JP5388342B2 - Lap welding method of steel strip - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a steel strip lap welding method in which a plurality of steel strips are sequentially overlap welded.

  When processing steel strips, etc., it is often the case that a plurality of steel strips are sequentially welded and connected to be continuously processed. For example, a plurality of steel strips are continuously processed by rolling, annealing pickling, electrolytic degreasing, plating, and the like. In welding for connecting steel strips, a welding method is appropriately selected according to the steel type and plate thickness. In the case of a steel strip having a relatively thin plate thickness, lap welding such as spot welding or seam welding is often used.

  FIG. 4 illustrates the configuration on the entry side of equipment conventionally used for continuous processing of a plurality of steel strips. On the entry side of the facility for continuously treating a plurality of steel strips 1, a dispenser 2, a deflector roll 3, a leveler 4, a shearing machine 5, and a lap welder 6 are provided. The dispenser 2 unwinds the steel strip 1 wound in a coil shape and inserts it into the continuous processing facility in the direction of the arrow 7. The steel strip 1 whose curl has been corrected by the leveler 4 is sheared at a desired position as necessary, and a lap joint is formed by the tail end portion of the preceding steel strip 1a and the tip portion of the succeeding steel strip 1b. Here, the case where the spot welder 6 which is a kind of lap welder is used is illustrated. The lap joint 8 formed by the preceding steel strip 1a and the succeeding steel strip 1b is spot welded.

  FIG. 5 shows a state of a welded portion by the spot welder 6 shown in FIG. The lap joint 8 is sandwiched between the electrodes 9 of the spot welder 6 and pressurized, and electricity is supplied from the power source (not shown) through the electrodes 9. The nugget 10 is formed by melting the inside of the lap joint between the steel strips by resistance heating due to energization. However, the overlap allowance at the lap joint 8 is about 200 mm, for example, whereas the diameter of the electrode 9 is about 25 mm, and the overlap allowance is displayed shorter than the electrode 9 in the figure. In addition, a plurality of electrodes 9 are arranged at intervals in the spot welder 6, and a plurality of spot welds are simultaneously performed.

  FIG. 6 shows the fracture state of the spot weld. When a healthy weld without cracks in the nugget 10 is subjected to tensile shear stress, the nugget 10 breaks at the heat affected zone (HAZ) around the nugget 10 or the base material. This rupture state is called plug rupture. In the case of plug rupture, the strength of the spot welded joint is greatly affected by the thickness of the steel strip being welded. For example, the breaking strength per nugget in a spot welded part of JIS standard steel grade SK5 is about 34.3 kN when the plate thickness is 2.90 mm, whereas it is 4.3 when the plate thickness is 0.40 mm. It drops to about 9kN.

  Spot welds between steel strips are repeatedly subjected to bending stress each time they circulate a transport roll provided in a continuous processing facility. In order to prevent breakage of the welded part due to this repeated bending stress, in the case of a welded part between steel strips having a thin plate thickness, the line tension applied to the steel strip by the continuous processing equipment is set low. However, when a steel strip having a large thickness is connected to a thin steel strip by spot welding, the line tension may have to be set in accordance with the steel strip having a larger thickness. In addition, the line tension may not be lowered below a certain value due to the nature of processing in the facility. In such a case, the strength of the welded portion of the steel strip having a thin plate thickness may be insufficient, and the steel strip may break in the continuous processing facility. Furthermore, in the welding of a steel strip with a thin plate thickness, the weld may be hardened and hardened in a rapid heating and quenching cycle. When quenched and hardened, the difference in mechanical properties between the nugget and HAZ and the base material portion becomes large, and breakage easily occurs.

  One method for improving the strength of such spot welds is to form a nugget by main energization of the lap joint, and then perform post-heat treatment energization, so-called temper energization, at a current smaller than the main energization to burn the weld. Returning is performed (see Patent Document 1). However, if the thickness of the steel strip is thin, the mass of the welded portion is small, so even if tempering is performed, the welded portion cannot be slowly cooled and the tempering effect is often not obtained.

