JP6743872B2 - Method of expanding the width of the slab during continuous casting - Google Patents

Description

The present invention relates to a method for expanding the width of a slab in continuous casting of steel by moving a short side of a mold during continuous casting.

In the continuous casting of steel, in order to improve the productivity of the continuous casting machine, the width of the mold is changed (enlarged or reduced) during the continuous casting to carry out the continuous casting of multiple charges (referred to as "continuous casting"). A technique for manufacturing slab slabs having different slab widths at the same casting opportunity is widely used. In addition, the slab in the mold shrinks due to the temperature drop and tries to separate from the inner wall surface of the mold, but in order to prevent this, in the mold, the mold internal space becomes narrower toward the casting direction downstream side. , Taper is provided.

For example, in Patent Documents 1 to 3, first, the upper end of the mold short side is moved to the mold anti-center side at a faster moving speed than the lower end of the mold short side (step 1), and then the slab shrinkage amount and the mold short length are set. With the side taper amount and the mold short side moving speed matching, the upper and lower ends of the mold short side are moved parallel to the mold anti-center side at the same speed (step 2), and then the lower end of the mold short side is moved to the mold short side. A method has been proposed in which the slab width is expanded in three steps of moving the mold toward the center side opposite to the mold at a moving speed faster than the upper end of the side (step 3).

Step 1 is intended to increase the taper of the short side of the mold to suppress the generation of a gap (hereinafter referred to as “air gap”) between the short side of the mold and the slab when the mold is moved. The purpose of 3 is to restore the taper of the short side of the mold. Here, increasing the taper of the short side of the mold means that the upper end of the short side of the mold is located closer to the center of the mold than the lower end. In other words, the mold short side is inclined so that the mold short side surface on the side in contact with the molten steel faces the upper side in the vertical direction. Moreover, the mold anti-center side is the opposite side of the mold center position where the immersion nozzle is installed.

The width of the ingot during the continuous casting is changed by moving the short side of the mold during the continuous casting. Therefore, in order to change the slab width during continuous casting, a pair of opposing mold long sides and a pair of mold short sides sandwiched between the mold long sides and movable in the mold long sides are provided. A continuous casting mold is required.

JP-A-56-102353 JP 61-144255 A JP-A-11-179508

During the continuous casting, when the width of the slab is expanded in the three steps 1 to 3 described above, the faster the moving speed of the short side of the mold in the step 2, the less the slab is affected by the width change. However, in order to increase the moving speed of the short side of the mold in step 2, in order to prevent the air gap between the solidified shell of the short side of the slab and the short side of the moving mold, the mold short side is set in step 1. It is necessary to increase the side taper.

As shown in FIG. 1 described later, the mold short side is supported and driven by a prime mover at two upper and lower positions on the back surface of the mold short side. Close to the center of the mold. Therefore, if the taper of the short side of the mold is increased in step 1, the lower end of the short side of the mold projects toward the center of the mold with the lower support position as the rotation axis. That is, when the taper of the short side of the mold is increased, the solidified shell of the short side of the slab is pushed toward the center side of the mold by the lower end of the short side of the mold protruding to the center side of the mold, and there is a risk of breakout.

Further, the nonuniformity of the solidified shell changes depending on the composition of the steel, and the higher the nonuniformity of the solidified shell, the higher the susceptibility to cracking and the higher the risk of breakout. The nonuniformity of the solidified shell correlates with the ferrite potential of the steel composition.

The faster the moving speed of the mold short side when expanding the width of the slab, the less the slab is affected by the width change. However, in order to increase the taper of the short side of the mold, the moving speed of the short side of the mold in step 1 should be changed. If it is made too large, the solidified shell is pushed toward the center of the mold, and the risk of breakout becomes high especially in the case of steel grades with low nonuniformity of the solidified shell. That is, it is important for stable operation to set the maximum value of the moving speed of the short side of the mold in step 1 according to the nonuniformity of the solidified shell determined by the ferrite potential of the steel component.

From this viewpoint, when Patent Documents 1 to 3 are verified, Patent Documents 1 and 3 do not consider setting the moving speed of the short side of the mold according to the composition of the steel at all. On the other hand, in Patent Document 2, the acceleration rate of the moving speed of the short side of the mold is obtained by using the deformation resistance of the solidification shell as a parameter, but the deformation resistance of the solidification shell correlates with the nonuniformity of the solidification shell. However, the deformation resistance of the solidified shell differs from the nonuniformity of the solidified shell.

That is, according to Patent Documents 1 to 3, the trouble at the time of expanding the slab width during casting was reduced, but Patent Documents 1 to 3 set the moving speed of the mold short side according to the nonuniformity of the solidified shell. Things have not been done and there is room for improvement.

