JPH08281304A - Complete continuous rolling method for hot rolled steel by tack welding and joining - Google Patents

Abstract

(57) [Summary] [Purpose] It is an object of the present invention to provide a continuous rolling method for hot-rolled steel that can be joined in a short time and at low equipment cost. [Composition] Both ends of the trailing edge and the trailing edge of the preceding material of the hot-rolled steel material running on the pass line are arranged in front of and behind each other.
It is characterized in that the area bonding rate is improved to 30% or more by performing pre-bonding by the welding method so that the area bonding rate becomes 5% or more and less than 20%, and then rolling at a rolling reduction of 20% or more. Online joining method for hot rolled steel.

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 materials to be rolled (sheet bar, bar, etc.) on-line between a rough rolling step and a finish rolling step when performing complete continuous hot rolling.

[0002]

2. Description of the Related Art For example, in hot tandem rolling of a thin plate, a slab sent from a steelmaking process is roughly rolled into a sheet bar (rough bar), and this sheet bar is rolled by a hot rolling mill with multiple stands. Then, it is wound into a coil to form a thin plate coil having a predetermined size.

However, in finish rolling, since the sheet bar has a finite length, unsteady rolling is inevitable when the front end of the sheet bar is caught and the rear end of the sheet bar is slipped out. Therefore, from the viewpoint of preventing passing defects such as narrowing of the plate, a method of slowing the passing speed at the time of passing the front and rear ends of the sheet bar is adopted, which is a factor that hinders productivity. There is.

As a countermeasure against this, it has been considered to join a sheet bar having a finite length between a rough rolling mill and a finish rolling mill to perform so-called endless rolling. That is, FIG.
The problem is to join the sheet bars in the part surrounded by the dotted line 5 of. Here, 1 is a roll for finish rolling, 2 is a preceding material of a sheet bar which is a material to be rolled, 2-1 is a trailing end of the preceding material, 3 is a trailing material, 3-1 is a leading end of the trailing material. 4 is a table roller and 5 is a joining position.

Japanese Unexamined Patent Publication (Kokai) No. 57-109574 discloses a process comprising a rough rolling mill, a coil box, a heat retaining device, an unwinding device, a movable joining machine (swing roller table), and a finishing rolling mill. There is. With this method,
It takes time to join the entire rear end portion of the preceding material and the leading end portion of the following material, and the traveling distance of the mobile joining machine becomes long.

A method of partial joining is disclosed in JP-A-60-2.
44401, JP-A-5-52905, JP-A-60-
184481, JP-A-60-213380, JP-A-4-71601, JP-A-61-52905 and the like. Is a method of joining 30% or more around the cross section by induction heating + upset. If only the inside of the cross section is joined, the plate will break during rolling, so it is necessary to join the periphery. Is a method of rolling in a state where the joining ratio in the plate thickness direction of the joined surfaces by causing relative slip and plastic deformation on the leading end surface and the trailing end surface is 20% or more. Is a method in which the front end surface and the rear end surface are inclined, and only the upper surface is joined by welding by 10% or more of the plate thickness and then rolled. Is a method in which only plate width ends are welded by 20% or more and then rolled. In this method, 20% or more of only the plate width end is welded and rolled.
Uses the arc welding method, but the welding ratio in the plate thickness direction is 6
It says that 7% or more is required.

When the above-mentioned various methods are compared in a unified manner based on the concept of the joint area ratio, it is said that the joint area ratio of 20% or more is required for all other methods. The joining area ratio is the ratio of the cross-sectional area of joining to the cross-sectional area perpendicular to the rolling direction of the sheet bar, and the joining ratio in the plate thickness direction (the joining thickness of the sheet bar in the rolling direction It is the product of the ratio of the vertical cross section to the plate thickness) and the plate width direction bonding ratio (the ratio of the plate width bonded to the sheet bar to the plate width of the cross section perpendicular to the rolling direction). The joint area ratio is 10%
However, in this case, both end faces are processed into inclined surfaces so that the joint area can be easily increased during rolling, and the joint ratio before rolling is not simply 10%, but the inclined end faces The effect of pressure welding by superposition is essential. That is, all of the conventional techniques require a large preliminary joining area ratio, and it is difficult in layout to secure such a preliminary joining area ratio by the moving welding method.

As an example of a fixed welder, Japanese Patent Laid-Open No. 61-1
No. 58285 and Japanese Patent Laid-Open No. 61-242768 disclose processes using electric heating and upset. In this method, since a fixed welding machine is used, a swing roller type table is unnecessary. However, considering that a seat bar storage device such as a looper is required, and the minimum bending radius of curvature that does not cause plastic deformation of the seat bar is often on the order of about 25 m, enlargement of equipment such as a looper is required. It has the drawback of inevitably increasing costs.

