is caused to flow from a water supply section (not shown) provided at the lower portion of the back plate to a large number of water guide grooves (not shown) provided on the outer surfaces of the long sides 11 and 12 and the short sides 13 and 14. Thus, the long sides 11 and 12 and the short sides 13 and 14 are cooled and the molten steel supplied to the mold space V is cooled to produce a slab. Note that the base materials of the long sides 11 and 12 and the base materials of the short sides 13 and 14 are made of copper or a copper alloy.

The short sides 13 and 14 have a thickness (thickness including a reinforcing coating) of, for example, about 5 mm to 100 mm, a width of about 50 mm to 400 mm, and a vertical length of about 600 mm to 1200 mm. . In addition, the long sides 11 and 12 have a thickness (thickness including a reinforcing film) of, for example, about 5 mm to 100 mm, and a distance between a pair of short sides 13 and 14 that are opposed to each other (a width that contacts a slab). Can be changed in a range of about 600 mm to about 3000 mm, and the length in the vertical direction is about the same as the short sides 13 and 14. Thereby, for example, a slab (an example of a cast piece) having a width of about 600 mm to 3000 mm and a thickness of about 50 mm to 400 mm can be manufactured.

The reinforcing coating may be a Co—Ni alloy plating, a thermal spray coating made of a Cr—Si—B alloy based on Ni or Co, or a carbide (for example, a Co, Ni, or Co—Ni alloy). A thermal spray coating made of a composite material to which any one or more of WC), nitride (eg, TiN), and boride (eg, CrB) is added can be used. In the case of a thermal spray coating made of a Cr-Si-B based alloy based on Ni or Co, by performing a fusing treatment, the reinforcing coating is densified, the reinforcing coating and the long-side base material, the reinforcing coating and the short coating. The bondability with the side base material can be improved, and the life of the reinforcing coating can be extended. On the other hand, in the case of a thermal spray coating made of a composite material in which any one or more of carbide, nitride, and boride is added to a Co, Ni, or Co—Ni alloy, It is possible to further prevent and improve the wear resistance of the reinforcing coating.

Three divided gradient regions L ₁ , L ₂ , and L ₃ are formed on the opposing long sides 11 and 12 so as to communicate vertically except for the uppermost portion. Divided gradient region L ₁ formed at the bottom, the minimum thickness is approximated to solidification shrinkage profile P ₁ of the slab, the bottom split gradient region L ₁ which is formed by the short sides 13 and 14 of minimum width The divided gradient regions L ₂ and L _{3 that} are sequentially formed at the upper positions are formed by the successively shorter wide sides 13 a, 14 a, 13 b, and 14 b, that is, the solidification shrinkage on the solidification start side of the slab that gradually increases in thickness. It is formed stepwise by approximating the profiles P ₂ and P ₃ .

Split gradient region L ₁ of the bottom is to approximate the solidification shrinkage profile P _1, it is formed by a plurality of straight lines, for example, two straight lines S _1, multitaper consisting S ₂ which connects. Here, arranged on the lower side of the split gradient region L _1, the gradient of the lower tapered portion consisting of linear S ₁ is disposed on the upper side of the divided gradient region L _1, greater than the slope of the upper tapered portion consisting of a straight line S ₂ (angle between the lower tapered portion and the vertical surface composed of straight lines S ₁ is smaller than the angle formed between the upper tapered portion and a vertical plane consisting of straight S _2), divided gradient formed in a long side 11, 12 opposite inner width of the upper end portion between regions L ₁ is larger than the inner width of the lower end portion (lower end portion of the long sides 11 and 12).
The divided gradient region L ₁ is a multitaper having three or more connecting straight lines approximating the coagulation shrinkage profile P ₁ (the taper portion formed of each connecting straight line has a lower slope than the tapered portion disposed on the lower side. It may be formed with a large gradient). By increasing the number of straight lines constituting the split gradient region L _1, it is possible to improve the approximation accuracy in approximating the solidification shrinkage profile P ₁ in multitaper.

