JP2008246520A - Method of manufacturing steel bar or wire rod - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a steel bar or a wire rod by which the generation of surface flaws is prevented when manufacturing the steel bar or the wire rod by performing the tandem rolling of a square steel product having an approximately regular square cross-sectional shape and also line flaws are not generated on the surface even when forging the obtained steel bar or the wire rod. <P>SOLUTION: When manufacturing the steel bar or the wire rod by rough rolling the square steel product having an approximately regular square in the cross-sectional shape with a tandem mill in which stands the rolling directions of which are crossed orthogonally each other are alternately lined up and, after that, further by continuing rolling, before rough rolling, the distances between two pairs of opposite sides are respectively measured about the cross section of the above square steel product and, when the difference between their distances excess a predetermined value, it is better to perform the tandem rolling after grinding the surface of the square steel product so as to be less than the predetermined value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a bar steel or a wire rod by roughly rolling a square steel material having a substantially square cross-sectional shape using a tandem rolling mill and then continuing the rolling.

  Steel bars and wire rods are manufactured by roughly rolling a square steel bar having a substantially square cross-sectional shape using a tandem rolling mill and then continuing the rolling. For example, Patent Document 1 has already proposed that a round steel bar having a circular cross-sectional shape can be manufactured by rolling a square steel material having a substantially square cross-sectional shape with a tandem rolling mill. That is, first, a square steel material having a substantially square cross-sectional shape is manufactured, and whether or not surface flaws are generated in the square steel material is examined using, for example, a magnetic flaw detector. This is because surface flaws may occur in the process of manufacturing a square steel material (for example, ingot rolling). Square steel that has been confirmed to have no surface flaws is roughly rolled by a tandem rolling mill in which stands that are orthogonal to each other in the rolling direction are arranged, and then round bar steel is manufactured by performing intermediate rolling and finish rolling. it can. On the other hand, square steel materials with surface defects are discarded as scrap if the defects are severe, but if the defects are mild, the surface defects are removed by grinding the surface of the square steel material and then tandem. Roll. An intermediate process of producing a round bar steel by tandem rolling a square steel material in this way will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a state in which a square steel material is being tandem-rolled, and a state in which the square steel material 11 is being rolled by tandem rolling rolls 21 a to 21 c is illustrated from the end side of the square steel material 11. The figure when it sees is shown. The rolling rolls 21a to 21c are attached to a stand that constitutes a tandem rolling mill, and the rolling rolls 21a and 21c have a horizontal rolling direction such that the rolling direction is a vertical direction (vertical direction). It is arranged to be in the direction. Although FIG. 1 shows three rolling rolls 21a to 21c in the tandem rolling mill, the number of rolling rolls is not limited to this.

  Groove-shaped hole shapes (calibers) are provided on the entire circumference of the rolling rolls 21a to 21c, and in the rough rolling process, the rolling rolls 21a to 21c whose caliber has a diamond caliber are used (a) → ( b) → Roughly rolling the square steel material 11 from the vertical direction and the horizontal direction in the order of (c), so that the cross-sectional shape of the square steel material 11 is a rhombus flattened in a square → lateral direction → a rhombus flattened in a vertical direction → Repetitively deformed with a rhombus flattened in the horizontal direction (11a → 11b → 11c), and rough rolling yields a square steel material having a reduced cross-sectional area. Next, the square steel material having a reduced cross-sectional area is subjected to tandem rolling using a rolling roll provided with a square caliber or an oval caliber in the intermediate rolling process, so that the cross-sectional shape is deformed from a square shape to an oval shape, An oval steel material having a reduced cross-sectional area is obtained. And in the finish rolling process, by performing tandem rolling using a rolling roll provided with oval caliber or round caliber, the cross-sectional shape was repeatedly deformed from oval → round → oval → round, and the cross-sectional area was reduced. Round steel bar can be manufactured.

  However, in the round bar steel obtained by tandem rolling, linear wrinkles may occur on the surface. Therefore, round steel bars obtained by tandem rolling are examined again for surface flaws, and only those found to have no surface flaws are shipped as products.

