Butt welding method

Abstract

The present invention provides a butt welding method capable of increasing the strength of the weld metal and preventing breakage at the welded portion during passage through a processing line, even when the weld metal is soft, such as a welded portion formed when a high Ni-content austenitic or low carbon ferritic filler wire is used. When the rear end of a preceding steel sheet and the front end of a succeeding steel sheet are butted together at the entry side of the processing line and the solidified welded portion is pressurized at the butted portion, the pressing force during the pressing is set to H, and the hardness of the welded portion after pressing is set to H. w When the hardness of the base material of the butted steel plates with the lower hardness is H1, 0≦H w Control is performed so as to satisfy the relationship -H1<100.

Description

[Technical field]

[0001] The present invention relates to a butt welding method for welding steel sheets together by butting the rear end of a preceding steel sheet and the front end of a following steel sheet at the entry side of the processing line and using laser welding when the steel sheets are passed through various processing lines. [Background technology]

[0002] In recent years, in the steel industry, in hot rolling facilities, pickling facilities, cold rolling facilities, annealing facilities and the like used to manufacture steel sheets, it has become mainstream to continuously process steel sheets wound around coils while uncoiling them.

[0003] In this way, in a manufacturing line that continuously processes steel plates, in order to pass the steel plates to be processed through the line without interruption, the rear end of the preceding steel plate and the front end of the following steel plate are butt-jointed and welded to each other at the entry side of the line.

[0004] Flash butt welding and laser welding are generally used to weld such steel plates together, but laser welding is often used especially for welding hard steel plates with poor toughness, such as electrical steel plates and high-strength steel plates.

[0005] However, in such laser welding, the welded part is rapidly cooled after welding, and as a result, it is not possible to harden it and ensure sufficient toughness. In particular, in steel plates containing a large amount of C or Si, the embrittlement of the welded part becomes more pronounced as the content of these elements increases.

[0006] Therefore, laser welds of steel sheets containing a large amount of C and Si are prone to fracture while passing through a continuous processing line. If a steel sheet fractures while passing through a processing line, it takes a long time to recover, resulting in a significant drop in operating rate and productivity.

[0007] Furthermore, in rolling machines and the like, rolls are damaged and the rolls must be replaced, resulting in not only a decrease in productivity but also an increase in maintenance costs.

[0008] Therefore, filler wire with a low alloy content has been used in the past for welding steel plates with a high alloy content, such as YGW12Y (C: approx. 0.08 mass%, Si: approx. 0.5 mass%) specified in JIS Z 3312 (2009) and SNI6625 (Si: approx. 0.29 mass%, Ni: approx. 61.3 mass%) specified in JIS Z 3334 (2017).

[0009] In other words, by diluting the C and Si concentrations in the weld metal with the filler wire, it is possible to prevent the formation of coarse ferrite structures or brittle martensite structures, thereby preventing the weld metal from becoming embrittled.

[0010] However, when the above-mentioned high Ni content austenitic or low carbon ferritic filler wire is used, the weld metal tends to be softer than the steel sheet, and deformation is concentrated in the weld metal when the sheet is passed through a continuous processing line, causing fracture at the weld.

[0011] Therefore, Patent Document 1 proposes a technology for obtaining a welded joint with excellent toughness of the weld metal by applying pressure to the excess weld bead after welding when performing butt welding while supplying a filler wire and controlling the structure of the weld metal that is formed.

[0012] Furthermore, Patent Document 2 proposes a technique in which a pressure device such as a press is used when applying pressure to a weld bead after welding. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Patent No. 4486639 [Patent Document 2] Patent No. 2948843 Summary of the Invention [Problem to be solved by the invention]

[0014] However, the technology described in Patent Document 1 is a technology in which the laser weld is pressurized in the temperature range of Ac1-Ac3 to refine the austenite grain size, promote transformation into ferrite and pearlite, and reduce brittle martensite. Therefore, it cannot be applied to increasing the strength of weld metal that does not undergo phase transformation, such as single-phase ferrite or single-phase austenite. In addition, even in the case of a weld metal that undergoes phase transformation, if there is a concentration distribution of the chemical composition in the weld metal, the above-mentioned transformation has a problem in that the strength of the entire weld metal cannot necessarily be increased.

[0015] The technology described in Patent Document 2 is a technology for removing irregularities in the weld bead, mitigating stress concentration at the weld, and preventing fracture at the weld when the plate is passed through a continuous processing line. However, when there is a strength difference between the weld and the base metal, such as a weld formed when using austenitic or low-carbon ferritic filler wire with high Ni content, fracture may occur at the weld.

