JPH08290206A - Method for manufacturing thick steel plate without seam flaws - Google Patents

Abstract

(57) [Summary] [Purpose] Prevents seam flaws that occur near the edges of thick steel plates when manufacturing thick steel plates from slabs by a hot rolling process consisting of a width direction rolling process and a longitudinal direction rolling process,
Provided is a method for manufacturing a thick steel plate capable of obtaining a steel plate having no surface flaw. [Structure] In the process of manufacturing a thick steel plate from a raw material slab through a widthwise rolling process and a lengthwise rolling process, in all or some of the rolling passes of the widthwise rolling process, the rear end of the material to be rolled in the pass Prior to the vicinity being caught in the rolling roll, a lubricant is applied to either one or both of the surface of the material to be rolled at the site and the surface of the rolling roll in contact with the site, and rolling is performed. [Effect] By reducing the wraparound amount of the rear end of the material to be rolled (widthwise end of the product) in the widthwise rolling process and keeping the seam flaw occurrence position in the product near the widthwise edge,
The yield reduction due to trimming or the like can be eliminated, and a thick steel plate having substantially no seam flaw can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-pass hot rolling process comprising a widthwise rolling step of rolling in a direction corresponding to the width direction of a product and a longitudinal rolling step of rolling in a direction corresponding to the length direction of a product. The present invention relates to a rolling method capable of preventing the generation of linear flaws in the longitudinal direction near the widthwise edges of the front and back surfaces of a product, that is, seam flaws, when manufacturing a thick steel sheet by rolling.

[0002]

2. Description of the Related Art Generally, near a width edge of a hot-rolled thick steel plate (a range of about 20 to 80 mm from the edge), a linear flaw (depth 0.1 mm) called a seam flaw is long in the rolling direction. (1 mm to 1 mm) is likely to occur, and it is necessary to remove the product by trimming or the like in a refining process before the product is manufactured. Therefore, the problems of an increase in process load and a decrease in yield are particularly large.

Therefore, conventionally, a technique has been proposed in which the seam flaw generation position is kept as close to the steel sheet edge as possible for the purpose of reducing the cut amount (width) at the time of trimming, but the present situation is that a sufficient effect is not obtained. Is. For example, JP-A-5
As disclosed in Japanese Laid-Open Patent Publication No. 9-27701, a method of rolling the slab side end surface before rolling with a vertical roll having a predetermined caliber shape and forming into a corrugated shape is performed with a small number of caliber rolls under various rolling conditions. It is difficult to obtain the effect, and it is necessary to provide various kinds of caliber rolls to obtain the sufficient effect, which causes an increase in equipment cost.

Further, as disclosed in Japanese Patent Laid-Open No. 1-210113, there is a method of changing the cooling degree of the front and back surfaces depending on the difference in the wraparound amount of the front and back surfaces. It is difficult to perform control with sufficient accuracy. Further, as a conventional technique disclosed in JP-A-1-150403, in a hot rough rolling pass (longitudinal rolling) of a slab, a lubricant is applied to the vicinity of both width ends of a material to be rolled and rolled. Although there is a method, this technology cannot sufficiently prevent the occurrence of seam flaws as described later.

[0005]

SUMMARY OF THE INVENTION The present invention prevents the occurrence of linear flaws in the longitudinal direction near the edges in the width direction, that is, seam flaws, without causing a particular increase in the process load and sufficiently. An object of the present invention is to provide a rolling method capable of obtaining a thick steel plate in which the occurrence of seam flaws is prevented.

[0006]

Means for Solving the Problems The gist of the present invention for achieving the above-mentioned object is to produce a thick steel sheet from a raw material slab through a width-direction rolling step and a length-direction rolling step. In all or part of the rolling pass of the process, before the rear end vicinity of the material to be rolled in the pass is caught in the rolling roll, the surface of the material to be rolled in the relevant part and the surface of the rolling roll in contact with the relevant part A method for producing a thick steel plate having no seam flaw is characterized in that one or both of them is coated with a lubricant and rolled.

[0007]

According to the present invention, the wraparound at the rear end of the material to be rolled during widthwise rolling, which is the main cause of seam flaws, is mitigated by the application of the lubricant, and as a result, the occurrence of seam flaws can be suppressed. The present invention will be described in detail below. FIG.1 (b) shows the whole rolling process (width direction rolling and longitudinal direction rolling process) from a raw material slab to a thick steel plate which is a product. Normally, a rectangular raw material slab is rolled in its short side direction. 90 for direction
After being turned by a rolling mill, it is rolled down to a specified length, that is, the width of the product by several passes (width direction rolling process), and then turned 90 ° again, and rolled in the long side direction of the raw material slab to a specified thickness. After that (longitudinal rolling process), a thick steel plate product is obtained.

