JPH04322805A - Continuous hot rolling method for steel slabs - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuous hot rolling of steel slabs, which is advantageous when a plurality of steel slabs are sequentially joined and rolled continuously. Conventionally, in hot rolling lines, after heating the steel billets to be rolled to a target temperature, each billet is subjected to a rough rolling process and then a finishing rolling process to finish it into a hot rolled plate with the desired thickness. In such a rolling method, troubles such as line stoppages due to poor biting of the rolled material are likely to occur, particularly during finish rolling, and yields are significantly reduced due to poor shapes at the leading and trailing ends of the rolled material. This is why early resolution of such problems is desired.

0002

[Prior Art] In order to eliminate the above-mentioned troubles in hot rolling lines and further improve productivity,
A rolling technology has been proposed in which the trailing end of a preceding steel billet and the leading end of a succeeding billet that is subsequently transported are sequentially joined and subjected to finish rolling in the entry conveyance line of a hot finish rolling mill. It was done. For example, in Japanese Unexamined Patent Publication No. 51-59749, after descaling the joint between the preceding steel billet and the following steel billet, or after descaling and raising the temperature, spot welding is carried out while each steel billet is pressed, and as it is. A method of sequentially joining and rolling by rolling is disclosed, and also disclosed in Japanese Patent Application Laid-open No. 5
No. 1-130665 discloses a method in which the rear end of a leading steel piece and the tip of a trailing steel piece are overlapped and the combined joint is cut diagonally across the width at a predetermined angle with respect to the axis of the steel piece. is disclosed. By following the technology of joining and rolling steel billets in this way, it is possible to improve productivity by eliminating the problems such as jamming that occurs when steel billets are fed one by one to the rolling line. become.

0003

[Problem to be solved by the invention] JP-A-51-59 mentioned above
Even if descaling is performed to join the steel pieces by the method disclosed in Publication No. 749, the scale formation reaches several tens of micrometers in 10 seconds, so the joining strength may not be sufficient. In addition, in order to suppress such scale, it is necessary to descale and raise the temperature immediately before rolling, which increases the length of the equipment. Furthermore, since the temperature is raised in a non-oxidizing atmosphere, there is a problem in that the equipment becomes large-scale.

[0004] Furthermore, in the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 51-130665, the process of overlapping the rear end of the leading steel piece and the tip of the trailing steel piece and the process of cutting with oxygen gas etc. take a long time. There was also the problem of scale formation on the cross section cut with oxygen gas. Furthermore, since the tip of the trailing steel piece is accelerated and pressed toward the rear end of the leading steel piece, there is a possibility that the joint surfaces of the two pieces do not come into contact with each other properly.

[0005] We have provided a continuous hot rolling method for steel billets that advantageously solves the above-mentioned problems, allows joining of steel billets in a short time, and advantageously increases the bonding strength of the steel billets to each other. It is the purpose of this invention to propose.

[0006]

[Means for Solving the Problems] The present invention provides a method for controlling the rear end of a steel billet that is conveyed in advance at the entry side of a hot rolling facility, and the following steel billet that is conveyed following this steel billet. A method of continuously rolling a steel billet by joining the tip end of the billet to the rear end of the billet being conveyed in advance and the tip of the billet being conveyed following this cutting the leading end into a shape that touches at least both ends in the width direction of the steel piece when they are butted; and cutting the rear end and the leading end at a predetermined angle with respect to the thickness direction of the steel piece. The process of cutting is combined with the step of cutting, and then the rear end and the front end are butted together and joined in a spliced state at both ends of the steel piece in the width direction, and then rolling is performed to join the unjoined area in the width direction of the steel piece. This is a method for continuous hot rolling of steel billets.

[0007] Here, it is advantageous to cut each steel piece into a shape in which both ends in the width direction are in contact with each other with the front end and the rear end facing each other, and the center portions are overlapped.

[0008]

[Operation] First, the circumstances that led to the development of the method for continuous hot rolling of steel slabs of the present invention will be explained. As a result of intensive research into a joining method that can join steel billets easily, quickly, and reliably, the inventors discovered that the rear end of the steel billet that is transported in advance (hereinafter referred to as the "preceding billet") and The tips of the steel pieces that are conveyed following the preceding steel pieces (hereinafter referred to as following steel pieces) are each cut into a shape that contacts at least at both ends in the width direction of each steel piece when the two are in butt contact, Next, we found that it was particularly effective to locally heat and press the area to be joined, and filed a patent application (see Japanese Patent Application No. 203992/1999).
. By the way, in hot rolling such steel billets, there are cases where it is required to further increase the strength of the joint area.
Therefore, the inventors conducted further research to increase the strength of the joint, and found that it is particularly advantageous to cut the end regions of each piece of steel to be joined at an angle to each other, creating a sawn joint. It is.

FIG. 1 shows a comparison of the changes in the joint interface before and after rolling in a cross section in the thickness direction of a steel slab between the conventional example (a in the same figure) and the present invention (a in the same figure). This increases the joint area and increases the amount of shear deformation of the joint due to rolling, resulting in high joint strength.

[0010] The present invention will be explained in more detail below with reference to the drawings. First, the steel pieces are cut into a shape in which at least both ends in the width direction of the steel pieces are in contact with each other when they are butted together, for example, a shape as shown in FIG. 2, which is a plan view of the leading steel piece 1 and the following steel piece 2. A drum shear with two curved blades is advantageously suited for this cutting. In addition, a guillotine cut type shearing device or the like may be used.

