JP7126097B2 - Steel plate butt welding method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for butt welding steel sheets in consideration of thickness variations.

For the purpose of improving the productivity of the steel strip, in the cold rolling process, the trailing end of the preceding material to be rolled and the leading end of the following material to be rolled are joined on the continuous rolling line. Welding methods applied to continuous rolling lines generally include flash butt welding and laser beam welding.
Laser welding provides superior quality characteristics compared to flash butt welding due to its high energy density and low heat input. However, when welding high-carbon steel, rapid cooling after welding causes a hardened low-temperature transformation structure (structure containing martensite and bainite) to occur in the weld, causing cracks in the weld. It can cause breakage problems. For this hardening of the welded portion, a post-heating treatment of reheating after welding is performed to temper and soften the hardened welded portion, thereby preventing the welded portion from breaking.
As a post-heating device that performs post-heating, a device integrated with a laser welding device has been developed to perform post-heating with high efficiency. Methods are known to provide heating.

In Patent Document 1, laser welding is applied in butt welding of high-carbon steel plates or steel strips, and post-heating is performed in a temperature range of 400 ° C. or higher and _Acl point or lower within 1 minute after the completion of welding. Disclosed is a method of welding high carbon steel plates or strips characterized.

In Patent Document 2, in a method of laser welding rolled materials for a continuous manufacturing process, a step of contacting rolled materials in which a low temperature transformation structure occurs and laser welding the contact portion of the rolled materials to contact. A laser welding method is disclosed for a continuous manufacturing process that includes the steps of forming a part and applying a pressure press against the welded part of the rolled stock.

JP-A-5-132719 JP 2007-175775 A

In the post-heating treatment of Patent Document 1, high-carbon steel can be welded in a short time and simply by limiting the temperature range of the post-heating treatment by high frequency, flame, high-temperature gas, or the like. Similarly, in the post-heating treatment of Patent Document 2, the temperature range of the post-heating treatment is also disclosed. However, these prior arts are not inventions for welding steel sheets by applying optimum post-heat treatment conditions in consideration of plate thickness variations.

The present invention has been made in view of the above problems, and an object of the present invention is to improve the productivity of coils by avoiding the occurrence of fracture troubles in welded portions when steel sheets are rolled.

FIG. 1 is a diagram showing a steel strip thickness chart after hot rolling. TOP and END shown in FIG. 1 indicate locations where the rear end of the preceding material to be rolled and the leading end of the following material to be rolled are welded. It can be seen that the plate thickness fluctuates more at these locations than at other locations. When welding is performed at this point, post-heating is insufficient if the measured plate thickness is greater than the preset setting plate thickness, and post-heating is insufficient if the measured plate thickness is smaller than the preset setting plate thickness. Excessive heating may occur, resulting in deviation from the optimum heat quantity range (passable range for post-heating). If the rolling is performed without noticing this, the post-heating cannot be stably performed under the optimum conditions, and the occurrence of troubles such as breakage of the weld zone cannot be avoided when the steel sheet is rolled, resulting in a decrease in the productivity of the coil.
In this way, there has not yet been established a technique for welding steel sheets by changing the current value for each weld zone during post-heating treatment in consideration of the plate thickness and applying the optimum post-heating conditions. .

The present invention is based on the above findings, and provides [1] to [8] below.
[1] A method of butt-welding a preceding steel plate and a succeeding steel plate, comprising a plate thickness measuring step of measuring the plate thickness of each welded portion of the preceding steel plate and the succeeding steel plate, and the preceding steel plate. A welding step of butt-welding the following steel plate and a post-heating current value for heating the welded portion after the butt welding based on the plate thickness measured in the plate thickness measuring step. Post-heating A steel plate butt welding method, comprising: a determining step; and heating the respective welded portions based on the post-heating current values determined in the post-heating determining step.
[2] In the post-heating determination step, the average measurement of the plate thickness of the portion to be the weld of the preceding steel plate measured in the plate thickness measurement step and the plate thickness of the portion to be the weld of the succeeding steel plate The steel plate butt welding method according to [1], wherein the post-heating current value is determined based on the plate thickness.
[3] In the post-heating determination step, the following formula (1) is satisfied based on the preset post-heating current value, the average set thickness of the preceding steel sheet and the succeeding steel sheet, and the average measured thickness. The steel plate butt welding method according to [1] or [2], wherein the post-heating current value is determined so as to

Ｉ_設定は予め設定された後加熱電流、ｌ_設定は平均設定板厚、Ｉ_補正後は後加熱電流値、ｌ_測定は平均測定板厚を示す。

I _setting indicates a preset post-heating current, l _setting indicates an average set plate thickness, post-heating current value after I _correction , and l _measurement indicates an average measured plate thickness.

