JP2000024701A - Method for preventing breaking near welded part in continuous rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent breaking near welded part when steel sheets are joined with each other by laser welding and continuously rolled in a continuous rolling line by providing plural grooves arranged in parallel in the width direction of the steel sheets and extended between preceding and following steel sheets at the welding part. SOLUTION: Plural grooves, four lines in this example, extended between a preceding steel sheet 1 and a following steel sheet 2 and arranged in parallel in the width direction of the steel sheets are provided at welding part 3. Thereby, rolling mill oil 7, conventionally sealed in spaces 6 while rolling, travels from the preceding steel sheet 1 side to the following steel sheet 2 side through the grooves in company with the motion of rolling rolls 4, 5, and is not sealed-in, thus generation of thickness-decreased part derived from the rolling mill oil 7 and pored part in addition is evaded. Preferably, the width of the grooves provided at the welded part 3 is >=1 mm and the mutual distance between the grooves is <=10 mm. In order to provide the grooves, for example, methods of working by a gear roll or of rolling-down with a die having projecting and recessed parts on a pressing surface are acceptable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a steel strip which is formed by welding and joining a preceding steel strip and a following steel strip and performing continuous rolling.
Particularly, the present invention relates to a method for preventing breakage occurring near a welded portion during rolling when manufacturing an extremely thin steel plate.

[0002]

2. Description of the Related Art In general, in order to continuously and continuously cold roll steel strips, a tail end of a preceding steel strip and a tip of a succeeding steel strip are welded at an entry side of a continuous rolling line. It is necessary to join steel strips.

[0003] For example, the thickness of the continuous rolling line on the entry side is 1.
A steel strip of about 0 to 5.0 mm with a thickness of 0.5 to
When continuously rolling to about 2.0 mm, the joining of the steel strips is performed by flash butt welding, and in continuous rolling, when the weld is caught in the roll, the breakage of the weld and the occurrence of roll flaws occur. From the viewpoint of prevention, grinding of a surplus of a welded portion is performed.

[0004] However, flash butt welding is
It is necessary to butt the steel strips accurately. However, when targeting ultra-thin steel sheets having a thickness of 1.0 mm or less on the entry side, if the accuracy at the time of butt is poor, the welding condition will deteriorate. .

Therefore, in the production of ultra-thin steel sheets, lap welding in which the tail end of a preceding steel strip and the tip of a following steel strip are overlapped and welded is often performed. At that time, the processing of the super-thick portion of the overlapping portion is described in JP-A-60-1304.
As disclosed in Japanese Patent Publication No. 82, it is common to crush with a roller.

On the other hand, in resistance welding such as flash butt welding and lap welding, the welding strength depends on the surface oxide film generated at the interface during welding, so that special steel such as stainless steel and electromagnetic steel is manufactured. In the line, laser welding is often performed. In laser welding, compared to flash butt welding and lap welding,
Since the thickness of the weld is thin and smooth, the grinding of the weld is omitted in the rolling process of the thin steel sheet.

[0007]

However, when the steel strips are joined to each other by laser welding on the entry side of the continuous rolling line and the continuous rolling is performed, 5 to 5 places from the welded portion to the preceding material side.
Holes are scattered in the width direction of the plate in the area 15 mm away,
There has been a problem that the steel strip breaks near the weld in the tandem rolling mill due to the perforation.

Therefore, the present invention solves the above problems,
It is an object of the present invention to propose a method for preventing breakage near a welded portion when steel strips are joined by laser welding in a continuous rolling line to perform continuous rolling.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies particularly on drilling near a welded portion generated in an ultra-thin steel sheet, and found that drilling occurs in an actual machine in rolling on a laboratory scale. Investigate that a thickened part occurs in the part, that is, the cause of the perforation is not the deterioration of the mechanical properties of the base plate due to the heat effect, and that the thinned part occurs when the welded part is thick did. As a result of further investigation, it was newly found that the direct cause of perforation was due to sealing of rolling oil in the rolling roll tool.

That is, the present invention is as follows. (1) In the continuous rolling line, the tail end of the preceding steel strip and the tip of the following steel strip are joined by laser welding, and when rolling is performed continuously, the preceding welded steel strip A method for preventing breakage in the vicinity of a welded portion in continuous rolling, wherein a plurality of grooves extending between the subsequent steel strip and the steel strip are provided in parallel in the width direction of the steel strip.

