JPH05305395A - Continuous casting method - Google Patents

Abstract

PURPOSE:To improve the low toughness, etc., of a base material in a flange part of a shape steel caused by defect of the center segregation, center porosity, etc., near the short side part of a cast slab and to produce the cast slab without quality defect at the time of producing an H-sections steel or an I-sections steel forming slitting parts to the short sides of the continuously cast slab. CONSTITUTION:In this continuous casting method, the light rolling reduction in the surface rolling reduction equipment is executed to the range of at least >=50mm from the position being apart from the solidified interface of the short side at >=10mm in <=0.5% the rolling reduction rate per one pass and >=1.0% the total rolling reduction rate with a surface member. By this method, the quality of the flange part in the H-sections steel or the I-sections steel is further improved and the cast slab having stable quality is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when manufacturing an H-shaped steel from a steel slab having a rectangular cross section (hereinafter referred to as a slab), has a center segregation and a center porosity present in the thickness center of the slab near the flange. The present invention relates to a continuous casting method for supplying a defect-free cast slab that prevents the generation of welding defects and hydrogen defects that occur at the starting point.

[0002]

2. Description of the Related Art In recent years, continuous casting has become an indispensable step in the production of steel, and so-called slabs such as slabs and blooms are produced in such a step, and H-shaped steel and Although I-shaped steel has been manufactured, wide cast slabs are required to manufacture these shaped steels of a predetermined size by the conventional manufacturing method, which increases the edging amount, A large capacity rolling mill is required.

Furthermore, since a very large fish tail is generated at the leading and trailing ends of the rough-shaped steel, the amount of cut-off after rough rolling is large, and the equipment cost and running cost such as the reduction of rolling yield and the number of rolling passes increase. Big increase was a problem.

To solve this problem, for example, Japanese Patent Laid-Open No. 2-1
In the techniques disclosed in Japanese Patent No. 4121 and Japanese Patent Laid-Open No. 52-20958, the short side of a rectangular cross-section steel piece is successively divided and expanded by an edging hole type group to form a flange bulge portion, and then the web pressing portion In the rough rolling method of H-section steel having flange shaping holes on both sides of the above, the hole width of the flange shaping hole is formed to be at least 10% larger than the flange bulging portion after the edging of the material to be rolled, and the entire width of the hole forming die. Is formed to be approximately equal to the height of the web after edging, and the web pressing portion is repeatedly pressed down the web portion of the material to be rolled by a forming hole die formed in the center direction of the curved surface in the width direction. These problems can be solved by manufacturing H-section steel and I-section steel by using the H-section steel manufacturing method of rolling while performing the metal flow to the flange part, and further, the conventional shape can be secured. Even a thin cast strip that could not be used for off-, H-section steel and I-section steel of a predetermined size have come to be manufactured.

However, in the case of the above-mentioned manufacturing method, since the edging and the rolling of the web portion are repeatedly performed after the short side of the slab is successively expanded to form the flange bulging portion, it is generally unavoidable for the continuous cast slab. Since the generated segregation zone at the center of the thickness gradually becomes closer to the surface of the flange, the segregation zone widens during welding when used in a building or the like, and there is a problem in that it easily becomes a defect.

Further, since the segregation zone at the center portion is the final solidification portion, a shrinkage hole commonly called center porosity is apt to be generated, and hydrogen and the like, which are easily diffused therein, are concentrated, so that at the time of rolling. Since the internal pressure of the defective portion increases, there is a problem that defects such as so-called cracks are likely to occur.

As a method for preventing defects of such continuous cast slabs, especially segregation of the central portion and solidification shrinkage holes called center porosity, for example, solidification shrinkage as disclosed in JP-A-3-133556 is suitable. And the solid line crater of the liquid phase crater of the slab by means of one or a plurality of pairs of reduction rolls, as disclosed in JP-A-49-121738. The rolling reduction rate per pair of rolls between the tip and
A method of eliminating such center segregation by continuously rolling down at 1.5% or less is performed.

