JP2013086179A - Sheet bar joining method - Google Patents

Abstract

A sheet bar capable of preventing plate breakage in complete continuous hot rolling by improving the bondability around the edge in the width direction of the sheet bar joint without increasing the size of the joining device. A bonding method is provided.
[MEANS FOR SOLVING PROBLEMS] Immediately before finishing rolling in a hot rolling line, the tail end portion of the preceding sheet bar and the leading end portion of the succeeding sheet bar are sheared with a shear, and then heated and upset joined to finish continuously. In the complete continuous hot rolling method for continuously producing a plurality of hot-rolled steel sheet coils from a plurality of slabs by rolling, both edge portions in the width direction of at least one joining end face of the preceding sheet bar or the succeeding sheet bar The sheet bar is joined by heating and joining after chamfering the taper.
[Selection] Figure 1

Description

  The present invention relates to a sheet bar joining method capable of preventing plate breakage in complete continuous hot rolling by improving the bondability around the edge portion in the width direction of the sheet bar joined portion.

  In the hot-rolled steel plate manufacturing process, the thinner the finished plate thickness, the more likely it is that problems such as bumping at the tip and drawing or folding at the tail end occur during finish rolling. The time required to remove the line is a factor that greatly deteriorates the efficiency of the line. This is because in sheet rolling, equipment asymmetry due to looseness in each part of the rolling mill and wear of the rolling rolls, asymmetric temperature distribution of the rolled material, and local bending called nose bending of the sheet bar and large bending over the entire length called camber. The main cause of this is that the rolled material deforms asymmetrically with respect to the rolling direction. And it becomes easy to be in an unstable rolling state especially at the tip end portion where no tension is applied, and is more susceptible to influence as the finished plate thickness becomes thinner. In addition, the thinner the finished plate, the more likely it is that the tip flying phenomenon (lifting phenomenon due to air resistance) occurs on the cooling table after finish rolling. It has become. For this reason, in a batch rolling process in which one hot-rolled steel sheet coil is manufactured in order from one conventional slab, the minimum sheet thickness that can be manufactured is limited to about 1.2 mm.

  As a measure to overcome this situation, after roughly rolling the hot slab, the final end of the preceding sheet bar and the end of the succeeding sheet bar are joined and finish-rolled to obtain a plurality of slabs. Has been put to practical use a complete continuous hot rolling method for continuously producing a plurality of hot-rolled steel sheet coils. In the fully continuous hot rolling method, except for the tip of the most advanced coil and the tail end of the last continuous coil, the finish rolling is almost steady with a tension applied during finish rolling. The plate in the machine is very stable and rolling is possible with almost no troubles such as drawing. And combined with running sheet thickness change technology, running coil cutting, winding technology, etc., it is also possible to continuously manufacture hot rolled steel sheet coils with different finishing plate thickness, including thin hot rolled steel sheets of 1.0 mm or less. Yes.

  As a joining method of the sheet bar which has been put into practical use, the joining surface of the sheet bar is heated to the vicinity of the melting point and the joining surface is upset to join.

  At that time, heating in the vicinity of the joint surface is conducted by induction magnetic flux in the sheet bar thickness direction, the temperature is rapidly raised by Joule heat due to induction current, and heating and upset are completed within only a few seconds. A technique has been proposed (for example, Patent Document 1).

  Further, in order to increase the temperature around the edge in the plate width direction of the joint and improve the bondability, it has been proposed to install a high-frequency coil dedicated to edge heating outside both edges of the joint (for example, Patent Document 2). ).

  Similarly, as a technique for improving the bondability around the edge portion, an alternating magnetic field penetrating in the plate thickness direction is applied to heat and raise the temperature of the joint portion over the entire width direction, and in the region where the temperature variation is large, There has been proposed a technique for improving the temperature distribution of the edge portion by generating an alternating magnetic flux opposite to the magnetic flux (for example, Patent Document 3).

  And the technique which improves the temperature distribution of an edge part is proposed by arrange | positioning a magnetic body around the edge part of a junction part, and applying the alternating magnetic field which penetrates in a plate | board thickness direction (for example, patent document 4).

