JP2568313B2 - Method for seam welding stainless steel strip in process line - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a seam welding method for a stainless steel strip in a process line.

<Conventional technology> As a process line of a steel strip, for example, in a continuous annealing line, a continuous plating line, a continuous pickling run, a continuous rolling line, etc., a steel strip coil is welded and connected continuously during a production process. By operating, the operation rate of the process line is raised. Seam welding, flash butt welding, laser welding and the like are applied as such a method of joining steel strip coils.

Among these joining methods, the seam welding method is a method in which the overlapped steel strip ends are sandwiched between a pair of upper and lower copper electrode discs and are continuously or intermittently energized and welded, and are simpler than other methods, and Since the welding speed is as high as 2 to 20 mpm, it is widely used in process lines.

However, when stainless steel strips are welded by this seam welding method, stainless steel has lower heat conduction and higher electric resistance than carbon steel, so intermittent current welding is applied for a short period of time (Takao Nakamura, Tokuo Kobayashi, Morimoto Kazuki, Resistance Welding, January 23, 1980, Sanyo Publishing, p. 145) was widely adopted. This is because, when continuous energization seam welding is performed on stainless steel, a mechanical property is reduced due to coarsening of crystal grains due to the influence of heat of the base material, or the stainless steel is melted off, so that a healthy weld cannot be formed.

<Problems to be Solved by the Invention> However, in the above-described method, the shape of a nugget (trace of solidification of molten steel) formed by a copper electrode disk is intermittent. Stress concentration occurs in the formed portion, the load of the threaded plate cannot be withheld, the welded portion may be broken in the line, it takes a long time to recover, and this is a major cause of reducing the operation rate of the equipment.

Furthermore, comparing the welding speed with intermittent current and the welding speed with continuous current in a low carbon steel strip with a thickness of 1.0 mm, the former is 2.5 mpm (see the above “resistance welding” on page 140) and the latter is 20 mpm
(See “Basic Research on Joint Formation Phenomena in High Speed Lap Seam Welding (8th Report)”, Vol. 48, 4, P. 222, 1979, Journal of the Japan Welding Society). We could only do welding at In intermittent current seam welding of stainless steel, it is necessary to further reduce the welding speed, and 1.
The welding speed of 0mm thickness is 1.8mpm or less.
46), and there is a drawback that it is necessary to reduce the sheet passing speed in the continuous process line.

An object of the present invention is to provide a high-speed seam welding method by continuously energizing a stainless steel strip in which the above-mentioned disadvantages have been improved.

<Means for Solving the Problems> According to the present invention for achieving the above object, the ends of stainless steel strips are overlapped, and this overlapped portion is joined by seam welding while moving a pair of upper and lower electrode disks. In the seam welding method for a stainless steel strip in a process line, the welding heat input from the electrode disk is heated by continuous energization so that the bonding interface temperature of the overlapped portion exceeds the recrystallization temperature and becomes lower than the melting point. A process line characterized by crushing the overlapped portion by a pair of upper and lower pressing rolls that continue to move to the electrode disk while the bonding interface temperature is maintained at the recrystallization temperature or higher and lower than the melting point. Is a method for seam welding of stainless steel strip.

<Operation> According to the present invention, since the continuous energization is performed, there is no intermittent formation of the nugget in the welding direction caused by the intermittent energization, and no stress concentration occurs. Further, since the welding heat input is lower than the melting point of the stainless steel, the temperature of the electrode contact surface can be kept low, so that the crystal grains do not become coarse, and since the bonding interface is lower than the melting point, there is no burn-through.

In the welding heat input by the welding electrode disc, nuggets are not formed because the joining interface does not reach the melting point, but since the temperature of the joining interface is maintained at the recrystallization temperature or higher, pressure is applied by the rolling roll. The nucleus of recrystallization is generated and grown, so that the overlapped portions are joined. At this time, the thickness of the stainless steel strip under the heat input conditions below the melting point and near the melting point
At less than 0.5 ton per mm, recrystallization does not occur on the entire overlap margin and the cross section becomes discontinuous. At more than 1.5 ton, the welded portion is crushed and a sound weld is not formed. Also, under heat input conditions near the recrystallization temperature exceeding the recrystallization temperature, recrystallization is not easily generated over the entire overlap margin at 1.0 ton or less, and at 2.0 ton or more, the weld is crushed and a sound weld is formed. Not done.