Also, it split gradient region L ₂ immediately above the bottom of the split gradient region L ₁ (second from the bottom), one of the straight line is approximated to a second-thin slab solidification starting end of solidification shrinkage profile P ₂ Is formed. Here, the gradient of the upper tapered portion of the split gradient region L ₁ is the angle between the split gradient greater than the gradient of the region L ₂ (upper tapered portion and the vertical plane, the angle between the dividing gradient region L ₂ and the vertical plane smaller), the inside width of the upper end portion between the opposed split gradient region L ₂ formed on the long sides 11 and 12 is larger than the inner width of the lower end portion (upper end portion between the divided gradient region L ₁₎ .
Incidentally, the division gradient region L _2, the articulated 2 or more straight lines approximating the solidification shrinkage profile P ₂ of the coagulation initiator (slope of the straight line which connects the large gradient as the straight line that is disposed on the lower side) You may form by the multitaper which becomes. By increasing the number of straight lines constituting the split gradient region L _2, it is possible to improve the approximation accuracy in approximating the solidification shrinkage profile P ₂ of the solidification starting side multitaper.

Further, the divided gradient region L ₃ directly above the divided gradient region L ₂ (third from bottom), were approximated to solidification shrinkage profile P ₃ thin third (the maximum thickness) cast piece solidification starting side of the 1 It is formed with a straight line. Here, the gradient of the divided gradient region L ₃ is the angle between the split gradient greater than the gradient of the region L ₂ (divided gradient region L ₂ and the vertical plane is smaller than the angle between the dividing gradient region L ₃ and vertical plane ), the inside width of the upper end portion between the opposed split gradient region L ₃ formed on the long sides 11 and 12 is larger than the inner width of the lower end portion (upper end portion between the divided gradient region L _2).
Incidentally, the division gradient region L _3, articulated 2 or more straight lines (gradient of each straight line connecting the straight line the larger the gradient is arranged on the lower side) may be formed in a multi-tapered consisting. By increasing the number of straight lines constituting the split gradient region L _3, it is possible to improve the approximation accuracy in approximating the solidification shrinkage profile P ₃ of the coagulation initiator in multitaper.

In addition, a division gradient region L ₄ having a larger gradient than the third division gradient region L ₃ from the bottom (smaller angle with respect to the vertical plane) is formed at the top of the opposing long sides 11 and 12. The uppermost divided gradient region L ₄ may be formed by extending the divided gradient region L ₃ , or may be formed as a vertical region parallel to the back side of the long sides 11 and 12. By forming the dividing gradient region L ₄ on the upper side of the _third dividing gradient region L _{3 from} the bottom, the molten steel is placed in the mold space V so that the upper end of the dividing gradient region L ₃ is at the molten steel surface height position. Can be injected.

On the other hand, the short sides combined with the long sides 11 and 12 (the short sides 13 and 14 having a width corresponding to the minimum thickness slab, the short sides 13a and 14a having the width corresponding to the second thinnest slab, and The contour shape of the side end face of the short sides 13b, 14b) having a width corresponding to the third thinnest (maximum thickness) slab matches the shape of the inner contour lines of the long sides 11, 12. And the gradient part (not shown) which approximates the solidification shrinkage profile of the width direction of a slab is formed in the inner surface (surface which contact | connects molten steel) of the short sides 13, 14, 13a, 14a, 13b, 14b. . The longitudinal section of the gradient portion is formed by one or two or more straight lines connected to each other, and the inner width between the opposing short sides 13, 14, 13a, 14a, 13b, 14b is the lower side from which the slab is pulled out. It is narrowing towards. Therefore, when the longitudinal section of the gradient portion is formed by two or more straight lines connected to each other, the gradient of each connected straight line is larger as the straight line arranged on the lower side.
In addition, on the inner surface of the short side, a bulging portion that matches the solidification shrinkage profile in the width direction of the slab is formed, and the inner width between the opposing short sides 13, 14, 13a, 14a, 13b, 14b is It can also be made to narrow gradually toward the lower side where the slab is pulled out.