JP 62-234679 A JP-A-7-164018 Japanese Patent Laid-Open No. 8-1203 Japanese Patent Laid-Open No. 8-1202 JP-A-9-85310

  However, each of the conventional techniques related to the sheet bar bonding heating method using induction heating has the following problems.

  In the technique disclosed in Patent Document 1, since a phenomenon occurs in which the circulating current generated by the alternating magnetic field bypasses the vicinity of the edge portion of the joint portion, compared to the plate width center portion in a semi-molten state, the edge In the vicinity of the part, the temperature does not rise and the hardness increases at a low temperature. For this reason, when upsetting by joining the joining surfaces, the unmelted portion around this edge becomes a resistance and the upset load increases, and the upset amount at the center of the plate width cannot be secured sufficiently, adversely affecting the overall joining state. Inevitably, there is a problem that the probability of sheet breakage during finishing rolling passes increases.

  Moreover, the technique currently disclosed by patent document 2-patent document 4 is the technique devised as the improvement method of the edge part temperature which becomes a problem in patent document 1, First, patent document 2 is alternating in the whole junction part. Although the induction heating coil dedicated to the edge part, which is different from the induction heating coil for applying the magnetic flux, is arranged to improve the edge part temperature, although the effect of reliably improving the edge part temperature is recognized, Larger equipment and increased construction costs were inevitable.

  In Patent Document 3, although an improvement in the temperature of the edge portion is recognized, a temperature rise is hardly obtained by the detour current in the vicinity of the re-edge portion.

  Further, in Patent Document 4, a magnetic material is arranged around the edge part, and the temperature rise amount around the edge part is improved by increasing the magnetic flux density, but the effect of improving the temperature of the edge part is recognized, It is necessary to adjust the vertical position of the heating coil for the arrangement of the magnetic material, and it is inevitable to increase the size of the equipment.

  The present invention has been intensively studied to overcome the above-mentioned problems of the prior art, and improves the jointability around the edge in the width direction of the seat bar joint without increasing the size of the joining device. By doing this, the joining method of the sheet | seat bar which can prevent the board fracture | rupture in complete continuous hot rolling is provided.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies and can improve the bondability around the edge portion of the sheet bar joint portion, thereby preventing plate breakage in complete continuous hot rolling. We came up with a method for joining the sheet bars. The present invention has been made in view of the above situation, and has the following features.

  [1] Immediately before finish rolling on the hot rolling line, the tail end portion of the preceding sheet bar and the leading end portion of the succeeding sheet bar are sheared with a shear, and then heated and upset joined for continuous finish rolling. In the complete continuous hot rolling method for continuously producing a plurality of hot-rolled steel sheet coils from a plurality of slabs, both edge portions in the width direction of at least one joining end surface of the preceding sheet bar or the succeeding sheet bar are tapered. A method for joining sheet bars, characterized in that heating and joining are performed after chamfering into a shape.

  [2] Immediately before finish rolling on the hot rolling line, the tail end portion of the preceding sheet bar and the leading end portion of the succeeding sheet bar are sheared with a shear, and then heated and upset joined for continuous finish rolling. In the complete continuous hot rolling method for continuously producing a plurality of hot-rolled steel sheet coils from a plurality of slabs, the width direction with respect to the center of the width of each joining end face of the preceding sheet bar and the succeeding sheet bar A method of joining a sheet bar, characterized in that heating and joining are carried out after chamfering a point-symmetrical edge portion into a tapered shape.

  [3] The taper shape formed on the edge portion in the width direction of the joining end face is 50 mm or more in length from the plate width end portion in the plate width direction, and the length in the longitudinal direction is 50% or more of the upset amount. The sheet bar joining method according to [1] or [2], wherein the amount is equal to or less than the amount.

  According to the present invention, without accompanying the increase in size of the joining device, the sheet bar joint is improved in the jointability around the edge portion in the width direction, thereby preventing the plate breakage in complete continuous hot rolling and stabilizing. Rolling becomes possible.