(2) The method for preventing breakage near a weld in continuous rolling according to (1), wherein the width of the groove is 1 mm or more and the interval between the grooves is 10 mm or less.

(3) In the above (1) or (2), a groove is formed by rolling with a gear roll in the width direction of the steel strip at the welded portion. Method.

(4) The method according to (1) or (2), wherein the groove is formed by rolling down the welded portion by using a mold having an unevenness on the press surface. Break prevention method.

(5) In a continuous rolling line, the tail end of the preceding steel strip and the tip of the following steel strip are joined by laser welding, and when rolling is performed continuously, the thickness of the welded part is A method for preventing breakage in the vicinity of a weld in continuous rolling, characterized in that the thickness is suppressed to 0.2 mm or less based on the thickness of a preceding steel strip.

(6) In the above (6), the thickness of the welded portion is
A method for preventing breakage in the vicinity of a weld in continuous rolling, wherein the thickness is made thicker than the thickness of a succeeding steel strip.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, the occurrence of perforation near a welded portion in continuous rolling is performed by laser welding a tail end of a preceding steel strip 1 and a front end of a following steel strip 2. When rolling down the vicinity of the welded portion 3 with the rolling rolls 4 and 5, the rolls 4 and 5, the steel strip 1
The rolling oil 7 is enclosed by the space 6 surrounded by the welded portion 3 and the thickness of the steel strip is reduced by the presence of the rolling oil 7, and a hole is formed around the reduced thickness portion. This phenomenon also occurs at the side edge of the steel strip, and in this case, the sealing of the rolling oil occurs because the side edge of the steel strip is also closed due to the flat roll.

According to the present invention, in order to roll the welded portion without forming a hole on the preceding steel strip side of the welded portion, as shown in FIG. This prevents rolling oil from being enclosed.

More specifically, as shown in FIG.
In addition, it is important to provide a plurality of grooves 8 (four in the illustrated example) in parallel with each other in the width direction of the steel strip, extending between the preceding steel strip 1 and the following steel strip 2. That is, conventionally, during rolling, the space 6
As shown in FIG. 3, the rolling oil 7 encapsulated in the steel strip 1 moves from the preceding steel strip 1 to the succeeding steel strip 2 through the grooves 8 as the rolling rolls 4 and 5 advance. And space 6
Therefore, the occurrence of the reduced thickness portion and, consequently, the perforation caused by the rolling oil 7 can be avoided.

Here, FIGS. 4 and 5 show the thickness distribution in the longitudinal direction after rolling in the vicinity of the welded portion in the case where the groove is provided in the welded portion according to the present invention and in the case where the groove is not provided.
The results of the survey are shown. The material used in this experiment was an electromagnetic steel sheet.
m in one pass. The thickness of the weld before rolling was about 0.75 mm.

First, as shown in FIG. 4, the result of the case where no groove is provided in the welded portion indicates that a reduced thickness portion is formed on the preceding steel strip side of the welded portion. On the other hand, when the groove is provided in the welded portion, as shown in FIG. That is, it is clear that by providing grooves in the welded portion, it is possible to prevent the inclusion of rolling oil and prevent the occurrence of a reduced thickness portion, and thus to prevent a hole break in an actual machine that performs multi-pass rolling.

It is preferable that the width of the groove provided in the welded portion is 1 mm or more and the interval between the grooves is 10 mm or less. If the width of the groove is less than 1 mm, the transfer of the rolling oil from the preceding steel strip side becomes incomplete, and a part of the rolling oil is sealed in the roll bite. Similarly, when the interval between the grooves exceeds 10 mm, the rolling oil remains and is sealed with a roll bite.
On the other hand, the thickness of the groove is preferably approximately the same as the thinner thickness of the preceding steel strip and the following steel strip. If the thickness of the groove is large, the effect of discharging the rolling oil is impaired. If the thickness is excessively thin, the rolling oil is sealed in the groove, which causes breakage.