Here, the short sides 13 and 14 having a width corresponding to the slab of minimum thickness, width at the height position corresponding to the upper end position of the dividing gradient region L ₁ is cast slab of minimum thickness continuously It coincides with the width at the bath level height position of the molten steel to the short sides of the casting mold, the lower end width of which corresponds to the lower end position of the dividing gradient region L ₁ is, the continuous casting mold for casting a slab of minimum thickness It corresponds to the width at the lower end of the short side (the outlet of the continuous casting mold). Then, the width of the short sides 13 and 14 at the height range corresponding to the height range of the divided gradient region _L 2 ~L ₄ long sides 11 and 12, the short side in the divided gradient region _{L 1} of the long sides 11, 12 It is determined by 13 and 14 in the width formed so as to match the inner width at the height range of the divided gradient region _L 2 ~L ₄ between the long sides 11, 12.

Also, the short side 13a having a width corresponding to the thin slab to the second, in 14a, the width at the height position corresponding to the upper end position of the dividing gradient region L _2, the continuous casting for casting thin slabs in the second coincides with the width at the bath level height position of the molten steel to the short sides of the mold, the width at the height position corresponding to the lower end position of the dividing gradient region L ₂ (the upper end position of the dividing gradient region L _1), the second It matches the width at a position located below only a thin cast distance corresponding piece from molten metal surface height of the molten steel relative to the short side of the continuous casting mold for casting the height of the divided gradient region L _2, the split gradient region L ₁ The width of the lower end corresponding to the position of the lower end corresponds to the width at the lower end (outlet of the continuous casting mold) of the short side of the continuous casting mold for casting the second thinnest slab. The widths of the short sides 13a and 14a in the height range corresponding to the height range of the divided gradient regions L ₃ and L ₄ of the long sides 11 and 12 are the divided gradient regions L _{1 and} L ₂ of the long sides 11 and 12, respectively. Are formed so as to coincide with the inner width in the height range of the divided gradient regions L ₃ and L ₄ between the long sides 11 and 12 determined by the width of the short sides 13a and 14a.

Moreover, the short side 13b having a width corresponding to the thin slab in the third, in 14b, the height width at a position corresponding to the upper end position of the dividing gradient region L ₃ are (the maximum thickness) thin third casting coincides with the width at the bath level height position of the molten steel relative to the short side of the continuous casting mold for casting pieces, height position corresponding to the lower end position (the upper end position of the dividing gradient region L ₂₎ divided gradient region L ₃ width matches the width at a position located below by a distance corresponding to the height of the divided gradient region L ₃ from the molten steel bath level height position of the relative short side of the continuous casting mold for casting a thin cast piece in the third in , the width at the height position corresponding to the lower end position of the dividing gradient region L ₂ (the upper end position of the dividing gradient region L ₁₎ is molten steel bath level height with respect to the short side of the continuous casting mold for casting a thin cast piece in the third height and dividing the slope of the divided gradient region L ₃ from the position Matches the width at a position located below by a distance corresponding to the sum of the height of the area L _2, the width of the lower end corresponding to the lower end position of the dividing gradient region L ₁ is continuous casting for casting thin slabs third It corresponds to the width at the lower end of the short side of the mold (the outlet of the continuous casting mold). Divided gradient region _{L 4} of the height range corresponding height range short side at 13b of the long sides 11 and 12, the width of 14b is divided gradient region _L 1 of the long sides 11 and _{12, L} 2, _{L 3} short sides 13b, formed so as to match the inner width at the height range of the divided gradient region L ₄ between the long sides 11 and 12 is determined by the width of 14b in.
Therefore, the width of the height position of the short side is determined by the gradient of the long side.