It is a figure which shows the joining method of the sheet | seat bar by Embodiment 1 of this invention. It is a figure which shows the joining method of the sheet | seat bar by Embodiment 2 of this invention. It is a figure which shows the joining method of the sheet | seat bar by Embodiment 3 of this invention. It is a figure which shows the taper shape of the edge part of the seat bar by embodiment of this invention. It is a figure which shows the joining method of the conventional seat bar. It is a figure which shows the flow of the induction current by the induction heating of a sheet bar.

  An embodiment of the present invention will be described with reference to FIGS.

  FIG. 6 shows a conventional sheet bar joining method, that is, the tail end portion of the preceding sheet bar 1 and the tip end portion of the succeeding sheet bar 2 are each cut in a straight line in the plate width direction with a shear to form a rectangular shape. In this state, alternating magnetic flux is applied by the induction heating coil 3 while keeping the joint surfaces of the sheet bars separated by several mm. At this time, an induced current 6 is generated in the vicinity of the leading end of each sheet bar, and the temperature in the vicinity of the joint surface is rapidly increased. Usually, the sheet thickness of the sheet bar is about 25 mm to 50 mm, and the temperature before finish rolling is about 1000 ° C. to 1100 ° C. From this temperature, the leading end of the sheet bar is heated and joined, but the temperature at which the steel starts to melt (solidus) varies depending on the amount of carbon contained, but the steel grade of the component used for thin plate applications is in a semi-molten state. In order to join, it is necessary to heat to at least about 1450 ° C. to 1500 ° C. In fully continuous hot rolling, it is necessary to perform joining with the succeeding material while finishing and rolling the preceding material, so that the induction has a heating capability of at least about 200 ° C / sec from the viewpoint of equipment space and heating efficiency. It is desirable to use a heating device to complete the bonding within a few seconds including upset. However, the induced current generated by this method, on the characteristics, bypasses the corners of the rectangular sheet bar as shown in FIG. 6, so even if the center of the plate width is heated to a temperature above the solidus line, It is difficult to greatly increase the temperature around the edge portion in the plate width direction. Also, if the output of the induction heating device is extremely increased so that the temperature around the edge part is equal to or higher than the solidus line, the temperature near the central part of the plate width will melt beyond the liquidus line. The heating conditions are set so that the temperature of the part is between the solidus and above the liquidus.

  FIG. 5 is a diagram showing a situation in which the vicinity of the joining surface is heated by the conventional sheet bar joining method, and both sheet bars are upset and joined, and the filled region 4 represents a semi-molten region. Usually, from the edge to about 50 mm is a region where the temperature rise is insufficient due to the detour current, and it is in a completely solid state even at the time of upset. Due to the upset, the semi-molten part 4 is deformed while being pushed out in the vertical direction, and becomes a joined state. However, since the edge part is in strong contact with a completely solid state, both edges toward the outside in the plate width direction Plastically deforms in the protruding direction. In such a situation, the strong contact portion of the edge portion is a resistance against upset deformation, and an upset force larger than necessary is required. For this reason, the upset load will be high especially for hard materials such as high-strength steel and wide materials, so it is possible to apply upset deformation to obtain sufficient joint strength to perform finish rolling. It becomes difficult. In particular, in recent years, the need for reducing the weight of automobiles has rapidly expanded due to global environmental problems, and the demand for increasing the tension of thin plates is rapidly increasing. To increase the strength, alloy components such as Si, Cr, and Mo are frequently used. . Among these reinforced alloys, the melting point of oxides such as Cr and Mo is several hundred degrees C. higher than the melting point of steel, so it tends to remain as a solid at the joint interface when the sheet bar is joined, which causes a reduction in joint strength. ing. In addition, Si, Mn, etc. have a melting point lower than that of steel and are easily mixed and agglomerated by mixing in semi-molten steel. When silica and manganese oxide are formed, the melting point becomes higher and solidifies and remains, thereby increasing the bonding strength. It becomes a factor to reduce. For this reason, it is desirable to discharge the oxide in the vicinity of the bonding interface from the bonding interface by the material flow in the vertical direction due to the upset deformation, and it is important to realize a necessary and sufficient upset amount. The amount of upset here is defined as the amount of movement of both seat bars in the compression direction.