The present invention has been made in view of the above circumstances, and an object of the invention is to increase the width of a cast piece by moving the mold short side during continuous casting, and to eliminate the solidification shell determined by the ferrite potential of the cast piece. An object of the present invention is to provide a method for enlarging the width of a cast piece by setting the allowable moving speed of the short side of the mold according to the uniformity and preventing breakout due to the solidified shell being pushed by the lower end of the short side of the mold.

The gist of the present invention for solving the above problems is as follows.
[1] During continuous casting of steel, while controlling the moving speed of the upper end of the mold short side and the moving speed of the lower end of the mold short side independently of each other, casting is performed by moving the mold short side to the mold anti-center side. A method for expanding the width of a piece, which is a method for expanding the width of a slab during continuous casting,
The continuous casting, characterized in that the moving speed of the mold short side is set to a speed equal to or lower than the maximum allowable moving speed set according to the nonuniformity of the solidified shell of the slab, which is determined by the ferrite potential of the slab. How to increase the width of the slab.
[2] During continuous casting of steel, the moving speed of the upper end of the mold short side is higher than the moving speed of the lower end of the mold short side, and the difference between the moving speed of the upper end and the moving speed of the lower end is constant. While maintaining the step 1 of moving the short side of the mold to the center side of the mold opposite to the center of the mold, the moving speed of the upper end of the short side of the mold and the moving speed of the lower end of the short side of the mold are kept equal and the short side of the mold is moved at the constant speed. Step 2 of performing parallel movement to the center side, the moving speed of the upper end of the mold short side is slower than the moving speed of the lower end of the mold short side, and the difference between the moving speed of the upper end and the moving speed of the lower end is made constant. A slab during continuous casting, in which the short side of the mold is moved to the center side of the mold and the width of the slab is expanded by moving the short side of the mold to the center side of the mold in three steps of maintaining and moving the short side of the mold to the center side of the mold How to increase the width,
In the step 1, the moving speed of the short side of the mold is set to a speed equal to or lower than the maximum allowable moving speed set according to the nonuniformity of the solidified shell of the slab, which is determined by the ferrite potential of the slab. The method of expanding the width of the slab during continuous casting.
[3] During continuous casting of steel, the moving speed of the upper end of the mold short side is higher than the moving speed of the lower end of the mold short side, and the difference between the moving speed of the upper end and the moving speed of the lower end is constant. While maintaining the step 1 of moving the short side of the mold to the center side of the mold opposite to the center of the mold, the moving speed of the upper end of the short side of the mold and the moving speed of the lower end of the short side of the mold are kept equal and the short side of the mold is moved at the constant speed. Step 2 of performing parallel movement to the center side, the moving speed of the upper end of the mold short side is slower than the moving speed of the lower end of the mold short side, and the difference between the moving speed of the upper end and the moving speed of the lower end is made constant. A slab during continuous casting, in which the short side of the mold is moved to the center side of the mold and the width of the slab is expanded by moving the short side of the mold to the center side of the mold in three steps of maintaining and moving the short side of the mold to the center side of the mold How to increase the width,
In the step 1, the maximum moving speed V _max of the mold short side determined by the following formula (1) is determined based on the ferrite potential defined by the following formula (2) according to the composition of the cast slab. The moving speed V _{U at} the upper end of the mold short side and the moving speed V _{L at} the lower end of the mold short side are set to be equal to or lower than the maximum allowable moving speed _Vable calculated by any one of the expressions (4) to (6). Is set based on the following equation (7) and the following equation (8),
In the step 2, the moving speed V _U of the upper end of the mold short side and the moving speed V _L of the lower end of the mold short side are set based on the following formula (9),
In the step 3, the moving speed V _U of the upper end of the mold short side and the moving speed V _L of the lower end of the mold short side are set based on the following formulas (10) and (11). How to increase the width of the slab during casting.
(I) Step _{1 (0 ≦ t ≦ t 1} )
_{V max = (V C / L} m) × θ B × t 1 ......... (1)
Fp=2.5×(0.5-Cp)... (2)
Here, Cp in the equation (2) is calculated by the following equation (3).
Cp=[%C]-0.0022×[%Si]+0.019×[%Mn]-0.179×[%P]+2.258×[%S]+0.019×[%Cu]+0.025×[%Ni]-0.0022 ×[%Cr]-0.04×[%Mo]-0.058×[%V]-0.438×[%Nb]-0.1226×[%Al]+0.376×[%N] ………(3)
When Fp<0.90 and 1.05<Fp; _Vable ≦3.5×θ _B ... (4)
When 0.90≦Fp<0.95; _Vable ≦3.0×θ _B ... (5)
When 0.95≦Fp≦1.05: _Vable ≦2.0×θ _B ... (6)
V _U =(V _C /L _m )×θ _B ×t... (7)
_{V L = (V C / L} m) × θ B × t-θ B ......... (8)
(II) Step 2 (t ₁ <t<t ₁ +t ₂ ).
V _U =V _L =V _P ≦V _max ....(9)
(III) Step 3 (t ₁ +t ₂ ≦t≦t ₁ +t ₂ +t ₃ ).
_{V U = (V C / L} m) × (θ B × t 1 -θ M × t) -θ M ......... (10)
_{V L = (V C / L} m) × (θ B × t 1 -θ M × t) ......... (11)
Here, V _max is the maximum moving speed (mm/min), V _C is the casting speed (mm/min), L _m is the mold length (mm), θ _B is the lower end deformation speed allowable amount (mm/min), and Fp. maximum allowable moving speed (mm / min) is ferrite _{potential, V ABLE} is, _{V U} is the moving speed of the upper end of the mold (mm / min), _{V L} is the moving speed of the lower end of the mold (mm / min), _{V P} is The parallel movement speed (mm/min) in step 2, θ _M is the upper limit deformation speed allowable amount (mm/min), t is the elapsed time from the start of the width change (min), and t ₁ is the time required for step 1 (min) , T ₂ is the time required for step 2 (min), and t ₃ is the time required for step 3 (min). Further, [%C] in the equation (3) is the carbon concentration (mass%) of the slab, similarly, [%Si] is the silicon concentration (mass%), and [%Mn] is the manganese concentration (mass%). , [%P] is phosphorus concentration (mass%), [%S] is sulfur concentration (mass%), [%Cu] is copper concentration (mass%), [%Ni] is nickel concentration (mass%), % Cr] is chromium concentration (mass %), [% Mo] is molybdenum concentration (mass %), [% V] is vanadium concentration (mass %), [% Nb] is niobium concentration (mass %), [% Al] ] Is aluminum concentration (mass %), [%N] is nitrogen concentration (mass %).