The product thus shipped is cut into a suitable length and then forged, for example, to be processed into a desired product. However, surface flaws were detected and no flaws were observed, and even for round bar steel shipped as a product, forging into a product shape, linear flaws sometimes occurred on the surface. The depth of the wrinkles sometimes reached a maximum of about 2.0 mm.
JP-A-60-240321

  The object of the present invention is to prevent the occurrence of surface flaws when producing a steel bar or wire by tandem rolling a square steel material having a substantially square cross-sectional shape. It is an object of the present invention to provide a method capable of producing a steel bar or a wire that does not generate a wrinkle.

  The method for producing a steel bar or wire according to the present invention that has solved the above-mentioned problems is to roughly roll a square steel material having a substantially square cross-sectional shape by a tandem rolling machine in which stands whose rolling directions are orthogonal to each other are alternately arranged. The method of manufacturing a steel bar or a wire rod by continuing further rolling after that, before rough rolling, measure the distance between two pairs of opposite sides of the cross section of the square steel material, and the difference between the distances is a predetermined value. In the case of exceeding, the gist is in that tandem rolling is performed after grinding the surface of the square steel material so that the difference in distance is not more than a predetermined value.

  Specifically, a step of producing a square steel material having a substantially square cross-sectional shape (Step 1), a step of performing surface flaw detection on the square steel material (Step 2), and a surface flaw found in Step 2 are used as a square steel material. A step of removing the surface by grinding (step 3), and a step of measuring the distance between two pairs of opposite sides of the section of the square steel material after the step 3 and calculating a difference between the distances (step 4). When the difference in distance exceeds a predetermined value, the step of grinding the square steel surface so that the difference in distance is equal to or less than the predetermined value (step 5), the difference in distance is equal to or less than the predetermined value. What is necessary is just to operate including the process (process 6) of carrying out the tandem rolling of a square steel material.

  According to the present invention, before roughly rolling a square steel material having a substantially square cross section with a tandem rolling mill, it is checked whether or not the cross sectional shape of the square steel material is an appropriate shape, and the corner that is not in a predetermined shape. Since the steel material is roughly rolled after the surface is ground so as to have a predetermined shape, the bar steel or wire obtained by performing intermediate rolling and finish rolling after the rough rolling has creases. In addition, it is possible to manufacture a bar or wire that does not generate linear wrinkles on the surface even if this bar or wire is forged. In the following description, among the steel bars or wire rods, description will be made mainly on round steel bars, but the present invention is not limited to round steel bars.

  The present inventors have used this round bar steel even though no surface flaws were observed when a round bar steel (product) obtained by tandem rolling a square steel material having a substantially square cross section was detected. The cause of flaws during forging was studied repeatedly. As a result, since the square steel material is not properly held by the rolling roll, the corner portion of the square steel material is expanded by the rolling roll, and the expanded portion (ear) comes into contact with the next rolling roll so that the square steel material is It was found that the phenomenon of folding into the side occurred. When a part of the steel material is folded in this way and rolling proceeds in this state, the folded part (ears) are brought into close contact with the steel material, so that the round bar steel finally obtained is subjected to surface flaw detection. However, it is thought that surface defects cannot be found. The phenomenon in which the corner portion of the square steel material is stretched, the stretched portion is held in this state in the rolling roll, is folded into the square steel material main body side, and is integrated with the square steel material is hereinafter referred to as steel return.

  A state when steel return occurs will be described with reference to the drawings. FIG. 2 is a diagram schematically showing a state in which steel return occurs. Parts corresponding to those in FIG. 1 are given the same reference numerals.

  The square steel material rolled in the vertical direction in the step (a) is rolled in the horizontal direction in the step (b). At this time, the corner portion (end portion) of the square steel material 11b is extended, and this extended portion 13 is expanded. Is folded to the square steel material 11c side in the step (c), and is wound up as shown by the line 14. When rolling proceeds in this state, the folded portion (ear) 14 becomes an integrated outer wall surface of the square steel material.

  Even if steel return occurs in this way, since the folded portion usually becomes a linear flaw, the surface of the round bar steel obtained by intermediate rolling and finish rolling a square steel material obtained by rough rolling When flaw detection is performed, linear wrinkles are recognized and it is found that steel return has occurred. For this reason, round steel bars with linear wrinkles are discarded as scrap.

