JPH07314005A - Hot rolling method for steel strips with different widths - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a hot rolling method that enables pressure welding of a material having a high thickness width ratio of a sheet bar of different width steel slabs and reduces fracture during rolling after pre-joining. [Structure] In hot rolling continuous rolling in which bar joining is performed before continuous finish rolling, when the width of a wide steel sheet is (W0 mm) and the width of a narrow steel sheet is (Wmm), the wide steel sheet is cut from both edges. Position (Tmm) of 0.4 (W0-W) ≦ T ≦ 0.6
With this position as a reference, the total cutting length is (W0-W) at an angle of 30 to 50 ° with respect to the rolling direction.
0-W), and after aligning the widths of both steel pieces, both the rear end of the preceding material and the front end of the following material so that the maximum gap of the joint end surface is 5 mm or less. Joining 5% or more of the narrow material cross-sectional area including the edge portion, and rolling immediately after joining between the maximum roll diameter (Mt) and the minimum roll diameter (Et) of the steel plate rolling portion, Mt-Et ≧ 100 μm Roll using a hot rolling roll having the following relationship.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling method for hot-rolled material joining in which hot strips (sheet bars) having different widths are joined and continuous in the field of hot rolling.

[0002]

2. Description of the Related Art As a joining method for continuous hot rolling, a method is known in which the trailing end portion of the preceding rolled material and the leading end portion of the trailing rolled material are butted against each other and pressed and joined together. As this joining method, Japanese Patent Laid-Open No. 61-144203 proposes a method of pre-joining both end portions in the width direction, followed by rolling at a reduction rate of 20% or more and pressure bonding. In addition, JP-A-5-
Japanese Laid-Open Patent Publication No. 104107 proposes a method of welding both edges of a preceding material and a following material and then crimping by changing the crown ratio of the plate material before and after rolling.

[0003]

The size of the hot rolled steel sheet varies depending on the order, and the width of the steel material varies, so that the continuity is interrupted only when the width is the same. Therefore, in order to maximize the effect of continuous hot rolling, it is necessary to enable joining of different width materials. In the above-mentioned prior art, when joining different width materials, it was often observed that both edges were not fixed and the joining position fluctuated, resulting in breakage during rolling immediately after joining.

An object of the present invention is to solve the above problems and to provide a manufacturing method which does not cause breakage due to rolling even when joining sheet bars having different widths.

[0005]

The gist of the present invention for solving the above-mentioned problems is that the width of a wide steel sheet in hot rolling continuous rolling in which bar joining is performed before continuous finishing rolling:
(W0mm) and width of narrow steel plate: (Wmm), the position (Tmm) of the wide steel plate from both edges is 0.4 (W0-
W) ≦ T ≦ 0.6 (W0-W) so that the total cutting length becomes (W0-W) at an angle of 30 to 50 ° with respect to the rolling direction based on this position. After cutting and aligning the width of both steel pieces, narrow width material including both edges of the trailing edge of the preceding material and the leading edge of the following material so that the maximum gap between the joint end faces is 5 mm or less. A hot rolling roll having a relationship of 5% or more of the cross-sectional area and having a relationship of Mt-Et ≧ 100 μm between the maximum roll diameter (Mt) and the minimum roll diameter (Et) of the steel sheet rolling portion during rolling immediately after joining. It is a hot rolling method for a steel strip with different width joints, characterized in that

At this time, the effect is increased by rolling the sheet bar immediately after joining at a rolling reduction of 35 to 60%.

[0007]

The present inventors have earnestly pursued the cause of breakage when rolling sheet bar joining materials having different widths. When the hot-rolled steel sheet is continuously rolled, since the rolled steel sheet is long, a slight bending occurs in the longitudinal direction. In particular, when joining both width edges of the bar and attempting to crimp the central unbonded portion by rolling, the width center portions of the different width steel plates to be joined are largely displaced, resulting in unevenness caused by bending. Since stress concentrates on the joint, it is easy to break. I realized that the following points were important as a solution.

(1) The deviation of the center of the plate width of the steel plates having different widths to be joined is small. (2) Variation in tension during continuous rolling of different width materials is small. (3) The bonding strength of both edges has a restraining force enough to press the unbonded portion. In the conventional method, for example, JP-A-5-104107
When the different width materials are bonded and rolled by the method proposed in Japanese Patent Publication, since the plates are crowned, it is difficult to center the plate width and thickness direction at the time of bonding, and as a result,
Left and right asymmetrical pre-joining tends to occur. Further, due to the different widths, an unbonded protruding portion is generated at the edge portion of the wide material, and this is the starting point, so that the breakage easily occurs. This is because the above (1) and (2) could not be performed.

In order to solve this, the present inventors first focused on the state of the seat bar before joining. As a result of various attempts, in order for the plate width center part of the different width steel plate to be continuous,
The bar should be flat and it is better to remove the crown of the slab before joining. Further, in order to accurately align the pre-bonded portion, the position (Tmm) of the wide steel plate from both edges is 0.4 (W0-W) ≤T≤0.6 (W0
-W), the total cutting length is (W0
-By cutting so as to be (W), it becomes possible to pre-join two sheet bars having different widths without displacement.

The cutting angle range at this time is 30 to 50 °.
The reason for this is that if it is larger than 50 °, the tension fluctuation during continuous rolling becomes large, and it is easy for fracture to occur.
This is because when the size is smaller, the amount of cut-off increases and the yield decreases. For the above reasons, the angle range is set to 3
It was set to 0 to 50 °. Since the problem of different width was solved, (3)
We started to study the method of joining two steel pieces more firmly, which is the issue of. The present inventors have noticed that, when hot rolling a steel material having both width edges joined, the thinner the sheet bar and the wider the width, the more the sheet bar is broken by the rolling after the joining. Therefore, when a rolling experiment after joining was performed with the joining area ratio kept constant and the thickness / width ratio varied, as shown in FIG. 1, the joining strength decreases and the fracture occurs as the thickness / width ratio increases. There was found.