  Therefore, the present inventors have formed the edge in the width direction into a taper shape at the time of joining the sheet bar as means for reducing the resistance due to the low temperature edge and promoting the discharge of oxide due to upset to improve the joining strength. Inspired.

[Embodiment 1]
FIG. 1 is a view showing a sheet bar joining method according to Embodiment 1 of the present invention. FIG. 1 shows an example in which both edge portions in the width direction of the joining end portion are tapered before induction heating of the tail end portion of the preceding seat bar 1 and the tip end portion of the succeeding seat bar 2. In order to form both edges in the width direction into a tapered shape, for example, a shear that can cut the tip and tail ends of a sheet bar as disclosed in Patent Document 5 with separate shear blades. And shear blades having inclined portions at both ends in the plate width direction may be installed in the opposite directions for the tip end and the tail end and cut. Alternatively, it is possible to use another shearing device that cuts the leading and trailing ends of the sheet bar in a straight line with a shear and cuts both ends of the rectangular sheet bar in the plate width direction into a tapered shape. It is. In this way, it is possible to prevent strong contact with the complete solid part around the width direction edge by inductively heating the sheet bar in which both edge parts in the width direction of the plate are formed into a tapered shape. The outflow deformation in the vertical direction is promoted. Furthermore, when the sheet bar having a taper having the shape shown in FIG. 1 is upset, the molten portion at the joining interface is squeezed out in the plate width direction, so that the discharge of oxide from the joining interface is greatly promoted.

  FIG. 4 is an enlarged view of the tapered portion 5. According to the study by the present inventors, it was inevitable that a range of a length of about 50 mm from the edge in the width direction becomes a non-joined state in the conventional joining method because of the bypass characteristic of the induced current by induction heating. For this reason, in this Embodiment 1, the length a of the plate | board width direction of the width direction taper part is 50 mm or more. Moreover, when the width | variety of a leading material tail end and a trailing material front-end | tip differs, 50 mm or more from the edge part of the narrow material was made into width direction length a. In addition, since it will become a junction fracture | rupture when the width direction length a is too large, it is good to make 100 mm into an upper limit.

  If the length b in the longitudinal direction of the taper portion is less than 50% of the amount of movement of one sheet bar during upset, that is, the amount of upset, contact between solids at the edge portion may occur. Therefore, in this Embodiment 1, it is 50% or more of the upset amount. Further, if the length b in the longitudinal direction is made longer than necessary, the shear blade's inclination angle increases and shearing at this portion becomes difficult, so the length b in the longitudinal direction of the taper portion is upset. It stipulates that it is less than the amount.

[Embodiment 2]
FIG. 2 is a diagram illustrating a method of joining sheet bars according to Embodiment 2 of the present invention. As shown in FIG. 2, in the second embodiment, the tail end portion of the preceding seat bar is sheared in a straight line in the plate width direction, and both edge portions of the leading end portion of the succeeding seat bar are formed in a tapered shape.

[Embodiment 3]
FIG. 3 is a view showing a method for joining sheet bars according to Embodiment 3 of the present invention. As shown in FIG. 3, in the third embodiment, one edge portion in the plate width direction of the tail end portion of the preceding sheet bar is formed into a taper shape, and is point-symmetric with respect to the center in the plate width direction of the joining portion of the succeeding seat bar. The other edge portion is formed into a taper shape. Thus, for example, by using a shearing device having a mechanism in which the shearing blade shifts in the plate width direction, it is possible to form equivalent tapered shapes for sheet bars having various plate widths.

  In any case, it is possible to prevent the width direction edge portion, which is insufficient in temperature rise by induction heating, from becoming a resistance at the time of joining, and the discharge of oxide in the plate width direction is also promoted.

  In the first embodiment (FIG. 1), the second embodiment (FIG. 2), and the third embodiment (FIG. 3), the effects are all the same, taking into account the shear equipment and the range of the plate width of the material to be joined. And select the format.

