阅读说明：本技术 连铸大方坯平辊和凸辊组合的轻压下方法 (Soft reduction method for combination of flat roll and convex roll of continuous casting bloom ) 是由 徐荣军 刘俊江 万根节 李成斌 柳向椿 孟庆玉 于 2018-08-31 设计创作，主要内容包括：一种连铸大方坯平辊和凸辊组合的轻压下方法,属金属铸造领域。首先算出铸坯到每台拉矫机部位时的三维温度场分布、两相区、固相区厚度和固相分率,确定压下起始和结束辊子的位置,根据铸坯的体积收缩量,制定每个拉矫机辊子的压下量；在铸坯固相分率f<Sub>s</Sub>＝0.9-1.0区间,实施重压下工作模式；在铸坯固相分率f<Sub>s</Sub>＝0.25-0.80区间,实施轻压下工作模式。其采用平辊拉矫机和凸辊拉矫机组合的轻压下方法,对铸坯进行凝固末端轻压下控制,以降低铸坯的中心疏松、缩孔与偏析,改善轧材内部质量；可使铸坯上表面产生的压痕形状开口变宽,能避免后工序轧钢过程产生折叠缺陷,且有利于减轻压下力,更有利于减轻凸辊拉矫机的压下力。可广泛用于金属铸造领域。(A soft pressing method for combining a flat roller and a convex roller of a continuous casting bloom belongs to the field of metal casting. Firstly, calculating three-dimensional temperature field distribution, a two-phase region, the thickness of a solid phase region and the solid phase fraction when a casting blank reaches each tension leveler part, determining the positions of initial and final rollers for reduction, and setting the reduction of each tension leveler roller according to the volume shrinkage of the casting blank; fraction of solid phase in casting blank f s Executing a heavy pressing working mode within the interval of 0.9-1.0; fraction of solid phase in casting blank f s And (5) implementing a soft-press working mode in an interval of 0.25-0.80. The method adopts a soft reduction method combining a flat roll withdrawal straightening machine and a convex roll withdrawal straightening machine to carry out solidification tail end soft reduction control on the casting blank so as to reduce the center porosity, shrinkage cavity and segregation of the casting blank and improve the internal quality of a rolled material; can widen the indentation-shaped opening generated on the upper surface of the casting blank, can avoid the folding defect generated in the steel rolling process of the post process, is favorable for reducing the pressing force and is more favorable for reducing the convex roll withdrawal and straightening machineThe depressing force of (a). Can be widely used in the field of metal casting.)

1. A soft reduction method for combining a flat roller and a convex roller of a continuous casting bloom comprises the steps of sequentially arranging a plurality of withdrawal and straightening machines on a continuous casting line to carry out compression casting on a casting blank; the method is characterized in that:

1) according to the continuous casting process and the casting blank forming theory, model calculation is carried out on the continuous casting solidification heat transfer and liquid-phase cave of the bloom, and according to different steel types, the casting blank drawing speed, the cooling condition and the superheat degree, the three-dimensional temperature field distribution, the two-phase region, the thickness of the solid-phase region and the solid-phase fraction f from the casting blank to each withdrawal and straightening machine are calculated_s；

2) Determining the positions of the initial and final pressing rollers according to model calculation, and corresponding to each withdrawal and straightening machine on the continuous casting line;

3) setting the reduction of each withdrawal and straightening machine roller according to the volume shrinkage of the casting blank;

4) fraction of solid phase in cast slab f_sPerforming a heavy reduction working mode on the casting blank in an interval of 0.9 to 1.0;

5) when the solid phase fraction is f_sWhen the rolling reduction is 0.9-1.0, each withdrawal and straightening machine performs the maximum rolling reduction of 10mm of a single roller;

6) fraction of solid phase in cast slab f_sIn the interval of 0.25 to 0.80, a casting blank is subjected to a soft reduction working mode;