[0009]

In the above-mentioned prior art, there is a problem that the welding of the seat bar requires a long time, so that the line length becomes long and the equipment cost becomes high. In order to solve this problem, it is necessary to develop a technique capable of joining in a short time. The present invention has been made to meet such a demand.

[0010]

As a result of various studies on the method of joining in a short time, the inventors of the present invention found that a method of preliminarily joining by welding and strengthening the joining by subsequent rolling is effective. all right. That is, the front end and the rear end of the preceding material of the hot-rolled steel running on the pass line are welded in front of and behind each other so that the joint area ratio is 5% or more and less than 20%. By pre-bonding, and then the first pass rolling is performed at a reduction rate of 20% or more. As a result, the joining area ratio of the joining portion can be improved to 30% or more, so that joining can be performed in a short time and finish continuous rolling can be performed without plate breakage. The technical contents will be described below.

In order to obtain a pre-bonded area ratio that does not cause rolling rupture, a test piece welded as shown in FIGS. 2 and 3 was rolled. In both figures, (a) is a longitudinal sectional shape before welding and (b) is a longitudinal sectional shape after welding. In addition, 6 is a welding part. Figure 2
Shows a shape in which the tip and the rear end of the rough bar are cut by a saw, for example, and FIG. 3 simulates the shape in which the tip and the rear end of the rough bar are cut by a crop shear, for example. As a result of investigating the rupture behavior during rolling by conducting rolling experiments with various changes in the welding depth in the plate thickness direction and the welding width in the plate width direction, it was found that there is a rolling rupture limit line as shown in FIG.

Curve A in FIG. 1 has a low tension between stands,
In the case of rolling by the first stand of the finish rolling mill close to zero, if the preliminary joining area ratio is smaller than this, the joining area is reduced by rolling and a limit line leading to fracture is shown. This line corresponds to a pre-bonded area ratio of approximately 5%. This is obtained by rolling various kinds of test pieces having different pre-bonding area ratios without tension and investigating the pre-bonding area ratios leading to breakage.

Curve C in FIG. 1 shows the rupture at the time of rolling when the tension between stands acts like the latter stage of the finish rolling mill. This is the result obtained by investigating the rate. The front and rear tensions in this case are 0.3 times the deformation resistance of the rolled material. Curve C corresponds to a bonding area ratio of approximately 30%. These curves A and C will be referred to as fracture limit lines during tensionless rolling and tension rolling.

The joining portion between the trailing end portion of the preceding material and the leading end portion of the following material corresponds to the strength corresponding to the rolling stage from the first stand of the finishing rolling mill having low tension to the latter stage of finishing rolling where tension acts. Since it suffices to secure the above-mentioned bonded area, the bonded area ratio of the bonded portion is between the curves A and C in FIG.
It is understood that it is enough if it is up to 30%.

The inventors examined the conditions for obtaining such a joint area ratio. That is, test pieces having various pre-bonded area ratios were subjected to one pass rolling at a normal rolling temperature of 900 to 1100 ° C. while changing the reduction ratio, and the bonded area ratio after rolling was investigated.

As a result, as shown in FIG. 4, when the preliminary bonding area ratio was less than 5%, the bonding area ratio was reduced by rolling, and the bonded portion was sometimes broken. 5% pre-bonding rate
It was found that with the above, the joint area ratio after rolling increases as the rolling reduction increases.

Further, it has been found that if the reduction ratio is 20% or more, the bonding area ratio exceeds 30% after the first pass rolling even if the preliminary bonding ratio is 5%. That is, the experimental result of FIG. 4 shows that the joint area ratio increases by performing tensionless rolling of the joint area ratio larger than A at various reduction ratios.
It shows that the area of the bonding area ratio of C or more is entered at the rolling reduction of 0% or more. That is, since there is almost no tension at the beginning of rolling, if the preliminary joining rate area (5%) of the breaking limit line of A in FIG. 1 can be secured, rolling can be performed without breaking. As the rolling progresses, the tension generally increases, but the joint area ratio due to the rolling also increases, and the fracture does not occur.

From the above results, it is possible to improve the bonding area ratio to 30% or more by setting the pre-bonding area ratio by welding to 5% or more and performing the first pass rolling with the reduction ratio of 20% or more. Finish rolling can be performed without strip breakage. However, in actual work, since the preliminary joining must be completed in a short time, the preliminary joining area ratio has an upper limit.