JP 2008-229720 A

  If the strength of the lap weld is insufficient and breaks in the continuous processing equipment, restoration work must be performed so that the steel strip can be continuously passed through the equipment again. In the restoration work, all the preceding steel strip is wound with the take-up winder, all the subsequent steel strip is wound in the reverse direction with the unwinder, and the threading material is passed through the continuous processing equipment. A trailing steel strip is connected to and charged into a continuous processing facility. This recovery operation takes a long time and reduces efficiency. Therefore, in order to avoid a reduction in efficiency, it is desired to improve the strength of the lap weld formed by a steel strip having a thin plate thickness and prevent the weld from being broken.

  The objective of this invention is providing the lap welding method of the steel strip which can improve the intensity | strength of the welding part obtained by lap welding of steel strips, when the plate | board thickness of a steel strip is thin.

The present invention is a steel strip lap welding method in which a plurality of steel strips are sequentially welded and connected,
When at least one of the preceding steel strip and the following steel strip is equal to or less than a predetermined plate thickness, the steel strip having a predetermined thickness or less of the lap joint formed by the preceding steel strip and the following steel strip The steel strip lap welding method is characterized in that lap welding is performed by applying a steel plate having a predetermined thickness or more.

According to the present invention, when at least one of the preceding steel strip and the following steel strip is equal to or less than a predetermined plate thickness, a steel plate having a predetermined thickness or more is applied to the side of the steel strip equal to or less than the predetermined plate thickness. And lap welding. Thus, on the side of the steel strip that is equal to or less than the predetermined plate thickness, the welded portion is formed in a region obtained by adding the thickness of the steel plate to the plate thickness of the steel strip, so that the strength of the welded portion can be improved.

FIG. 1 is a diagram showing a lap welding method for a steel strip 11 according to one embodiment of the present invention. FIG. 2 is a diagram showing a lap welding method for a steel strip 21 according to another embodiment of the present invention. FIG. 3 is a diagram showing a lap welding method for a steel strip 31 according to still another embodiment of the present invention. FIG. 4 is a diagram illustrating the configuration of the entrance side of equipment conventionally used for continuous processing of a plurality of steel strips. FIG. 5 is a view showing a state of a welded portion by the spot welder shown in FIG. FIG. 6 is a cross-sectional view showing a fracture state of the spot weld.

  FIG. 1 shows a lap welding method for a steel strip 11 according to one embodiment of the present invention. The lap welding method of the steel strip 11 of this embodiment is used for connecting a plurality of steel strips 11 by sequentially lap welding. Here, the case where spot welding is used as lap welding will be exemplified. In the lap welding method, when the preceding steel strip 11a is equal to or less than a predetermined thickness, a predetermined thickness is provided on the preceding steel strip 11a side of the lap joint 12 formed by the preceding steel strip 11a and the succeeding steel strip 11b. Spot welding is performed by applying the steel plate 13 described above.

FIG. 1 shows a lap welding method for a steel strip 11 according to one embodiment of the present invention. The lap welding method of the steel strip 11 of this embodiment is used for connecting a plurality of steel strips 11 by sequentially lap welding. Here, the case where spot welding is used as lap welding will be exemplified. Lap welding method, when the preceding steel strip 11a is plate thickness less the predetermined, on the side of the preceding steel strip 11a of lap joint 12 formed in the preceding steel strip 11a and the succeeding steel strip 11b, the thickness of predetermined Spot welding is performed by applying the steel plate 13 described above.

  The plate thickness of 0.4 mm is the nominal plate thickness for the entire steel strip 11. Since fluctuations in the plate thickness increase at the end of the leading steel strip 11a and the tip of the trailing steel strip 11b forming the lap joint 12, the actual plate thickness is 0. It is estimated to be in the range of 35 mm to 0.45 mm.