Observation of this fractured surface revealed that the fractured material was not joined at any portion other than the preliminary joining. Then, when the elongation margin of the tail of the preceding material was measured by another experiment, it was found that the greater the thickness width ratio, the smaller the elongation margin at the central portion of the plate width and the poorer the joint at the unbonded portion. Therefore, the inventors of the present invention have made extensive studies on a method of increasing the expansion margin at the center of the plate width of the tail. As a result, it was found that by changing the shape of the rolling roll after the pre-bonding to a convex curve, the elongation margin was increased. The convexity of the roll for obtaining an effective elongation is Mt−Et ≧ 100 μm between the maximum roll diameter (Mt) and the minimum roll diameter (Et) of the steel plate rolling portion, and this is the scope of the present invention. .

However, this effect does not occur if the strength at both edges of the width due to the preliminary joining is small. This is because there is a binding force to both steel pieces that are joined to both edges,
This is because the central portion of the width is crimped. In order to increase the crimping area of the unbonded portion in the center of the width, pre-bonding does not require welding at one point on both edges, but pre-welding of at least 5% or more of the cross-sectional area is required. As a result, the central portion of the plate width can be stretched and pressed against the central portion to form a strong bonded state.

Further, in order to crimp the central portion by this method, it is necessary to keep the gap at the joint end portion to a maximum of 5 mm or less. If the pressure is higher than this, the pressure bonding force becomes weak, and it is impossible to expect an increase in the bonding strength. As a joining method for effectively exhibiting the above-mentioned effects, a method such as arc welding or laser joining is more effective than an electric heating method in which a smaller welding area is more effective.

In the usual rolling of a material having a width of about 1 m or less, this method can be used for rolling without problems. However, as the plate width becomes wider, the joining area at both edges of the width cannot be sufficiently obtained, or the amount of stretching of the plate at the center of the width is insufficient, so the joining force is small and there is a risk of breakage. Therefore, in addition to the above-mentioned conditions of the invention, the bonding force can be increased by increasing the rolling reduction in the first pass to 35% or more.

The upper limit of the rolling reduction is set to 60% because
This is because as the width becomes wider, the rolling load becomes higher, and if it is more than that, there is a risk of roll damage.

[0016]

Example A bar joining experiment was conducted using a 7-stand tandem rolling mill. First, an experiment was conducted to examine the conditions for joining steel strips of different widths. The results are shown in Table 1. a ~
d was tested by changing the positions of cuts from both edges. Other conditions are the same. There was a large misalignment except for c, which was cut at both edges almost the same. Breakage occurred at a, b, and d.

F to j are the results of changing the cutting angle. I, j, which are angles of 50 ° or less, did not break, but f, g, h with large angles did break. Further, e and k, which are the conditions of the present invention, did not fracture regardless of the material having a wide plate width or the material having a narrow plate width. Next, preliminary joining conditions and rolling conditions immediately thereafter were investigated. The results are shown in Table 2.

Experiment No. For Nos. 1 to 4, the thickness ratio, the rolling reduction immediately after joining, and the roll convexity were made the same, and the tests were carried out by changing the end shape of the joined portion and the joining method. No. whose end shape exceeds a gap of 5 mm In Nos. 1 and 2, rupture occurred during rolling regardless of the joining method. When this was flattened, the pre-joining rate was low and the temperature immediately after rolling was low because the welding speed was slow in arc welding, but the temperature did not break during rolling because it was within the range of the present invention.

No. In No. 7, since the thickness width ratio is large and the rolling reduction is as small as 30%, the binding force at both width edges is weak, and No. In Roll No. 8, the roll convexity was as small as 50 μm, so the stretching in the width center portion was small, and all were broken. In all the other examples, the conditions were within the range of the present invention, and no fracture was caused by rolling.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

As described above, according to the present invention, bar joining materials having different widths can be rolled without breaking, and the amount of continuous hot rolling can be increased.

[Brief description of drawings]

FIG. 1 is a diagram showing a change in bonding strength (breaking limit) depending on a thickness width ratio.

FIG. 2 is a schematic diagram of joining of steel strips of different widths.

Claims (2)

[Claims] 1. When the width of a wide steel sheet is (W0 mm) and the width of a narrow steel sheet is (W mm) in hot rolling continuous rolling in which bar joining is performed before continuous finishing rolling, the wide steel sheet has both edges. Position (Tmm) from the part is 0.4 (W0-W) ≤ T ≤ 0.6
With this position as a reference, the total cutting length is (W0-W) at an angle of 30 to 50 ° with respect to the rolling direction.
0-W), and after aligning the widths of both steel pieces, both the rear end of the preceding material and the front end of the following material so that the maximum gap of the joint end surface is 5 mm or less. 5% or more of the narrow material cross-sectional area including the edge portion is joined, and rolling immediately after joining is performed between the maximum roll diameter (Mt) and the minimum roll diameter (Et) of the steel sheet rolling portion with Mt-Et ≧ 100 μm. A method for hot rolling of different width joint steel billets, which comprises rolling using a hot rolling roll having the following relationship. 2. A rolling reduction ratio of 35 to 60 is applied to the rolling of steel strips having different widths.
%, The hot rolling method for a different width joint steel billet according to claim 1.