JP4029702B2 - Method for detecting epidermal defects in metal slabs - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for detecting a subcuticular defect of a steel slab, and more particularly to a technique for easily detecting vertical cracks generated in the subcutaneous surface of a steel slab called a beam blank which is a material of H-shaped steel.
[0002]
[Prior art]
The continuous casting method is a technique in which a molten metal is cast into a bottomless mold and continuously drawn downward while solidifying to produce a long slab of the metal. One of the missions of the technology is to obtain a slab that is as close to the product as possible. Therefore, in the steel industry, it has been conventionally practiced to produce an intermediate material having a shape close to a product by continuous casting. For example, molten steel is cast into a mold having an opening having an H shape in a plan view and solidified to obtain a long steel slab having a substantially “H” cross section as shown in FIG. This steel slab is called a beam blank, and is used as a material for producing a so-called “H-shaped steel” useful as a construction / civil engineering material.
[0003]
By the way, on the surface of the beam blank obtained by such continuous casting, as shown in FIG. 4, vertical cracks 2 having a depth of about 1 mm along the longitudinal direction may occur. The cause of this vertical crack 2 is that cooling during solidification is performed nonuniformly over the entire beam blank. Therefore, when the vertical crack 2 is visible on the surface of the beam blank 1, the surface vertical crack 2 is melted with a high-temperature gas to remove the vertical crack and then sent to the next rolling process. , Rolled into “H-section steel” of the product.
[0004]
However, not all of the vertical cracks 2 can be detected with the naked eye, and often exist in the epidermis of the beam blank 1. If nondestructive inspection such as ultrasonic flaw detection is performed, the vertical crack can be found, but there is an increase in inspection equipment, man-hours, etc., which is not economical. Therefore, when the subepidermal longitudinal crack 2 cannot be found with the naked eye, it appears as wrinkles in the rolled product “H-shaped steel”, which reduces the product yield.
[0005]
In view of such circumstances, an object of the present invention is to provide a method for detecting a subepidermal defect of a steel slab that can easily and easily find a longitudinal crack existing in the subsurface of a steel slab called beam black obtained by continuous casting. It is said.
[0006]
[Means for Solving the Problems]
The inventor has intensively studied to achieve the above object, and the results have been embodied in the present invention.
[0007]
That is, the present invention measures the inclination amount of the edge of a metal slab, which is a beam blank having a “H” cross section obtained by continuous casting, with reference to the horizontal in a sectional view, and the measured value is It is a method for detecting the epidermal defect of a metal slab, which is compared with a threshold value for determining the presence of an epidermal defect.
[0008]
In this case, the measurement may be performed with an [L] -shaped ruler or a perpendicular shape measuring instrument .
[0009]
According to the present invention, vertical cracks existing in the epidermis of a metal blank called a beam blank obtained by continuous casting can be found easily and easily. As a result, the vertical cracks of the material can be almost removed before rolling, and the yield of the product “H-section steel” is improved as compared with the conventional one.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below based on the circumstances leading to the invention.
[0011]
First, the inventor examined whether it was possible to estimate the presence of longitudinal cracks hidden under the epidermis of the beam blank. As a result, it has been found that the inclination of the edge of the metal slab obtained by continuous casting is related. Specifically, as shown in FIG. 1, at the edge of the beam blank in cross-sectional view, the amount of inclination is measured as a distance X (mm) with respect to the horizontal, and the measured value and the cross section of the beam blank 1 are measured. When the relationship with the vertical crack obtained in the investigation was investigated, the relationship shown in FIG. 2 was obtained. That is, when the distance X representing the amount of inclination exceeds 3 mm, it can be determined that almost vertical cracks exist in the epidermis with a probability of approximately 80% or more of the whole.
[0012]