[0016] The present invention has been made in consideration of the above circumstances, and has an object to provide a butt welding method that can increase the strength of the weld metal and prevent fracture at the weld when the sheet is passed through a continuous processing line, even when the weld metal is soft, such as a weld formed when a high Ni-content austenitic or low-carbon ferritic filler wire is used. [Means for solving the problem]

[0017] The inventors have conducted extensive research in order to achieve the above object. As a result, it was discovered that by controlling the pressure applied to the weld with rolls after the above-mentioned weld has solidified so that a predetermined relationship is satisfied between the hardness of the weld after pressing and the hardness of the lower base metal of the butted steel plates, the strength of the weld metal can be appropriately increased and fracture of the weld in a continuous processing line can be prevented.

[0018] In addition, it was also found that the strength of the weld metal can be increased and fracture of the welded portion in a continuous processing line can be more effectively prevented by appropriately pressurizing the weld bead in accordance with the wire feed rate for the gap at the butt joint between the steel sheets, where the wire feed rate is the ratio b / a of the volume b of the filler wire per unit weld length to the volume a per unit weld length in the gap at the butt joint between the steel sheets. Hereinafter, the gap at the butt joint between the steel sheets will be referred to as the “butt gap.” The butt gap G means the butt gap length, that is, the distance between the rear end of the preceding steel sheet and the front end of the following steel sheet.

[0019] The inventors consider the above-mentioned mechanism of increasing the strength of the weld metal as follows. That is, by applying pressure to the weld metal formed by laser welding under appropriate conditions, processing strain is introduced into the pressurized portion, and the strength of the weld metal increases. Regarding the strength difference between the weld metal and the steel plate, when the butt gap is small, the dilution rate of the weld metal by the base steel plate (the ratio of base metal components in the weld metal) is high and the components of the weld metal are close to the components of the steel plate, so the strength difference is considered to be small. On the other hand, when the butt gap is large, the dilution rate of the weld metal by the base steel plate is low and the components of the weld metal are close to the components of the filler wire, so the strength difference is considered to be large. Therefore, in order to eliminate the strength difference, the larger the butt gap is, the greater the pressing force must be applied to reduce the strength. Also, in order to eliminate the strength difference, the higher the wire feed rate is, the greater the volume of the pressurized part is, so that it is necessary to apply a high pressing force to reduce the strength and introduce a large processing strain.

[0020] The present invention is based on the above findings, and has the following gist and configuration. 1. A butt welding method in which, when a plurality of steel sheets are continuously passed through a processing line, the rear end of a preceding steel sheet and the front end of a succeeding steel sheet are butted together at the inlet side of the processing line, a filler wire is supplied to the butted portion while irradiating it with a laser, the filler wire is melted and solidified to weld, and the solidified welded portion is pressurized, and the pressing force during the pressing is set to a value that is equal to the hardness of the welded portion after pressing, and is expressed as H w When the hardness of the base material of the butted steel plates with the lower hardness is H1, 0≦H w -A butt welding method in which the relationship H1<100 is satisfied.

[0021] 2. The butt welding method according to claim 1, wherein the pressing force P [kN] during the pressing satisfies any one of the following formulas (1) to (3) depending on the butt gap G [mm] at the butt joint and the wire supply rate X for the gap at the butt joint. When 0≦G<0.20, 1.1X(1.5G+2.1)≦P<10X(2G+0.5) …(1) When 0.20≦G<0.50, 1.2X(2G+1.8)≦P<5X(3G+1.2) …(2) When 0.50≦G, 1.3X(3G+1.1)≦P<1.2X(3.5G+9.5) …(3)

[0022] 3. The butt welding method according to 1 or 2 above, wherein the pressing force P [kN] during the pressing satisfies any one of the following formulas (4) to (6) depending on the butt gap G [mm] at the butted parts and the wire supply rate X for the gap at the butted parts. When 0≦G<0.20, (1+X / 30)×(1.5G+2.5)≦P<(1+X / 30)×(15G+18)…(4) When 0.20≦G<0.50, (1+X / 20)×(2G+2.3)≦P<(1+X / 20)×(10G+18)…(5) When 0.50≦G, (1+X / 10)×(2.5G+1.8)≦P<(1+X / 10)×(9G+17)…(6)