[0008]

However, the above-mentioned Japanese Unexamined Patent Application Publication No.
-133556, using the method disclosed,
Alternatively, the method disclosed in Japanese Unexamined Patent Publication No. 49-121738 is an excellent method for eliminating center segregation and center porosity over the entire width direction of the cast piece, but the cast piece having a wide width In order to carry out a light reduction over the entire surface, an extremely large reduction force is required.

When the H-section steel or I-section steel is manufactured by the above-mentioned rolling method, the only problematic position in use is the end portion in the width direction of the slab as described above. Segregation of only a specific part called flange part like steel,
To apply it as a measure against center porosity, these methods and equipment management are too large, and segregation on the entire surface is reduced or in order to reduce center porosity, extremely strict control of the amount of reduction and equipment for solidification shrinkage compensation. This requires extremely strict maintenance and management, and not only equipment costs but also operation management and machine maintenance costs are extremely high.

The present invention has been made in view of the above problems,
In addition to significantly reducing the equipment cost, operation and equipment management load, segregation and center porosity that cause quality deterioration of the flange of H-section steel and I-section steel are equal to or higher than those of the cast pieces produced by the conventional method. A continuous casting method of steel that guarantees quality is provided.

According to the present invention, the short side of the rectangular cross-section steel piece is successively divided and expanded by the edging hole type group to form the flange bulging portion, and then rough rolling of the H-section steel having the flange shaping holes on both sides of the web pressing portion is performed. Method, the flange width of the flange shaping hole is at least 1 from the flange bulging portion after the edging of the rolled material is completed.
Formed by a forming die which is formed to have a width of 0% or more, the entire width of the die is substantially equal to the height of the web after edging, and the web pressing portion is formed in a center-projecting gentle curved surface in the width direction. In the production of H-section steel in which the web portion of the material is repeatedly pressed and rolled while performing metal flow to the flange portion, when the steel piece is produced by continuous casting, the shell thickness which is solidified with respect to the thickness of the slab is 2 In the region where the solidification rate defined by the double ratio is 90% or more and 99% or less, once per surface member over the width of at least 50 mm on the center side in the width direction with respect to the distance from the end defined by the following formula 1. In the continuous casting method, the reduction amount is 0.5% or less and a total reduction of 1.0% or more is performed.

[0012]

[Equation 2] Uncompressible area (mm) = k√t + 10 (1)

Here, k = solidification constant, t = time (minutes) required for the slab in the rolled portion to be cast into the mold and to start rolling by the surface member.

[0014]

The feature of the present invention is that when the raw materials such as H-section steel and I-section steel produced by the above-mentioned rolling method are produced and supplied by continuous casting, the width end portion of the slab corresponding to the flange portion of the section steel is produced. It is a continuous casting method for steel that eliminates segregation and center porosity in the vicinity extremely economically and stably.

In general, when a cast piece is manufactured by a continuous casting machine,
As is well known, concentrated molten steel accumulates in the final portion of so-called solidification, that is, the central portion, and segregation and solidification defects called center porosity occur at the central portion of the thickness of the slab.

In the case of manufacturing by the above-mentioned rolling method, such a defect in the central portion is caused by bulging the flange portion by repeatedly performing strong reduction in the width direction after inserting an interrupt at the width end portion, and particularly, in the width of the slab. There is a characteristic that not only the edge portion is widened in the thickness direction of the cast product, but also the defect near the edge portion is brought close to the surface of the flange portion.

The inventors of the present invention repeatedly conducted a rolling test of a slab having such a defect, and ascertained the causal relationship between the segregation or the center porosity existing near the width end and the defect in the flange by the rolling method. For the sake of clarity, various shaped steels were prototyped and investigated.

As a result, although there is a slight difference depending on the size of the product, the segregation zone existing in the center of thickness has the defect present within at least 100 mm from the end portion of the unpressurizable region defined by the above formula (1). The inventors have found that they approach within a few millimeters from the outer surface of the flange portion and that they are detected as defects by an ultrasonic flaw detection test when butt welding between products is performed.