The mechanism of seam flaw generation has not been completely clarified at this time, but at least the flaws generated near the corners of the material to be rolled during the rolling process are accompanied by a metal flow due to the subsequent rolling. Wrap around to the back),
It is thought that it will become apparent as a surface flaw. Therefore, the present inventors first conducted a rolling experiment in accordance with a rolling process as shown in FIG. 1 (b), and obtained the following knowledge as a result of a detailed investigation on the occurrence state of seam flaws and the wraparound phenomenon due to rolling. .

First, as shown in FIG. 2, the larger the total rolling reduction (width reduction ratio) in the width direction rolling step (a plurality of passes), the closer the seam flaw generation position is to the center of the width, that is, the wraparound amount. It has been found that it becomes significantly large, and in some cases, a noticeable difference between the front and back surfaces occurs in the wraparound amount. In the case of only the longitudinal rolling process (width ratio 1.
It was also found that the wraparound significantly increases due to the addition of the width direction rolling step as compared with 0). This means that it is essential to reduce the amount of wraparound at the front and rear edges of the material to be rolled during widthwise rolling in order to fix seam flaws near the width edge of the product (thick steel plate) and render the flaws harmless, The above-mentioned Japanese Patent Laid-Open No. 1-1
In the prior art disclosed in Japanese Patent No. 50403, that is, in the hot rough rolling pass (longitudinal rolling) of a slab, a method of applying a lubricant to the vicinity of both width end portions of a material to be rolled and rolling the rolled material has seam flaws. This means that the occurrence cannot be prevented sufficiently.

It is considered that the effect of reducing the wraparound amount at both width end portions of the rolled material by applying the lubricant can also be expected for the wraparound of the front and rear edges of the rolled material, and the rolled material is subjected to widthwise rolling. The lubricant may be applied when the front end and the rear end of the above are caught in the rolling roll. However,
Applying a lubricant when the tip of the rolled material bites
Since the biting property is extremely lowered, a new problem arises in that the necessary reduction ratio cannot be set in some cases.

Therefore, the wraparound phenomenon of the front and rear edges of the material to be rolled during widthwise rolling was observed in detail. As a result, FIG.
As shown in (1), it was found that in the one-pass widthwise rolling, there was almost no wraparound at the leading end of the material to be rolled, and significant wraparound occurred only at the trailing end. To this phenomenon, as shown in FIG. 4 (a), the wraparound at the rear end is promoted in the advanced region where the frictional force (the frictional force between the roll and the material to be rolled) in the direction urging the wraparound of the tip acts. It is considered that the reverse region in which the directional frictional force acts is generally wider. In addition, the above-mentioned difference in front and back of the wraparound amount also changes the posture before the rear end of the material to be rolled contacts (engages) with the roll due to the difference in vertical temperature during widthwise rolling, and the contact length with the upper and lower rolls. It is understood that the difference between the front surface and the rear surface in the reverse drive range is generated through the difference (FIG. 4B). That is, by applying a lubricant when the rear end of the material to be rolled comes into contact with the roll, it is possible to reduce the frictional force with the rolling roll in the reverse travel region, and effectively prevent the wraparound of the rear end that is larger than the front end. You can see that it can be suppressed.

From the above knowledge, in the method of the present invention, that is, in the width direction rolling pass, the lubricant is applied and rolled before the vicinity of the rear end of the material to be rolled is caught in the rolling roll, and the above-mentioned biting is performed. It is possible to sufficiently reduce the wraparound amount of the front and rear edges of the material to be rolled during widthwise rolling without causing the problem of penetration, and it is possible to keep the flaw occurrence position on the thick steel plate, which is a product, close to the width edge. , Can virtually eliminate seam flaws.

The portion to which the lubricant is applied may be either the surface in the vicinity of the rear end of the material to be rolled, the surface of the rolling roll contacting the portion, or both. Further, when the front and back (upper and lower) surface difference of the wraparound amount (or the seam flaw occurrence frequency) is significant, it may be applied only to the side where the wraparound amount (or the seam flaw occurrence frequency) is large. The vicinity of the rear end of the material to be rolled is a region related to the wraparound phenomenon of the rear end at the time of widthwise rolling, and generally, from the rear end to a position several times or more the contact arc length of the rolling pass, It is sufficient to apply the lubricant until the end comes off the roll bite. As for the widthwise portion to which the lubricant is applied, the entire width of the rear end of the material to be rolled in the widthwise rolling pass is sufficient, but it may be limited to the portion where the wraparound is remarkable.