According to the present invention, when expanding the slab width during continuous casting, the mold short side is set at a speed equal to or lower than the maximum allowable moving speed set according to the nonuniformity of the solidified shell determined by the ferrite potential of the slab. Since it moves, the taper of the short side of the mold does not become excessively large, the indentation of the solidified shell of the slab by the lower end of the short side of the mold is reduced, and the occurrence of strain in the solidified shell is suppressed. As a result, it is possible to prevent the occurrence of breakout when the width is changed, even if the solidified shell has high nonuniformity.

It is a perspective view showing an example of a variable width mold used by the present invention. It is a figure which shows the moving speed of the upper end and lower end of a mold short side at the time of changing the width of a cast piece based on this invention. It is a schematic diagram which shows the movement condition of the mold short side at the time of slab width expansion based on this invention.

The method for expanding the mold width during continuous casting according to the present invention will be specifically described below. First, a continuous casting mold (hereinafter, referred to as “variable width mold”) capable of changing a slab width (mold width) during continuous casting of steel used in the present invention will be described.

FIG. 1 is a perspective view showing an example of a variable width mold used in the present invention. As shown in FIG. 1, a variable width mold 1 capable of changing a slab width during continuous casting is sandwiched between a pair of opposing mold long sides 2 and an opposing mold long side 2 and has an opposing mold length. It is composed of a mold short side 5 slidable between the sides 2. The mold long side 2 comprises a long side copper plate 3 and a long side backup frame 4, and the mold short side 5 comprises a short side copper plate 6 and a short side backup frame 7. The long side copper plate 3 and the short side copper plate 6 are provided with grooves (not shown) or holes (not shown) for passing cooling water, and the long side backup frame 4 and the short side backup frame 7 are provided. A water box (not shown) for supplying cooling water is installed.

A clamp force adjusting device 8 is installed on the mold long side 2 on one side, and the clamping force adjusting device 8 controls the clamping force of the mold short side 5 by the mold long side 2. Further, on the back surface of the mold short side 5, there are installed prime movers 9 such as electric motors and hydraulic motors at two positions, and by operating this prime mover 9, the mold short sides 5 are formed on opposite sides of the mold long side. The space between the two is slid in the lateral direction while being in contact with the long side copper plate 3, and the width of the mold, that is, the width of the slab can be freely changed. By independently operating the two prime movers 9 at the upper and lower positions, it is possible to move the mold short side 5 in various forms different from each other. Reference numeral 10 is a sliding surface which is a contact surface of the short side copper plate 6 with the long side copper plate 3, and 11 is a spindle which connects the prime mover 9 and the mold short side backup frame 7.

