JP6992898B2 - Grinding method of steel pieces, manufacturing method of steel bars and manufacturing method of wire rods - Google Patents

Description

The present invention relates to a method for grinding steel pieces, a method for manufacturing steel bars, and a method for manufacturing wire rods.

As a method of reducing the surface flaws of steel bar products, it is known that the entire surface of the steel piece used as a material is melted, the surface flaws are detected by a surface inspection device, and the detected surface flaws are ground by a grinder to remove them. (For example, Patent Document 1). The process from total surface milling to removal of surface defects by a grinder is also called maintenance. The finished steel pieces are rolled into steel bars. Further, Patent Document 2 discloses a technique relating to a method for manufacturing a large-diameter wire rod for cold forging, which has a high effect of suppressing the occurrence of scratches. According to the technique of Patent Document 2, when a square steel piece is hot-rolled to produce a large-diameter wire rod having a diameter of 20 mm or more, a flaw detected by magnetic particle flaw detection and a scratch and scratch not detected by magnetic particle flaw detection are found on the square steel piece. It is characterized by hot rolling after removing flaws. Here, in Patent Document 2, since the flaws and scratches that are not detected by magnetic particle inspection exist at the corners of the square steel pieces, all the corners are chamfered along the longitudinal direction thereof and then hot-rolled. A method for manufacturing a diameter wire has also been proposed.

Japanese Unexamined Patent Publication No. 2013-27906 Japanese Unexamined Patent Publication No. 2008-68297

As described above, even if the steel bar is made of a steel piece that has been completely melted and ground the surface defect of the steel piece as a raw material, the steel piece may have a defect. In order to complete the removal of flaws, a method of forcibly grinding the entire surface of the unrolled steel pieces with a grinder has also been implemented, but this method increases the time required for maintenance and the amount of grinding. As a result, the productivity of steel pieces decreases.

Further, in Patent Document 2, when a square steel piece is rolled into a thick wire rod having a diameter of 20 mm or more, the scratches and scratches present on the square steel piece cause the wire rod to have a scratch after rolling. There is. However, even in the case of rolling into a wire rod having a diameter of less than 20 mm, a flaw may remain in the steel bar or the wire rod after rolling. In addition, even if the corners that are thought to have scratches or scratches are chamfered over the entire length, the presence of extremely small scratches is not recognized, and the level of demand for scratch removal by consumers is high. In some cases, there may remain a problem in the occurrence of flaws in steel bars and wire rods after rolling.

It is an object of the present invention to provide a method for grinding steel pieces, a method for producing steel bars, and a method for producing wire rods, which can further reduce surface defects while suppressing a decrease in productivity.

The present inventors investigated the cast structure by observing the cross section of the steel bar obtained by rolling the steel pieces with a microscope. Then, from the investigation result, the present inventors identified the position where the surface flaw (hereinafter, also referred to as the surface flaw) is particularly likely to occur in the steel piece before rolling. From this identification, it was clarified that in the steel piece before rolling, a large number of surface flaws were present at the corners of the steel piece and its vicinity. The present invention has been made based on such findings.

The method for grinding a piece of steel according to one aspect of the present invention is to grind the piece of steel before rolling the piece of steel, which is long in one direction and has a rectangular cross section cut in a plane orthogonal to the one direction. A step of grinding a region including a range from a corner portion of the rectangle to 26% or more and 30% or less of the length of the one side along one side of the rectangle over the entire length of the steel piece is provided.
The method for manufacturing steel bars according to one aspect of the present invention includes a step of grinding the above-mentioned steel pieces and a step of rolling the steel pieces whose regions have been ground to manufacture steel bars.
The method for manufacturing a wire rod according to one aspect of the present invention includes a step of performing the above-mentioned method for grinding a steel piece and a step of rolling a steel piece whose region has been ground to manufacture a wire rod.

