Patent ID: 12220770

BEST MODE FOR INVENTION

FIG.1a schematic diagram of a pre-stressed steel sheet according to an embodiment of the present disclosure. Hereinafter, a pre-stressed steel sheet according to an embodiment of the present disclosure will be described with reference toFIG.1.

A pre-stressed steel sheet according to an embodiment of the present disclosure is characterized in that it has a base material10and a plurality of weld lines20formed on the base material10. At this time, it is preferable that the weld line has higher strength than the base material. Through this, as shown inFIG.1, a compressive residual stress corresponding to the tensile residual stress generated by the contraction of the weld material is applied to the base material and at the same time, by increasing the strength of the steel sheet itself, it is possible to improve the deformation resistance against loads such as welding deformation and deflection of the steel sheet.

In the present disclosure, the type of the base material is not particularly limited, and all weldable steel materials applied to structure, etc. in the art can be used, for example, general structural steel, carbon steel for classification, SUS for classification, carbon steel for building structure and carbon steel for Built-UP H-beam, etc. can be used.

In the present disclosure, the thickness of the base material is not particularly limited, but, for example, the base material may have a thickness of 6 to 60 mm. When the thickness of the base material is less than 6 mm, welding deformation may occur greatly during welding, and all stress may be lost during deformation correction through roller correction after welding. On the other hand, if it exceeds 60 mm, the possibility of cracks may occur during the process increases due to the number of welding times and the restraint of the base material. Therefore, it is preferable that the thickness of the base material has a range of 6 to 60 mm. The lower limit of the thickness of the base material is more preferably 8 mm, even more preferably 10 mm, most preferably 12 mm. The upper limit of the thickness of the base material is more preferably 40 mm, more preferably 30 mm, most preferably 25 mm.

An average spacing between a weld line and an adjacent weld line among the plurality of weld lines is equal to or greater than five times a width of the weld lines and equal to or less than ½ times a width of the steel sheet. If the above conditions are not satisfied, the residual compressive stress caused by the weld lines may not be sufficiently applied to the base material, and thus the possibility that the deflection resistance of the steel sheet may be lowered may increase.

It is preferable that the number of weld lines is 2×(L/W) or more. Here, L is the length of the steel sheet and W is the width of the steel sheet. When the number of weld lines is less than 2×(L/W) , the residual compressive stress caused by the weld lines may not be sufficiently applied to the base material, and thus the possibility that the deflection resistance of the steel sheet may be lowered may increase. In addition, in order to reduce mechanical properties deviation in the width direction, the weld line is preferably formed so as to be bilateral symmetry based on the width of the steel sheet. For example, if the number of weld lines is an even number, it is preferable to make it bilateral symmetrical about the center of the steel sheet based on the width direction of the steel sheet. If the number of the weld lines is an odd number, it is preferable to make it bilateral symmetrical based on the weld line, after the weld line is formed in the center based on the width direction of the steel sheet.

Preferably, the weld line has a thickness of up to ¼ t from the surface of the base material. In this case, t is the thickness of the steel sheet. In this way, by securing the thickness of the weld line at a certain level, it is possible to improve the strength of the steel sheet and suppress the sagging of the steel sheet. When the thickness of the weld line exceeds ¼ t from the surface of the base material, the temperature gradient in the thickness direction becomes small, which can reduce the generation of residual stress. If the penetration depth is increased, the welding deformation may be larger, and a large cost may be incurred to correct the welding deformation in the thick plate by rolling.

In the present disclosure, the shape of the weld line is not particularly limited, and for example, it may have a straight shape, a curved shape or a winding shape.

FIG.2is a schematic diagram for comparing the amount of deflection between a pre-stressed steel sheet according to an embodiment of the present disclosure and a general steel sheet, when a load is applied. As shown inFIG.2, the pre-stressed steel sheet of the present disclosure not only reduces welding deformation as compared to a general steel sheet, but also improves bending performance, so that the amount of deflection when a load is applied can be reduced. Thereby, the pre-stressed steel sheet of the present disclosure can be preferably applied to structural members such as girders and beams etc. that require excellent bending.

Hereinafter, a method of manufacturing a pre-stressed steel sheet according to an embodiment of the present disclosure will be described.

First, a groove is machined in an area in which a weld line will be formed on a base material. The grooving may use various methods, for example, a method of rolling using a roll having projections formed thereon may be used. In the case of rolling using the roll having projections formed thereon, there is an advantage that a continuous process is possible. Meanwhile, in the present disclosure, the shape of the groove is not particularly limited, and the groove may only have a weldable shape so that a weld line can be formed.

Then, the weld line is formed on the groove in the base material. In the present disclosure, the welding method for forming the weld line is not particularly limited, and, for example, any one of SAW, FCAW, MAG welding, TIG welding, and laser welding may be used. In this case, when using a method such as SAW, FCAW, or MAG welding that can use a welding material, the welding material may have the form of a round bar or wire, or may have a strip shape. In addition, the welding may be performed through one pass or multiple passes, or by a method of parallel welding with a plurality of welding materials.

When forming the weld line, it is preferable that a bead height of the weld line be 1 to 2 mm. If the bead height of the weld line is less than 1 mm, there is a possibility that welding defects such as underfill may occur, and if the bead height of the weld line exceeds 2 mm, there is a possibility that a fracture by fatigue crack due to stress concentration may occur.

On the other hand, after forming the weld line, in order to remove the weld bead, polishing the surface of the steel sheet may be further included.

Thereafter, the base material on which the weld line is formed is correction rolled.FIG.3is a schematic diagram illustrating a state before and after correction rolling of a base material having a weld line formed thereon according to an embodiment of the present disclosure. As shown inFIG.3, before correction rolling, both ends of the base material on which the weld line is formed are bent in the direction in which the weld line is formed due to compressive stress. Accordingly, in the present disclosure, the flatness of the steel sheet can be improved by correcting the warpage thereof through correction rolling. At this time, the correction rolling is preferably performed to the extent that the shape of the steel sheet is flattened, rather than applying a reduction force. If rolling force is applied, the compressive stress applied to the steel sheet may be reduced, and thus the effect to be obtained by the present disclosure may be reduced.

EXPLANATION OF SYMBOLS

10: Base Material20: Weld Lines