[0023] 4. The butt welding method according to claim 1, 2 or 3, wherein the filler wire is either or both of a ferritic and austenitic filler wire. Effect of the Invention

[0024] According to the present invention, it is possible to provide a butt welding method that can increase the strength of the weld metal even when the weld metal is soft, and can prevent fracture at the welded portion when the plate is passed through a continuous processing line. [Brief description of the drawings]

[0025] [Figure 1] 1A to 1C are schematic diagrams showing a laser welding method and a pressurizing method. [Diagram 2] FIG. 2 is a schematic diagram showing hardness measurement points in hardness evaluation of a welded portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present invention will be described. Note that the present invention is not limited to the following embodiment. In addition, in this specification, a numerical range expressed using "to" means a range including the numerical values ​​before and after "to" as the lower and upper limits.

[0027] The present invention relates to a technology for producing a butt-welded component, in which, when steel sheets are passed through a continuous processing line, the rear end of a leading steel sheet 1 and the front end of a following steel sheet 2 are butted together at the entry side of the line as shown in FIG. 1, a filler wire 4 is supplied to such butt joint 3 while a laser 5 is irradiated, the steel sheets 1, 2 and filler wire 4 at such butt joint 3 are melted and welded, and a solidified weld bead 6 formed after welding is pressed.

[0028] First, a welding device and the like used to carry out the present invention will be described. The type of laser used in the welding of the present invention is not particularly limited, and fiber laser, disk laser, semiconductor laser, CO2 laser, etc. may be used. The composition and diameter of the filler wire are not particularly limited, but from the viewpoint of preventing embrittlement of the weld metal constituting the weld bead 6, for example, the composition is preferably ferritic with low C and Si content or austenitic with high Ni content. The type and installation method of the shielding gas are not particularly limited, but in the case of a CO2 laser, it is preferable to use He gas. This is because He gas has a higher ionization voltage than Ar gas and is less likely to generate plasma.

[0029] In addition, the means for applying pressure to the welded portion made of the weld metal is not particularly limited as long as it satisfies the conditions described below. As one example, it is preferable to arrange rolls for flattening the welded portion (hereinafter also referred to as flattening rolls) such as pressure roll 7 shown in Fig. 1 so as to face the front and back surfaces of the welded portion, and to apply pressure to the weld bead from the top and bottom surfaces of the steel sheet while rotating the flattening rolls in the welding direction.

[0030] The steel sheet used in the present invention may be either a hot-rolled steel sheet or a cold-rolled steel sheet, but is preferably a steel sheet containing 0.5 mass% or more of Si. In order to obtain the effects of the present invention more advantageously, the steel sheet should contain 2.5 mass% or more of Si, at which point fracture at the welded portion becomes prominent. On the other hand, the upper limit of the Si content is not particularly limited, but from the viewpoint of ensuring cold rolling properties, it is preferably 4.5 mass% or less.

[0031] The steel plate used in the present invention may contain 0.010 mass% or more of C. If the C content is high, fracture at the welded portion becomes significant, so the C content is more preferably 0.100 mass% or more. There is no particular upper limit for the C content, but it is preferably 0.500 mass% or less. Here, either one of Si and C may be contained, or both of them may be contained.

[0032] The other components (including unavoidable impurities) of the steel plate used in the present invention are not particularly limited, and any of the components or amounts thereof of the steel plate passed through the continuous processing line described below can be suitably used.

[0033] In addition, the steel plate used in the present invention preferably has a plate thickness in the range of 0.8 to 6.0 mm. If the plate thickness is less than 0.8 mm, the amount of the steel plate to be melted is small, so that the welded portion may melt down and a weld bead may not be formed. On the other hand, if the plate thickness exceeds 6.0 mm, in order to melt the steel plate to the back side, it is necessary to increase the laser output or reduce the welding speed to increase the heat input, which may reduce the toughness of the heat-affected zone (HAZ).

[0034] The processing line in the present invention refers to a line that continuously processes the above-mentioned steel sheets. That is, the present invention is preferably applied to a continuous processing line in which the rear end of a preceding steel sheet and the front end of a succeeding steel sheet are laser-welded at the line entry side of a hot rolling facility, a pickling facility, a cold rolling facility, a cleaning facility, a continuous annealing facility, a temper rolling facility, a fine adjustment facility, etc., and the like, and the welded steel sheet is passed through the line. Note that the continuous processing line in the present invention includes a processing line in which the rear end of a preceding steel sheet and the front end of a succeeding steel sheet are laser-welded at the line entry side of the line, and the welded steel sheet is passed through the line, and also includes a case in which an operator manually installs steel sheets one by one.