The clamping force by the clamping force adjusting device 8 is such that no gap is created between the long side 2 and the short side 5 of the mold due to the static pressure of the molten steel injected into the internal space of the mold of the variable width mold 1 during casting. , And is controlled to be larger than the static pressure of molten steel acting on the long side 2 of the mold. Similarly, when changing the width of the slab during casting, control is performed so that no gap is created between the long side 2 of the mold and the short side 5 of the mold. However, when changing the width of the slab during casting, in order to facilitate the movement of the short side 5 of the mold, the clamping force by the clamping force adjusting device 8 becomes weaker than when the width of the slab is not changed. Is controlled.

FIG. 2 shows the moving speeds of the upper end and the lower end of the mold short side 5 when changing the width of the slab according to the present invention. In FIG. 2, the moving speed is indicated by + (positive) when moving toward the center of the mold and by-(negative) when moving toward the center of the mold. In FIG. 2, the solid line indicates the moving speed (V _U ) at the upper end of the mold short side, and the broken line indicates the moving speed (V _L ) at the lower end of the mold short side.

As shown in FIG. 2, in the present invention, in expanding the width of the slab, the moving speed V _U of the upper end of the mold short side 5 is higher than the moving speed V _L of the lower end of the mold short side 5, and Step 1 of moving the mold short side 5 to the mold anti-center side while keeping the difference (difference=θ _B ) between the moving speed V _{U of the} upper end and the moving speed V _{L of the} lower end constant; Step 2 in which the moving speed V _{U of the} upper end and the moving speed V _L of the lower end of the mold short side 5 are kept equal and the short side 5 of the mold is moved parallel to the center side of the mold at a constant speed (parallel moving speed V _P ). , The moving speed V _U of the upper end of the mold short side 5 is slower than the moving speed V _L of the lower end of the mold short side 5, and the difference (difference between the moving speed V _{U of the} upper end and the moving speed V _{L of the} lower end). =θ _M ) is kept constant, and the mold short side 5 is moved to the mold anti-center side in three steps, ie, step 3 of moving the mold short side 5 to the mold anti-center side.

FIG. 3 is a schematic view showing the movement state of the mold short side 5 at the time of expanding the width of the cast piece, in which the mold short side indicated by the solid line indicates the position of the mold short side before the start of width expansion and after the end of width expansion. The short side of the mold shown by means the movement of the short side of the mold when the width is enlarged. The moving speed in each step will be described below.

In step 1, the moving speed V _U of the upper end of the mold short side 5 is gradually increased with the lapse of time, and step 1 is continued until the maximum moving speed V _max is reached. When the moving speed V _U reaches the maximum moving speed V _max , the process proceeds to step 2.

In the present invention, the maximum moving speed V _max is set as follows.

The non-uniformity of the solidified shell of the slab changes depending on the composition of the slab, and the higher the non-uniformity of the solidified shell, the higher the susceptibility to cracking and the higher the risk of breakout. That is, it is necessary to suppress the moving speed of the short side 5 of the mold when changing the width of the slab of steel in which the solidification shell has high nonuniformity. The non-uniformity of the solidified shell correlates with the ferrite potential obtained from the composition of the slab.

According to publication 1, ferrite potential slab, the composition of the slab is defined by the following equation (2) (publication _{1; M.wolf, 1 st European Conference} on continuous casting, 1991, 2489 -2499).

Fp=2.5×(0.5-Cp)... (2)
Here, Fp is a ferrite potential, and Cp in the equation (2) is calculated by the following equation (3).

Cp=[%C]-0.0022×[%Si]+0.019×[%Mn]-0.179×[%P]+2.258×[%S]+0.019×[%Cu]+0.025×[%Ni]-0.0022 ×[%Cr]-0.04×[%Mo]-0.058×[%V]-0.438×[%Nb]-0.1226×[%Al]+0.376×[%N] ………(3)
Here, [%C] in the equation (3) is the carbon concentration (mass%) of the slab, similarly, [%Si] is the silicon concentration (mass%), and [%Mn] is the manganese concentration (mass%). ), [%P] is phosphorus concentration (mass %), [%S] is sulfur concentration (mass %), [%Cu] is copper concentration (mass %), [%Ni] is nickel concentration (mass %), [%Cr] is chromium concentration (mass %), [%Mo] is molybdenum concentration (mass %), [%V] is vanadium concentration (mass %), [%Nb] is niobium concentration (mass %), [% [Al] is the aluminum concentration (mass %), and [% N] is the nitrogen concentration (mass %).