As for the method of applying the lubricant, for example, as shown in FIG. 1 (a), the slab rear end detector 4 detects the time when the vicinity of the rear end of the material 1 to be rolled is caught in the rolling roll 2.
The lubricant supplied by the lubricant supply pump 6 is opened / closed by the valves 5, 5'according to the detection signal, and a predetermined portion (rolling roll or / and material to be rolled, upper side or / And the lower side, etc.). Instead of the lubricant application spray 3, 3 ', a lubricant application roll or a brush for application of a lubricant is used to directly contact the rolling roll or / and the material to be rolled to transfer the lubricant. You may let me.

As for the rolling pass for applying the lubricant, it is best to perform all the passes in the width direction rolling process, but some of the multiple passes that are considered to increase the wraparound amount of the rear end of the material to be rolled, for example, reduction The number of passes may be limited to a relatively large number of passes / or a few passes after the widthwise rolling step.

[0016]

[Example] Thickness 250 mm, width 1000 mm, length 5 m
The continuous cast slab of ordinary steel of 1 is heated to 1200 ° C., and a 4-roll reverse rolling machine with a work roll diameter of 1200 mm is used to perform a total of 16 passes including 8 passes in the width direction (width ratio of 2.5) and 8 passes in the length direction. By rolling the pass, the thickness was reduced to 12 mm. Table 1 shows the trailing edge lubrication of the rolled material during widthwise rolling.
As shown in Fig. 2, the graphite roll is sprayed onto the rolling rolls at the trailing edge of about 500 mm for all passes and only for the latter four passes (thickness 170 mm → 100 mm). It was carried out in the form of coating. Also,
As a comparative example, it was also carried out under the condition that the trailing edge lubrication was not performed at all during the widthwise rolling. The occurrence of seam flaws shown in Table 1 is the result of evaluation by surface observation after cutting and sampling the test piece after rolling, performing pickling.

As is clear from Table 1, by applying the present invention, the position where the seam flaw is generated is moved to the vicinity of both width edges of the product, which is not a practical problem (usually trimming both width ends). It has been improved to some extent. Further, during the widthwise rolling, a condition was also applied in which a lubricant was applied to the tip of the material to be rolled, but the material to be rolled did not get caught in the rolling rolls and could not be rolled.

[0018]

[Table 1]

[0019]

As described in detail above, according to the present invention,
The position where the seam flaws occur on the thick steel plate after rolling can be remarkably improved, and the product yield can be improved, which is extremely beneficial to the industry.

[Brief description of drawings]

FIG. 1 (a) is a schematic view showing an embodiment of an apparatus for applying a lubricant to the rear end of a rolled material for carrying out the method of the present invention, and FIG. 1 (b) is an application of the method of the present invention. It is a schematic diagram which shows the rolling pass (width direction rolling process) which lubricates the rear-end part of a to-be-rolled material as an example.

FIG. 2 is a diagram showing an example of a relationship between a total reduction rate (width-feeding ratio) in a width direction rolling process and a seam flaw generation position (a distance from a thick steel plate width edge after the entire rolling process).

FIG. 3 is a front end of a material to be rolled, which is generated by one-pass widthwise rolling,
It is a figure which shows an example of the wraparound amount of a rear end.

FIG. 4 is a schematic diagram showing a relationship between a difference in a wraparound amount between a front end and a rear end of a material to be rolled during widthwise rolling and friction with a rolling roll.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Slab (rolled material) 2 Rolling rolls 3, 3'Spray for applying lubricant 4 Slab rear end detector 5, 5'Valve 6 Lubricant supply pump

Claims (1)

[Claims] 1. When manufacturing a thick steel sheet from a raw material slab through a width direction rolling step and a longitudinal direction rolling step, in all or a part of rolling passes of the width direction rolling step,
Before the rear end of the material to be rolled in the pass is caught in the rolling roll, a lubricant is applied to one or both of the surface of the material to be rolled at the site and the surface of the rolling roll in contact with the site. A method for producing a thick steel plate having no seam flaw, which comprises rolling.