JPH0671306A - Hot joining method for hot rolled steel sheets - Google Patents

Abstract

(57) [Summary] [Structure] Before performing superposition, a warp-shaped bend is applied to the rear end of the preceding hot-rolled steel plate or the tip of the subsequent hot-rolled steel plate,
Next, the preceding hot-rolled steel sheet and the subsequent hot-rolled steel sheet that are running are superposed, and then the superposed portion is heated in a reducing atmosphere,
The hot-rolled steel sheet is rolled and joined in the longitudinal direction. [Effect] It is possible to perform pressure welding by a relatively simple method while the scale is attached to the joint portion of the hot rolled steel sheet and the hot rolled steel sheet is running. Moreover, the joint strength of the joint is extremely high. Therefore, continuous finish rolling becomes possible, and the yield and productivity of the rolling line can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining hot rolled steel sheets on a rolling line with high yield and high efficiency.

[0002]

2. Description of the Related Art In the rolling process of an iron manufacturing plant, continuous lines are being used mainly for the purpose of improving yield and improving productivity.

In the conventional hot rolling, the heated slabs are supplied one by one to a rough rolling machine and a finishing rolling machine to perform rolling intermittently. In such intermittent rolling, particularly in the case of rolling with a thin plate thickness, the front end of the hot-rolled steel plate is often struck by the guide roll, or the rear end of the hot-rolled steel plate is often narrowed when leaving the rolling mill. Therefore, in order to solve these problems, it is necessary to reduce the rolling speed to reduce the efficiency of the rolling process. Further, in the front end and the rear end of the hot-rolled steel sheet, the balance of the rolling speed is often unbalanced as compared with the central portion thereof, and often out of the appropriate rolling temperature range,
Along with this, dimensional deviation easily occurs. Therefore, the leading end and the trailing end of the hot-rolled steel sheet, which becomes defective as a product, are discarded. As a result, the yield of the rolling process is reduced.

In recent years, a method has been proposed in which a rear end of a preceding hot-rolled steel sheet and a leading end of a subsequent hot-rolled steel sheet are joined between a rough rolling mill and a finish rolling mill, and continuous finish rolling is performed. For example, JP-A-58-
Japanese Patent Publication No. 151971 discloses a method in which the rear end of the preceding hot-rolled steel sheet and the leading end of the subsequent hot-rolled steel sheet are butted against each other while the welding machine is traveling in synchronization with the traveling hot-rolled steel sheet. However, this method has a problem in that the electrode is easily damaged, and the scale is still attached to the welded portion, the current flow is unstable, and the welding is insufficient, so that sufficient joint strength cannot be obtained. Further, it is substantially difficult to accurately synchronize a large-scale welding machine with a hot-rolled steel sheet traveling at high speed. Further, JP-A-61-1489 discloses a method in which the trailing end of the preceding hot-rolled steel sheet and the leading end of the subsequent hot-rolled steel sheet that are running are overlapped and pressed together. However, in this method, although the scale is removed before pressure welding, the hot-rolled steel sheet is at a high temperature, so that the joint portion is instantaneously oxidized and scale is generated again, so that there is a problem that sufficient joint strength cannot be obtained. Furthermore, as a method of superimposing, the table for transporting the hot-rolled steel sheets is moved up and down in order to superimpose the leading edge of the subsequent hot-rolled steel sheet on the rear edge of the preceding hot-rolled steel sheet. It is extremely difficult to raise and lower the table. Moreover, in a severe environment in which the scale falls and the temperature is high, the lifting device is likely to malfunction.

A method has also been proposed in which hot-rolled steel sheets are held stationary and joined by welding or pressure welding.

However, this method requires a long looper between the joining machine and the finish rolling machine. Further, since the hot-rolled steel sheet is in contact with the roll for a long time while it is stationary, the hot-rolled steel sheet is locally cooled, which also causes a change in the plate thickness in the subsequent finish rolling.