In order to prevent the occurrence of such a defect at the width end portion, the present inventors further conducted an experiment and, for example, using the surface pressure reduction equipment described in the above-mentioned Japanese Patent Laid-Open No. 3-133556, The reduction bar at the center of the width is removed, or it is not removed but is not actively reduced, and only the amount of reduction force corresponding to the molten steel static pressure is applied to prevent bulging caused by the molten steel static pressure. A reduction experiment was performed in which the width of the reduction bar at the end and the amount of reduction were variously changed.

From this experiment, from the width end of the slab (1)
By performing a reduction of 0.5% or less and a total reduction of 1.0% or more in a region of 50 mm or more from the position shown in the formula, segregation or center porosity that occurs in the thickness center of the slab is obtained. Can be eliminated extremely economically and without any strict adjustment of pass intervals or fine adjustment of the amount of reduction between the inner and outer bars and between the inner and outer bars.As a result, defects in the flange of the shaped steel can be eliminated. We have found that they can be virtually eliminated.

The results of the casting test that found the above findings will be described below.

FIG. 1 shows the relationship between the amount of reduction per operation, the center segregation index within 100 mm from the inner surface of the solidified shell on the short side, and the center porosity index detected by the X-ray flaw detection test. FIG. 2 shows the relationship between the total amount of reduction and the center segregation index and center porosity index within 100 mm from the inner surface of the solidified shell on the short side.

Further, in FIG. 3, the solidification rate on the inlet side of the draft zone, which is determined by a generally used heat balance equation, the central segregation index within 100 mm from the inner surface of the solidified shell on the short side, and the center porosity index. Shows the relationship. FIG. 4 shows the center segregation index and the center porosity index at the above-mentioned positions in the relationship between the distance from the inner surface of the solidified shell at the width end of the cast piece to the end of the reduction bar and the reduction bar width obtained by the heat balance equation. Indicates the rolling condition region satisfying the usage conditions.

As is clear from FIG. 1, the central segregation index tends to be improved as the rolling reduction per time increases. On the other hand, if the reduction amount per time is 0.5% or more, internal cracking occurs due to overpressure and quality deterioration occurs, so the reduction amount per time needs to be 0.5% or less. ..

On the other hand, as shown in FIG. 2, the total reduction amount is 1.0.
It has been found that when the ratio is less than or equal to%, the central segregation index effective for ensuring the quality of the product cannot be suppressed to 2 or less, and it is difficult to stably secure the center porosity index to 0.5 or less.

In FIG. 3, in order to obtain the effects shown in FIGS. 1 and 2, the casting speed, the superheat degree of molten steel during casting and / or in the mold are variously changed, and the unsolidified thickness immediately before the surface draft zone is variously adjusted. These are the results of analysis of the data obtained by conducting experiments.

From FIG. 3, when the above-mentioned reduction amount is applied after the solidification rate reaches 99% or more, the segregation variation is large, and the center segregation index and the center porosity index can be rolled as cast to manufacture a product. We have found that it is necessary to perform segregation diffusion treatment or pressure bonding treatment because the level cannot be achieved.

Further, when the solidification rate is 90% or less, the critical reduction amount at which the internal cracks occur decreases as the solidification rate decreases, so the reduction amount per operation must be reduced. In addition, if the economical minimum rolling reduction to obtain the desired segregation improvement effect is set to about 1% and passed through the rolling reduction zone, coagulation does not complete completely within the prescribed rolling reduction zone, so it passes through the rolling reduction zone. Later, the concentrated molten steel accumulates again in the center, and center segregation occurs again, so
There is a problem that more rolling strips are needed.

FIG. 4 is an analysis of the results of an experiment conducted in determining the proper reduction position in the width direction of the slab by varying the reduction distance from the width end of the slab and the width of the reduction bar while satisfying the appropriate conditions. The result is illustrated.

From FIG. 4, at least 50 mm from the position where the reduction area is slightly away from the center segregated end portion in the width direction of the slab.
It was found that the desired center segregation index and center porosity index can be obtained by rolling down the region under the above conditions.