<Embodiment> FIG. 1 is a side view of a welding apparatus showing an embodiment of the present invention. In joining the upper stainless steel strip 1 and the lower stainless steel strip 2 welded in the direction of arrow 5 in FIG.
First, the steel strips 1 and 2 are overlapped, and the unwelded portion 3 is sandwiched between the welding electrode discs 6 and continuously energized while being pressed by the electrode pressing device 7 attached to the welding device frame 10. The welding current (welding heat input) at this time is in a temperature range where the temperature of the superposed joining interface exceeds the recrystallization temperature of the stainless steel and is lower than the melting point, and is set not to exceed the melting point. These temperatures can be easily determined by performing preliminary experiments without applying the rolling rolls 8 for each steel type.

Next, while the bonding interface between the steel strips 1 and 2 is in the above-mentioned temperature range, a load is applied by the pressing roll press device 9 using the pressing roll 8, and the overlapped portions are crushed and joined. FIG. 2 is a diagram showing a relationship between welding conditions and welding results of the welded portion 4 joined by the above-described operation. The vertical axis represents the pressing force of the reduction roll, and the horizontal axis represents the welding current (welding heat input). As is clear from FIG. 2, the heat input was lower than the recrystallization temperature and 9 kA
In the following, the recrystallization generation at the overlap margin is discontinuous, and when the heat input exceeds the melting point, that is, 18 kA or more, the dispersion is large and the burn-through occurs.

Further, when the rolling pressure is zero, continuous recrystallization is not generated, and recrystallization can be generated in the case where a roll pressure of 0.5 ton is applied with a heat input of 12 kA to 15 kA. Under the condition of high heat input (15kA or more) and high roll pressure, crushing occurs. That is, since the joining portion is heated by energization from the welding electrode disk 6 to a temperature exceeding the recrystallization temperature and less than the melting point, and then appropriately pressed by a reduction roll, a good joining having a continuous joining interface by recrystallization in a wide range of welding conditions. The result was obtained.

<Effects of the invention> In the present invention, since the joining is performed by continuous energization and continuous reduction, it becomes possible to continuously and uniformly join,
Since the heating is performed to a temperature lower than the melting point, joining can be performed without welding effects such as heat influence on the base material, distortion and burn-through.

Further, since joining can be performed even with a small heat input, there is also an effect that wear of the welding electrode disk, which is a problem in seam welding of stainless steel, is extremely reduced. Furthermore, since it is not the joining at the time of pressurization with a welding electrode, high-speed welding of 2 to 20 mpm is possible even with joining of a stainless steel strip, and the speed of the process line can be increased.

[Brief description of the drawings]

FIG. 1 is a side view of a seam welding apparatus showing one embodiment of the present invention, and FIG. 2 is a graph showing a relationship between welding conditions and welding results. 1 ... upper stainless steel strip, 2 ... lower stainless steel strip, 3 ... unjoined part, 4 ... joined part, 5 ... welding direction, 6 ... welding electrode disk, 7 ... electrode Pressure device, 8 ...
Roll-down roll, 9 ... Roll-down roll pressurizing device, 10 ... Frame of welding device.

Claims (1)

(57) [Claims] 1. A method for seam welding a stainless steel strip in a process line in which end portions of a stainless steel strip are overlapped, and the overlapped part is joined by seam welding while moving a pair of upper and lower electrode disks. The welding heat input from the plate is heated by continuous energization so that the joining interface temperature of the overlapped portion exceeds the recrystallization temperature and falls below the melting point, and this joining interface temperature is kept above the recrystallization temperature and below the melting point. A method for seam welding a stainless steel strip in a process line, wherein the overlapped portion is crushed by a pair of upper and lower pressing rolls that continue to move on the electrode disk while being laid.