In the pressure welding method disclosed in Japanese Patent Laid-Open No. 61-1489, it has been conventionally considered necessary to remove the scale of the joint surface in advance and clean it. However, the present applicant has previously patented the invention of "a method for hot joining steel materials" based on the finding that prior descaling is not necessarily required if pressure welding is performed in a reducing atmosphere. Filed (Japanese Patent Application No. 2-268748, hereinafter referred to as prior invention). The invention of the prior application is a method of heating the lapped portion or the butted portion of the hot rolled steel sheet in a reducing atmosphere and press-contacting the hot rolled steel sheet in the width direction. If the pressure welding is performed in a reducing atmosphere, the pressure welding can be performed without positively removing the scale, so that the hot-rolled steel sheets can be joined efficiently by a simple method. However, in this method, the rolling reduction of the joint is usually 50%, and plastic deformation occurs in the width direction of the hot-rolled steel sheet due to the rolling, which may cause troubles such as breakage during finish rolling.

[0008]

FIG. 4 is a view showing a state in which the joint portion is pressure-welded in the width direction of the hot-rolled steel sheet. Figure 4
(A) is a plan view of the joint, (b) is a sectional view taken along the line AA of (a), and (c) is a sectional view taken along the line AA of (a) before pressure welding. In FIG. 4, 1 and 2 are hot rolled steel sheets after rough rolling, and 3 and 4 are pressure rolls. Pressure roll 3,
When the hot-rolled steel sheets 1 and 2 are joined by moving the pressure rolls 3 and 4 in the direction of the arrow Y shown in FIG. , The mouth opens on the side surface of the joint due to plastic deformation due to rolling (hereinafter, this phenomenon is referred to as "mouth opening"). If this opening is large, the joint strength will decrease, cracks will occur in the joint in the continuous rolling process after hot joining, and in the worst case, the joint will break.

The object of the present invention is, in hot joining of hot-rolled steel sheets, pressure-welding is performed during running of the hot-rolled steel sheets without causing a mouth opening with a scale attached to the joining portion, and yet a high joining strength is obtained. To get.

[0010]

SUMMARY OF THE INVENTION According to the present invention, a warp-shaped bend is applied to a rear end of a preceding hot-rolled steel sheet or a leading end of a subsequent hot-rolled steel sheet before superposing, and then the preceding hot-rolling sheet during traveling is performed. The gist is a hot-joining method for hot-rolled steel sheets, in which a steel sheet and a subsequent hot-rolled steel sheet are superposed, and then the superposed portion is heated in a reducing atmosphere and rolled in the longitudinal direction of the hot-rolled steel sheet to be joined.

Here, the reducing atmosphere means an atmosphere surrounded by a reducing gas such as a mixed gas of _Ar and H ₂ or acetylene or propane gas with oxygen that is less than the amount of combustible gas completely burned, It means the atmosphere obtained when the joint is heated using a flame (referred to as “reduction flame”) generated when LPG, coke oven gas, etc. are burned.

Hot-joining means joining hot-rolled steel sheets in a hot state, for example, on a rolling line.

[0013]

The main feature of the method of the present invention is that the end portions of the hot-rolled steel sheets are positively bent into an upward warped shape and overlapped without descaling, and then the overlapped portion is aligned in the longitudinal direction of the hot-rolled steel sheet. The purpose is to perform hot joining of hot rolled steel sheets by rolling.

Before the superposition, the superposition is facilitated by bending either the rear end of the preceding hot-rolled steel plate or the front end of the subsequent hot-rolled steel plate with a certain size and shape.

FIG. 2 shows a method of bending the rear end or the front end of the hot rolled steel sheet. 2A shows the roll bender method, and FIG. 2B shows the press method. Figure 2
In (a), the fixed roll 6 is set to a standard height, and the rear end or the front end of the hot-rolled steel plates 1 and 2 is pushed down by the bending roll 5 and at the same time pushed up by the bending roll 7 to bend. In FIG. 2B, the upper die 8 is set to a standard height, and the rear end or tip of the hot-rolled steel plates 1 and 2 is bent by being pushed up by the lower die 9.

When bending the rear end of the preceding hot-rolled steel sheet, it is necessary to slide the roll bender or the press in synchronization with the running hot-rolled steel sheet. When bending the tip of the subsequent hot-rolled steel sheet, the bending may be applied by sliding the roll bender or press in synchronization with the hot-rolled steel sheet that is running, as in the case of the trailing edge, or running. The hot rolled steel sheet may be momentarily stopped, that is, the bending may be applied with the roll bender or press still in place.