  Examples of the present invention will be described with reference to Table 1.

  The target material is high-tensile steel with a tensile strength at room temperature of 590 MPa, and the sheet bar dimensions are 28 mm thick and 1300 mm wide for both the preceding and succeeding materials. In addition, the heating temperature was set so that the sheet bar temperature before bonding heating was about 1050 ° C. under all conditions. The induction heating conditions for heating the sheet bar joint were a frequency of 1 kHz and an input power of 1060 kW. By changing the shape of the shearing blade of the shear before the joining device, the tail end portion of the preceding material and the tip portion of the succeeding material are respectively formed into the shapes shown in FIGS. 1 to 3 and FIG. Went. The amount of upset was two levels of 15 mm and 25 mm. Then, after joining the sheet bar, using another shear installed before finish rolling, cut out a sample with a length of about 500 mm across the joint in the longitudinal direction, and observe the state of the joint after cooling to room temperature did.

  Table 1 shows a comparison between the edge unjoined part length (average value of both edges) of the joint and the upset load under each joining condition.

  In the conventional joining method of FIG. 5 which is a conventional example, the edge unjoined part length is about 100 mm, while in the present invention examples (Invention Examples 1 and 2), both are greatly improved to about 30 to 65 mm. In addition, the load required to perform the predetermined same amount of upset was also significantly reduced compared to the conventional example. Particularly, when the length a in the plate width direction of the tapered portion is 50 mm or more and the length b in the longitudinal direction is 50% or more of the upset amount, the upt load is low and the edge unjoined portion length Was significantly improved to 30-40 mm.

  In addition, after rolling the sheet bar under exactly the same conditions as in Table 1, finish rolling was performed. In that case, the joint part after finishing rolling was observed with the CCD system camera installed on the cooling table after finishing rolling. The edge unjoined portion in the sheet bar state expands in the longitudinal direction by finish rolling, and ◎ if the unjoined portion length from the edge in this state is less than 50 mm, ○ if it is 50 mm or more and less than 100 mm, 100 mm If it was less than 200 mm, it was evaluated as Δ, and if it was 200 mm or more, it was evaluated as x.

  In the conventional example, the joint portion was broken in the finishing mill under the condition that the upset amount was 15 mm (×). Moreover, the unjoined part length of the edge part after finish rolling became 200 mm or more also on the conditions of the upset amount of 25 mm (x).

  In contrast, all of the inventive examples (Inventive Examples 1 and 2) were evaluated as ◎ or ◯, and it was confirmed that stable finish rolling was possible.

DESCRIPTION OF SYMBOLS 1 Leading material 2 Subsequent material 3 Induction heating coil 4 Semi-molten part 5 Tapered part 6 Inductive current

Claims (3)

  Immediately before finishing rolling of the hot rolling line, by shearing the tail end portion of the preceding sheet bar and the leading end portion of the succeeding sheet bar with a shear, by heating, upset joining and continuously finish rolling, In a completely continuous hot rolling method for continuously producing a plurality of hot-rolled steel sheet coils from a plurality of slabs, both edge portions in the width direction of at least one joining end surface of a preceding sheet bar or a succeeding sheet bar are chamfered in a tapered shape. A method for joining sheet bars, comprising heating and joining after molding.   Immediately before finishing rolling of the hot rolling line, by shearing the tail end portion of the preceding sheet bar and the leading end portion of the succeeding sheet bar with a shear, by heating, upset joining and continuously finish rolling, In a fully continuous hot rolling method for continuously producing a plurality of hot-rolled steel sheet coils from a plurality of slabs, point symmetry in the width direction with respect to the center of the width of each joining end face of the preceding sheet bar and the succeeding sheet bar A method of joining a sheet bar, characterized in that heating and joining are performed after chamfering and forming the edge portion of the taper.   The taper shape formed on the edge portion in the width direction of the joining end surface is such that the length from the plate width end portion in the plate width direction is 50 mm or more, and the length in the longitudinal direction is 50% or more of the upset amount and below the upset amount. The method according to claim 1 or 2, wherein the sheet bar is joined.