Therefore, the present invention has been completed because it is considered that if this relationship is set as a threshold value, the presence of a subepidermal defect of the beam blank 1 can be determined easily and easily. The reason why the threshold is not limited to 3 mm is that this relationship changes depending on the steel type and size of the beam blank 1, and the 3 mm threshold also changes. Therefore, when there is a change in the steel type or size of the beam blank 1, the relationship is obtained in advance by test operation, past operation data analysis, etc., and a corresponding threshold value is determined. In the case of H-section steel, the amount of inclination indicates the distance X (mm) between the line connecting both flange end faces 9 of the H-section steel and the flange side face end 10 as shown in FIG.
[0013]
In addition, although the measurement of the amount of inclination of the edge portion was performed by an operator using a [L] -shaped ruler as a measurement jig, the present invention is not limited thereto, and any jig that can measure the degree of inclination is used. Things can be used. For example, a perpendicular shape measuring instrument as shown in FIG. 3 may be used for the beam blank 1 that moves horizontally. This perpendicular shape measuring instrument is a suspension of a plurality of rod-like bodies 5 having different lengths in a line, and the amount of inclination of the beam black 1 is determined by the presence or absence of contact with the beam blank 1 passing therebelow. Is. In FIG. 3, the distance Y between the tip 6 of the rod 5 located at the end of the row and the rod 5 located at the center of the row may be set to be a threshold value. This method can be measured while moving the beam blank 1, and is preferable for ensuring productivity.
[0014]
Further, the present invention may be applied not only to the beam blank 1 having a complicated shape and easily causing non-uniform cooling, but also to a billet or a rectangular bloom having a square cross-sectional shape. Even in these cases, the appearance frequency is small, but vertical cracks exist in the epidermis.
[0015]
【Example】
An H-section steel having a steel type of SM50A and a size of 500 mm × 300 mm was produced by so-called caliberless rolling. At that time, a beam blank 1 manufactured by a vertical bending type continuous casting machine was used as a material. The standard size of the beam blank 1 is 560 mm × 400 mm (see FIG. 1). Before rolling, the subsurface defect detection method according to the present invention was applied to the beam blank 1 and the operation was performed while investigating the vertical cracks 2 of the beam blank 1. Longitudinal cracks 2 were investigated by placing the perpendicular shape measuring instrument with the threshold value set to 3 mm on the conveying line 8 of the beam blank 1 and those determined to be “vertically split” were longitudinal cracks due to the above-mentioned welding. After canceling, it was sent to the rolling process. As a result, the yield of the product “H-shaped steel” was greatly improved from 92% to 99%.
[0016]
In addition, although the said Example showed in the case where a continuous cast piece was a steel beam blank, this invention is applicable also to manufacture of continuous cast pieces, such as a bloom and a billet. Moreover, it cannot be overemphasized that the object metal of this invention may be not only steel but the slab of copper, zinc, aluminum, and those alloys.
[0017]
【The invention's effect】
As described above, according to the present invention, vertical cracks existing in the epidermis of a metal slab obtained by continuous casting can be easily and easily found. As a result, the vertical cracks of the material can be almost removed before rolling, and the yield of the product “section steel” is improved as compared with the conventional one.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a beam blank for explaining a method for detecting a subepidermal defect of a metal cast according to the present invention.
FIG. 2 is a diagram showing a relationship between an inclination amount X of a beam blank edge and a vertical crack occurrence rate.
FIG. 3 is a diagram for explaining a perpendicular shape measuring instrument used for carrying out the present invention.
FIG. 4 is a perspective view showing a vertical crack generated in a beam blank.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Beam blank 2 Vertical crack 3 Web 4 Flange 5 Rod body 6 Rod end of row end 7 Rod end of row central portion 8 Beam blank conveyance line 9 Flange end surface 10 Flange end of flange

Claims (1)

The amount of inclination of the edge of the metal slab, which is a beam blank having a “H” cross section obtained by continuous casting, was measured with respect to the horizontal in a cross-sectional view, and the measured value was determined for the presence of subepidermal defects. A method for detecting a subdermal defect of a metal slab, comprising comparing with a threshold value for determination.

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