Next, in FIG. 3, the leading steel piece 1 and the following steel piece 2
As shown in the cross section in the thickness direction, the steel piece is cut diagonally so that the contact surface of the steel piece in the butt state has a predetermined angle with respect to the thickness direction of the steel piece. 3 in the figure is a drum shear that controls such cutting. In addition to the drum shear 3, a guillotine cut type shearing device or the like is advantageously suitable for this cutting. The diagonal cutting angle (α in FIG. 3) is preferably in the range of more than 0° and less than 60° with respect to the thickness direction of the steel piece.

[0012] In the above cutting process, contrary to the above, it is also possible to first cut diagonally and then cut into a shape in which both ends are in contact with each other.

Next, as shown in a plan view (FIG. 4(a)) and a cross-sectional view in the thickness direction (FIG. 4(b)), the rear end of the leading steel billet 1 and the tip of the trailing steel billet 2 are connected. After the two ends of the steel strip in the width direction are joined in a spliced state by abutting against each other, rolling is performed, and the unjoined portions in the width direction of the steel strip are joined by this rolling. Since the time between such cutting and joining in the post-process is short, the generation of scale on the cut surface is suppressed. In the butt joint between the rear end of the leading slab 1 and the tip of the trailing slab 2, Fig. 5 shows a cross-sectional view in the thickness direction ((a) in the same figure) and a plan view ((b) in the same figure).
It is advantageously suitable to use a joining device 5 as shown in FIG. It has been confirmed that the minimum welding allowance at the ends of the steel strip in the width direction is at least 0.1 times the width of the steel strip at each end region, and 0.2 times in total.

In this invention, as shown in FIG. 6, which shows a cross section in the thickness direction at the center of the steel piece in the width direction, each steel piece is brought into contact with both ends in the width direction, with the leading end and the rear end facing each other. However, it is preferable to cut the steel pieces in an overlapping shape at the center in order to more advantageously improve the bonding strength between the steel pieces.

[0015]

[Example] Figure 5 shown above with tandem rolling mill on stand
Using the equipment shown in , thickness: 30 mm, width: 12
The radius of curvature of a 00 mm low carbon steel billet at the rear end of the leading steel billet and the tip of the trailing steel billet as shown in Figure 2:
After cutting into a curved shape of 19m,
It was cut diagonally at an angle of 5°, then both ends in the width direction were butted together and joined by spot welding, and then supplied to a finishing mill to produce a hot rolled sheet with a thickness of 3 mm. As a result, even when tension was applied during rolling, the butt joints of the steel billets did not separate and break, and stable rolling was possible.

[0016] In the above example, when the tip and rear ends are pressed against each other with a radius of curvature of 60 m and an angle of 30° with respect to the thickness direction of the steel billet, each steel billet has both ends in its width direction. When the joints were cut in a shape that only touched the parts and overlapped in the center, the joints became even stronger, and even when tension was applied during rolling, the butt joints of the steel slabs did not separate and break, resulting in stable joints. It was possible to roll it.

[0017]

[Effects of the invention] The method for continuous hot rolling of steel billets according to the present invention is as follows:
The rear end of the steel billet that is conveyed in advance and the tip end of the following steel billet that is conveyed following this steel billet are shaped so that they touch at least at both ends in the width direction of the steel billet when they are brought into contact with each other. The joint strength is improved by cutting the rear end and the leading end of the steel piece diagonally at a predetermined angle with respect to the thickness direction of the steel piece, and joining both widthwise ends of the steel piece in a spliced state. can be further increased.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating changes in the joint interface before and after rolling in a cross section in the thickness direction of a steel bill, comparing a conventional example (a in the same figure) and the present invention (a in the same figure).

FIG. 2 is a plan view of a leading steel piece and a following steel piece.

FIG. 3 is a sectional view in the thickness direction of a leading steel piece and a following steel piece.

FIG. 4 is an explanatory view of a situation where the rear end of the leading steel piece and the tip of the following steel piece are butted against each other.

FIG. 5 is an explanatory diagram of a state of butt jointing between the rear end of the leading steel piece and the leading end of the trailing steel piece.

FIG. 6 is a diagram showing an example of a cross section in the thickness direction at the central portion in the width direction of the steel piece.

[Explanation of symbols]

1 Preceding steel piece 2 Tracking steel piece 3 Drum shear 4 Finishing mill 5　Joining device

Claims (2)

[Claims] [Claim 1] At the entry side of hot rolling equipment, the rear end of a steel billet that has been conveyed in advance and the tip end of a subsequent steel billet that is conveyed following this steel billet are joined. , a method of continuously rolling steel billets, in which the rear end of a steel billet that is conveyed in advance and the tip of a subsequent steel billet that is conveyed following this billet are brought into contact with each other. In this state, a step of cutting the steel piece into a shape in which at least both ends in the width direction are in contact with each other, and a step of cutting the rear end and the front end obliquely at a predetermined angle with respect to the thickness direction of the steel piece are combined, and then The steel billet is characterized in that the rear end portion and the tip end are butted together, and the steel billet is joined at both ends in the width direction in a spliced state, and then rolled to join the unjoined areas in the width direction of the steel billet. Continuous hot rolling method. 2. Continuous hot heating of the steel billet according to claim 1, wherein each steel billet is cut into a shape in which both ends in the width direction are in contact with each other in a state where the front end and the rear end are butted, and the center portions are overlapped. Rolling method.