  However, even if steel return occurs during rough rolling, if the stretched part is folded into the outer wall of the steel material and integrated with the steel material, the surface of the round bar steel obtained by finish rolling has linear wrinkles. There are times when it is not allowed. That is, if the front edge of the wrinkle is narrow and bends diagonally along the outer wall surface, the wrinkle signal level is lowered even if surface flaw detection is performed, and it is considered that it is not detected. For this reason, round steel bars in which no linear wrinkles are observed on the surface are sometimes shipped as products despite the occurrence of steel return. However, when this product is forged, the folded portion is released and linear wrinkles are generated.

  Therefore, the present inventors have repeatedly studied in order to prevent the occurrence of steel turning when the square steel material is roughly rolled with a tandem rolling mill. As a result, it is checked whether or not the cross-sectional shape of the square steel material is appropriate before rough rolling with a tandem rolling mill, and the square steel material that is not in the predetermined shape is ground to adjust it to the predetermined shape. The present invention was completed by finding that steel rolling can be prevented from occurring during rough rolling if rolling is performed thereafter. Hereafter, the characteristic part of this invention is demonstrated, explaining the process which came to complete this invention.

  The inventors pay attention to the cross-sectional shape of the square steel material used for rolling, prepare a steel material having a substantially square cross-sectional shape with respect to the longitudinal direction, change the cross-sectional shape, and then perform tandem rolling. An experiment was conducted to determine whether steel return occurred. The prepared square steel material is a square steel material having a substantially square cross-sectional shape. A schematic diagram of the cross section of this square steel material is shown in FIG. As shown in FIG. 3, each side of the square steel material is A to D, and each corner portion is a to d.

  First, it is thought that the cause of the steel return is the shape of the corner portion of the square steel material, and the corner portions a to d are ground as shown by dotted lines in FIG. The test material was roughly rolled with a tandem rolling mill. Two types of test materials were prepared, among which sample material 1 was prepared by grinding the corner portion of a square steel material to 15C, and sample material 2 was prepared by grinding to 25C. In addition, the cross section of the square steel material was a square of 155.2 mm × 155.0 mm. As shown in FIG. 4, 15C means a state in which one side is ground 15 mm from the corner when the corner portion is ground. Similarly, 25C means a state where one side is ground 25 mm from the corner.

  Next, the corner portion of the square steel material was ground, and the two surfaces of the square steel material were ground to produce two types of test materials, which were each subjected to rough rolling. Of these, the test material 3 was prepared by grinding a square steel material having a cross section of 154.7 mm × 154.4 mm to a corner portion of 15 C in the same manner as the test material 1, and then a pair of opposite sides (the side B in FIG. 3). Grinding was performed so that the distance of side D) was 151.3 mm. On the other hand, the specimen 4 was prepared by grinding a square steel material having a cross section of 154.8 mm × 155.3 mm to a corner portion of 25 C in the same manner as the specimen 2 above, and then a pair of opposite sides (the sides shown in FIG. 3). Grinding was performed so that the distance between B and side D) was 148.4 mm.

  If the distance between side A and side C is x, and the distance between side B and side D is y, the difference in distance between the two pairs of opposite sides (xy) is 3.5 mm for specimen 3 and the specimen. 4 was 6.2 mm.

  Next, while grinding the corner part of a square steel material, 2 types of test materials which made the cross-sectional area small by grinding 4 surfaces of a square steel material were each rough-rolled. Of these, the test material 5 was prepared by grinding a square steel material having a cross section of 154.7 mm × 154.2 mm into a corner portion of 15 C in the same manner as the test material 1, and then all sides (side A to side D in FIG. 3). ). That is, grinding was performed so that the distance between side A and side C was 152.7 mm, and the distance between side B and side D was 151.9 mm. On the other hand, the test material 6 was prepared by grinding a square steel material having a cross section of 154.9 mm × 154.4 mm to a corner portion of 25 C in the same manner as the test material 2 and then all sides (side A to side D in FIG. 3). ). That is, grinding was performed so that the distance between side A and side C was 151.8 mm, and the distance between side B and side D was 151.1 mm.

  When the distance between side A and side C is x, and the distance between side B and side D is y, the difference in distance between two pairs (xy) is 0.8 mm for specimen 5, 6 was 0.7 mm.

  As a comparison object, the same experiment was performed when the corner portion was not ground. That is, the prepared square steel material (test material 7) was roughly rolled as it was with a tandem rolling mill. The cross section of the steel material was a 155.0 mm × 155.0 mm square.