[4] The steel plate butt welding method according to any one of [1] to [3], wherein Vickers hardness of the preceding steel plate and the following steel plate is 100 HV or more and 1000 HV or less.
[5] The steel plate according to any one of [1] to [4], wherein the hardness of the weld formed by butt welding the preceding steel plate and the following steel plate has a Vickers hardness of 100 HV or more and 1000 HV or less. butt welding method.
[6] The preceding steel sheet and the succeeding steel sheet, in mass%, C: 0.5% or more,
Si: 0.1% or more and 0.5% or less,
Mn: 0.3% or more and 0.6% or less,
P: 0.05% or less,
S: 0.05% or less,
Cu: 0.5% or less,
Ni: 3% or less,
Cr: 0.05% or more and 0.5% or less,
Al: 0.05% or less,
The method for butt welding steel sheets according to any one of [1] to [5], wherein the steel plate has a chemical composition consisting of the balance Fe and unavoidable impurities.
[7] The preceding steel sheet and the succeeding steel sheet, in mass%, C: 0.5% or more and 2.2% or less,
Si: 0.1% or more and 0.5% or less,
Mn: 0.3% or more and 0.6% or less,
P: 0.05% or less,
S: 0.05% or less,
Cu: 0.5% or less,
Ni: 3% or less,
Cr: 0.05% or more and 0.5% or less,
Al: 0.05% or less,
The steel plate butt welding method according to [6], wherein the steel plate has a chemical composition consisting of the balance Fe and unavoidable impurities.
[8] The butt welding method for steel plates according to any one of [1] to [7], wherein the butt welding is a laser welding method.

According to the present invention, by changing the post-heating current value among the post-heating conditions, insufficient post-heating or excessive post-heating is prevented in consideration of plate thickness variations, and the post-heating of the weld is performed stably. Therefore, when the steel plate is rolled, it is possible to avoid the trouble of breaking the welded portion and improve the productivity of the coil.

It is a figure showing the steel strip board thickness chart after hot rolling. It is a figure showing the flow of the butt welding method of the present invention. (a) is a conceptual diagram of a welding machine in which a post-heat treatment device is integrated with a laser welding device. (b) is a conceptual cross-sectional view of a welder in which a post-heat treatment device is integrated with a laser welding device. FIG. 10 is a diagram showing the correlation between the optimal average set plate thickness and the current value that allows cracking of the welded portion of the test piece after the Erichsen test of the high carbon equivalent material is within the acceptable range. It is a figure showing the steel plate plate|board thickness measuring method before steel plate welding in this invention.

Preferred embodiments of the invention are described below.
The steel plate butt welding method of the present invention is a method of butt welding a preceding steel plate that is an end of a steel strip and a following steel plate that is an end of another steel strip, wherein the preceding steel plate and the following steel plate are respectively After butt welding based on the plate thickness measured in the plate thickness measurement process of measuring the plate thickness of the part that will be the welded part, the welding process of butt welding the preceding steel plate and the following steel plate, and the plate thickness measured in the plate thickness measurement process a post-heating determination step of determining a post-heating current value for heating the weld; and a step of heating the weld based on the post-heating current value determined in the post-heating determination step (also referred to as a post-heating step). including.
FIG. 2 is a diagram showing the flow of the butt welding method of the present invention. The steel plate butt welding method of the present invention is preferably performed in the order shown in FIG. 2, but the order of the welding process and the post-heating determination process may be changed. Alternatively, the welding process, plate thickness measurement process, post-heating determination process, and post-heating process may be performed in this order.