The line length between the rough rolling mill and the finish rolling mill is
Usually, it is about 100 m at the longest. Due to various equipment restrictions, the length that can be used for preliminary joining is about 50 m, which is half this length. The maximum bar speed on the entry side of the finishing mill is 100.
It is about m / min. Therefore, the joining time is 30 seconds, but when the various positioning operations and the cooling time after welding are subtracted, the net pre-welding time is usually about 5 seconds. As a result of various studies on the area ratio at which welding is possible in about 5 seconds, it has been found that a joint area ratio of less than 20% can be applied to various sizes of ordinary coarse bars. For example, when the plate thickness is 50 mm and the plate width is 2200 mm, which are usually the maximum dimensions of a rough bar, the plate thickness bonding ratio is 30% and the plate width bonding ratio is 67%, that is, it takes about 5 seconds to weld about 20% of the bonding area ratio. Needed The arc welding method was adopted as the welding method. The welding conditions are as follows.

Welding current: 1000 to 2000 A Arc voltage: 20 to 35 V Shielding gas: CO ₂ , He Torch number: 6 units Speed of one torch in plate width direction: 3 m / min

With a coarse bar having a smaller cross-sectional area, the pre-bonded area ratio can be increased to 20% or more even if the same welding conditions are applied, but the rollability does not change even if it is increased to 20% or more. On the contrary, if the welding time becomes long, the temperatures of the trailing edge of the preceding material and the leading edge of the following material decrease and the frequency of dents and scratches increases, which is a disadvantage. Therefore, the preliminary bonding area ratio is set to 20% or less. A limit line having an area ratio of 20% is shown by a line B in FIG.

From the above examination results, pre-joining was carried out so that the joining ratio was between the limit lines A and B, and the joining was performed by applying a reduction of 20% or more in the first pass having low tension. It can be seen that it is appropriate to raise the area ratio to 30% or more and to perform the post-finishing rolling after-stage in the region of the bonding area ratio larger than the limit line C.

[0023]

Example Preliminary joining rolling was performed under the following conditions. <Sheet bar> Material: Low carbon Al killed steel Dimension: Plate thickness t = 50 mm, plate width W = 2200 mm End face dimension: The cut surface shape by shear is shown in FIG. In the figure, t is the plate thickness. The approximate dimensions of the end face are x1 = 25 mm y1 = 10 mm x2 = 10 mm y2 = 26 mm.

<Preliminary joining conditions> Gas shield arc welding conditions Welding current: 1500A Arc voltage: 30V Shielding gas: Number of CO ₂ torches: 6 groups Preliminary joining rate: Strip width joining rate 67% Sheet thickness joining rate 30%

<Finishing rolling conditions> Rolling mill: 7-stand continuous rolling mill Speed: 60 mpm (on entry side of finishing rolling mill) Temperature: 1000 ° C (on entry side of finishing rolling mill) 1st pass rolling reduction: 40 % Finished plate thickness: 2.5mm

FIG. 6 schematically shows the shape after rolling, and 90% or more of the entire cross section was joined. The broken line indicates the joining position.

[0027]

As described above, according to the present method, since the joining can be performed in a short time of about 5 seconds or less, it can be applied to most of the existing hot rolling processes, and greatly improves the productivity and the product quality. Can contribute.

[Brief description of drawings]

1] Rolling fracture limit line.

FIG. 2A is a vertical cross-sectional shape of a trailing end portion of a preceding material and a leading end portion of a following material after saw cutting, and FIG. 2B is a longitudinal sectional view after welding of FIG. 2A.

FIG. 3A is a vertical cross-sectional shape of a trailing end portion of a preceding material and a leading end portion of a following material after crop shear cutting, and FIG. 3B is a longitudinal sectional view after welding of FIG. 3A.

FIG. 4 shows the relationship between the joint area ratio after rolling and the preliminary joint area ratio.

FIG. 5 is a cross-sectional view showing an example of a cut surface shape by a shear.

FIG. 6 is a plan view showing an example of the shape of the joint after finish rolling.

FIG. 7 is a finish rolling mill and its front equipment arrangement.

[Explanation of symbols]

 1 Finishing Roller 1st Stand 2 Seat Bar (Preceding Material) 2-1 Preceding Material Rear End 3 Sheet Bar (Reverse Material) 3-1 Trailing Material Tip 4 Table Roller 5 Joining Position 6 Weld

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Kouhei Nakajima 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd.

Claims (1)

[Claims] 1. A joint area ratio of 5% or more and less than 20% between both ends of a trailing end of a preceding material and a leading end of a following material of a hot rolled steel material running on a pass line in front of and behind each other. As described above, the method for online joining of hot-rolled steel products is characterized in that pre-joining is performed by welding and then the first pass rolling is performed at a reduction rate of 20% or more.