The inventors of the present invention conducted a reduction experiment of cast pieces having various thicknesses to investigate the cause, and measured the behavior of the reduction bar. As a result, the deformation resistance of the solidified portion of the short side and the unsolidified portion were measured. It was found that due to the difference in the deformation resistance of the remaining portion, when both were deteriorated at the same time, non-uniform deformation occurred and non-uniform segregation remained at the corresponding position.

Therefore, as a result of various experiments in which the rolling position was changed, the center segregation was stably performed only by rolling down a region of at least 50 mm or more by a surface member closer to the center in the width direction than the region shown in the formula (1). It was discovered that the center porosity can be improved. The present invention has been made based on the above findings.

[0033]

EXAMPLES The present invention will be specifically described below with reference to examples.

35.4 m to 37.9 m from the meniscus of a vertical bending type continuous casting machine having a vertical portion of 2.5 m including the mold.
At the position of m, the rolling reduction, clamping, and conveying devices shown in FIGS. 5 to 10 are installed, and the steel types of various components shown in Table 1 are shown in Table 2.
Manufactured under the casting conditions and rolling conditions shown in Table 3,
The results shown in Table 3 were obtained.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[Implementation conditions / definition, etc.] (1) Method for detecting unsolidified width / thickness of solidification tip General heat balance based on solidification temperature of molten steel, injection temperature, drawing speed, sprinkling density of secondary cooling water, etc. The calculation calculation by the formula and / or the ultrasonic measurement device is used together.

(2) Method of detecting rolled-down reaction force The pressure block of the load cell is inserted between the bearing and the mounting base for detection.

(3) Center porosity index

[0041]

[Formula 3] Center porosity index = (G ₀ −G) / G
₀ x 100%

G ₀ : Defect area ratio of 3 to 13 mm portion (healthy portion) from the surface of the slab G: ± 5.0 mm (10 mm thickness) portion centered on the central segregation portion within 100 mm from the widthwise end of the segregation zone Defect area ratio of 0.5 or less is harmless, and if it exceeds 0.5, crimping treatment is required

(4) Adjustment of the reduction width of the walking bar As shown in FIG. 10, the reduction width of the walking bar is adjusted by connecting the dovetail joints H ₁ to the bars 7E at the left and right ends of the outer bar 7,
H ₂ is provided, and liners R ₁ and R ₂ are formed slidably on the liner, and the reduction width from the width end of the cast slab S and the presence / absence of reduction are selected by changing the width of the liner or attaching / detaching the liner. The rolling width is set within the above range.

(5) Center Segregation Index The criteria for the segregation index are shown in Table 4 below. (Segregation index within 100 mm from the widthwise end of the segregation zone)

[0045]

[Table 4]

(6) Rolling Down / Pinching / Conveying Device FIG. 5 is a side view showing an example of the rolling down / pinching / conveying device embodying the present invention, FIG. 6 is a front view thereof, and FIG. 7 is a wheel with inner and outer bars under pressure. bearing 3 _1, 3 _2, 4 _1, 4 ₂ and a cross-sectional view of arrow A~D in FIG 6 showing the motion of the eccentric cam E,
FIG. 8 is a bird's-eye view of the guide device. The device shown in these figures is used at a location for guiding continuously cast slabs in the horizontal direction.

The basic structure of this apparatus is that a rigid frame 1 is provided with two upper and lower support shafts 2 in total, and a total of four support shafts 2 are attached. The loop is used as an internal force, and basically only the weight of the device is applied to the foundation.

The support shaft 2 has four eccentric cams E and bearings with wheels, and two bearings 3 on the outside.
₁ and 3 ₂ are outer bars and 2 inner bearings 4 ₁ and 4 ₂
Is for the inner bar. These bearings 3 ₁ , 3 ₂ ,
4 ₁ and 4 ₂ have an intermediate eccentric cam E and a hydraulic cylinder 6,
It can be moved up and down arbitrarily by rotating with 9.