  Next, two types of test materials were prepared by grinding two surfaces of the square steel material, and each was roughly rolled. Among them, the specimen 8 was a square steel material having a cross section of 155.8 mm × 152.1 mm, which was ground so that the distance between one pair of opposite sides (side A and side C in FIG. 3) was 155.5 mm. On the other hand, the test material 9 was a square steel material having a cross section of 155.2 mm × 154.8 mm and was ground so that the distance between one pair of opposite sides (side B and side D shown in FIG. 3) was 149.5 mm. .

  When the distance between side A and side C is x, and the distance between side B and side D is y, the difference in distance between the two pairs of opposite sides (xy) is 3.4 mm for specimen 8 and the specimen. 9 was 5.7 mm.

  Next, a sample material having a reduced cross-sectional area was prepared by grinding four surfaces of a square steel material, and rough rolling was performed. The specimen 10 was prepared by grinding a square steel material having a cross section of 155.3 mm × 154.9 mm on all sides (side A to side D in FIG. 3). That is, grinding was performed so that the distance between side A and side C was 152.6 mm, and the distance between side B and side D was 151.0 mm. When the distance between the side A and the side C is x and the distance between the side B and the side D is y, the difference in distance between the two pairs of opposite sides (xy) was 1.6 mm for the test material 10.

  For each specimen, the length of each side of the square steel material before surface grinding, the difference in the distance between two sets of opposite sides, the amount of grinding of the corner part after surface grinding, the length of each side of the square steel material, The difference in distance between opposite sides is shown in Table 1 below. The presence or absence of steel return during rough rolling is also shown in Table 1 below.

  From Table 1, it can be considered as follows. As is clear from the test materials 1 and 2 and the test material 7, even when the corner portion of the square steel material was ground, no steel return occurred during rough rolling. Therefore, it is understood that the cause of the steel return is not in the shape of the corner portion. As shown in the test materials 5 to 6 and the test material 10, even when the entire cross-section of the square steel material was ground to reduce the cross-sectional area, no steel return occurred during rough rolling.

  On the other hand, when one set of opposite sides is ground with respect to the cross section of the square steel material as in the specimen 3 and the specimen 8, the distance difference (xy) between the two sets of opposite sides is 3.5 mm (provided) In the case of Sample 3) or 3.4 mm (Sample 8), no steel return occurred during rough rolling.

  On the other hand, even when one set of opposite sides is ground with respect to the cross section of the square steel material like the sample material 4 and the sample material 9, there is a difference in distance (xy) between the two sets of opposite sides. It was found that steel return occurs during rough rolling when the thickness is 6.2 mm (sample 4) or 5.7 mm (sample 9).

  From the above experimental results, it is considered that the cause of the steel return is not the shape of the corner portion of the square steel material or the cross-sectional area of the square steel material, but the difference in the distance between the two pairs of opposite sides. The reason why the cross-sectional shape of the square steel material used for tandem rolling has an influence on the occurrence of steel return is thought to be because the following phenomenon occurs during tandem rolling. That is, like the test material 4 and the test material 9, the cross-sectional shape of the square steel material just before rough rolling becomes a rectangle by surface grinding performed to remove surface defects, and the distance between two sets of opposite sides ( When xy) becomes large, a surface that is not held by the rolling roll comes out of the outer wall surface of the square steel material, and it is considered that the square steel material rotates as rolling progresses. This will be described with reference to FIGS.

  The square steel material 12 indicated by the dotted line in the step (b) of FIG. 1 indicates the position of the square steel material immediately before being rolled by the rolling roll 21b, and the square steel material 14 indicated by the dotted line in the step (b) of FIG. Indicates the position of the square steel material immediately before being rolled by the rolling roll 21b. When a square steel material having a small difference (xy) between two sets of opposite side distances and a substantially positive cross section is tandem-rolled, as shown in step (a) of FIG. 1, the entire surface of the square steel material 11a is applied to the rolling roll 21a. Since it is held, the square steel material 11a does not rotate until the square steel material 11a reaches the next rolling roll 21b. Therefore, when the square steel material 12 is rolled by the rolling roll 21b, the four surfaces of the square steel material 12 are rolled while being held by the rolling roll 21b.

