JP2007237203A - Method and equipment for joining steel strip - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joining method which brings a tensile strength of ≥300 N/mm<SP>2</SP>of a weld zone in butt welding of steel strips in which at least either the preceding strip or the succeeding strip is a special steel having a thickness of ≥4.5 mm and an Si content of ≥1.5%, in a flash butt welding of a special steel whose welding is difficult compared with a soft steel. <P>SOLUTION: After the butt welding by flash butt welding, a pressure is applied in the abutting direction of the steel strips so that a forge length is 1.5-2.0 times as large as the strip thickness. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a steel strip connection method and apparatus for connecting by connecting the front end of a succeeding steel strip fed from a new coil to the rear end of a preceding steel strip fed from a coil and performing flash butt welding.

  One of the areas where steel strips are connected is a continuous pickling line, where the steel strips are butted together in the line from the line entry side in order to connect the individual steel strips in a continuous manner. Flash butt welding is performed. At this time, special steel containing a lot of carbon C or special steel containing a lot of strengthening alloy elements such as silicon Si, manganese Mn, vanadium V, etc. are difficult to weld compared to mild steel with a small amount of C. In addition, when welding special steel strips and tension plates, reinforcing polymer elements such as Si, Mn, and V in special steel are easily oxidized, and the generated oxide causes a decrease in the strength of the connection part. It is easy to break when passing through. The breakage of the connecting portion is forced to stop the line for a long time, resulting in a decrease in productivity.

Regarding the method of improving the strength of the connection part by welding, the following Patent Document 1 discloses a method of performing the welding under a gas shield to suppress the formation of oxides of reinforced polymer elements contained in the steel strip. In Reference 2, when connecting steel strips of special steel containing a lot of reinforced polymerizing elements, low kinematic viscosity oil and fat having a kinematic viscosity of 5 to 100 cst is supplied to the rear end of the preceding steel strip and the front end of the subsequent steel strip. And the method of connecting in the state which burned fats and oils at the time of welding is disclosed.
JP 56-50789 JP-A-9-262680

  The present invention connects special steel, and it is necessary to solve the problem of the strength of the connection part. However, in the method disclosed in Patent Document 1, the equipment cost increases due to gas shielding, Running costs are also high. Further, in the method disclosed in Patent Document 2, the equipment cost is not increased, but since the fats and oils have a low kinematic viscosity, a shielding effect cannot be expected.

  The inventors have conducted various studies on a method of connecting steel strips in which at least one of the preceding steel strip or the subsequent steel strip has a thickness of 4.5 mm or more and an Si content of 1.5% or more. For steel with low content and special steel with thin plate thickness even though there is a large amount of Si, there is no problem in strength at the connection part, but the Si content is 1.5% or more and the plate thickness is 4. It has been found that for special steels of 5 mm or more, satisfactory results cannot be obtained at the connection.

  As a result of further investigations on special steels having a plate thickness of 4.5 mm or more and an Si content of 1.5% or more, the present inventors have tried to press the steels against each other after welding. It has been found that when the upset cost (details will be described later) is 1.5 times the plate thickness or more, the problem of the strength of the connecting portion is solved, and the present invention has been completed.

That is, in the invention according to claim 1, at least one of the preceding steel strip or the subsequent steel strip is flush-butt welded with a steel strip having a thickness of 4.5 mm or more and a Si content of 1.5% or more. Then, the upset allowance when both steel strips are pressed in the butting direction is 1.5 to 2.2 times the average plate thickness of both steel strips, preferably 1.5 to 2.0 times, It is characterized by extruding and removing the oxides of strengthened alloy elements such as Si, Mn, and V formed from the welded part,
The invention according to claim 2 relates to an apparatus for carrying out the invention according to claim 1, and includes a flash butt welder having electrodes for clamping the ends of both steel strips to be connected from above and below, and each steel strip. A roll that clamps the roll from above and below, and a feed device that includes a motor that rotationally drives the roll in the forward or reverse direction.

  FIG. 1 shows a schematic view of the present apparatus. The upper electrode 2 and the lower electrode 3 that clamp the vicinity of the rear end of the preceding steel strip 1 from above and below, and the top of the front end of the trailing steel strip 4 that is clamped from above and below. From a flash butt welder composed of an electrode 2 and a lower electrode 3, rolls 5 and 5 for clamping the steel strips 1 and 4 from above and below, and a motor (not shown) for rotationally driving the rolls 5 and 5 in the forward or reverse direction As shown in FIG. 2, both steel strips 1 and 4 are butt-joined as shown in FIG. 2 and then butt-welded with a flash butt welder. The steel strip is strongly pressed in the abutting direction (FIG. 3). This pressurization is performed until the upset cost is 1.5 to 2.2 times the average plate thickness of both steel strips. The upset cost of the present invention can be represented by a difference Dd between the distance D between the electrodes shown in FIG. 2 and the distance d between the electrodes after pressing.