Outer bar wheel bearings 3 ₁ , 3
₂ is configured to move the outer bar 7 up and down by operating the eccentric cam E through the outer bar pressure hydraulic cylinder 6 via the outer bar pressure linking mechanism 5 and the outer bar pressure link 5 _1. There is. By this vertical movement, force is transmitted to the slab S through the outer bar 7.

Alternately to the application of force through the outer bar, the inner bar 10 is also eccentric via the inner bar pressure reducing cylinder 9, the bar pressure reducing link mechanism 8 and the outer bar pressure reducing link 8 _1. The mechanism is such that E is rotated by a predetermined angle to move the inner bar 10 up and down, and the force is transmitted to the slab S through this.

In order to maintain the pressure contact state between the inner bar 10 and the outer bar 7 and the bearing, the lower side is pressure-contacted by the weight of the bar, and the upper side is lifted by the lifting devices 11 and 12, respectively. .. This enables the release operation from the slab S.

In order to perform further run / return, the inner and outer bars 10, 7 are provided with inner bar run / return hydraulic cylinders 13 and outer bar run / return hydraulic cylinders 14, respectively. Then, the upper and lower inner bars 10 and the outer bar 7 are mechanically synchronized with each other through the inner bar run / return hydraulic link mechanism 15 and the outer bar run / return hydraulic link mechanism 16, respectively, to perform the run / return. ..

Inner bar 10 and outer bar 7 in this embodiment
The operation is basically based on the overlap reduction, but this is one pattern, and there is no great difference in the effect regardless of the reduction pattern.

Specifically, in a state where the outer bar 7 is applying a reduction to the slab S, the inner bar 10 operates the inner bar hydraulic cylinder 9 for chucking, and the inner bar 10 is operated as described above. Lower it. At the same time, at the time of chucking, the slab S
In order to prevent an abnormal force from being applied to the upper and lower inner bars 10, the upper and lower inner bars 10 are simultaneously accelerated so as to move at a speed substantially equal to the casting speed. The accelerating operation is completed at the time of chucking, and the inner bar 10 moves by being driven by the driving force applied to the slab S from the other while holding the slab S until the release.

Further, the outer bar 7 is released later than the chucking of the inner bar 10.

At the same time that the outer bar 7 is separated from the slab S by a predetermined distance, the outer bar approaching / returning hydraulic cylinder 14 is at the same time.
To quickly return to the specified position.
Then, the outer bar chucking process is started. This process is performed similarly to the inner bar chucking.

After the slab S is chucked by the inner bar 10 or the outer bar 7, in order to apply the predetermined amount of reduction to the slab S, the point where the pressure corresponding to the bulging force is generated in the pressure gauge 19 is zero. And the subsequent displacement is the displacement detector 17 for the inner bar.
Alternatively, the displacement is measured by the outer bar displacement detector 18, oil is supplied to the inner bar hydraulic cylinder 9 or the outer bar hydraulic cylinder 6 via the controller 21, and these cylinders are actuated to adjust the amount of reduction. To obtain the reduction amount of.

As is apparent from FIGS. 1 to 4 and Tables 2 and 3, the slabs obtained from the examples of the present invention have the center segregation and the center porosity extending from the width end portion to a predetermined rolling reduction region or more. The city was significantly improved, and further uniformly improved in the length direction of the slab, and the usage conditions were sufficiently satisfied even under the severe rolling conditions in the use of the shaped steel manufactured from the slab.

In contrast to this invention example, in the comparative example, center segregation and non-uniformity of center porosity were observed in the width side edge portion of the slab, which was an obstacle in the use of the above steel material.

While subjecting each of these slabs to rolling,
The relief process was performed according to the result of investigating the characteristics of the slab before supplying to the rolling step. A part of them could be subjected to segregation diffusion treatment by high temperature heating and / or pressure bonding treatment to satisfy the use condition for a predetermined application, but the steel material manufacturing cost inevitably increased. Further, some of the steel materials, which cannot be repaired at all, were generated as in the conventional example (non-countermeasure material example).