In the present invention, using a steel strip manufactured in a hot rolling process, the optimal post-heating determination conditions when joining a preceding steel strip of a steel strip in a cold rolling process and a succeeding steel strip of another steel strip are determined. It has the characteristic of finding out.
In the present invention, the preceding steel plate refers to a steel strip that precedes the production line in the welding process, and the following steel plate refers to another steel strip that is arranged immediately after the preceding steel plate.
In the present invention, as shown in FIGS. 3(a) and 3(b), a device in which the post-heat treatment device is integrated with the laser welding device may be used. In the laser welding device 20 in which the post-heating device 30 is integrated, the adjusting roll, processing head, back roll, swaging roll (not shown) and the post-heating device 30 operate integrally. For example, as shown in FIGS. 3(a) and 3(b), the laser welding device 20 and the post-heat treatment device 30 are welded between the preceding steel strip 10 and the succeeding steel strip 11 of another steel strip in the cold rolling process. It is arranged above and below with respect to the end which becomes 50 . As the laser welding device 20 advances in the direction of the arrow in FIG. 3A, the leading steel plate 10 and the trailing steel plate 11 are butt-welded, and the welded portion 50 is post-heated by the post-heating device 30. .
As can be seen from FIG. 1, it can be seen that the thickness of the end portion of the steel plate corresponding to the welded portion between the leading steel plate and the trailing steel plate used here varies greatly at the end portion. If welding is performed at this point, post-heating will be insufficient if the edge thickness is greater than the preset thickness, and if the edge thickness is smaller than the preset thickness, the post-heating will be insufficient. Excessive heating may occur, and the amount of heat for post-heating may fall outside the optimum range (acceptable range). Therefore, the present inventors determined that the average set plate thickness (a value obtained by averaging the preset plate thicknesses of a pair of preceding steel plates and subsequent steel plates. See the method for calculating the average set plate thickness described below.) 2.0 mm ~ 2.5 mm, the current value (A) is changed by 10 A in the range of 50 A to 130 A, and the cracking of the welded part of the test piece after the Erichsen test is within the acceptable range. Correlations of current values were investigated. The results are shown in FIG.
In FIG. 4, the X-axis is the average set plate thickness (mm), and the Y-axis is the current value of post-heating (A). It is a diagram showing the correlation between the optimum average set plate thickness and the current value. As shown in FIG. 4, when the average set plate thickness is 2.0 mm, the optimum current value is 90 A (indicated by ○ in the figure), and when the average set plate thickness is 2.25 mm, the optimum current value is 90 to 100 A ( ), and when the average set plate thickness was 2.5 mm, the optimum current value was 90 to 100 A (indicated by ◯ in the figure). From Fig. 4, if the post-heating current value for each average plate thickness is within the acceptable range (points indicated by ○ in the figure), there is no problem with cracking, and welds that can occur when the steel strip is rolled. It is possible to prevent the occurrence of breakage troubles. On the other hand, if it is out of the acceptable range (the location indicated by x in the figure), there is a problem with cracking, and when the steel strip is rolled, it causes the occurrence of fracture troubles at the welded portion.

The plate thickness measurement step is to measure the plate thickness of the portions to be welded between the preceding steel plate and the succeeding steel plate before welding. In the plate thickness measurement process, there is a method of measuring one point at the center of the width of each of the preceding steel plate and the following steel plate (see Fig. 5), and a method of measuring the full width of the welded part with a plate thickness gauge attached to the welding machine. . For example, in the case of the method of measuring one width center point of each of the leading steel plate and the trailing steel plate, the leading steel plate 10 is and the following steel plate 11 may be measured at one point in the center of the width thereof. In addition, in the case of the method of measuring the plate thickness of the entire width of the welded part with a plate thickness gauge attached to the welding machine, the plate thickness at arbitrary multiple positions among the measured plate thickness of the full width is measured, and the post-heating current value is It may be used as the plate thickness for determination. For example, a method of determining the post-heating current value using the plate thickness at three points in the width direction is exemplified.
Determining the post-heating current value based on the average measured plate thickness of the plate thickness of the portion to be the weld of the preceding steel plate and the plate thickness of the portion to be the weld of the subsequent steel plate measured in the plate thickness measurement process. As a result, it is possible to perform the post-heating treatment of the weld zone with an optimum amount of heat, and to prevent the trouble of breaking the weld zone, which may occur when the steel strip is rolled. As shown in FIG. 5, the plate thicknesses of the welded portions of the preceding steel plate and the succeeding steel plate refer to the plate thicknesses of the ends of the preceding steel plate and the succeeding steel plate (50-1 and 50-2 in FIG. 5). ).

The welding process of the present invention is a process of butt-welding a preceding steel plate and a succeeding steel plate. Laser welding is preferably used as the welding method applied to the continuous rolling line of the present invention.
In the laser welding of the present invention, the steel sheets are butted against each other, the distance between the steel sheets is set to less than 0.2 mm, and the steel sheets and the wire are melted by a laser while feeding a wire between the steel sheets.
Laser welding provides superior quality characteristics compared to flash butt welding due to its high energy density and low heat input. However, in welding using high carbon equivalent materials, etc., rapid cooling after welding produces a hardened low-temperature transformation structure (structure containing martensite and bainite) in the weld, which causes cracks in the weld. It will cause the breakage trouble of the part. As for the hardening of the welded portion, it is known that post-heating is performed after welding to temper and soften the hardened welded portion, thereby preventing the welded portion from breaking.