According to one aspect of the present invention, it is possible to provide a method for grinding steel pieces, a method for producing steel bars, and a method for producing wire rods, which can further reduce surface defects while suppressing a decrease in productivity.

FIG. 1 is a flowchart showing a method for grinding a steel piece according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing each step of surface inspection and surface grinding of a steel piece according to an embodiment of the present invention. FIG. 3 is a diagram schematically showing a grinding method in the vicinity of a corner of a steel piece according to an embodiment of the present invention. FIG. 4 is a cross-sectional view showing a steel piece after the vicinity of the corner portion has been ground. FIG. 5 is a cross-sectional view showing a steel bar according to an embodiment of the present invention. FIG. 6 is a cross-sectional view showing a wire rod according to an embodiment of the present invention. FIG. 7 is a graph showing the results of investigating the relationship between the presence or absence of grinding in the vicinity of the corners and the occurrence rate of defects in steel bars. FIG. 8 is a microstructure observation photograph of the C cross section of the steel bar product, where (a) shows the entire cross section and (b) shows the position where the flaw is generated.

An embodiment of the present invention will be described below. In the description of the drawings below, the same or similar parts are designated by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the plane dimensions, the ratio of the thickness of each device and each member, etc. are different from the actual ones. Therefore, the specific thickness and dimensions should be determined in consideration of the following explanation. In addition, it goes without saying that parts having different dimensional relationships and ratios are included between the drawings.

Further, in the following description, the positive side in the Z-axis direction may be referred to as "upper", and the negative side in the Z-axis direction may be referred to as "lower". "Top" and "bottom" do not necessarily mean vertical to the ground. That is, the "up" and "down" directions are not limited to the direction of gravity. "Upper" and "lower" are merely expedient expressions for specifying the relative positional relationship in the steel pieces and the like described later, and do not limit the technical idea of the present invention. For example, if the paper surface is rotated 180 degrees, it goes without saying that "upper" becomes "lower" and "lower" becomes "upper".
Further, in the following description, the direction may be described by using the words in the X-axis direction, the Y-axis direction, and the Z-axis direction. For example, the X-axis direction and the Y-axis direction are horizontal directions, and the Z-axis direction is a vertical direction. The X-axis, Y-axis and Z-axis are orthogonal to each other. The X-axis, Y-axis and Z-axis form, for example, a left-handed system.

The steel pieces according to the embodiment of the present invention are manufactured by continuous casting. Steel pieces produced by continuous casting are long in one direction (hereinafter, also referred to as longitudinal direction), and scratches such as cracks and non-metal inclusions (that is, surface scratches) are present on the surface thereof. In order to remove this surface defect, in the embodiment of the present invention, first, a melting facility such as a hot scarfer or a cold scarfer is used, and oxygen gas for melting is sprayed on the surface of the steel piece to cover the entire surface of the steel piece. Is melted to a thickness of, for example, about 2 mm.
Even after the melting, if the surface scratches are deeper than the melting depth, the surface scratches are not sufficiently removed and remain. Further, when the variation in the melting depth of the steel piece is large, an unmelted portion may occur. Therefore, in the embodiment of the present invention, the surface inspection and the surface grinding based on the result of the surface inspection are performed on the steel pieces that have been subjected to the melt treatment.

FIG. 1 is a flowchart showing a method for grinding a steel piece according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing each step of surface inspection and surface grinding of a steel piece according to an embodiment of the present invention. In the embodiment of the present invention, as shown in FIG. 2, the slab-treated steel piece 2 is placed on one side in the longitudinal direction of the steel piece 2 by the transport roller 3 (for example, the arrow side in the X-axis direction). ). The steel piece 2 is a semi-finished product before rolling (that is, an unfinished product in the middle of the manufacturing process), and is called a bloom or billet depending on the use, shape, and size. The steel piece 2 is inspected for surface defects by the surface inspection device 1 while being conveyed in the X-axis direction (step ST1 in FIG. 1).