The solidification form of steel changes according to the value of the ferrite potential Fp. That is, when the ferrite potential Fp is less than 0.90 and more than 1.05, hypoperitectic solidification hardly occurs, and a uniform solidified shell is likely to be generated. That is, the nonuniformity of the solidified shell is low. On the other hand, in the range where the ferrite potential Fp is 0.90 or more and 1.05 or less, hypoperitectic solidification occurs, and the nonuniformity of the solidified shell is high. Particularly, in the range where the ferrite potential Fp is 0.95 or more and 1.05 or less, the nonuniformity of the solidified shell is high. Here, sub-peritectic solidification means that in the iron-carbon system equilibrium diagram, the carbon concentration is lower than the peritectic point at which the carbon concentration is 0.17 mass% (there are also references to "0.18 mass%"). This is a solidification form in which the residual liquid phase and primary crystal δ-iron, which occur in the low region, are solidified at a peritectic temperature all at once and γ-iron is produced. Equilibriumly, if the carbon concentration is 0.09 mass% or less, solidification is completed at a temperature above the peritectic temperature and subperitectic solidification does not occur, while the carbon concentration exceeds 0.17 mass%. For example, it becomes a hyperperitectic region, and in this case, subperitectic solidification does not occur.

In the present invention, the maximum allowable moving speed _Vable (mm/min) of the mold short side 5 is set according to the following formulas (4), (5) and (6) according to the ferrite potential Fp determined by the composition of the slab. Set with an expression. Θ _B in the equations (4) to (6) is a lower limit deformation rate allowable amount (mm/min) determined by the composition of the cast piece, and θ _B is a crack surface observed in actual operation and cracks are observed. It is the allowable deformation speed amount (mm/min) in which “cracking does not occur”, which is calculated from the widening operation condition of the slab that has not occurred, and is a value obtained from accumulated data of past slab survey results.

When Fp<0.90 and 1.05<Fp; _Vable ≦3.5×θ _B ... (4)
When 0.90≦Fp<0.95; _Vable ≦3.0×θ _B ... (5)
When 0.95≦Fp≦1.05: _Vable ≦2.0×θ _B ... (6)
As shown in the formulas (4) to (6), the maximum permissible transfer speed _Vable is increased in the slab in the composition range in which the hypoperitectic solidification does not occur, and the slab in the composition range in which the subperitectic solidification occurs is increased. , The maximum allowable movement speed _Vable is reduced. In the composition range in which the ferrite potential Fp in which the hypoperitectic solidification most remarkably occurs is 0.95 or more and 1.05 or less, the maximum allowable moving speed _Vable is reduced particularly.

In step 1, the moving speed V _U of the upper end of the mold short side 5 is increased in proportion to the elapsed time t from the start of the width change, and the maximum moving speed V _max (mm/min) of the mold short side 5 is as follows. It is calculated by the equation (1).

_{V max = (V C / L} m) × θ B × t 1 ......... (1)
Here, V _C is the casting speed (mm/min), L _m is the mold length (mm), and t ₁ is the time required for step 1 (min).

In the present invention, the maximum moving speed V _max is determined based on the ferrite potential Fp defined by the above equation (2) according to the composition of the ingot during casting, among the above equations (4) to (6). Control is performed within a range that is equal to or lower than the maximum allowable moving speed _V.sub.able calculated by any of the equations. Further, the maximum moving speed V _max is controlled within a range equal to or lower than the maximum allowable moving speed _Vable , and the moving speed V _U (mm/min) of the upper end of the mold short side 5 is set based on the following formula (7). In addition, the moving speed V _L (mm/min) of the lower end of the mold short side 5 is set based on the following equation (8). In the equations (7) and (8), t is the elapsed time (min) from the start of the width change.

V _U =(V _C /L _m )×θ _B ×t... (7)
_{V L = (V C / L} m) × θ B × t-θ B ......... (8)
That is, the upper end of the mold short side 5 is moved to the mold anti-center side according to the above equation (7) until the moving speed V _{U of the} upper end reaches the maximum moving speed V _max . Therefore, the required time t ₁ of step 1 changes depending on the magnitude of the maximum moving speed V _max . Specifically, if the maximum moving speed V _max becomes small, the time t ₁ required for step 1 becomes short, and the increase amount of the taper of the mold short side 5 also becomes small. In other words, for steel having a high degree of non-uniformity in the solidified shell, the required time t ₁ is short, and the taper of the short side 5 of the mold is small. In step 1, the difference between the moving speed V _{U at} the upper end of the mold short side 5 and the moving speed V _{L at the} lower end becomes a constant value (θ _B ).