FIG. 3 shows the dimensions of the desired warp shape. Although FIG. 3 shows the dimension of the warp shape at the rear end of the hot-rolled steel sheet, it is exactly the same at the front end of the hot-rolled steel sheet. In FIG. 3, (a) is a roll bender method, and (b) is a press method. In the case of a hot rolled steel sheet with a wall thickness t, FIG.
It is preferable to bend g = (3 to 10) × tmm in the longitudinal direction and h = (1.5 to 3) × tmm in the thickness direction as shown in FIG. If the longitudinal dimension g is shorter than 3 × tmm, the bonding strength will be insufficient, and if it is longer than 10 × tmm, the yield will be poor.
If the dimension h in the thickness direction is shorter than 1.5 x tmm, the leading edge of the subsequent hot-rolled steel sheet will easily collide with the trailing edge of the preceding hot-rolled steel sheet, and
If it is longer than tmm, the hot-rolled steel sheet having a bend at the end will not be caught in the press rolling mill.

FIG. 1 shows that the tip of the succeeding hot-rolled steel sheet is bent, the rear end of the preceding hot-rolled steel sheet and the tip of the succeeding hot-rolled steel sheet are overlapped, and heated in the reducing atmosphere as they are to be pressure-welded. It is a figure. In FIG. 1, the preceding hot-rolled steel sheet 1 is a finish rolling mill.
Rolled in the direction of arrow A at 12. On the other hand, the subsequent hot-rolled steel sheet 2 is bent at its tip by the upper die 8 and the lower die 9 and then accelerated by the pinch roll 13 to catch up with the preceding hot-rolled steel sheet 1. When the tip of the subsequent hot-rolled steel sheet is overlapped so as to cover the rear end of the preceding hot-rolled steel sheet, the joint is heated by the reduction burner 10 and the rolling machine for pressure welding 11 at a predetermined temperature while maintaining the reduced state. Is pressed in. Further, the object of the present invention can be achieved also in a case where the planned portion to be joined is heated by the reduction burner 10 before superposition, superposed while maintaining the reduced state, and press-contacted by the press-contact rolling mill 11 at a predetermined temperature.

The reason why the pressure welding is performed in the reducing atmosphere obtained by the reducing burner 10 is that the pressure welding can be performed without removing the scale adhering to the joint portion of the hot rolled steel sheet.
Usually, even if pressure welding is performed with the scale attached to the joint, sufficient joint strength cannot be obtained. However, when pressure welding is performed in a reducing atmosphere, the oxides forming the scale are reduced,
Ignore the scale and overlap the joints, and you can press them as they are. The joint strength of the joint is the same as that when the scale is removed. Therefore, the scale removing device is not required in the rolling line, and the layout of the rolling line is simplified.

In the reducing atmosphere, a large number of round burners are arranged in both the width direction and the longitudinal direction of the hot rolled steel sheet, or a plurality of linear burners are arranged in the longitudinal direction of the hot rolled steel sheet, for example, acetylene or propane gas. Combustible gas such as
It can be obtained by appropriately controlling the oxygen ratio at that time. This reducing atmosphere is a gas containing a large amount of hydrogen and carbon monoxide. Further, in order to maintain this reducing atmosphere until the completion of the pressure welding of the joining portion, it is better to dispose the burner as close as possible to the pressure welding rolling mill 11. The time required to reduce the joint depends on the scale thickness attached to the joint and the heating temperature of the joint.

The pressure welding is performed by the rolling machine 11 for pressure welding in the longitudinal direction of the hot rolled steel sheet. By rolling and joining in the longitudinal direction (the direction of arrow X in FIG. 4), the opening that decreases the joining strength does not occur. The reduction rate in the pressure contact may be within the range of the reduction rate in the case of ordinary superposition. That is,
The plate thickness after pressure contact is made almost equal to the plate thickness of the non-pressure contact part, and the rolling reduction is set to about 50% so as not to cause trouble in the next finish rolling process.

Further, in order to secure the bonding strength, it is desirable that the lower limit of the rolling reduction is 20%.