The surface inspection device 1 is, for example, a fluorescent magnetic particle flaw detector that detects surface defects using fluorescent magnetic powder. The surface inspection device 1 detects surface flaws and unmelted portions remaining on the surface of the steel piece 2 after the melting process, displays the detected positions on the surface grinding apparatus, and identifies the flawed positions. When a surface defect or an unmelted portion is detected (step ST2 in FIG. 1; Yes), the surface grinding machine is identified as having the above-mentioned detected position on the surface of the steel piece 2, that is, a defect. The grinder 4 is brought into contact with the position to grind the surface. As a result, the surface grinding apparatus removes surface defects and unmelted portions remaining on the steel piece 2 (step ST3 in FIG. 1).

On the other hand, when no surface flaw or unmelted portion is detected (step ST2; No in FIG. 1), the surface grinding apparatus does not bring the grinder 4 into contact with the surface of the steel piece 2. That is, the grinder 4 does not grind the surface of the steel piece 2. At that time, the grinding process proceeds to step ST4 of FIG. 1, and the surface grinding device operates the grinder 4 (see FIG. 3 described later) to grind the corner portion of the steel piece 2 and its vicinity (step of FIG. 1). ST4).

FIG. 3 is a diagram schematically showing a grinding method of a corner portion of a steel piece and its vicinity according to an embodiment of the present invention. FIG. 3 shows a cross section of a steel piece 2 cut along a plane (for example, a YY plane) orthogonal to its longitudinal direction (for example, the X-axis direction). As shown in FIG. 3, the shape of the cross section of the steel piece 2 cut in the YY plane is rectangular. In step ST4 of FIG. 1, the four corners of the rectangle and the portions in the vicinity thereof are ground. In the description of the embodiment of the present invention, the corner portion and the portion in the vicinity thereof are collectively referred to as the vicinity of the corner portion.

The vicinity of the corner to be ground is a region including a range from the corner of the rectangle to 26% or more and 30% or less of the length of the side along one side of the rectangle. For example, as shown in FIG. 3, the rectangle having the cross-sectional shape of the steel piece 2 has four corner portions 2A, 2B, 2C, and 2D. Let y be the length of one side parallel to the width direction (for example, the Y-axis direction) of this rectangle, and z be the length of one side parallel to the thickness direction (for example, the Z-axis direction). Further, the length of the corner portion 21 including the corner portion 2A in the Y-axis direction is y21, and the length of the corner portion vicinity 21 in the Z-axis direction is z21.

The length y21 in the Y-axis direction of the corner portion 21 to be ground is 26% or more and 30% or less of the length y of one side parallel to the Y-axis direction of the rectangle. The length z21 in the Z-axis direction of the corner portion 21 to be ground is 26% or more and 30% or less of the length z of one side parallel to the Z-axis direction of the rectangle.
Similarly, the length of the corner portion 22 including the corner portion 2B in the Y-axis direction is y22, and the length of the corner portion vicinity 22 in the Z-axis direction is z22. The length y22 in the Y-axis direction of the corner portion 22 to be ground is 26% or more and 30% or less of the length y of one side parallel to the Y-axis direction of the rectangle. The length z22 in the Z-axis direction of the corner portion 22 to be ground is 26% or more and 30% or less of the length z of one side parallel to the Z-axis direction of the rectangle.

Let y23 be the length of the corner portion 23 including the corner portion 2C in the Y-axis direction, and let z23 be the length of the corner portion vicinity 23 in the Z-axis direction. The length y23 in the Y-axis direction of the corner portion 23 to be ground is 26% or more and 30% or less of the length y of one side parallel to the Y-axis direction of the rectangle. The length z23 in the Z-axis direction of the corner portion 23 to be ground is 26% or more and 30% or less of the length z of one side parallel to the Z-axis direction of the rectangle.
Let y24 be the length of the corner portion 24 including the corner portion 2D in the Y-axis direction, and let z24 be the length of the corner portion vicinity 24 in the Z-axis direction. The length y24 in the Y-axis direction of the corner portion 24 to be ground is 26% or more and 30% or less of the length y of one side parallel to the Y-axis direction of the rectangle. The length z24 in the Z-axis direction of the corner portion 24 to be ground is 26% or more and 30% or less of the length z of one side parallel to the Z-axis direction of the rectangle.