  According to the first aspect of the invention, it is possible to use special steel that is difficult to weld compared to mild steel by simply setting the upset cost to 1.5 times or more and 2.2 times or less of the average thickness of the front and back and performing flash butt welding. In particular, it is possible to easily obtain a bonded steel strip having a bonding strength exceeding the fracture limit value even for special steels that contain a large amount of Si, Mn, etc., which are particularly susceptible to oxidation. Can be prevented and productivity can be improved.

  In the invention according to claim 2, if an existing conveying device is used for the steel strip feeding device, no special equipment for connecting the steel strip is required in addition to the flash butt welder, and the equipment cost may increase. Absent.

  Following the two types of high-thickness special steels G and H shown in Table 1 below, the steel strips (thickness 4.5 mm) of the same steel type are pressed by flash butt welding using the method shown in FIGS. Welded together and changed the upset cost after welding within the range of 1.5 to 2.2 and pressurized in the butt direction. Thereafter, a welding vicinity portion having a width of 200 mm is cut in the longitudinal direction of the steel strip before and after the welded joint portion 6 of the steel strips 1 and 4 shown in FIG. 3, and further 50 mm from both edges along the welding vicinity portion 6. A total of five test pieces were cut out at 50 mm × 200 mm at the position, 1/4 position in the width direction, and center position in the width direction. And about each test piece, the tension test was done and the tensile stress which a welded joint part fracture | ruptures was measured. The joint tensile strength in Table 2 shows the average value of five test pieces.

Comparative Example Two types of low Si special steels A to D shown in Table 1 and three types of high Si special steels E to H were butt welded in the same manner as in the examples, and after welding, The set-up allowance was set to 1 or 1.2 and pressure was applied in the butt direction. Then, a total of five test pieces were prepared by the same method as in the examples, and tensile tests were performed to measure the tensile stress leading to breakage. Table 2 shows the average value of the five test pieces.

From past investigations and experiences, it has been found that the tensile strength of the joint is required to be 300 N / mm ² or more so that the welded joint does not break during threading or rolling. Looking at Table 2 from this point of view, sample no. The low Si content of the test material of 9-12, upset allowance is also tensile strength identical to the plate thickness in 366~381N / mm ^2, sufficient to satisfy the 300N / mm ² of fracture limit value, also the sample No. Even though the high-Si steel of 13 is a thin steel plate having a thickness of 2.3 mm, the tensile strength is 324 N / mm ² and the fracture limit value is satisfied. A high steel plate of 14 to 16 and a steel plate thickness of 4.5 to 6 mm does not satisfy the fracture limit with a tensile strength of 242 to 297 N / mm ² . Sample Nos. 17 and 18 For the same thick steel plate as 15 and 16, even if the upset cost was increased to 1.2 times the plate thickness, the tensile strength was 280-302 N / mm ² , but sufficient satisfactory results were not obtained. . From the above, the strength of the joint depends greatly on the Si amount and the plate thickness. For special steel with a Si amount of 1.5% or less, and for a thin plate with a thickness of less than 4.5mm even if the Si amount is 1.5% or more There is no problem in the joint strength, and with high Si steel with a plate thickness of 4.5mm or more and Si content of 1.5% or more, the joint strength can be satisfied even if the upset cost is increased to 1.2 times the plate thickness. It turned out not to be obtained.

  Sample No. As for Examples 1 to 8, even when high Si steel having a plate thickness of 4.5 mm or more and a Si amount of 1.5% or more is satisfied when the upset amount is 1.5 to 2.2 times the plate thickness. It was found that a sufficiently strong joint strength was obtained, and in particular, when the upset allowance was 1.5 to 2.0 times the plate thickness, a sufficiently satisfactory joint strength could be obtained.

The figure which shows the state before the start of flash butt welding. The figure which shows a state when flash butt welding is started. The figure which shows a state when it pressurizes after welding.

Explanation of symbols

1 .... Leading steel strip 2 .... Upper electrode 3 .... Lower electrode 4 .... Subsequent steel strip 5 .... Roll 6 ... Weld joint

Claims (2)

  When flash butt welding is performed on a steel strip having a thickness of 4.5 mm or more and a Si content of 1.5% or more when at least one of the preceding steel strip or the subsequent steel strip is welded, both steel strips are thrust after welding. A method for connecting steel strips, characterized in that the upset margin when pressed in the mating direction is 1.5 to 2.2 times the average plate thickness of both steel strips.   It consists of a flash butt welder equipped with electrodes that clamp the ends of both steel strips connected from above and below, a roll that clamps each steel strip from above and below, and a motor that drives the rolls to rotate forward or backward. The apparatus which implements the connection method of the steel strip of Claim 1 characterized by having a feeding apparatus.

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