When the moving speed V _U of the mold short side 5 reaches the maximum moving speed V _max , the moving speed V _U of the upper end of the mold short side 5 and the moving speed V _L of the lower end of the mold short side 5 are maintained equal and constant. The process moves to step 2 in which the short side 5 of the mold is translated to the center side opposite to the mold at a speed.

The parallel movement speed V _P (mm/min) during the parallel movement is within a range that satisfies the following expression (9).

V _U =V _L =V _P ≦V _max ....(9)
That is, in step 2, the mold short side 5 is moved in parallel to the mold anti-center side at an arbitrary constant speed equal to or lower than the maximum moving speed V _max . However, in order to shorten the width change time, it is preferable that the parallel movement speed V _P be the same as the maximum movement speed V _max .

The required time t ₂ (min) of step 2 is determined by the target width change amount. For example, if the absolute value of the acceleration of the moving speed in step 1 and the absolute value of the deceleration of the moving speed in step 3 are the same, the required time t ₁ (min) in step ₁ and the required time t ₃ (in step 3) min) and the moving distance in step 1 and the moving distance in step 3 are also the same. Thus, the moving distance in step ₂ is calculated, and the required time t _{2 of} step ₂ is calculated by dividing the calculated moving distance by the parallel moving speed V _P in step 2. Even when the absolute value of the acceleration of the moving speed in step 1 and the absolute value of the deceleration of the moving speed in step 3 are not the same, the required time t ₂ of step 2 can be obtained by the target width change amount by a similar method. it can.

When the short side 5 of the mold is translated to the center side opposite to the mold at the translation speed V _P for the required time t ₂ , the process proceeds to step 3.

In Step 3, the moving speed V _U (mm/min) of the upper end of the mold short side 5 is set based on the following equation (10), and the moving speed V _L (mm/min) of the lower end of the mold short side 5 is set. ) Is set based on the following equation (11). In the equations (10) and (11), θ _M is the upper limit deformation speed allowable amount (mm/min) determined by the composition of the cast piece, and t is the elapsed time (min) from the start of width change. Like the above-mentioned θ _B , θ _M is the allowable deformation rate “without cracking” calculated from the operating condition of widening the slab without cracks by observing the surface of the slab in actual operation. Amount (mm/min), which is a value obtained from accumulated data of past slab survey results.

_{V U = (V C / L} m) × (θ B × t 1 -θ M × t) -θ M ......... (10)
_{V L = (V C / L} m) × (θ B × t 1 -θ M × t) ......... (11)
In step 3, the difference between the moving speed V _{U at the} upper end and the moving speed V _{L at the} lower end becomes a constant value (θ _M ). Further, also in step 3, it is preferable that the moving speed V _L of the lower end of the mold short side 5 is equal to or less than the maximum moving speed V _max obtained by the equation (1).

If the periods of step 1, step 2, and step 3 are displayed by the elapsed time t from the start of the width change, step 1 is the period of “0≦t≦t ₁ ”, step 2 is “t ₁ <t<t ₁ +t ₂ ” period, step 3 is a period of “t ₁ +t ₂ ≦t≦t ₁ +t ₂ +t ₃ ”.

As described above, according to the method for expanding the slab width during continuous casting according to the present invention, when expanding the slab width during continuous casting, the nonuniformity of the solidified shell determined by the ferrite potential of the slab Since the mold short side is moved at a speed equal to or lower than the maximum allowable movement speed set according to, the taper of the mold short side does not become excessively large, and the indentation of the slab solidified shell by the lower end of the mold short side is reduced, Generation of strain in the solidified shell is suppressed. As a result, it is possible to prevent the occurrence of breakout at the time of changing the width even in the case of steel having a high degree of nonuniformity in the solidified shell.

By FEM simulation, the stress generated in the solidified shell is evaluated for each condition of changing the width of the slab during continuous casting in the slab continuous casting machine and for each chemical composition of steel, and the amount of deformation of the solidified shell exceeds a predetermined threshold value. Whether or not the risk of breakout was evaluated.

Targeting carbon steel having a carbon concentration of 0.01 to 0.20 mass%, the length from the meniscus of the mold to the mold outlet is 800 mm, the thickness of the cast piece is 250 mm, and the cast piece width before widening is 1250 mm, The short side of the mold was moved in the pattern shown in FIG. 2 to perform FEM simulation.