  In this embodiment, the lap joint 12 in which the plate thickness of the preceding steel strip 11a is 0.4 mm and the plate thickness of the trailing steel strip 11b is 1.0 mm is illustrated. In FIG. 1, the thickness of the steel strip with respect to the electrode diameter is slightly exaggerated. Moreover, the overlap margin of the lap joint 12 with respect to the electrode diameter is shown relatively short. The same applies to the following figures. For example, a thickness of 1.0 mm is used for the steel plate 13 (hereinafter referred to as a contact plate) applied to the preceding steel strip 11a having a plate thickness of 0.4 mm. Three lap joints 12 having a thickness of 1.0 mm, 0.4 mm, and 1.0 mm are sandwiched between electrodes 9 to be pressurized and energized. By this spot welding, the nugget 14 is formed so as to extend from the preceding steel strip 11 a to the subsequent steel strip 11 b and the contact plate 13. When the tensile shear test of the spot welded joint having the nugget 14 formed in this way is performed, the HAZ around the nugget 14 formed between the preceding steel strip 11a and the contact plate 13 or the preceding steel strip 11a and the succeeding steel strip 11b. Alternatively, the plug breaks at the base metal part. Even when the plug is ruptured by either the HAZ or the base material, the thickness of the rupture portion around the nugget 14 is 1.4 mm, which is obtained by adding 0.4 mm and 1.0 mm. Therefore, when spot welding is performed with two sheets of a steel strip having a thickness of 0.4 mm and a trailing steel strip having a thickness of 1.0 mm, the thickness of the fracture portion around the nugget is 0.4 mm. Compared to the strength of the welded portion.

  FIG. 2 shows a lap welding method for a steel strip 21 according to another embodiment of the present invention. In the lap welding method of the steel strip 21 of the present embodiment, when the thickness of the trailing steel strip 21b is 0.4 mm or less, the lap joint 22 formed by the leading steel strip 21a and the trailing steel strip 21b is used. It is characterized in that lap welding is performed on the side of the row steel strip 21b using a contact plate 23. Here, a lap joint 22 in which the plate thickness of the trailing steel strip 21b is 0.4 mm and the plate thickness of the preceding steel strip 21a is 1.0 mm is illustrated. The thickness of the contact plate 23 used for the trailing steel strip 21b is, for example, 1.0 mm. The nugget 24 obtained by spot welding the three lap joint 22 is formed to extend from the trailing steel strip 21b to the preceding steel strip 21a and the contact plate 23. The thickness of the fracture portion obtained by the tensile shear test of the spot welded joint having the nugget 24 formed in this way is 1.4 mm, which is obtained by adding 0.4 mm and 1.0 mm. Therefore, when spot welding is performed with two sheets of a trailing steel strip 21b having a thickness of 0.4 mm and a preceding steel strip 21a having a thickness of 1.0 mm, the thickness of the fracture portion around the nugget becomes 0.4 mm. Compared to the above, the strength of the welded portion is improved.

  FIG. 3 shows a lap welding method of the steel strip 31 which is still another embodiment of the present invention. The lap welding method of the steel strip 31 of this embodiment is formed by the preceding steel strip 31a and the succeeding steel strip 31b when the plate thickness of the preceding steel strip 31a and the succeeding steel strip 31b is 0.4 mm or less. It is characterized in that lap welding is performed on both sides of the preceding steel strip 31a and the succeeding steel strip 31b of the lap joint 32 by using contact plates 33 and 34. Here, the lap joint 32 in which the plate thickness of the preceding steel strip 31a and the succeeding steel strip 31b is 0.4 mm is illustrated. The thickness of the contact plates 33 and 34 used for both the steel strips 31a and 31b is, for example, 1.0 mm. The nugget 35 obtained by spot welding the four lap joint 32 is formed so as to extend from the preceding steel strip 31a and the trailing steel strip 31b to the both abutting plates 33 and 34. The thickness of the plug fracture portion obtained by the tensile shear test of the spot welded joint having the nugget 35 formed in this way is 1.4 mm, which is 0.4 mm and 1.0 mm added. Therefore, when spot welding is performed with two sheets of a steel strip having a thickness of 0.4 mm and a trailing steel strip having a thickness of 0.4 mm, the thickness of the fracture portion around the nugget becomes 0.4 mm. Compared to the strength of the welded portion.