7) when the solid phase fraction is f_sWhen the grain size is 0.25-0.80, each withdrawal and straightening machine carries out the rolling reduction of which the single roller is not more than 5 mm;

namely: for the front-end withdrawal and straightening machine far away from the solidification tail end, a flat roller withdrawal and straightening machine is still adopted to carry out compression casting on the casting blank;

for a rear-end withdrawal and straightening machine close to the solidification tail end, performing compression casting on a casting blank by adopting a convex roller withdrawal and straightening machine;

the soft reduction method adopts a soft reduction method combining a flat roll withdrawal straightening machine and a convex roll withdrawal straightening machine to carry out soft reduction control on the solidification tail end of the casting blank so as to reduce the center porosity, shrinkage cavity and segregation of the casting blank and improve the internal quality of a rolled material;

by adopting the soft reduction method, the opening of the indentation shape generated on the upper surface of the casting blank is widened, so that the folding defect generated in the steel rolling process of the post procedure can be avoided, the reduction of the reduction force is facilitated, and the reduction of the reduction force of the convex roller withdrawal and straightening machine is more facilitated;

the soft pressing method can reduce the pressing force of the convex roller withdrawal and straightening machine; meanwhile, the withdrawal resistance of the continuous casting process of the casting blank is reduced.

2. The soft reduction method of the combination of the continuous casting bloom flat roll and the convex roll according to claim 1, characterized in that the upper roll of the convex roll withdrawal and straightening unit is a convex roll and can be lifted to adjust the roll gap, and the convex roll is connected with a motor and a speed reducer;

the lower roll of the convex roll withdrawal and straightening machine is a flat roll;

the upper roller and the lower roller are connected by a frame, and a pressing force is applied to the middle casting blank by four pairs of driving hydraulic oil cylinders.

3. The soft reduction method of a combination of a flat roll and a convex roll for a continuous casting bloom as claimed in claim 2, wherein said upper roll is a convex roll and is a driving roll.

4. The soft reduction method of a combination of a flat roll and a convex roll for a continuous casting bloom as claimed in claim 2, wherein the lower roll is a flat roll and is a stationary driven roll.

5. The soft reduction method of a combination of a flat roll and a convex roll for a continuous casting bloom as set forth in claim 2, wherein the contour curve of the working portion of the roll body of the convex roll is formed by connecting a first straight line segment AB, a first transition curve segment BC, a second straight line segment CD, a second transition curve segment DE and a third straight line segment EF in this order;

the first straight line section AB and the third straight line section EF are arranged coaxially or on the same plane, and the second straight line section CD is arranged in parallel with the first straight line section AB or the third straight line section EF;

the first curve segment BC and the second curve segment DE are respectively composed of sine curves or two sections of mutually tangent concave and convex arc lines, and the radiuses of the two arcs are equal or unequal;

for the section of the convex roller in the axial length direction, a convex structure in the form of a boss is formed on the surface of the convex roller by the first transition curve section BC, the second straight section CD and the second transition curve section DE.

6. The soft reduction method of a combination of a continuous casting bloom flat roll and a crown roll as set forth in claim 5, characterized in that the first transition curve segment BC curve sine curve equation of the crown is:

y＝Hsin(x*π/2nH)；

in the formula: h is the height of the boss; n is the projected length of the first transition curve segment BC of the plateau on the x-axis.

7. The soft reduction method of a combination of a continuous casting bloom flat roll and a convex roll according to claim 5 or 6, characterized in that the second transition curve DE is mirror-symmetrical to the first transition curve BC; the mirror symmetry center line is a straight line which passes through the middle point of the second straight line segment CD and is vertical to the second straight line segment CD.

8. The soft reduction method of a combination of a flat roll and a convex roll for a continuous casting bloom as set forth in claim 5, wherein the solid fraction f of the cast slab_sIn the interval of 0.25 to 0.80, the indentation-shaped opening produced on the upper surface of the casting blank is equal to the length of the second straight line segment CD of the roller body of the convex roller for each withdrawal and straightening machine.