Then, the continuous casting method which concerns on one embodiment of this invention is demonstrated.
In the continuous casting method according to the present embodiment, three types of short sides 13, 14, 13 a, 14 a having a width corresponding to the thickness of a cast piece to be cast are provided between the long sides 11, 12 arranged opposite to each other. 13b and 14b are arranged to face each other in a replaceable manner, and molten steel is put into a mold space V formed in a vertically penetrating state so as to cast slabs of three different thicknesses. In the three divided gradient regions L ₃ , L ₂ , and L ₁ that communicate with the long sides 11 and 12 from the top to the bottom except the uppermost portion, the short sides in which the divided gradient regions L ₃ and L ₂ are sequentially narrowed 13b, 14b, 13a and 14a are formed by approximating the solidification shrinkage profiles P ₃ and P ₂ on the solidification start side of the slab determined by the width of each slab, and the divided gradient region L ₁ is formed with the short side 13 having the minimum width, The slab determined by the width of 14 (minimum width slab) Is approximated to shrinkage profile _{P 1} formed by a short side 13,14,13a selected, 14a, 13b, corresponding to the width of the slab is determined by 14b divided gradient region _{L 1,} L 2, _{L 3} For example, casting is performed by aligning the molten steel surface height position of the molten steel with the upper end portions of the divided gradient regions L ₁ , L ₂ , and L ₃ . Details will be described below.
Here, the shape of the contour line of the side end surfaces of the short sides 13, 14, 13a, 14a, 13b, 14b is made to match the shape of the inner contour line of the long sides 11, 12, so the thickness of the cast slab to be cast Even if the short side is exchanged accordingly, it is possible to prevent a gap from being generated between the end surfaces of the short sides 13, 14, 13a, 14a, 13b, and 14b and the inner surfaces of the long sides 11 and 12.

When casting a slab having a minimum thickness, the continuous casting mold 10 is configured using the short sides 13 and 14 having a width corresponding to the slab having the minimum thickness. Then, poured into the bottom of the divided gradient region L ₁ of the upper end molten steel continuous casting mold 10 so that the molten metal surface height of the molten steel (mold space V). The molten steel in the continuous casting mold 10 contacts the long sides 11 and 12 and the short sides 13 and 14 and is cooled to form a solidified shell. Here, dividing the gradient region L ₁ is, since a multi-taper which approximates the thickness direction of the solidification shrinkage profile P ₁ of the slab of minimum thickness, the solidified shell and length which is formed in the divided gradient region L ₁ Generation | occurrence | production of a clearance gap between the edge | sides 11 and 12 inner surface is suppressed, the solidification shell can fully be cooled, and the thickness of the solidification shell can be made to grow. Moreover, since the slope part which approximates the solidification shrinkage profile of the width direction of a slab is formed in the inner surface of the short sides 13 and 14, a clearance gap may generate | occur | produce between the solidification shell and the inner surface of a short side. The solidified shell can be efficiently cooled and the solidified shell thickness can be increased. As a result, no solidification delay occurs in the solidified shell, and cracking of the solidified shell can be prevented to produce a high-quality slab.

When casting the second thin slab, the continuous casting mold 10 is configured by replacing the short sides 13a and 14a having a width corresponding to the second thin slab. Then, the molten steel is poured into the continuous casting mold 10 (mold space V) so that the upper end portion of the _second divided gradient region L2 from the bottom is the molten steel surface height position. The molten steel in the continuous casting mold 10 contacts the long sides 11 and 12 and the short sides 13 and 14 and is cooled to form a solidified shell. Since the split gradient region L ₂ has a second thin slab 1 of a straight line approximating the solidification shrinkage profile P ₂ in the thickness direction of the solidification starting side of the solidified shell at the time of casting, split it is prevented that a gap is generated between the solidified shell and the long 11 and 12 the inner surface formed in the slope region L _2. Moreover, since the slope part which approximates the solidification shrinkage profile of the width direction of a slab is formed in the inner surface of the short sides 13 and 14, a clearance gap generate | occur | produces between the solidification shell and the inner surfaces of the short sides 13 and 14. Is suppressed. As a result, it is possible to divide the slope (in the coagulation initiator) in the region L ₂ perform the cooling of the solidified shell efficiently promote the growth of the solidified shell thickness.