  On the other hand, when the square steel material having a large difference (xy) between the two sets of opposite sides and having a rectangular cross section is tandem-rolled, as shown in step (a) in FIG. It is not uniformly held, and a held surface and a non-held surface are generated. Therefore, the square steel material 11a is in an unstable state and rotates before reaching the next rolling roll 21b, and the rolled steel bar 14 is forcibly rolled in the rolling roll 21b. Therefore, when the corner portion of the square steel material 11b is stretched and supplied to the next rolling roll 21c in this state, the stretched corner portion 13 is folded.

  As mentioned above, when manufacturing round bar steel from a square steel material using a tandem rolling mill, the distance of two sets of opposite sides is measured about the section of the square steel material supplied to a tandem rolling mill, and the difference of those distances ( When xy) exceeds a predetermined value, it is considered that the occurrence of steel return can be prevented by performing tandem rolling after grinding the surface of the square steel material so that the difference in distance is equal to or less than the predetermined value. . In addition, although demonstrated above centering on the process which manufactures a round bar steel from a square steel material, the form manufactured as a product by this invention is not limited to a round bar steel, A square bar steel may be sufficient, and a hexagonal steel Etc. Moreover, it is not limited to a steel bar but may be a wire rod.

  The predetermined value is a value determined in advance according to the tandem rolling mill, and can be determined by analyzing rolling data, for example. That is, after calculating the difference between the distances between the two sets of opposite sides of the cross section of the square steel material before tandem rolling, the steel bar is produced by tandem rolling. The obtained bar steel or wire is subjected to surface flaw detection, the bar steel or wire without surface flaw is forged, and the difference in the distance when no surface flaw occurs even after forging is determined by tandem rolling. What is necessary is just to set it as the predetermined value in a machine.

  Whether or not steel return has occurred during tandem rolling may be confirmed by providing a current fluctuation meter in a motor provided in the rolling roll and measuring fluctuations in current. When the steel return does not occur, the corner portion of the square steel material is expanded and no folding occurs, so that the cross-sectional shape of the square steel material does not change extremely. Therefore, the electric current supplied to the motor provided in the rolling roll becomes substantially constant, for example, maintains about 800A. However, when steel return occurs, the cross-sectional shape of the square steel material changes extremely, and the surface is uneven, so that a load is applied to the rolling roll, and the current supplied to the motor provided in the rolling roll fluctuates. At this time, the current increases to, for example, about 1260A. Therefore, when an increase in current occurs with respect to the steady state, it can be confirmed that steel return has occurred.

  When the distance between two pairs of opposite sides of the section of the square steel material supplied to the tandem rolling mill is measured, the difference between the distances (xy) exceeds the predetermined value. When investigating whether or not surface flaws occur in the steel material, if the flaws are mild among the square steel materials with surface flaws, the surface of the square steel material is ground to remove the surface flaws. Is considered to be at a point that becomes a rectangle.

  Therefore, when removing surface defects, specifically, by operating according to the following procedure, it is possible to produce a steel bar or wire that has no surface defects and does not generate surface defects even when hot rolled. That is, a square steel material having a substantially square cross section is manufactured (step 1), surface flaw detection is performed on the obtained square steel material (step 2), and when surface flaws are found in step 2, The wrinkles are removed by grinding the surface of the square steel material (step 3). And in this invention, after the said process 3, the distance of two sets of opposite sides is each measured about the cross section of a square steel material, the difference of those distances is calculated (process 4), and the difference of the said distance exceeds predetermined value First, the surface of the square steel material is ground so that the difference in distance is not more than a predetermined value (step 5). Next, in Step 6, a desired steel bar or wire can be manufactured by tandem rolling a square steel material in which the difference in distance is equal to or less than a predetermined value. Hereinafter, each step will be described in detail.

[Step 1]
In step 1, a square steel material having a substantially square cross-sectional shape is manufactured. The manufacturing method of this square steel material is not particularly limited, and means a billet or the like obtained by continuous casting or ingot rolling according to a conventional method. The square steel material (billet) may have a substantially square cross-sectional shape in the vertical direction with respect to the longitudinal direction, and the length of one side of the steel material may be about 100 to 250 mm. The term “substantially square” means that the difference between the lengths of the sides perpendicular to the cross section of the square steel material is within about 4% of the length of the longer side.