Table 1 shows the casting conditions when expanding the width of the slab, the width change amount, the ferrite potential of each steel type, the lower limit deformation speed allowable amount θ _B , the maximum allowable movement speed _Vable determined from the ferrite potential, and the maximum movement of the short side of the mold. The velocity V _max and the breakout risk of the solidified shell evaluated by the simulation are shown. In Table 1, in the remarks column, conditions under which the width of the slab is changed within the scope of the present invention are indicated as "invention examples", and other conditions are indicated as "comparative examples".

The stress and strain when the solidified shell on the short side of the slab was pushed in at the lower end of the mold during width expansion were analyzed by FEM simulation to determine the breakout risk of the solidified shell. At that time, since the strain was greatest at the center of the thickness of the short side of the cast slab, the breakout risk was determined based on this strain. As a reference, the analysis result under the condition when the breakout occurred in the actual machine was used as the limit strain, and this limit strain was used as the threshold value to judge the risk of breakout.

It was found that when the width change condition according to the present invention was adopted when expanding the width of the slab during continuous casting, the strain generated in the solidified shell was small and the risk of breakout was reduced. On the other hand, it has been found that when the width of the slab is increased outside the scope of the present invention, the strain generated in the solidified shell increases and the risk of breakout also increases.

Specifically, for example, comparing the conditions 1 and 11 in which the ferrite potentials are the same, the maximum moving speed _max of the mold short side is 18.0 mm/min, which is higher than the maximum allowable moving speed _able. Then, since the amount of deformation of the solidified shell due to the movement of the mold short side exceeds the threshold value that there is a risk of breakout as described above, the breakout risk is “×”, that is, “there is a risk of breakout”. Has become.

On the other hand, under the condition 1 in which the maximum moving speed _max of the mold short side is 12.0 mm/min, the maximum moving speed _max of the mold short side is smaller than the maximum allowable moving speed _able, which is caused by the movement of the mold short side. The amount of deformation of the solidified shell does not reach the above-mentioned threshold value indicating that there is a risk of breakout, and the breakout risk level is “◯”, that is, “no breakout risk”.

In the above embodiment, the spindle which connects the prime mover 9 and the mold short side backup frame 7 when the width between the upper ends of the two mold short sides 5 facing each other in step 1 is widened when the width is widened. 11 specifically shows a method for preventing a breakout that occurs when the lower end side of the mold short side 5 pushes the solidified shell at a position lower than the connecting portion on the mold short side of 11 in FIG. ..

On the other hand, also in step 3 which is the end stage of width expansion, the interval between the mold short sides on the lower end side of the mold short side 5 below the connecting portion of the spindle 11 widens just before the end of step 3. Therefore, the contact between the short side of the mold and the solidified shell may become uneven depending on the location, and the solidified shell may also grow unevenly, increasing the risk of breakout. With respect to the breakout in step 3, the operating conditions in step 3 represented by the equations (10) and (11) described above are the same as those in the method of preventing the breakout in step 1 described above. It is effective in preventing

Although the embodiments to which the present invention is applied have been described above, the present invention is not limited to the description and the drawings that form part of the disclosure of the present invention according to the present embodiments.

1 Width variable mold 2 Mold long side 3 Long side copper plate 4 Long side backup frame 5 Mold short side 6 Short side copper plate 7 Short side backup frame 8 Clamping force adjusting device 9 Motor 10 Sliding surface 11 Spindle

Claims (3)