9. The soft reduction method of a combination of a continuous casting bloom flat roll and a crown roll as claimed in claim 5, wherein the length of the second straight line segment CD of the crown roll body of each withdrawal straightening machine is determined by the width D of the non-solidified two-phase zone of the continuous casting slab at the position of each withdrawal straightening machine.

10. The soft reduction method of the combination of the flat roll and the convex roll for the continuous casting bloom as claimed in claim 9, wherein the length of the second straight line segment CD of the roll body of the convex roll on each withdrawal and straightening unit is not less than D +40 mm.

Technical Field

The invention belongs to the field of metal casting, and particularly relates to a method for carrying out post-treatment or post-processing on a cast blank on site.

Background

In the continuous casting process of steel, due to the external cooling, the surface of a casting blank is solidified earlier than the inside of the casting blank, so that the surface has larger shrinkage than the inside of the casting blank, as the solidification and crystallization are finished, columnar crystals at two sides of a certain local area are bridged, and when liquid enclosed below the bridge is solidified, the molten steel at the upper part of the bridge in a liquid cavity is prevented from being supplemented, so that shrinkage cavities and looseness are generated when the molten steel below the bridge is solidified, along with the formation of the shrinkage cavities and looseness, the vacuum shrinkage cavities can suck solute-enriched liquid among dendrites to flow to the center, and meanwhile, macroscopic segregation is generated.

The soft reduction is equivalent to compression casting, and has the function of eliminating shrinkage cavity, porosity and macro segregation at the same time, so that the flat roll soft reduction technology of the casting blank is widely applied to the field of continuous casting.

Because the surface of the casting blank is solidified earlier than the inside of the casting blank, the casting blank is thicker and has lower temperature when being closer to the solidified tail end, because both sides of the blank shell are completely solidified, the deformation resistance is larger when the reduction process is closer to the solidified tail end, the prior art adopts a pair of flat rollers to compress, and the compression force is the same because the tension leveler is exchanged, so that the pressure of the front tension leveler is rich and the pressure of the rear tension leveler is insufficient. This conflict becomes more pronounced as high alloy steels are produced more and more. A technique of performing more effective soft reduction at an unsolidified portion using a convex roller has been proposed.

Chinese patent application publication No. CN 105983668A, published as 2016.10.05, discloses a light weight bottom roll, a light weight reduction device having the same, and a method for manufacturing a cast slab, in which a diameter of an end portion of the light weight bottom roll is smaller than a diameter of an intermediate portion, wherein when a cross section including a rotation axis of the light weight bottom roll is observed, an outer periphery between the intermediate portion and the end portion has a 1 st arc bulging toward the rotation axis on the end portion side, and a 2 nd arc bulging in a direction opposite to a bulging direction of the 1 st arc on the intermediate portion side, and an angle formed by a tangent line tangent to both the 1 st arc and the 2 nd arc and the rotation axis is 40 ° or less. The technical scheme includes that a constant-curvature boss-free convex roller (a drum-shaped roller) is installed at a position with a solid phase ratio of 0.2 to implement large reduction, a gradually-changing curvature boss convex roller is located at a solidification end point, and large-deformation reduction is sequentially adopted at the position with the central solid phase ratio of 0.2 and the solidification end point to overcome the defects of chemical composition segregation, solidification center shrinkage and serious loosening quality. However, according to the solidification principle of the cast slab, the soft reduction corresponds to compression casting, and the reduction amount is used for compensating the shrinkage amount of the current molten steel and limiting the molten steel with low-melting-point impurities enriched between dendrites to flow toward the center, and the excessive reduction amount is not beneficial to the improvement of solidification segregation.

In the above-mentioned chinese invention patent application, a soft reduction device is also disclosed, in which the convex roller transition curve is formed by two sections of concave and convex arc lines tangent to each other, the radii of the two arcs are not equal, and the radius of the convex arc 1 is generally smaller than the radius of the concave arc 2, so as to reduce the folding defect caused by the concave casting blank in the post-process steel rolling process.