[Step 2]
In step 2, according to a conventional method, the surface flaw detection of the square steel material obtained in the above step 1 is performed to inspect whether flaws are generated on the surface of the square steel material. The surface flaw detection may be performed by, for example, a magnetic particle inspection method.

  When surface flaw detection is performed, internal flaw detection is usually performed. For the internal flaw detection, for example, ultrasonic flaw detection may be performed. If internal flaws are found after internal flaw detection, they are discarded as scrap.

  If surface flaw detection is performed and no surface flaws are observed, and internal flaw detection is not performed and internal flaws are not found, tandem rolling may be performed as it is (step 6 described later).

  On the other hand, internal flaws cannot be found even if internal flaw detection is performed, but if surface flaws are detected and surface flaws are observed, if this surface flaw is large and deep and cannot be removed by surface grinding, Discard the square steel as scrap. However, when the surface flaw is small and the depth is shallow, the surface flaw is usually removed by surface grinding (step 3).

[Step 3]
As described above, when a surface defect is found in step 2 and the surface defect is small and the depth is shallow, in step 3, the surface of the square steel material is ground to remove the surface defect. At this time, if the surface flaws are small, the portion of the wrinkles may be locally chipped and removed, but if there are many surface flaws, usually all the surface flaws are included in the surface where the surface flaws are recognized. Thus, the whole surface is ground with a grinder in the width direction of the square steel material. However, when this entire surface grinding is performed, the section of the square steel material is deformed into a rectangle.

  Therefore, in the present invention, after removing surface flaws in Step 3, as Step 4, the distances between two sets of opposite sides are measured for the cross section of the square steel material, and in the following Step 5, the difference between the distances becomes a predetermined value. When exceeding, the surface of the square steel material is ground so that the difference in distance is not more than a predetermined value, and then tandem rolling is performed.

[Step 4]
In step 4, the distance between two sets of opposite sides is measured for the cross section of the square steel material, and the difference between the distances is calculated. The distance between the two pairs of opposite sides means the distance x between the sides A and C in FIG. 3 and the distance y between the sides B and D, and the difference between the distances means xy.

  The position for measuring the distance between the two sets of opposite sides may be near the tip of the square steel material or near the end of the square steel material. The vicinity of the tip and the end of the square steel material is not held by the rolling roll until it passes through the nth rolling roll and reaches the next n + 1th rolling roll, and is in a free state. It is because it is easy to rotate and easily generates steel return.

  Here, the vicinity of the front end and the vicinity of the end mean a region corresponding to a distance between stands provided for rough rolling in the tandem rolling mill. That is, for the stands provided for rough rolling, the distance between adjacent stands is measured, and the maximum distance among these distances is determined. If the position corresponding to the determined distance is measured from the tip or end of the square steel material, and the distance from the tip or end to the determined position is measured by measuring the distance between two pairs of opposite sides of the cross section of the square steel material Good.

  In the above step 3, when surface grinding is performed on a plurality of locations of a square steel material, and there are a plurality of locations where the surface grinding is performed near the front end or the end of the square steel material, two sets of opposite sides What is necessary is just to judge based on the value of the difference in the position where the difference of distance becomes the maximum.

  It should be noted that the time for measuring the distance between the two pairs of opposite sides of the cross section of the square steel material is after the end of the surface grinding and until the square steel material is charged in the heating furnace and heated.

[Step 5]
In step 5, based on the distance difference (xy) calculated in step 4 above, when the distance difference exceeds a predetermined value, the square steel material surface is set so that the distance difference is equal to or less than the predetermined value. Grind. When the difference in distance is not more than a predetermined value, tandem rolling may be performed after heating without performing surface grinding.

[Step 6]
In step 6, the square steel material in which the difference in distance is equal to or less than a predetermined value in step 5 is rough-rolled with a tandem rolling mill.

  The tandem rolling mill is a rolling mill in which stands whose rolling directions are orthogonal to each other are alternately arranged, and the stands are provided with rolling rolls so that the rolling direction is a vertical direction or a horizontal direction.