[0061]

According to the continuous casting method of the present invention, the center segregation and the center porosity generated in the slab at the position corresponding to the flange portion of the H-section steel and the I-section steel are uniform in the length direction of the slab. The quality of the slab is greatly improved. As a result, the yield was significantly improved in the production of H-section steel and I-section steel.

As a result, fearing the existence of these defects, the process cost and the process for investigating the quality condition of the continuously cast slab are generally omitted, and the high temperature heating and holding for a long time, which is performed before the rolling, are performed. Processes such as segregation / diffusion treatment can be omitted, and it has become possible to save a large amount of heat energy as well as equipment costs.

[Brief description of drawings]

FIG. 1 is a drawing showing the relationship among the amount of reduction per time, the central segregation index, and the occurrence of internal cracks.

FIG. 2 is a drawing showing the relationship between the total amount of reduction and the center segregation index and center porosity index.

FIG. 3 is a drawing showing the relationship between the solidification rate on the entrance side of a rolled zone and the center segregation index and center porosity index.

FIG. 4 is a drawing showing the distribution of the center segregation index and the center porosity index in the relationship between the distance from the inner surface of the shell on the short side to the end of the pressing terminal and the width of the pressing terminal.

FIG. 5 is a side view showing an example of a rolling-down / pinching / conveying device for carrying out the present invention.

FIG. 6 is a front view of FIG.

FIG. 7 is a cross-sectional view taken along arrows A to D in FIG. 6, illustrating the movement of the wheeled bearing and the eccentric cam when the internal and external pressure is reduced.

8 is a perspective view of the rolling-down, pinching-conveying device of FIG.

9 is a control system diagram of the rolling-down, pinching, and conveying device in FIG.

FIG. 10 is a diagram illustrating a rolling width of a walking bar.

[Explanation of symbols]

1 Vertical frame 2 Support shaft fixed in the width direction E Eccentric cam mounted on the support shaft S Cast piece 3 ₁ , 3 ₂ Wheeled bearings (for outer bar) 4 ₁ , 4 ₂ Wheeled bearings (for inner bar) R ₁ , R ₂ liner 5 Outer bar pressure reduction link mechanism 6 Outer bar pressure reduction hydraulic cylinder 7 Outer bar 8 Inner bar pressure reduction link mechanism 9 Inner bar pressure reduction hydraulic cylinder 10 Inner bar 11 Inner bar lifting device 12 Outer bar lifting device 13 Inner bar run / return hydraulic cylinder 14 Outer bar lifting device 15 Inner bar run / return link mechanism 16 Outer bar run / return link mechanism 17 Inner bar displacement detector 18 Outer bar displacement detector 19 Pressure gauge 20 Load cell 21 Controller 22 Servo valve

Claims (1)

[Claims] 1. A rough rolling method of H-section steel having a flange shaping hole on both sides of a web pressing portion after successively expanding and expanding a short side of a rectangular cross-section steel piece in an edging hole type group to form a flange bulge portion. The width of the flange shaping hole is formed to be at least 10% larger than the flange bulging portion after the edging of the material to be rolled, and the overall width of the die is substantially equal to the height of the web after the edging. In the production of H-section steel, in which the pressing portion is formed in the central curved shape with a gentle curved surface in the width direction, the web portion of the material to be rolled is repeatedly pressed to perform metal flow to the flange portion while rolling. In producing the steel slab by continuous casting, the solidification rate defined by the ratio of twice the thickness of the solidified shell to the thickness of the slab is 90% or more and 99% or less. Characteristic of performing a total reduction of 1.0% or more at a reduction of 0.5% or less per time by a surface member over a width of at least 50 mm on the center side in the width direction from the distance from the defined end. And continuous casting method. [Equation 1] Unreduced area (mm) = k√t + 10 Here, k = solidification constant, t = time (minutes) required for the slab of the reduced portion to be cast into the mold and to start reduction by the surface member is there.