Then, the solidified shell may have entered the split gradient region L ₁ immediately below from dividing the gradient region L _2, divided gradient region L ₁ approximates the minimum thickness of the thickness direction of the slab solidification shrinkage profile P ₁ because it is formed by multi-taper, the solidification shrinkage of the solidified shell in it so that a gap is generated, divided gradient in region L ₁ between the divided gradient region L ₁ of the inner surface and the solidified shell is split gradient It becomes smaller than the solidification shrinkage of the solidified shell in the within region L _2, a gap greatly increases is prevented. Note that the inner surface of the short sides 13 and 14, since the gradient portion that approximates the width direction of the solidification shrinkage profile of the slab are formed, also in divided gradient region L _1, the solidified shell and short 13,14 Generation of a gap between the inner surface and the inner surface is suppressed. Therefore, solidified shell even enters the split gradient region L _1, the solidified shell is continued can be cooled, can be grown the thickness of solidified shell. As a result, it is possible to avoid the occurrence of a solidification delay in the solidified shell, and to prevent cracking of the solidified shell and to manufacture a high quality slab.

Further, when casting the third thinnest (maximum thickness) slab, the continuous casting mold 10 is configured by replacing the short sides 13b and 14b having a width corresponding to the third thinnest slab. Then, the molten steel is poured into the continuous casting mold 10 (mold space V) so that the upper end portion of the _third divided gradient region L3 from the bottom is the molten steel surface height position. The molten steel in the continuous casting mold 10 is cooled in contact with the long sides 11 and 12 and the short sides 13b and 14b to form a solidified shell. Since the split gradient region L ₃ has a third thin slab 1 of a straight line approximating the solidification shrinkage profile P ₃ in the thickness direction of the solidification starting side of the solidified shell at the time of casting, split it is prevented that a gap is generated between the solidified shell and the long 11 and 12 the inner surface which is formed in the slope region L _3. Moreover, since the slope part which approximates the solidification shrinkage profile of the width direction of a slab is formed in the inner surface of short side 13b, 14b, a clearance gap generate | occur | produces between the solidification shell and the inner surface of short side 13b, 14b. Is suppressed. As a result, it is possible to divide the slope (in the coagulation initiator) in the region L ₃ performs cooling of the solidified shell efficiently promote the growth of the solidified shell thickness.

When the solidified shell enters the division gradient region L ₂ immediately below the division gradient region L ₃ , the division gradient region L ₂ has a solidification shrinkage profile P on the solidification start side in the thickness direction of the second thin slab. because it is formed in one straight line approximating the _2, although the gap between the split gradient region L ₂ of the inner surface and the solidified shell will occur, the solidified shell in the split gradient region L ₂ solidification shrinkage amount, becomes smaller than the solidification shrinkage of the solidified shell of the inside split gradient region L _3, a gap greatly increases is prevented. Incidentally, the short side 13b, on the inner surface of 14b, since the gradient portion that approximates the width direction of the solidification shrinkage profile of the slab are formed, divided also in the gradient region L _2, the solidified shell and short 13b, 14b Generation of a gap between the inner surface and the inner surface is suppressed. As a result, the solidified shell even enters the split gradient region L _2, the solidified shell is continued can be cooled, it can be grown the thickness of solidified shell.