The four corners 2A, 2B, 2C, and 2D each have a roundness of radius of curvature R. For example, the radius of curvature R is 15 mm or more and 25 mm or less.
Specific examples are shown for each dimension of the steel piece 2 and the corner portions 21, 22, 23, 24. When the steel piece 2 is a billet, y = 160 mm, z = 160 mm, y21 = y22 = y23 = y24 = 45 mm, z21 = z22 = z23 = z24 = 45 mm, R = 25 mm. When the steel piece 2 is bloom, y = 400 mm, z = 300 mm, y21 = y22 = y23 = y24 = 112 mm, z21 = z22 = z23 = z24 = 84 mm, R = 25 mm. It should be noted that these dimensions are merely examples, and do not limit the embodiments of the present invention.

FIG. 4 is a cross-sectional view showing a steel piece after the vicinity of the corner portion has been ground. In step ST4 of FIG. 1, the surfaces of 21, 22, 23, and 24 near the corners are ground by the grinder 4. As shown in FIG. 4, where d is the grinding depth, d is 1 mm or more and 3 mm or less, for example, 2 mm. After the corners 21, 22, 23, 24 of the steel piece are ground, the surface of the corners 21, 22, 23, 24 becomes a shape recessed by a depth d from the periphery as a trace of grinding. ..

In step ST5 of FIG. 1, for example, an operator visually observes the surfaces of 21, 22, 23, and 24 near the corners to confirm the presence or absence of uncut parts. Alternatively, instead of the operator, an inspection device may visually inspect the surfaces of 21, 22, 23, and 24 near the corners to confirm the presence or absence of uncut parts. If there is uncut portion (step ST6; No), the process returns to step ST4. When there is no uncut portion (step ST6; Yes), the grinding process of the steel piece 2 shown in FIG. 1 is completed.

FIG. 5 is a cross-sectional view showing a steel bar according to an embodiment of the present invention. FIG. 6 is a cross-sectional view showing a wire rod according to an embodiment of the present invention. The steel piece 2 that has completed the grinding process of FIG. 1 proceeds to the rolling process. In the rolling process, the steel pieces 2 are rolled. As a result, the steel bar 11 as shown in FIG. 5 or the wire rod 12 as shown in FIG. 6 is manufactured from the steel pieces 2.

FIG. 7 is a graph showing the results of investigating the relationship between the presence or absence of grinding in the vicinity of the corners and the occurrence rate of defects in steel bars. In FIG. 7, the data shown on the far left is the case where no grinding is performed near the corners. The second data from the left is the case where grinding is performed over the entire length of the steel piece only at the corners (only the rounded portion of the radius of curvature R). The three data on the right side are the cases where the total length of the steel piece is ground from the corner to the length region of 25%, 26%, and 30% of the side length of the steel piece, respectively.

As shown in FIG. 7, grinding is performed in the vicinity of a corner portion over the entire length of the steel piece, that is, a region including a range from the corner portion of the rectangle to 26% or more and 30% or less of the length of one side along one side of the rectangle. As a result, compared with the case where no grinding was performed on or near the corner (leftmost data in FIG. 7) and when only the corner was ground (second data from the left in FIG. 7). The present inventor has confirmed that the incidence of defects caused by surface defects is reduced in steel bars manufactured from this piece of steel.