The invention discloses a method for improving the center density of a bearing steel casting blank, which is a Chinese patent application with application publication No. CN 107377919A and application publication No. 2017.11.24, and discloses a method for improving the center density of a bearing steel casting blank, wherein in the continuous casting process, the casting speed of a casting machine is controlled to be 0.50-0.65 m/min, the superheat degree of tundish molten steel is controlled to be 20-30 ℃, a solidification end heavy pressing mode is adopted, the solid phase rate is distributed under light pressing and heavy pressing, the heavy pressing is started from fs being 0.9, and the heavy pressing is performed by using a convex roller when fs is l.0. The technical scheme adopts a solidification tail end heavy pressing mode, and uses a single convex roller to perform heavy pressing when fs is 0.9-1.0 so as to reduce shrinkage cavities. But it does not address the problem of how to perform a light press down.

Disclosure of Invention

The invention aims to solve the technical problem of providing a soft reduction method for combining a flat roller and a convex roller of a continuous casting bloom. The soft reduction method of the combination of the continuous casting bloom flat roll and the convex roll is adopted, the convex roll is used for partially reducing the reduction force of the withdrawal and straightening machine, and the withdrawal resistance is reduced. The convex rollers on different tension leveler adopt bosses with different lengths, and finally the opening of the indentation shape generated on the upper surface of the casting blank is widened, so that the folding defect generated in the post-process steel rolling process can be avoided, the reduction of the pressing force is more facilitated, and the reduction of the pressing force of the convex roller tension leveler is more facilitated.

The technical scheme of the invention is as follows: the soft reduction method for the combination of the flat roll and the convex roll of the continuous casting bloom comprises the steps of sequentially arranging a plurality of withdrawal and straightening machines on a continuous casting line to carry out compression casting on a casting blank; the method is characterized in that:

1) according to a continuous casting process and a casting blank forming theory, performing model calculation on continuous casting solidification heat transfer and liquid-phase holes of a bloom, and calculating three-dimensional temperature field distribution, a two-phase region, a solid-phase region thickness and a solid-phase fraction of a casting blank to each withdrawal and straightening machine part according to different steel types, withdrawal speeds, cooling conditions and superheat degrees;

2) determining the positions of the initial and final pressing rollers according to model calculation, and corresponding to each withdrawal and straightening machine on the continuous casting line;

3) setting the reduction of each withdrawal and straightening machine roller according to the volume shrinkage of the casting blank;

4) fraction of solid phase in cast slab f_sPerforming a heavy reduction working mode on the casting blank in an interval of 0.9 to 1.0;

5) when the solid phase fraction is f_sWhen the rolling reduction is 0.9-1.0, each withdrawal and straightening machine performs the maximum rolling reduction of 10mm of a single roller;

6) fraction of solid phase in cast slab f_sIn the interval of 0.25 to 0.80, a casting blank is subjected to a soft reduction working mode;

7) when the solid phase fraction is f_sWhen the grain size is 0.25-0.80, each withdrawal and straightening machine carries out the rolling reduction of which the single roller is not more than 5 mm;

namely: for the front-end withdrawal and straightening machine far away from the solidification tail end, a flat roller withdrawal and straightening machine is still adopted to carry out compression casting on the casting blank;

for a rear-end withdrawal and straightening machine close to the solidification tail end, performing compression casting on a casting blank by adopting a convex roller withdrawal and straightening machine;

the soft reduction method adopts a soft reduction method combining a flat roll withdrawal straightening machine and a convex roll withdrawal straightening machine to carry out soft reduction control on the solidification tail end of the casting blank so as to reduce the center porosity, shrinkage cavity and segregation of the casting blank and improve the internal quality of a rolled material;

by adopting the soft reduction method, the opening of the indentation shape generated on the upper surface of the casting blank is widened, so that the folding defect generated in the steel rolling process of the post procedure can be avoided, the reduction of the reduction force is facilitated, and the reduction of the reduction force of the convex roller withdrawal and straightening machine is more facilitated;

the soft pressing method can reduce the pressing force of the convex roller withdrawal and straightening machine; meanwhile, the withdrawal resistance of the continuous casting process of the casting blank is reduced.