In the present invention, the preceding steel sheet and the succeeding steel sheet are, in mass%, C: 0.5% or more, Si: 0.1% or more and 0.5% or less, Mn: 0.3% or more and 0.6% or less, P: 0.05% or less, S: 0.05% or less, Cu: 0.5% or less, Ni: 3% or less, Cr: 0.05% or more and 0.5% or less, Al: 0.05% or less , the balance being Fe and unavoidable impurities. By welding a preceding steel sheet and a subsequent steel sheet having such a composition, it is possible to prevent fracture troubles in the weld zone caused by the low-temperature transformation structure that occurs. It is for In addition, it is more preferable that the amount of C is 2.2% or less. In addition, the unavoidable impurities include, for example, N, Ti, Nb, V, W, B, Mo, Zr, Sn, Sb, Ta, Ca, Mg, Ce, La, REM, etc., and the content of these is allowable if it is 0.5% by mass or less in total.

The Vickers hardness of the preceding steel sheet and the succeeding steel sheet is preferably 100 HV or more and 1000 HV or less, more preferably 100 HV or more and 400 HV or less, and even more preferably 100 HV or more and 200 HV or less. If it is within the above range, troubles of breakage of the welded portion are less likely to occur.
In addition, the hardness of the welded portion formed by butt welding the preceding steel plate and the following steel plate has a Vickers hardness of preferably 100 HV or more and 1000 HV or less, more preferably 100 HV or more and 400 HV or less, and 100 HV or more and 200 HV or less. It is even more preferable to have Within the above range, the difference in hardness between the preceding steel plate and the subsequent steel plate and the welded portion is small, so that the fracture trouble of the welded portion is less likely to occur.
The above Vickers hardness may be measured based on JIS Z2244:2009.

A high carbon equivalent material that is used as a material for a steel plate is martensitic as the steel type has a higher carbon equivalent. Therefore, it is preferable to subject the weld zone to a post-heat treatment to soften it as tempered martensite and reduce the difference in hardness between the weld zone and the steel plate. Therefore, in the present invention, the hardness of the welded portion formed by butt welding the preceding steel plate and the succeeding steel plate preferably has a Vickers hardness of 100 HV or more and 1000 HV or less.

In the post-heating process, if the post-heating process is applied to the welded part with a uniform amount of heat without considering the plate thickness variation of the welded part, there may be insufficient post-heating when the plate thickness is greater than the preset value, or the pre-set value. It is difficult to prevent excessive post-heating when the plate thickness is thinner than the plate thickness. In such a case, the optimum post-heating heat quantity range (also called the acceptable range) is exceeded, and it is difficult to perform post-heating treatment stably and to avoid problems such as breakage of the weld zone when the plate is rolled. However, the productivity of the coil decreases.

Therefore, in the post-heating treatment, the welded part is heated after butt welding based on the plate thickness measured in the plate thickness measurement process, instead of post-heating the welded part with a uniform amount of heat. Determine the post-heating current value and heat the weld.
In the post-heating determination step of the present invention, based on the average measured plate thickness of the plate thickness of the portion to be the weld of the preceding steel plate measured in the plate thickness measurement step and the plate thickness of the portion to be the weld of the subsequent steel plate is a step of determining the post-heating current value.

First, the pre-set plate thicknesses of a pair of leading steel plates and trailing steel plates are averaged to calculate an average plate thickness (average set plate thickness). Then, a current value for post-heating the average set plate thickness is also determined (average set current, that is, a preset post-heating current value).
Next, the average measured plate thickness is calculated by averaging the measured plate thicknesses of the preceding steel plate and the following steel plate.
Averaging here means adding the plate thicknesses of the preceding steel plate and the succeeding steel plate and dividing by two.
Finally, the following formula (2) is derived based on the plate thickness (l) and the post-heating current value (I) in the post-heating temperature calculation formula represented by the following formula (3). Next, the post-heating current value is calculated by substituting the average set plate thickness, the average set current, and the average measured plate thickness into the following formula (1) based on the following formula (2). The post-heating current value is the current value derived as described above, and is the current value used for the post-heating treatment.
The post-heating current value calculated by the above procedure is used as the post-heating treatment condition, and the post-heating treatment is performed on each welded portion.