[0035] The welding method of the present invention includes a step of performing butt welding by laser welding, and a step of applying pressure to the welded portion formed by the laser welding.

[0036] Here, as described above, when a low-alloy ferritic or austenitic filler wire with a high Ni content is supplied, it is considered that the weld metal becomes soft and the strength of the weld metal becomes excessively low compared to the steel plate.

[0037] The strength of such weld metal is significantly affected by the dilution rate of the base metal, and it is believed that the strength of the weld metal decreases as the butt gap increases and the wire feed rate increases. Therefore, in the present invention, it is necessary to improve the strength of the weld metal to be equal to or greater than that of the steel plate by adjusting the pressing force according to the butt gap and the wire feed rate.

[0038] That is, in order to improve the strength of the weld metal, the pressure is increased to H w When the hardness of the base material of the butted steel plates with the lower hardness is H1, 0≦H w It is necessary to control (adjust) so as to satisfy the relationship -H1<100.

[0039] More specifically, in the butt welding method of the present invention, when the butt gap is G [mm], the wire feed rate is X, and the pressing force when pressing the weld is P [kN], the pressing force P may satisfy any one of the following formulas (1) to (3) depending on the butt gap G.

[0040] When 0≦G<0.20, 1.1X(1.5G+2.1)≦P<10X(2G+0.5) …(1) When 0.20≦G<0.50, 1.2X(2G+1.8)≦P<5X(3G+1.2) …(2) When 0.50≦G, 1.3X(3G+1.1)≦P<1.2X(3.5G+9.5) …(3)

[0041] Alternatively, any one of the following expressions (4) to (6) may be satisfied. When 0≦G<0.20, (1+X / 30)×(1.5G+2.5)≦P<(1+X / 30)×(15G+18)…(4) When 0.20≦G<0.50, (1+X / 20)×(2G+2.3)≦P<(1+X / 20)×(10G+18)…(5) When 0.50≦G, (1+X / 10)×(2.5G+1.8)≦P<(1+X / 10)×(9G+17)…(6)

[0042] Here, for example, when G=0.10, either one of formula (1) and formula (4) may be satisfied, or both of formula (1) and formula (4) may be satisfied. Similarly, when 0.20≦G<0.50, either one of formula (2) and formula (5) may be satisfied, or both of formula (2) and formula (5) may be satisfied. Furthermore, when 0.50≦G, either one of formula (3) and formula (6) may be satisfied, or both of formula (3) and formula (6) may be satisfied.

[0043] Here, the pressure P in the present invention is the force applied to the weld bead reinforcement by, for example, roll 7 shown in FIG. 1, and is a value measured by a load cell or the like attached to roll 7 of the pressure device.

[0044] When the pressure P is below the lower limit of the above formulas (1) to (3), the hardening of the welded portion by the pressure is insufficient, whereas when the pressure P is above the upper limit of the above formulas (1) to (3), the welded portion is excessively hardened.

[0045] Moreover, when the pressure P is below the lower limit of the above formulas (4) to (6), the hardening of the welded portion by the pressure is insufficient, whereas when the pressure P is above the upper limit of the above formulas (4) to (6), the welded portion is excessively hardened.

[0046] In addition, in the formulas (1) to (3) and the formulas (4) to (6), for example, when the base metal is ferritic steel and the wire is a nickel alloy, the structure of the weld metal tends to be an α-phase single-phase structure when 0≦G<0.20, a structure of α or γ phase or a mixture of both phases depending on the welding conditions when 0.20≦G<0.50, and a γ-phase single-phase structure when 0.50≦G.

[0047] Here, the above-mentioned butt gap G is the size of the gap that occurs when the rear end of the preceding steel sheet and the front end of the following steel sheet are butted together, and is a value measured by a sensor or the like before welding. As the sensor, for example, a laser displacement meter can be used. As the butt gap G increases, the dilution of the base metal in the weld metal decreases, and the filler wire components become the main component. Therefore, the strength of the weld metal becomes lower than that of the steel sheets.

[0048] That is, it is necessary to increase the pressing force P and to increase the processing strain introduced into the weld metal as the butt gap G increases. Also, as the wire feed rate X increases, both the width and height of the weld bead increase, so the volume of the pressed part increases and a large pressing force is required. In addition, since the butt gap G [mm] is likely to cause burn-through if it exceeds 2.00, it is preferable that it is 0 or more and 2.00 or less. Also, the pressure P [kN] is preferably 2 or more and 20 or less.