Specifically, the upper roll of the convex roll withdrawal and straightening machine is a convex roll, the roll gap can be adjusted by lifting, and the convex roll is connected with a motor and a speed reducer; the lower roll of the convex roll withdrawal and straightening machine is a flat roll; the upper roller and the lower roller are connected by a frame, and a pressing force is applied to the middle casting blank by four pairs of driving hydraulic oil cylinders.

Furthermore, the upper roller is a convex roller and is a driving roller. The lower roller is a flat roller and is a fixed driven roller.

Furthermore, the contour curve of the working part of the roller body of the convex roller is formed by sequentially connecting a first straight line section AB, a first transition curve section BC, a second straight line section CD, a second transition curve section DE and a third straight line section EF;

the first straight line section AB and the third straight line section EF are arranged coaxially or on the same plane, and the second straight line section CD is arranged in parallel with the first straight line section AB or the third straight line section EF;

the first curve segment BC and the second curve segment DE are respectively composed of sine curves or two sections of mutually tangent concave and convex arc lines, and the radiuses of the two arcs are equal or unequal;

for the section of the convex roller in the axial length direction, a convex structure in the form of a boss is formed on the surface of the convex roller by the first transition curve section BC, the second straight section CD and the second transition curve section DE.

Specifically, the first transition curve segment BC curve sinusoidal equation of the boss is as follows:

y＝Hsin(x*π/2nH)；

in the formula: h is the height of the boss; n is the projection length of the first transition curve segment BC of the boss on the shaft.

Further, the second transition curve DE is mirror symmetric to the first transition curve BC; the mirror symmetry center line is a straight line which passes through the middle point of the second straight line segment CD and is vertical to the second straight line segment CD.

Furthermore, in the interval of 0.25 to 0.80 of the solid fraction of the casting blank, the indentation shape opening generated on the upper surface of the casting blank is equal to the length of the second straight line segment CD of the roller body of the convex roller for each withdrawal and straightening machine.

Further, the length of the second straight-line segment CD of the roller body of the convex roller on each withdrawal and straightening machine depends on the width D of the unconsolidated two-phase region when the continuous casting slab reaches the position of each withdrawal and straightening machine.

Furthermore, the length of the second straight-line segment CD of the roller body of the upper convex roller of each withdrawal and straightening machine is more than or equal to D +40 mm.

Compared with the prior art, the invention has the advantages that:

1. the solidification tail end soft reduction control and the comprehensive application are carried out by a soft reduction method of combining a flat roll and a convex roll of a continuous casting bloom to reduce the center porosity, shrinkage cavity and segregation of a casting blank and improve the internal quality of a rolled material;

2. the technical scheme avoids the situation that the solidified shell on the two sides generates larger deformation resistance, and can reduce the pressing force of the convex roll withdrawal and straightening machine; the friction force is reduced, so the withdrawal resistance of the casting blank in the continuous casting process is also reduced;

3. according to the technical scheme, soft reduction is not completed on a single convex roller by using large reduction amount, but dispersed reduction is performed, the rollers are pressed by bosses with different lengths, and after the soft reduction is completed, the openings of the indentations formed on the upper surface of a casting blank are widened, so that the folding defect generated in the post-process steel rolling process can be avoided, and the reduction force of the convex roller withdrawal and straightening machine can be reduced.