Succeeded in, if the solidified shell enters the split gradient region L ₁ immediately below the divided gradient region L _2, divided gradient region L ₁ approximates the minimum thickness of the thickness direction of the slab solidification shrinkage profile P ₁ because it is formed by multi-taper, further it will be a gap occurs, the solidification shrinkage of the solidified shell in the divided gradient in region L ₁ between the divided gradient region L ₁ of the inner surface and the solidified shell, since split gradient region L is smaller than the solidification shrinkage of the solidified shell at the inside _2, a gap is prevented to increase further greatly. On the other hand, the short side 13b, on the inner surface of 14b, since the gradient portion that approximates the width direction of the solidification shrinkage profile of the slab are formed, divided also in the gradient region L _1, the solidified shell and short 13b, 14b Generation of a gap between the inner surface and the inner surface is suppressed. Therefore, solidified shell even enters the split gradient region L _1, the solidified shell is continued can be cooled, can be grown the thickness of solidified shell. As a result, it is possible to avoid the occurrence of a solidification delay in the solidified shell, and to prevent cracking of the solidified shell and to manufacture a high quality slab.

(Example)
When the thickness of the slab to be cast is changed, the short side having a width corresponding to the thickness of the slab is changed. The continuous casting mold capable of casting slabs of three types (200 mm, 250 mm, and 300 mm) was produced. Here, the height (long side, short side height) of the mold space is 900 mm, and the lower end width between the short sides of the mold space is 1200 mm.

The taper ratio of the uppermost part formed in the short side (range from the upper end of the short side to 200 mm below) is 3% / m, and the taper ratio of the second part from the top (the range from 200 mm below the upper end of the short side to 200 mm below) is 2% / m, the taper rate of the third part from the top (range from 400 mm below the upper end of the short side to 200 mm below) is 1.5% / m, the lowest part (the range from 600 mm below the upper end of the short side to 300 mm below) The taper rate is 1.0% / m.

The lowermost division gradient area formed on the long side (the area from the position 240 mm below the upper end of the long side to the position 660 mm below (the lower end of the long side)) is formed from two straight lines connected to each other, and from the upper end of the long side The taper rate in the range from 240 mm below to 260 mm below is 1.6% / m, and the taper rate in the range from 500 mm below to 400 mm below from the upper end of the long side is 1.0% / m. The second divided gradient region from the bottom (the range from 160 mm below the upper end of the long side to 80 mm below) is formed by a straight line having a taper rate of 2.5% / m. Further, the third divided gradient region from the bottom (in the range from 80 mm below the upper end of the long side to 80 mm below) is formed as a straight line having a taper ratio of 3.7% / m. Note that the uppermost divided gradient region (the range from the upper end of the long side to the lower 80 mm) is formed by a straight line having a taper ratio of 2.0% / m.

A continuous casting mold is constructed using a short side for casting a slab having a thickness of 300 mm, and the upper end of the third divided gradient region from the bottom of the long side of the continuous casting mold (80 mm below the top of the long side) is molten steel. The shrinkage profile of the solidified shell formed in the continuous casting mold was simulated when the molten steel was poured so as to be at the molten metal surface height and continuous casting was performed.

FIG. 3 shows the shrinkage profile of the solidified shell when casting a slab having a thickness of 300 mm, and the upper end portion (position 80 mm below the upper end of the long side) of the third divided gradient region from the bottom of the long side of the continuous casting mold. The relationship with the distribution of the shrinkage | contraction amount which shows the reduction | decrease of the inner width between mold long sides when molten steel is poured so that it may become the molten metal surface height position of molten steel is shown. From FIG. 3, when the molten steel surface height position of the molten steel is set to be 80 mm below the upper end of the long side, the shrinkage profile of the solidified shell and the shrinkage amount of the inner width between the long sides are about 200 mm below the molten metal surface. The range shows a good match. For this reason, in this range, the solidified shell can be sufficiently cooled, and the growth of the solidified shell thickness can be promoted.

