CN-116897093-B - Laser cutting method for steel strip, laser cutting apparatus, cold rolling method, and method for manufacturing cold rolled steel strip

Abstract

The laser cutting method of the present invention is a laser cutting method of a steel strip in which a vicinity of a joint portion between a rear end portion of a preceding steel strip and a front end portion of a succeeding steel strip is cut by using a pulsed laser, wherein an output power of the pulsed laser is set to 0.5kw or more every 1 millisecond, a processing point diameter of the pulsed laser is set to 0.1mm or more and less than 0.6mm, and a ratio of a pulse cycle time to a rest time is set to 0.3 or more and less than 0.8.

Inventors

• FUJITA NOBORU
• Matsuhara Yukihiro
• FUKUNAGA HIROYUKI

Assignees

• 杰富意钢铁株式会社

Dates

Publication Date

20260505

Application Date

20211026

Priority Date

20210215

Claims (8)

1. 1. A laser cutting method for a steel strip by cutting a vicinity of a joint between a rear end portion of a preceding steel strip and a front end portion of a succeeding steel strip by using a pulse laser, The output power of the pulsed laser is set to 0.5kw or more every 1 millisecond, the processing point diameter of the pulsed laser is set to 0.1mm or more and less than 0.6mm, and the ratio of the pulse cycle time to the rest time is set to 0.3 or more and less than 0.8.
2. 2. The laser cutting method of a steel strip according to claim 1, wherein the cutting portion cut by the pulse laser includes both widthwise end surfaces and one or more closed cross-sectional shapes of the steel strip.
3. 3. The laser cutting method of a steel strip according to claim 1 or 2, wherein compressed air of 0.5MPa or more is used as the gas for the pulsed laser.
4. 4. A laser cutting apparatus for cutting a steel strip by using a pulsed laser in the vicinity of a joint between a rear end portion of a preceding steel strip and a front end portion of a succeeding steel strip, The output power of the pulsed laser is set to 0.5kw or more every 1 millisecond, the processing point diameter of the pulsed laser is set to 0.1mm or more and less than 0.6mm, and the ratio of the pulse period time to the pulse time is set to 0.3 or more and less than 0.8.
5. 5. The laser cutting apparatus of steel strip according to claim 4, wherein the cutting portion cut by the pulse laser includes both widthwise end surfaces of the steel strip and one or more closed cross-sectional shapes.
6. 6. The laser cutting apparatus of steel strip as claimed in claim 4 or 5, wherein compressed air of 0.5MPa or more is used as the gas for the pulsed laser.
7. 7. A method of cold rolling a steel strip, wherein the steel strip cut by the laser cutting method of any one of claims 1 to 3 is cold rolled.
8. 8. A method for producing a cold-rolled steel strip, wherein the cold-rolled steel strip is produced by a process comprising the cold-rolling method for a steel strip according to claim 7.

Description

Laser cutting method for steel strip, laser cutting apparatus, cold rolling method, and method for manufacturing cold rolled steel strip Technical Field The present invention relates to a laser cutting method, a laser cutting apparatus, a cold rolling method, and a manufacturing method of a cold rolled steel strip. Background In the cold rolling process of a steel strip, a rear end portion of a preceding material (preceding steel strip) is generally joined to a front end portion of a succeeding material (succeeding steel strip) for the purpose of improving productivity and yield, and the steel strip is continuously supplied to a cold rolling line. This makes it possible to roll the steel strip while applying tension over the entire length, and to control the thickness and shape of the steel strip at the front and rear ends of the steel strip with high accuracy. With the progress of high alloying of cold-rolled steel strips and laser welding machines, the joining of a preceding material and a following material by laser welding has been the mainstream in place of conventional flash butt welding and the like. However, regardless of the welding method such as flash butt welding or laser welding, a level difference is inevitably formed at the width-direction end of the joint (welded portion) between the preceding material and the succeeding material due to the difference in width and thickness between the preceding material and the succeeding material, positional displacement, or the like. Therefore, when rolling the steel strip in such a state, stress concentration occurs in the height difference portion, and the steel strip may break at the welded portion. When the welded portion of the steel strip breaks, the cold rolling line has to be stopped, and the productivity is significantly lowered. In addition, since the work rolls damaged by the broken pieces need to be replaced, the production cost increases. In particular, in recent years, demands for thin gauge and high strength of cold-rolled steel strip have been increasing for the purpose of weight reduction and improvement of characteristics of components. In addition, as the reduction ratio and rolling load required for cold rolling increase with this, the fracture rate of the steel strip increases with an increase in stress concentration at the level difference portion. Therefore, in order to suppress breakage of the steel strip at the welded portion, grooving is performed to form a notch (cutout) at the end portion in the width direction of the welded portion in order to alleviate stress concentration in the vicinity of the height difference portion, and then a step of rolling the steel strip is performed. In addition, since welding is insufficient at the widthwise ends of the steel strip due to poor butt accuracy and the like and strength is easily lowered, grooving is also performed with the purpose of cutting off the portions having low strength (approximately 30mm from the widthwise ends). As a method of grooving, for example, as described in patent document 1, a method of mechanically shearing a semicircular notch having no corner is generally used. However, in the semicircular notch, the curvature of the outer edge is the same, and the width of the steel strip is the smallest at the welded portion, so that the maximum stress is generated at the welded portion. Accordingly, patent document 2 describes a method of forming a notch by laser cutting as a method for shortening the grooving time. Patent document 3 describes a laser cutting method in which the amount of dross (molten material during laser cutting) generated is small. Prior art literature Patent literature Patent document 1 Japanese patent laid-open No. 5-76911 Patent document 2 Japanese patent laid-open No. 60-115387 Patent document 3 Japanese patent No. 6354793 Disclosure of Invention Problems to be solved by the invention However, in the grooving method described above, particularly in cold rolling of brittle materials such as silicon steel sheets and high tensile steel sheets having a large content of Si and Mn and high alloy materials, the effect cannot be sufficiently exhibited, and the breakage of the steel strip at the welded portion cannot be sufficiently suppressed. The present invention has been made in view of the above-described problems, and an object thereof is to provide a laser cutting method and a laser cutting apparatus for a steel strip capable of suppressing breakage of the steel strip at a welded portion even in the case of a brittle material or a high alloy material. Another object of the present invention is to provide a cold rolling method of a steel strip, which can stably perform cold rolling while suppressing breakage of the steel strip at a welded portion even in the case of a brittle material or a high alloy material. Another object of the present invention is to provide a method for producing a cold-rolled steel strip, which can stably produce a cold-rolled st