ここで、Ｔは後加熱温度、Ｒは抵抗、Ｉは後加熱電流値、ρは密度、ｃは比熱、ｗは後加熱幅、ｖは溶接速度、ｌは板厚、Ｔ_０は後加熱前温度を示している。

Here, T is post-heating temperature, R is resistance, I is post-heating current value, ρ is density, c is specific heat, w is post-heating width, v is welding speed, l is plate thickness, T ₀ is before post-heating showing the temperature.

Ｉ_設定は、予め設定された後加熱電流、ｌ_設定は、平均設定板厚、Ｉ_補正後は、後加熱電流値、ｌ_測定は、平均測定板厚を示している。

I _setting indicates a preset post-heating current, l _setting indicates an average set plate thickness, post-heating current value after I _correction , and l _measurement indicates an average measured plate thickness.

The post-heating current value calculated as described above is used as the post-heating treatment condition, and the step of heating the welded portion is performed. If only one point in the center of the width of each of the preceding steel plate and the following steel plate is measured, the post-heating conditions can be obtained by calculating and setting the post-heating current value once. If so, it is necessary to perform calculation and setting multiple times. In the present invention, the post-heating heat treatment condition is preferably within ±10% of the post-heating current value calculated by formula (1), more preferably within ±5%. It is preferably carried out in a post-heat treatment apparatus by heating.
The specifications of the laser welding apparatus used in the present invention are an oscillator output of 12 kW, oscillator mode: low-order multimode (TEM01), and shield gas: _CO2 gas, but are not limited to these specifications.
In addition, the specifications of the post-heating apparatus used in the present invention are that it uses a high-frequency induction coil, has a heating area of 72 mm x 380 mm, a rated output of 40 kW, a frequency of 30 kHz, and a mobile heating method. is not limited to

When post-heating is performed by induction heating, the current value (calorie) during post-heating calculated based on the above post-heating determination step is applied as the post-heating treatment condition instead of the temperature during post-heating. I do. Therefore, even for steel sheets having the same optimum post-heating temperature, the optimum current value differs depending on the thickness of the steel sheet, so the current value is set for each weld zone.

Preferred embodiments in accordance with the present invention are described below, but are not limited thereto.

As a component composition, in mass %, C: 0.95%, Si: 0.2%, Mn: 0.45%, P: 0.01%, S: 0.01%, Cu: 0.08%, Steel sheets containing Ni: 0.08%, Cr: 0.2%, Al: 0.01%, the balance Fe and unavoidable impurities were used as the preceding and following steel sheets.
The average set plate thickness obtained by averaging the preset plate thicknesses of the preceding steel plate 10 and the succeeding steel plate 11, and the width center of the end portion of the preceding steel plate and the succeeding steel plate are measured using a plate thickness meter 40, and these are averaged. Table 1 below shows the results of the converted average measured plate thickness.
The plate thickness meter 40 irradiates the steel plate with laser from above and below so as to be perpendicular to the steel plate, and measures the plate thickness from the distance from the laser irradiation port to the surface of the steel plate.
In addition, the preset post-heating current was set to 100A.

The average set plate thickness of the preceding steel plate 10 and the following steel plate 11, the average measured plate thickness of the preceding steel plate 10 and the following steel plate 11, and the preset post-heating current value 100 A are calculated using the above-described formula (1). and calculated the post-heating current value, it was calculated to be 110A.

The obtained post-heating current value (110 A) is used as the post-heating condition of the post-heating device 30, and the leading steel plate 10 and the trailing steel plate 11 are welded together with the laser welding device 20 and the post-heating device 30 as shown in FIG. After welding with an integrated laser welding machine, the welded portion 50 of the steel strip 1 was subjected to a post-heating treatment while applying induction heating of 110 A in the post-heating device 30 .