The grinding here is performed with the grinding depth set to 1 mm. In addition, the occurrence rate of defects is confirmed by investigating the presence or absence of surface defects in the steel bars obtained by hot rolling steel pieces 2 (2000 pieces for each condition, 10,000 pieces in total) that have passed each grinding condition. rice field. To confirm the presence or absence of surface scratches, the microstructure of the C cross section of the obtained steel bar was observed with an optical microscope, and if there were scratches on the surface of the steel bar with a depth of more than 0.050 mm, it was considered as flawed (see Fig. 8 and Fig. 8). (Example) with a defect with a depth of 0.076 mm), and no other defects. Then, the rate of defects for each of 2000 grinding conditions was used as the failure rate.

FIG. 8 shows the structure of the C cross section of a steel bar having a product diameter of 15 mmφ, which is obtained by grinding the surface at a position identified as having a defect by surface inspection with a grinding machine in the steel piece stage before rolling and then hot rolling. It is an observation photograph. The surface of this steel bar product was found to have scratches at the product stage after rolling. FIG. 8 (a) shows the entire cross section of the steel bar product, and FIG. 8 (b) shows the position of the scratch. The case of observing at a higher magnification (200 times) is shown. When the circumferential position of the steel bar product is specified for the flaw occurrence location as shown in FIG. 8 (b) and the microstructure observation result as shown in FIG. 8 (a) is associated with the flaw occurrence location, the steel piece (hot) It is known that a flaw has occurred at a position corresponding to a corner in the stage (before rolling). In other words, it was found that the surface inspection of the steel piece could not detect the flaw near the corner, and the grinding at the specific position based on the surface inspection result was insufficient for the vicinity of the corner. This finding is in good agreement with the result shown in FIG. 7 that the occurrence rate of flaws was reduced by grinding the vicinity of the corner portion regardless of the presence or absence of flaw detection in the surface inspection.

As described above, the method for grinding a piece of steel according to the embodiment of the present invention is long in one direction (for example, in the X-axis direction) and cut in a plane orthogonal to one direction (for example, YY plane). Before rolling the steel piece 2 having a rectangular cross-sectional shape, the steel piece 2 is provided with a step of grinding 21, 22, 23, 24 in the vicinity of the corners of the rectangle over the entire length (for example, step ST4 in FIG. 1). .. As described above, surface scratches such as small cracks are likely to occur on the surfaces of 21, 22, 23, and 24 near the corners of the steel piece 2 manufactured by continuous casting. It is considered that the cause of this is that fine internal cracks and segregation are likely to occur in 21, 22, 23, and 24 near the corners due to the oscillation marks generated on the surface of the steel piece 2 and the solidification form.

Of the results shown in FIG. 7, when only the second corner from the left is ground over the entire length, visible scratches or scratches are found in the vicinity of the corner of the steel piece 2 after the corner is ground. It is confirmed that there are no scratches. For this reason, it is not possible to grind and remove only visually identifiable defects such as scratches and scratches, or to grind only the corners where visually identifiable defects are considered to have occurred over the entire length of the steel piece 2. It can be seen that the defect occurrence rate cannot be significantly reduced. Then, from FIG. 7, the above-mentioned oscillation mark, internal cracks, surface defects considered to be caused by segregation, etc. are the length of one side along one side of the rectangle from the corner of the rectangle of the steel piece. It can be seen that the region including the range of 26% or more and 30% or less can be significantly reduced by grinding over the entire length of the steel piece.

According to the method for grinding steel pieces according to the embodiment of the present invention, the surfaces of 21, 22, 23, and 24 near the corners where surface defects such as small cracks are particularly likely to occur are forced before rolling of the steel pieces 2. Grinded to. Thereby, the surface flaw of the steel piece 2 can be further reduced. As a result, it is possible to reduce the occurrence of defects caused by surface defects in the steel bar 11 and the wire rod 12 manufactured by rolling the steel piece 2. The method for grinding a steel piece according to the embodiment of the present invention can shorten the time required for grinding as compared with the method for forcibly grinding the entire surface of the steel piece with a grinder in order to remove surface defects. Since the amount of grinding can be suppressed to a low level, it is possible to suppress a decrease in the productivity of the steel piece 2.