[0049] As described above, the wire feed rate X is the ratio b / a of the feed volume b of the filler wire per unit weld length to the volume a per unit weld length in the gap where the steel sheets are butted together. Therefore, from the geometric relationship of the amount of weld metal required to fill the butt gap, X is calculated by: F is the filler wire feed speed [mm / min], A is the cross-sectional area of ​​the filler wire [mm 2 ], W is the welding speed [mm / min], G is the butt gap length [mm], and T is the average thickness of a pair of steel plates [mm], then it is calculated using the following formula (7). X = (F × A) / (W × G × T) … (7)

[0050] In order to apply pressure to the weld bead, it is desirable that the thickness of the weld be thicker than at least the thicker of the steel plates (also referred to as having excess weld in the present invention). In butt welding, such conditions (having excess weld) are usually adopted. Specifically, the average thickness of the weld before pressure is t w[mm], and the thickness of the thicker plate of the butted plate is t1 [mm], t w It is desirable to satisfy the condition t1 in order to effectively carry out the present invention. Moreover, since excessive pressure reduces the plate thickness of the base metal, it is preferable that the average thickness of the welded portion after pressure is equal to or greater than the thickness of the thicker of the butted plates.

[0051] In addition, in actual welding, the molten metal is scattered from the molten pool due to spatters and plumes, and the wire feed rate X is less than the above-mentioned geometric relationship. Taking these factors into consideration, it is preferable that X is 1.1 or more. On the other hand, although there is no particular upper limit for X, it is preferable that the upper limit is less than 5.0 because the cross-sectional shape of the weld becomes asymmetric above and below the center of the plate thickness.

[0052] Furthermore, in the present invention, the pressurization after laser welding must be performed while the weld is solidified. If the weld is at or above the recrystallization temperature before solidification, dislocations are less likely to accumulate due to processing, and the work hardening ability decreases. Therefore, the time from the end of laser irradiation to the start of pressurization is not particularly limited, but is preferably 0.1 seconds or more.

[0053] In the butt welding method according to the present invention, any items not described in this specification can be performed by using conventional methods. EXAMPLES

[0054] An embodiment of the present invention is given below. For each of the steel plates shown in Table 1, two of the steel plates were butt-welded to each other using a laser welding machine and a pressure device installed at the entrance of a line for continuously processing the steel plates. That is, butt welding was performed under the welding conditions and pressure conditions shown in Table 1 to form butt-welded members for each steel plate.

[0055] For the laser welding, a disk laser with a wavelength of 1030 nm was used, and WEL MIG625 (WEL: registered trademark) manufactured by Japan Welding Rod Co., Ltd. with a wire diameter of 0.9 mm was used as the filler wire. The pressure device arranged flattening rolls facing the front and back surfaces of the welded portion, and applied pressure to the welded portion formed by the laser welding while rotating the flattening rolls in the welding direction.

[0056] The butt gap G was obtained by measuring the gap between the rear end of the leading steel plate and the front end of the trailing steel plate using a laser displacement meter before welding, and taking the average value in a range excluding an area 20 mm from each end of the steel plate in the width direction toward the center. Specifically, the average value was taken from three points: a position 20 mm from each end of the steel plate in the width direction toward the center and a position in the center of the weld length direction. The reason for the measurement being in a range excluding 20 mm from each end of the steel plate in the width direction is that the areas 20 mm from each end of the steel plate in the width direction correspond to the start and end of the weld after welding, and the start and end are non-stationary parts and may be removed in the production line.

[0057] The average thickness of the weld before pressure is: t w was obtained by using the above-mentioned laser displacement meter to calculate the average thickness of the weld in an area excluding an area 20 mm from the start and end of the weld toward the center. The average value was calculated from three points: 20 mm from both ends of the steel plate in the width direction and the center in the weld length direction.

[0058] The wire feed rate X was calculated according to the above formula (7). That is, the filler wire feed rate F and the welding speed W were set values, the cross-sectional area A of the filler wire was calculated from the wire diameter measured with a caliper or the like, and the butt gap G and the average plate thickness T of the pair of steel plates were actual measured values, and the wire feed rate X was calculated according to formula (7).