The formability of the weld zone was determined for the test piece after the post-heat treatment. The Erichsen test was mainly used to determine the formability of the weld zone.
In the Erichsen test, the test piece including the welded part of the leading steel plate and the trailing steel plate is placed on the die of the Erichsen test machine, a hemispherical punch is pushed into the center and squeezed out with the die, and at least one place on the test piece The punch was inserted until a crack was generated, and the cracking of the weld was visually determined.
The test results were evaluated by the following judgments. Table 2 shows the judgment criteria of the Erichsen test.
○: Cracks perpendicular to the weld △: Partial weld cracks ×: Weld cracks

When post-heating was performed at the obtained post-heating current value (110 A), the degree of cracking of the welded portion was ◯, which satisfied the present invention.
In addition, test pieces with different average set plate thickness are prepared, the post-heating current value is set as the condition of the post-heating device 30, and after welding the preceding steel plate 10 and the succeeding steel plate 11, welding is performed by induction heating of the post-heating device 30. Part was post-cooked. The test piece welded by setting the post-heating current value as the post-heating treatment condition of the post-heating device 30 causes a vertical crack in the welded portion (judgment “○”), and the welded portion is firmly welded. It has been found.
On the other hand, in the case where the post-heating current value was not set as the post-heating condition of the post-heating device 30, the test piece cracked along the welded portion and (judgment "X") and partially weld cracked test pieces (judgment "△") were mixed, and the formability of the weld zone was not stable.

1 Steel strip 10 Leading steel plate 11 Trailing steel plate 20 Laser welding device 30 Post-heat treatment device 40 Plate thickness gauge 50 Welded portion 50-1 Plate thickness of the portion to be the welded portion of the leading steel plate (plate thickness at the end of the leading steel plate)
50-2 Plate thickness of the welded part of the trailing steel plate (plate thickness of the edge of the trailing steel plate)

Claims (8)

A method for butt welding a preceding steel plate and a following steel plate,
A plate thickness measuring step of measuring the plate thickness of each welded portion of the preceding steel plate and the succeeding steel plate;
a welding step of butt-welding the preceding steel plate and the following steel plate;
a post-heating determining step of determining a post-heating current value for heating the welded portion after the butt welding based on the plate thickness measured in the plate thickness measuring step;
and heating each of the welded portions based on the post-heating current value determined in the post-heating determination step. In the post-heating determination step, the average measured plate thickness of the plate thickness of the portion to be the welded portion of the preceding steel plate measured in the plate thickness measurement step and the plate thickness of the portion to be the welded portion of the subsequent steel plate The steel plate butt welding method according to claim 1, wherein the post-heating current value is determined based on In the post-heating determination step, a preset post-heating current value set based on an average set plate thickness calculated by averaging preset plate thicknesses of a pair of preceding steel sheets and succeeding steel sheets; , the average set thickness of the preceding steel plate and the following steel plate, the plate thickness of the portion to be the weld of the preceding steel plate measured in the plate thickness measurement step, and the thickness of the portion to be the weld of the following steel plate 3. The steel plate butt welding method according to claim 1, wherein the post-heating current value is determined so as to satisfy the following formula (1) based on the plate thickness and the average measured plate thickness.

I _setting indicates a preset post-heating current, l _setting indicates an average set plate thickness, post-heating current value after I _correction , and l _measurement indicates an average measured plate thickness. The steel plate butt welding method according to any one of claims 1 to 3, wherein Vickers hardness of said preceding steel plate and said succeeding steel plate is 100 HV or more and 1000 HV or less. Butt welding of steel plates according to any one of claims 1 to 4, wherein the hardness of the weld formed by butt welding the preceding steel plate and the following steel plate has a Vickers hardness of 100 HV or more and 1000 HV or less. Method. The leading steel plate and the trailing steel plate, in mass%, C: 0.5% or more,
Si: 0.1% or more and 0.5% or less,
Mn: 0.3% or more and 0.6% or less,
P: 0.05% or less,
S: 0.05% or less,
Cu: 0.5% or less,
Ni: 3% or less,
Cr: 0.05% or more and 0.5% or less,
Al: 0.05% or less,
The steel plate butt welding method according to any one of claims 1 to 5, wherein the steel plate has a chemical composition consisting of the balance Fe and unavoidable impurities. The preceding steel sheet and the succeeding steel sheet, in mass%, C: 0.5% or more and 2.2% or less,
Si: 0.1% or more and 0.5% or less,
Mn: 0.3% or more and 0.6% or less,
P: 0.05% or less,
S: 0.05% or less,
Cu: 0.5% or less,
Ni: 3% or less,
Cr: 0.05% or more and 0.5% or less,
Al: 0.05% or less,
The method for butt-welding steel plates according to claim 6, wherein the steel plate has a chemical composition consisting of the balance Fe and unavoidable impurities. The butt welding method for steel plates according to any one of claims 1 to 7, wherein the butt welding is a laser welding method.

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