Further, the distribution of the shell thickness at the corner of the solidified shell when casting a 300 mm thick slab using a continuous casting mold was obtained by calculation. FIG. 4 shows the calculation result of the shell thickness distribution. In the distribution of the shell thickness shown in FIG. 4, as shown in FIG. 5, the solidified shell starts from the corner of the solidified shell and the direction toward the center in the long side width direction is the negative region of the horizontal axis. The direction toward the center side in the short side width direction is shown as a positive region on the horizontal axis.

As shown in FIG. 4, regarding the distribution of the shell thickness of the solidified shell facing the short side, the center side in the width direction from the corner portion to the short side at a position (200 mm level) 200 mm below the position of the molten metal in the continuous casting mold. A portion having a minimum thickness is formed at a position of about 20 mm, but the thickness decreases as it goes downward from the upper end of the continuous casting mold (that is, as the thickness of the solidified shell increases). The difference is gradually eliminated, and the minimum portion of the shell thickness disappears at the lower end of the continuous casting mold.
This is because a gap is formed between the solidified shell and the inner surface of the short side by forming, on the inner surface of the short side, a gradient portion consisting of four multitapes approximating the solidification shrinkage profile in the width direction of the slab of 1200 mm width. It is possible to suppress the occurrence of the solidified shell, and the solidified shell can be uniformly grown by continuously cooling the solidified shell.

Regarding the distribution of the shell thickness of the solidified shell facing the long side, a portion where the thickness is minimized is not formed in the range of 400 mm downward (400 mm level) from the position of the molten metal in the continuous casting mold. This is because, in the range of 400 mm downward from the molten steel surface height position, the generation of a gap between the solidified shell and the long side inner surface is suppressed, and the solidified shell is efficiently cooled. This corresponds to the fact that the thickness can grow uniformly.
On the other hand, at a position 600 mm below the level of the molten metal surface in the continuous casting mold (600 mm level), a portion having a minimum thickness appears at a position about 30 mm from the corner to the center in the width direction of the long side. The difference from the thickness of the central portion in the width direction of the steel tends to increase toward the lower end of the continuous casting mold. This is because the gap generated between the solidified shell and the long side inner surface gradually expands in the range exceeding 600 mm below the molten steel surface height position, as shown in FIG. This corresponds to the fact that the cooling effect of the shell gradually decreases and the solidified shell thickness is difficult to grow uniformly. However, the reduction rate of the thickness with respect to the thickness (20 mm) of the long side of the long side of the solidified shell is as small as 10%, and the solidified shell is continuously cooled (the thickness of the solidified shell grows). It is considered that the occurrence of a solidification delay in the solidified shell can be avoided.

(Comparative example)
In the continuous casting mold for casting slab having a thickness of 300 mm configured in the example, the bottom end of the third division gradient region from the bottom of the long side of the continuous casting mold (position 160 mm below the top of the long side) is the molten steel surface. A simulation of the shrinkage profile of the solidified shell formed in the continuous casting mold was performed when molten steel was poured into the height position and continuous casting was performed.

FIG. 6 shows the contraction profile of the solidified shell when a 300 mm thick slab is cast, and the lower end of the third divided gradient region from the bottom of the mold long side (160 mm below the top of the long side) is molten steel. The relationship with the distribution of the shrinkage | contraction amount which shows the reduction | decrease of the internal width between mold long sides when molten steel is poured so that it may become a molten metal surface height position is shown. FIG. 6 shows that when the molten steel surface height position of the molten steel is set to be 160 mm below the upper end of the long side, a gap is formed between the solidified shell and the long side inner surface and expands.
Further, the distribution of the shell thickness at the corner of the solidified shell in the case of casting a slab of 300 mm thickness using the continuous casting mold of the comparative example was obtained by calculation. FIG. 7 shows the calculation result of the shell thickness distribution.