Drawings

FIG. 1 is a schematic diagram of the calculation process of continuous casting solidification heat transfer in the present technical solution;

FIG. 2 is a schematic view of the installation position of the bloom for soft reduction withdrawal and straightening unit according to the present invention;

FIG. 3 is a schematic view of the two-phase region width at the solidification end of the bloom in accordance with the present invention;

FIG. 4 is a schematic view of the press down of the convex roller of the bloom straightening and withdrawal machine of the present invention;

FIG. 5 is a schematic view of the profile shape of a male roll;

fig. 6 is a schematic view of the shape of the indentation of the upper surface of the cast slab.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

In fig. 1, first, a model calculation is performed on a bloom continuous casting solidification heat transfer and a liquid cavity according to a current continuous casting process and a casting blank forming theory:

according to the solidification heat transfer equation:

given the initial conditions:

T|₀＝T(x,y,z,0) (2)

boundary conditions:

one type of boundary condition:

T|_w＝T_w＝T_w(t) (3)

two types of boundary conditions:

three types of boundary conditions:

substituting physical parameters of steel, and simulating three-dimensional temperature field distribution, two-phase regions, thickness of solid phase regions and solid phase fraction of different steel types, billet drawing speeds, cooling conditions, and the time when a billet with superheat degree reaches each withdrawal and straightening machine part by finite element calculation.

In fig. 2, the position or location of each withdrawal straightening machine (i ═ 1 to n, where n is the total number of withdrawal straightening machines on a continuous casting line) on the continuous casting line is shown.

The arrows in the figure indicate the direction of the continuous casting process line, i.e. the direction of advancement of the cast strand.

In fig. 3, three-dimensional temperature field distribution, two-phase region and solid-phase region thickness of the cast slab are given.

In the drawing, D is a two-phase region, P is a reduction region, and an arrow indicates the direction of the continuous casting process route, i.e., the advancing direction of the cast slab.

According to the calculation result of fig. 3, the withdrawal and straightening machine farther from the solidification end (i.e., the front withdrawal and straightening machine with a smaller number i, which can be selected as the value of i between 1 and 4) can meet the requirement of light reduction due to the thin billet shell and the high temperature of the cast billet, and the withdrawal and straightening machine closer to the solidification end (i.e., the rear withdrawal and straightening machine with a larger number i, which can be selected as the value of i between 5 and 8) cannot meet the requirement of light reduction due to the thick billet shell and the low temperature of the cast billet due to the large required light reduction force.

Therefore, the technical scheme of the invention adopts a soft pressing method combining the flat roller and the convex roller, and adopts the flat roller scheme for the front-end withdrawal and straightening machine and the convex roller scheme for the rear-end withdrawal and straightening machine. Particularly, the combined proposal is very suitable for soft reduction of the existing continuous casting machine due to the insufficient reduction capability of the rear tension leveler.

In fig. 4, a schematic diagram of a convex roller withdrawal and straightening machine is shown, wherein an upper roller 1 is a convex roller and a driving roller, can be lifted to adjust a roller gap, and is connected with a motor and a speed reducer; the lower roller 3 is a flat roller and is a fixed driven roller, the upper roller and the lower roller are connected by a frame, and a pressing force is applied to the middle casting blank by four pairs of driving hydraulic oil cylinders.

And the casting blank 2 is positioned between the upper roller and the lower roller.

Fig. 5 shows a schematic structural diagram of the shape of the convex roll withdrawal and straightening unit in the technical solution, and it can be known from the diagram that the contour curve of the working part of the roll body of the convex roll (for short, the convex roll) is composed of a first straight line segment AB, a first transition curve segment BC, a second straight line segment CD, a second transition curve segment DE and a third straight line segment EF.

The first transition curve segment BC and the second transition curve segment DE are formed by sinusoidal curves, or two sections of mutually tangent concave and convex arc lines, and the radiuses of the two arcs are equal or unequal.

It is clear that for a longitudinal section of each male roll in the axial length direction, the first transition curve segment BC, the second straight segment CD and the second transition curve segment DE form a raised structure 4 in the form of a plateau on the surface of the male roll.

The coordinate system of fig. 5 has point B as the origin of coordinates, the x-axis being parallel to the central axis of the roll and the y-axis being perpendicular to the central axis of the roll.

The sinusoidal equation of the first transition curve segment BC is:

y＝Hsin(x*π/2nH)

in the formula: h is the boss height. n is the projection length of the first transition curve segment BC of the boss on the shaft.

n is a multiple of the boss height H, i.e. the projection length of the first transition curve segment BC of the boss on the shaft is nH.