In order to provide the groove in the welded portion, for example, a processing method using a gear roll 9 as shown in FIG. 6 or a method of pressing down with a mold 10 having unevenness on a press surface as shown in FIG. It is better to adopt such as. In addition, grinding and grinding methods using grinding stones are also conceivable, but in ultra-thin steel sheets, misalignment often occurs at the welded part, and extremely thin parts may be generated by grinding and cutting processing, Not suitable for the present invention.

Next, another method shown in FIG. 1 for preventing the rolling oil from being trapped between the roll, the steel strip and the weld during rolling will be described with reference to FIG. I do. That is, as shown in FIG. 8, the thickness of the welded portion 3, specifically, the maximum thickness T of the welded portion 3 is controlled to an increase of 0.2 mm or less based on the thickness T ₁ of the preceding steel strip 1. It is possible to avoid enclosing the rolling oil in the cutting tool.

[0024] Here, the results of investigating the relationship between the thickening amount and perforated generation to thickness thickness T ₁ of the preceding steel strip 1 in T weld 3 is shown in FIG. In the same figure, a black circle indicates a case where a hole was formed on the preceding steel strip side of the welded portion, and a white circle indicates a case where no hole was formed. The thickness T of the welded portion 3 was adjusted by changing the feed speed of the welding wire from 0.6 to 2.2 m / min while keeping the welding speed constant at 4.5 m / min. The thickness of this weld was measured at the center in the steel strip width direction.

FIG. 9 shows that the occurrence of perforation can be avoided by suppressing the thickness of the welded portion to an increase of 0.2 mm or less with respect to the thickness of the preceding steel strip. On the other hand, the thickness T of the weld, it is the thickness T ₂ or more of the trailing steel strip are preferred. This is because, when the thickness T of the welded portion is less than the thickness T ₂ of the succeeding steel strip, the welding strength becomes insufficient, because rupture in the weld occurs. Incidentally, if the thickness T ₂ of the succeeding steel strip is thicker than the thickness T ₁ of the preceding steel strip 1 prior steel strip thickness T ₁ in the thickness of thin order succeeding steel strip thickness T _2, the thickness of the welded portion T a order, further, weld thickness T is smaller than the value obtained by adding 0.2mm to the preceding steel strip thickness T _1.

In order to suppress the thickness of the welded portion to an increase of 0.2 mm from the thickness of the preceding steel strip, processing such as controlling welding conditions and partially grinding the welded portion is performed. Just do it.

[0027]

EXAMPLE 1 In a continuous rolling line of a four-stand tandem mill,
A grain-oriented electrical steel sheet containing 2.5 to 3.2 wt% Si, having a thickness of 0.75 to 0.4 mm on the line entry side, a thickness of 0.35 to 0.15 mm on the exit side, and a sheet width 900-1200
mm, the steel strips (thickness difference:
The groove shown in FIG. 2 was provided in the welded portion where the thickness was 0.15 mm or less. The rolling mill is a tandem rolling mill having a four-stand configuration, and has a work roll diameter of 330 to 375 mm.
It was carried out in the range of.

That is, in Example 1-1, grooves were provided with a width of 2 mm and an interval of 20 mm, and in Example 1-2, grooves were provided with a width of 2 mm and an interval of 10 mm, and continuous rolling was performed. This groove processing was performed while repeatedly pressing down and moving a mold (see FIG. 7) having irregularities on the pressed surface in the width direction of the steel strip. In addition, as a comparative example, rolling was similarly performed without performing any processing on the welded portion.

With respect to the steel sheet thus obtained, the occurrence of a hole near the weld was examined. As a result, as shown in FIG. 10, in the comparative example, perforation occurred at a frequency of 1% in the material having the target size, but in Example 1-1, perforation was reduced to 0.2%. In Example 1-2, perforations could be reduced to 0.1%. That is, it is apparent that the present invention can prevent breakage due to perforation that has occurred on the preceding steel strip side near the welded portion.

Example 2 In a continuous rolling line of a four-stand tandem mill,
A grain-oriented electrical steel sheet containing 3.0 wt% Si has a thickness of 0.75 to 0.4 mm on the line entrance side and a thickness of 0.05 to 0.4 mm on the exit side.
When rolling under the conditions of 35 to 0.15 mm and a sheet width of 900 to 1200 mm, the steel strips (sheet thickness difference: 0.1
(5 mm or less) was changed in the thickness of the welded portion. The rolling mill was a tandem rolling mill having a four-stand configuration, and the work roll diameter was in the range of 330 to 375 mm.