During continuous casting of steel, while independently controlling the moving speed of the upper end of the mold short side and the moving speed of the lower end of the mold short side, the short side of the mold is moved to the mold anti-center side and the width of the slab. Is a method of expanding the width of a slab during continuous casting,
The continuous casting, characterized in that the moving speed of the mold short side is set to a speed equal to or lower than the maximum allowable moving speed set according to the nonuniformity of the solidified shell of the slab, which is determined by the ferrite potential of the slab. How to increase the width of the slab. During continuous casting of steel, the moving speed of the upper end of the mold short side is faster than the moving speed of the lower end of the mold short side, and the difference between the moving speed of the upper end and the moving speed of the lower end is kept constant. Step 1 of moving the mold short side toward the mold anti-center side, and maintaining the moving speed of the upper end of the mold short side and the moving speed of the lower end of the mold short side equal to each other, keeping the mold short side toward the mold anti-center side at a constant speed. Step 2 of moving in parallel, the moving speed of the upper end of the mold short side is slower than the moving speed of the lower end of the mold short side, and maintaining a constant difference between the moving speed of the upper end and the moving speed of the lower end. Step 3 of moving the short side of the mold to the center side opposite to the mold, and expanding the width of the slab by moving the short side of the mold to the center side opposite to the mold, increasing the width of the slab during continuous casting. Method,
In the step 1, the moving speed of the short side of the mold is set to a speed equal to or lower than the maximum allowable moving speed set according to the nonuniformity of the solidified shell of the slab, which is determined by the ferrite potential of the slab. The method of expanding the width of the slab during continuous casting. During continuous casting of steel, the moving speed of the upper end of the mold short side is faster than the moving speed of the lower end of the mold short side, and the difference between the moving speed of the upper end and the moving speed of the lower end is kept constant. Step 1 of moving the mold short side toward the mold anti-center side, and maintaining the moving speed of the upper end of the mold short side and the moving speed of the lower end of the mold short side equal to each other, keeping the mold short side toward the mold anti-center side at a constant speed. Step 2 of moving in parallel, the moving speed of the upper end of the mold short side is slower than the moving speed of the lower end of the mold short side, and maintaining a constant difference between the moving speed of the upper end and the moving speed of the lower end. Step 3 of moving the short side of the mold to the center side opposite to the mold, and expanding the width of the slab by moving the short side of the mold to the center side opposite to the mold, increasing the width of the slab during continuous casting. Method,
In the step 1, the maximum moving speed V _max of the mold short side determined by the following formula (1) is determined based on the ferrite potential defined by the following formula (2) according to the composition of the cast slab. The moving speed V _{U at} the upper end of the mold short side and the moving speed V _{L at} the lower end of the mold short side are set to be equal to or lower than the maximum allowable moving speed _Vable calculated by any one of the expressions (4) to (6). Is set based on the following equation (7) and the following equation (8),
In the step 2, the moving speed V _U of the upper end of the mold short side and the moving speed V _L of the lower end of the mold short side are set based on the following formula (9),
In the step 3, the moving speed V _U of the upper end of the mold short side and the moving speed V _L of the lower end of the mold short side are set based on the following formulas (10) and (11). How to increase the width of the slab during casting.
(I) Step _{1 (0 ≦ t ≦ t 1} )
_{V max = (V C / L} m) × θ B × t 1 ......... (1)
Fp=2.5×(0.5-Cp)... (2)
Here, Cp in the equation (2) is calculated by the following equation (3).
Cp=[%C]-0.0022×[%Si]+0.019×[%Mn]-0.179×[%P]+2.258×[%S]+0.019×[%Cu]+0.025×[%Ni]-0.0022 ×[%Cr]-0.04×[%Mo]-0.058×[%V]-0.438×[%Nb]-0.1226×[%Al]+0.376×[%N] ………(3)
When Fp<0.90 and 1.05<Fp; _Vable ≦3.5×θ _B ... (4)
When 0.90≦Fp<0.95; _Vable ≦3.0×θ _B ... (5)
When 0.95≦Fp≦1.05: _Vable ≦2.0×θ _B ... (6)
V _U =(V _C /L _m )×θ _B ×t... (7)
_{V L = (V C / L} m) × θ B × t-θ B ......... (8)
(II) Step 2 (t ₁ <t<t ₁ +t ₂ ).
V _U =V _L =V _P ≦V _max ....(9)
(III) Step 3 (t ₁ +t ₂ ≦t≦t ₁ +t ₂ +t ₃ ).
_{V U = (V C / L} m) × (θ B × t 1 -θ M × t) -θ M ......... (10)
_{V L = (V C / L} m) × (θ B × t 1 -θ M × t) ......... (11)
Here, V _max is the maximum moving speed (mm/min), V _C is the casting speed (mm/min), L _m is the mold length (mm), θ _B is the lower end deformation speed allowable amount (mm/min), and Fp. maximum allowable moving speed (mm / min) is ferrite _{potential, V ABLE} is, _{V U} is the moving speed of the upper end of the mold (mm / min), _{V L} is the moving speed of the lower end of the mold (mm / min), _{V P} is The parallel movement speed (mm/min) in step 2, θ _M is the upper limit deformation speed allowable amount (mm/min), t is the elapsed time from the start of the width change (min), and t ₁ is the time required for step 1 (min) , T ₂ is the time required for step 2 (min), and t ₃ is the time required for step 3 (min).
Further, [%C] in the equation (3) is the carbon concentration (mass%) of the slab, similarly, [%Si] is the silicon concentration (mass%), and [%Mn] is the manganese concentration (mass%). , [%P] is phosphorus concentration (mass%), [%S] is sulfur concentration (mass%), [%Cu] is copper concentration (mass%), [%Ni] is nickel concentration (mass%), % Cr] is chromium concentration (mass %), [% Mo] is molybdenum concentration (mass %), [% V] is vanadium concentration (mass %), [% Nb] is niobium concentration (mass %), [% Al] ] Is the aluminum concentration (mass %), and [%N] is the nitrogen concentration (mass %).

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