  Examples of the present invention will be described below. Here, for the lap joint formed by the preceding steel strip and the succeeding steel strip, the strength of the welded portion was tested by spot welding for the example using the backing plate and the comparative example not using the backing plate. did. As an example, both the steel strip thickness of the preceding steel strip and the succeeding steel strip are 0.4 mm or less, and spot welding is performed on a four-lap joint using a 1.0 mm-thick backing plate on each side of both steel strips. Went. As a comparative example, both the preceding steel strip and the subsequent steel strip had a thickness of 0.4 mm or less, and spot welding was performed on the two-lap joint without using a backing plate.

  Special steel and plain steel were used for the steel strip of the test material, and the same type of steel plate as the steel strip of the test material was used for the backing plate. The specimens used are ordinary steel with C of 0.1% by weight or less and special steel with C of 0.8 to 0.9% by weight. As the special steel, the aforementioned SK5 and the like are applicable. Table 1 shows the spot welding conditions for the four-lap joint of the example, and Table 2 shows the spot welding conditions for the two-lap joint of the comparative example.

  The strength of the spot welded joint was tested according to JIS-Z3136. Moreover, the cross-sectional specimen of the welded part was collected, and the hardness of the nugget part and the peripheral part of the nugget was measured with a load of 5 kN using a Vickers hardness meter.

  Table 3 shows the test results for the examples, and Table 4 shows the test results for the comparative examples. When the plate thickness of the preceding steel strip and the subsequent steel strip of the normal steel was 0.10 mm, the strength of the example was improved about 1.6 times compared to the comparative example. In addition, when the plate thickness of the preceding steel strip and the subsequent steel strip of special steel is 0.25 mm, the strength of the example is about 13 times that of the comparative example, and when the plate thickness is 0.40 mm, Compared to the example, the strength of the example was improved about 2.1 times. Thus, it turns out that the intensity | strength of a spot weld part can be improved by using a contact plate.

  Further, in the embodiment using the contact plate, even in the case of special steel that is easily hardened by hardening, the hardness of the peripheral portion of the nugget is about 200 Hv or less when the plate thickness is 0.25 mm, and about 300 Hv when the plate thickness is 0.40 mm. Is suppressed. In the case of the comparative example that does not use a backing plate, the hardness of the nugget periphery is about 700 Hv and about 800 Hv, respectively. From this, it can be seen that in the examples, the hardenability is reduced by increasing the mass of the weld.

  In addition, the plate | board thickness used as the reference | standard of using a backing plate can also be set according to steel types. For example, in ordinary steel, the standard plate thickness can be made thinner than 0.4 mm. From Tables 3 and 4, it is presumed that quench hardening of the welded portion can be avoided without using a backing plate if the plate thickness of ordinary steel is 0.25 mm. Moreover, in the case of using ordinary steel, it is estimated that the thickness of the backing plate can be made thinner than 1.0 mm, for example, 0.4 mm even when a backing plate is used. However, in terms of process management, preparation of a backing plate, etc., it is preferable to set a standard that does not depend on the steel type and to unify the thickness of the backing plate as well.

  As described above, in the present embodiment, the lap welding method is used for spot welding. However, the present invention is not limited to this and can be effectively used for seam welding.

1,11,21,31 Steel strip 8, 12, 22, 32 Lap joint 13, 23, 33, 34 Plate 9 Electrode 10, 14, 24, 35 Nugget

Claims (1)

In the lap welding method of steel strips, in which a plurality of steel strips are sequentially overlap welded,
When at least one of the preceding steel strip and the following steel strip is equal to or less than a predetermined plate thickness, the steel strip having a predetermined thickness or less of the lap joint formed by the preceding steel strip and the following steel strip A method for lap welding of steel strips, wherein lap welding is performed by applying a steel plate having a predetermined thickness or more.

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