The vicinity of the corner to be ground is a region including a range from the corner of the rectangle to 26% or more and 30% or less of the length of the side along one side of the rectangle. According to this, surface defects can be efficiently removed while keeping the grinding amount of the steel piece 2 low. For example, when the steel piece 2 is a billet having y = 160 mm and z = 160 mm, a large number of surface defects remain in the range of 20 mm from the corners 2A, 2B, 2C, and 2D of the steel piece 2 by observing the cross section with a microscope. It was confirmed that By forcibly grinding and removing this range with a grinder, surface defects on the steel piece 2 can be efficiently removed.

In the step of grinding the vicinity of the corner portion, the surface near the corner portion is ground to a depth of 1 mm or more and 3 mm or less. According to this, since the surface scratches are often present in the range of 1 mm or more and 3 mm or less from the surface, the surface scratches can be removed while keeping the grinding amount of the steel piece 2 low. Surface flaws can be removed efficiently.

The method for grinding a steel piece according to an embodiment of the present invention is a step of inspecting the surface of the steel piece 2 to identify a position having a surface defect before the step of grinding the corner portions 21, 22, 23, 24. (For example, step ST1 in FIG. 1) and a step of grinding the surface at a position where the surface of the steel piece 2 is identified as having a surface defect to remove the surface defect (for example, step ST2 and step ST3 in FIG. 1). And. According to this, in the steel piece 2, surface flaws can be efficiently removed even on the surfaces other than the corner portions 21, 22, 23, and 24.

The method for manufacturing steel bars according to the embodiment of the present invention includes the step of grinding the steel pieces described above and rolling the steel pieces 2 in which the corners 21, 22, 23, and 24 are ground to manufacture the steel bars 11. The process of rolling out is provided. According to this, since the surface flaws of the steel piece 2 are reduced, it is possible to reduce the occurrence of defects caused by the surface flaws in the steel bar 11 made of the steel piece 2.
The method for manufacturing the wire rod according to the embodiment of the present invention includes the step of performing the above-mentioned method for grinding the steel piece and rolling the steel piece 2 in which the corners 21, 22, 23, and 24 are ground to manufacture the wire rod 12. The process of rolling out is provided. According to this, since the surface flaws of the steel piece 2 are reduced, it is possible to reduce the occurrence of defects caused by the surface flaws in the wire rod 12 made of the steel piece 2.

1 Surface inspection device 2 Steel pieces 2A, 2B, 2C, 2D Corners 3 Conveyor rollers 4 Grinder 11 Steel bars 12 Wires 21, 22, 23, 24 Near the corners

Claims (5)

Before rolling a steel piece that is long in one direction and has a rectangular cross section cut in a plane orthogonal to the one direction, for each of the four sides of the rectangle, from the corner of the rectangle to one side of the rectangle. A method for grinding a steel piece, comprising a step of grinding a region including a range of 26% or more and 30% or less of the length of the side along the entire length of the steel piece. The method for grinding a piece of steel according to claim 1, wherein in the step of grinding the region, the surface of the region is ground to a depth of 1 mm or more and 3 mm or less. Prior to the step of grinding the area, the step of inspecting the surface of the steel piece to identify the position of the flaw and the step of identifying the flawed position.
The method for grinding a steel piece according to claim 2, further comprising a step of grinding a surface at a position where the steel piece is identified to have a flaw to remove the flaw. The step of performing the method for grinding a steel piece according to any one of claims 1 to 3 and
A method for manufacturing a steel bar, comprising a step of rolling a steel piece whose region has been ground to manufacture a steel bar. The step of performing the method for grinding a steel piece according to any one of claims 1 to 3 and
A method for manufacturing a wire rod, comprising a step of rolling a steel piece whose region has been ground to manufacture a wire rod.

Images