In the method of the present invention, it is not necessary in principle to correct the bend originally existing at the end of the hot-rolled steel sheet.
However, when the original bend of the end of the hot-rolled steel sheet that is not bent is too large, it is desirable to correct the bend.

This is because, if straightening is performed, the scale (thin scale or floating scale), which is basically a negative factor for hot joining, can be removed at the same time. Although descaling of the hot rolled steel sheet before pressure welding is not essential, it is desirable to remove extremely thick scale in advance.

[0025]

Example A low carbon steel plate having a plate thickness of 10 mm, a width of 300 mm and a length of 700 mm was heated to 1150 ° C. in a heating furnace.

After extracting the steel sheet from the heating furnace, the preceding hot-rolled steel sheet 1 and the subsequent hot-rolled steel sheet 2 were conveyed in this order to the rolling line shown in FIG. In the rolling line, the preceding hot-rolled steel sheet 1 is finished by the rolling mill 12
During rolling, the subsequent hot-rolled steel sheet 2 is bent by a press-type bending machine having an upper die 8 and a lower die 9, and then the pinch roll 13 accelerates the subsequent hot-rolled steel sheet 2 I was able to catch up with the preceding hot-rolled steel sheet 1. The bending applied to the tip of the subsequent hot-rolled steel sheet 2 was set to the value shown in Table 1 within the range of the dimension (longitudinal direction g × thickness direction h) shown in FIG. When the front end of the subsequent hot-rolled steel plate 2 is superposed on the rear end of the preceding hot-rolled steel plate 1, a reducing flame generated by a reducing burner 10 which uses propane gas as a main combustion gas is directly blown to the joint to give a predetermined pressure contact temperature (1200 The joint was reduced for 15 seconds while heating to (° C). Immediately after reaching the pressure welding temperature, the joint was pressure welded by the pressure welding rolling mill 11. The rolling reduction at this time was changed within the range of 20 to 50%. Next, the rolling line was stopped and the joint was cut before the joint was rolled by the finish rolling mill 12. After that, a tensile test at room temperature was performed on the joint, and the fracture state was observed. In the normal temperature tensile test, it was considered that the joint had good joint strength when it fractured at the non-joint part, and it was considered that the joint strength of the joint part was insufficient when it fractured at the joint part. .

The results are shown in Table 1. In this example, it was found that all the joints were broken and the joints had good joint strength.

[0028]

[Table 1]

[0029]

EFFECTS OF THE INVENTION According to the method of the present invention, pressure welding can be performed relatively easily while the scale is attached to the joint portion of the hot rolled steel sheet and the hot rolled steel sheet is running. Moreover, the joint strength of the joint is extremely high. Therefore, continuous finish rolling becomes possible, and the yield and productivity of the rolling line can be improved.

As shown in the method of the present invention, if either the rear end or the front end of the hot-rolled steel sheet is bent, the hot-rolling is performed by a device that requires complicated timing control in a harsh environment. Hot-rolled steel sheets can be stacked without changing the pass line of the steel sheets. Therefore, the structure and layout of the rolling line are extremely simple.

[Brief description of drawings]

FIG. 1 is a schematic view of a rolling line for explaining a hot joining method for a hot rolled steel sheet according to the present invention.

2A and 2B are diagrams showing a method of bending a rear end or a front end of a hot-rolled steel sheet, wherein (a) is a roll bender method and (b) is a press method.

FIG. 3 is a diagram showing dimensions of a desired warp shape,
(a) is for the roll bender method, and (b) is for the press method.

FIG. 4 is a diagram showing a state in which a joint portion is pressure-welded in a width direction of a hot-rolled steel sheet, (a) is a plan view of the joint portion, and (b) is a plan view.
It is an AA sectional view of (a), (c) is A- of (a) before pressure welding.
FIG.

Claims (1)

[Claims] 1. A warp-shaped bend is applied to the trailing end of the preceding hot-rolled steel sheet or the leading end of the subsequent hot-rolled steel sheet before the superposition, and then the preceding hot-rolled steel sheet and the subsequent hot-rolled steel sheet that are running are overlapped. A hot-joining method for hot-rolled steel sheets, which comprises joining and then heating the overlapped portion in a reducing atmosphere and rolling and rolling in the longitudinal direction of the hot-rolled steel sheet.