[0059] The welding pressure in the present invention is a value measured by a load cell or the like attached to the roll 7 shown in Figure 1, and specifically, it is the average of measurements taken at three points: positions 20 mm from both ends of the steel plate in the width direction and at the center position in the welding length direction. The welds obtained as described above were evaluated as follows.

[0060] <Evaluation of hardness of welded parts> As shown in Figure 2, cut the specimen perpendicular to the welding direction and measure the maximum weld thickness t w1 Based on this, 1 / 8t w1 , 1 / 2t w1 and 7 / 8t w1 The Vickers hardness HV0.2(10) of the weld metal at each position is measured at 0.2 mm intervals on both sides from the center of the cut surface, and the average of all the measured values ​​is the hardness H of the weld after pressure application. w Regarding the base metal hardness, the Vickers hardness was measured at one point each at 1 / 8T, 1 / 2T, and 7 / 8T in the thickness direction, 10mm away from the boundary between the base metal and the weld metal, where T is the thickness of the steel plate, and HV0.2(10) was measured. The average of the three points was taken, and the lower value of the butted steel plates was designated as H1. w -H1 values ​​between 0 and 100 are examples of the invention, and values ​​outside this range are comparative examples. Note that for welds produced under the same welding conditions, HV0.2(10) was measured at each position in the same manner as above, and the average of all the measured values ​​was taken as the hardness Hs of the weld before pressure application.

[0061] <Threading test> The weld beads were passed through a cold rolling mill with a rolling tension of 150 MPa and a reduction rate of 50% relative to the steel plate thickness. Those that did not fracture at the weld metal were rated as passing (◯), and those that fractured at the weld metal were rated as failing (×).

[0062] The above evaluation results are shown in Table 1 along with the welding conditions.

[0063] [Table 1]

[0064] From these results, the butt-welded components (invention examples) in which the pressure was set so as to satisfy the requirements of the present invention were passed (◯) in all of the above evaluations. [Explanation of symbols]

[0065] 1 Leading steel plate 2 Trailing steel plate 3 Butt joint (butt gap) 4 Filler Wire 5 Laser 6 Weld Bead 7 Pressure Roll

Claims

1. A butt welding method comprising the steps of: butting a rear end of a preceding steel sheet and a front end of a succeeding steel sheet at an entry side of the processing line when a plurality of steel sheets are continuously passed through the processing line; supplying a filler wire to the butted portion while irradiating the portion with a laser; melting and solidifying the filler wire to weld the portion; and applying pressure to the solidified welded portion, The applied pressure during the pressing is defined as Hw, the hardness of the welded part after pressing is defined as H, and the hardness of the base material of the butted steel plates with the lower hardness is defined as H. １ When 0≦Hw−H １ < 100, and the pressing force P [kN] during the pressing satisfies any one of the following formulas (1) to (3) depending on a butt gap G [mm] at the butted parts and a wire supply rate X for the gap at the butted parts. In the case of 0≦G<0.20, 1.1X (1.5G+2.1)≦P<10X(2G+0.5)…(1) In the case of 0.20≦G<0.50, 1.2X (2G+1.8)≦P<5X(3G+1.2)…(2) In the case of 0.50≦G, 1.3X (3G+1.1)≦P<1.2X (3.5G+9.5)…(3)

2. A butt welding method comprising the steps of: butting a rear end of a leading steel sheet and a front end of a trailing steel sheet at an entry side of the processing line when a plurality of steel sheets are continuously passed through a processing line; supplying a filler wire to the butted portion while irradiating the portion with a laser; melting and solidifying the filler wire to form a weld; and applying pressure to the solidified weld portion, a butt welding method in which the pressing force during the pressing is controlled to satisfy the relationship 0≦Hw−H1<100, where Hw is the hardness of the weld after pressing and H1 is the hardness of the base metal of the butted steel sheets which has the lower hardness, and the pressing force P [kN] during the pressing satisfies any of the following formulas (4) to (6) depending on a butt gap G [mm] at the butted parts and a wire supply rate X for the gap at the butted parts. In the case of 0≦G<0.20, (1+X / 30)×(1.5G+2.5)≦P<(1+X / 30)×(15G+18)…(4) In the case of 0.20≦G<0.50, (1+X / 20)×(2G+2.3)≦P<(1+X / 20)×(10G+18)…(5) In the case of 0.50≦G, (1+X / 10)×(2.5G+1.8)≦P<(1+X / 10)×(9G+17)…(6)

3. 3. The butt welding method according to claim 1, wherein either or both of a ferritic and austenitic filler wires are used as the filler wire.

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