As shown in FIG. 7, regarding the distribution of the thickness of the solidified shell facing the long side, at a position 200 mm below the upper end of the continuous casting mold, a position of about 20 mm from the corner to the center in the width direction of the long side. A portion having a minimum thickness occurs, and the difference from the thickness of the central portion in the width direction of the long side of the solidified shell tends to increase toward the lower end of the continuous casting mold. As shown in FIG. 6, since a large gap is generated between the solidified shell and the long side inner surface from the beginning, it is considered that the solidified shell is not sufficiently cooled by the long side.
On the other hand, regarding the distribution of the shell thickness of the solidified shell facing the short side, at a position 200 mm below the upper end of the continuous casting mold, the thickness is about 15 to 20 mm from the corner to the center in the width direction of the short side. Is formed, and as it goes to the lower end of the continuous casting mold (that is, as the thickness of the solidified shell increases), the thickness of the short side of the solidified shell with the thickness of the central portion in the width direction The difference is substantially constant, and the place where the thickness becomes minimum gradually moves toward the center in the width direction of the short side. As shown in FIG. 6, a large gap is generated between the solidified shell and the inner surface of the long side, as shown in FIG. 6, in which the minimum thickness appearing in the shell thickness distribution of the solidified shell facing the short side does not disappear. Therefore, it is considered that the solidified shell is not sufficiently cooled even on the short side.
Therefore, the solidified shell is not sufficiently cooled (the thickness of the solidified shell is difficult to grow uniformly), and there is a possibility that solidification delay may occur in the solidified shell.

As described above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the configuration described in the above-described embodiment, and the matters described in the scope of claims. Other embodiments and modifications conceivable within the scope are also included.
Further, the present invention also includes a combination of components included in the present embodiment and other embodiments and modifications.
Further, in this embodiment, the continuous casting method for casting slabs with three types of thickness has been described. However, when slabs with two types of thickness are cast, slabs with four or more types of thicknesses are cast. Also in the case of casting, the continuous casting method of the present invention can be applied.
Furthermore, in the present embodiment, the molten steel surface height position of the molten steel is aligned with the upper end portions of the divided gradient regions L ₁ , L ₂ , L ₃ corresponding to the width of the slab determined by the selected short side. Although casting was performed, casting can be performed by setting the molten steel surface height position at an arbitrary position in the divided gradient regions L ₁ , L ₂ , and L ₃ .
In this embodiment, the continuous casting mold of the present invention is applied to a mold used in a vertical bending type continuous casting machine. However, the continuous casting mold of the present invention is used in a curved continuous casting machine. The present invention can also be applied to a casting mold (curved casting mold).

10: Continuous casting mold, 11, 12: Long side, 13, 14, 13a, 14a, 13b, 14b: Short side

Claims (5)

N types of short sides having a width corresponding to the thickness of the cast slab to be cast are exchangeably arranged between the long sides opposed to each other in a mold space portion formed in a vertically penetrating state. A continuous casting method capable of casting slabs of N types of thickness with molten steel,
Solidification shrinkage on the solidification start side of the slab determined by the widths of the short sides of N divided gradient regions communicating from the top to the bottom except for the uppermost portion on the long sides facing each other. Each of the molten steel surface height positions of the molten steel is set in the divided gradient region corresponding to the width of the slab determined by the selected short side. Casting method. 2. The continuous casting method according to claim 1, wherein a molten steel surface height position of the molten steel is adjusted to an upper end portion of the divided gradient region corresponding to a width of a slab determined by the selected short side. Continuous casting method. 3. The continuous casting method according to claim 1, wherein the divided gradient region at the bottom is formed by a plurality of straight lines approximated to a solidification shrinkage profile of the slab formed by the short side having the minimum width. A continuous casting method characterized. The continuous casting method according to any one of claims 1 to 3, wherein the divided gradient region formed at an upper position of the lowermost divided gradient region is approximated to a solidification shrinkage profile on the solidification start side. A continuous casting mold characterized by being formed by one straight line or two or more straight lines connected. 5. The continuous casting method according to claim 1, wherein a shape of a contour line of a side end surface of the short side is made to coincide with a shape of an inner contour line of the long side. Method.

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