That is, in Example 2-1, the thickness of the welded portion is suppressed to 0.2 mm or less as compared with the preceding steel strip by changing the welding conditions, and the thickness is made larger than the thickness of the succeeding steel strip. In addition, in Example 2-2, by grinding a part of the welded portion, the thickness of the welded portion is suppressed to 0.2 mm or less as compared with the preceding steel strip, and the thickness of the subsequent steel strip is reduced. It was thickened and subjected to continuous rolling. As a comparative example, welding was performed under conventional welding conditions and rolling was performed in the same manner.

With respect to the steel sheet thus obtained, the occurrence of perforation in the vicinity of the weld was examined. As a result, as shown in FIG. 11, in the comparative example, perforation occurred at a frequency of 1% in the material having the target size, but in the example, the perforation was reduced to about 0.1%. . That is, according to the present invention,
It is clear that breakage due to perforation that occurred on the side of the preceding steel strip near the weld can be prevented.

[0033]

According to the present invention, in the process of rolling ultra-thin steel sheets including special steels such as stainless steel and electromagnetic steel,
The welded portion can be rolled without causing a hole or break on the side of the preceding steel strip near the welded portion, and continuous rolling, which has been difficult in the past, can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a cause of perforation near a welded portion.

FIG. 2 is a diagram showing a specific method of the present invention.

FIG. 3 is a diagram illustrating the operation of the present invention.

FIG. 4 is a diagram showing a thickness distribution before and after a weld.

FIG. 5 is a diagram showing a thickness distribution before and after a weld.

FIG. 6 is a diagram illustrating a method of processing a groove provided in a welded portion.

FIG. 7 is a diagram illustrating a method of processing a groove provided in a welded portion.

FIG. 8 is a diagram showing a specific method of the present invention.

FIG. 9 is a diagram showing a relationship between a thickness of a welded portion and a hole.

FIG. 10 is a diagram showing a measurement result of a frequency of occurrence of perforations.

FIG. 11 is a diagram showing measurement results of the frequency of occurrence of perforations.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lead steel strip 7 Rolling oil 2 Trailing steel strip 8 Groove 3 Welding part 9 Gear roll 4 Rolling roll 10 Die 5 Rolling roll 6 Space

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B23K 31/00 B23K 31/00 C (72) Inventor Atsuro Uemura 1-chome, Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture None) Inside the Mizushima Works of Kawasaki Steel Corporation (72) Inventor Isao Akagi 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Prefecture Kawasaki-dori 1-chome (without address) Kawasaki Steel Corporation Mizushima Works F-term (reference) 4E002 AD05 BD05 4E068 BA00 DB01

Claims (6)

[Claims] In a continuous rolling line, a tail end of a preceding steel strip and a front end of a following steel strip are joined by laser welding and rolling is performed continuously. A method for preventing breakage in the vicinity of a welded portion in continuous rolling, wherein a plurality of grooves extending between a strip and a succeeding steel strip are provided in parallel in a width direction of the steel strip. 2. The method according to claim 1, wherein the width of the groove is at least 1 mm and the interval between the grooves is at most 10 mm. 3. The method for preventing breakage in the vicinity of a weld in continuous rolling according to claim 1 or 2, wherein the groove is formed by rolling with a gear roll in the width direction of the steel strip at the weld. 4. The method for preventing breakage near a welded portion in continuous rolling according to claim 1 or 2, wherein the groove is formed by pressing down the welded portion by using a mold having unevenness on a press surface. 5. In a continuous rolling line, a tail end of a preceding steel strip and a front end of a following steel strip are joined by laser welding, and when rolling is performed continuously, the thickness of a welded part is reduced.
A method for preventing breakage in the vicinity of a weld in continuous rolling, characterized in that the thickness is suppressed to 0.2 mm or less based on the thickness of a preceding steel strip. 6. The method according to claim 5, wherein the thickness of the welded portion is made larger than the thickness of a subsequent steel strip.