The second transition curve DE may be formed by mirroring the midpoint of the first transition curve BC along the line segment CD as a centerline.

In particular, the length of the second straight section CD in the middle of the barrel of the crown roll depends on the width D of the uncondensed two-phase zone of the strand in fig. 3 up to the position of each withdrawal straightening unit.

Because the width D of the two-phase region which is not solidified when the casting blank reaches the position of each tension leveler is different, the length of the second straight line section (also called as the middle straight line section) CD of each convex roller is also different according to the position of the tension leveler.

Theoretically, the length CDi of the second straight line segment of the convex roller corresponding to each withdrawal and straightening machine (where i is the position number of each withdrawal and straightening machine on the continuous casting line) should be greater than or equal to the width Di of the non-solidified two-phase region when the casting blank reaches the position of each withdrawal and straightening machine (where i is the position number of each withdrawal and straightening machine on the continuous casting line), and the value Di may change due to different casting speeds, steel types, superheat degrees and cooling strengths. Considering that the casting blank deviates from the casting flow central line (called bias flow) in the downward casting process of the casting blank, the smaller bias flow has no great influence on the flat roll withdrawal and straightening machine, and the flat roll can always press the non-solidified two-phase area part in the center of the casting blank, but the protruding part (namely the boss) of the convex roll can also press the non-solidified two-phase area part in the center of the casting blank.

Considering comprehensively, the length of the second straight line segment CDi recommended by the corresponding convex roller is more than or equal to Di +40mm for each withdrawal and straightening machine i (wherein i is the position number of each withdrawal and straightening machine on the continuous casting line).

The height H of the boss is determined according to the total shrinkage of the solidification volume and the linear shrinkage of the pressing interval of all the withdrawal and straightening machines, and the height H is 30% larger than the theoretical calculated value in consideration of the universality.

FIG. 6 shows the shape of the indentation finally produced on the upper surface of the casting blank after the soft reduction by using the press rolls with bosses of different lengths.

Obviously, the opening of the indentation T is widened (precisely, the opening is gradually widened from the bottom of the opening upwards and is approximately an inverted equilateral trapezoid), so that the folding defect generated in the steel rolling process in the subsequent process can be avoided, and the reduction of the pressing force of the convex roller withdrawal and straightening machine is facilitated.

According to the technical scheme, the solidification tail end soft reduction control and comprehensive application are carried out by a soft reduction method of combining a flat roller and a convex roller of a continuous casting bloom to reduce the center porosity, shrinkage cavity and segregation of a casting blank and improve the internal quality of a rolled material.

The casting blank generates great volume shrinkage in the process of casting blank solidification, so that a larger reduction is needed to compensate the volume shrinkage of the casting blank, and the casting blank generates deformation resistance in the process of reduction, and the deformation resistance is mainly concentrated on the blank shells solidified on two sides.

The soft pressing method of the combination of the flat roller and the convex roller of the continuous casting bloom avoids the billets which are solidified at two sidesThe shell generates larger deformation resistance, and the pressing force of the convex roller withdrawal and straightening machine can be reduced. Can be applied to the solidification end f of the cast slab_sThe heavy reduction is carried out when the rolling speed is 0.9-1.0, the central density of the casting blank is improved, and simultaneously, the contact area between the convex roller and the casting blank is small, and the friction force is reduced, so the casting resistance in the continuous casting process of the casting blank is also reduced.

Meanwhile, the soft reduction method of the combination of the flat roller and the convex roller is not completed by using large reduction amount on a single convex roller but is dispersedly reduced, and the roller is pressed by the bosses with different lengths, and finally the opening of the indentation shape generated on the upper surface of the casting blank is widened after the soft reduction is finished, so that the folding defect generated in the post-process steel rolling process can be avoided, and the reduction force of the convex roller withdrawal and straightening machine can be reduced.