  The conditions for rough rolling are not particularly limited, and for example, rolling may be performed according to a diamond square pass schedule. In other words, the rolling roll is provided with a rhombus caliber, and the cross-sectional shape of the square steel material is reduced by repeatedly deforming the cross-sectional shape of the square steel material from square → rhombus flattened in the horizontal direction → rhombus flattened in the vertical direction → rhombus flattened in the horizontal direction. What is necessary is just to roll.

  After rough rolling, steel bars and wire rods can be manufactured by performing intermediate rolling and finish rolling. The conditions for intermediate rolling and finish rolling are not particularly limited, and may be performed according to a conventional method.

  The steel bars and wires of the present invention obtained through the above steps 1 to 6 are free of surface flaws during tandem rolling, so that surface flaws do not occur, and even if this steel bar or wire is forged, the surface No wrinkles occur.

  The cross-sectional shape of the steel bar or wire obtained in the present invention is not particularly limited, and may be round, square, or hexagonal.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.

[Preliminary experiment]
A square steel material having a cross-sectional shape of approximately square (about 155 mm × about 155 mm) was manufactured, and the surface of the square steel material was ground to change the difference between two pairs of opposite side distances in various ways, followed by tandem rolling. At this time, the motor provided in the rolling roll was provided with a current fluctuation measuring device, and the occurrence of steel return was examined by monitoring fluctuations in the current supplied to the motor. Next, the round bar steel (φ32.0 mm) obtained without steel return was hot forged to examine whether surface defects occurred.

  As a result, in order to produce a round bar steel that does not generate steel return during tandem rolling and does not generate surface defects when the obtained round bar steel is forged, two sets of square steel cross sections before tandem rolling are produced. It has been found that the difference in the distance between the opposite sides may be adjusted to 3.5 mm or less. This 3.5 mm is set as a predetermined value of the tandem rolling mill used in this example.

  In addition, about the stand provided for rough rolling among tandem rolling mills, when the distance between adjacent stands was measured, the maximum distance was 2.5 m.

[Comparative Example 1]
As a square steel material, a square steel material having a cross section of 153.1 mm × 156.7 mm and a difference in distance between two pairs of opposite sides of 3.6 mm was manufactured (step 1).

  The obtained square steel was subjected to surface flaw detection (Step 2). At this time, internal flaw detection was also performed. For surface flaw detection, magnetic flaw detection was automatically performed, and a portion where surface flaws occurred was visually confirmed and marked automatically or manually.

  For internal flaw detection, ultrasonic flaw detection was performed to check whether there was any abnormality inside the square steel. Those found with internal dredging were discarded as scrap.

  In Comparative Example 1, as a result of surface flaw detection and internal flaw detection, neither surface flaws nor internal flaws were observed.

  Since neither surface flaws nor internal flaws were observed, rough rolling was performed with a tandem rolling mill as it was, and then intermediate rolling and finish rolling were performed to produce round steel bars (φ32.0 mm) (Step 6).

  Of the tandem rolling mill, a motor provided on a rolling roll for rough rolling was provided with a current fluctuation measuring device, and the occurrence of steel return was examined by monitoring fluctuations in the current supplied to the motor. As a result, steel return occurred. When the surface of the obtained round steel bar was observed, linear wrinkles were observed.

[Comparative Example 2]
As a square steel material, a square steel material having a cross section of 153.4 mm × 156.7 mm and a difference in distance between two sets of opposite sides of 3.3 mm was manufactured (step 1).

  About the obtained square steel material, surface flaw detection was performed similarly to the said comparative example 1 (process 2). At this time, as in Comparative Example 1, internal flaw detection was also performed. As a result of internal flaw detection, internal flaws were not recognized, but as a result of surface flaw detection, a plurality of surface flaws were observed on the square steel material surface at a position near 1 m from the tip of the square steel material. Surface grind was performed by grinding the entire surface in the width direction of the square steel material so as to include all the recognized surface defects (Step 3).

  After surface grinding to remove surface defects, surface flaw detection was performed again. As a result, it was confirmed that the surface defects were completely removed.

  Next, for the cross section of the square steel material after removing the surface flaws, the distance between the two opposite sides was measured and the difference between the opposite sides was calculated to be over 3.5 mm. Rough rolling was performed with a machine, and then intermediate rolling and finish rolling were performed to produce a round steel bar (φ32.0 mm) (step 6). During rough rolling, steel turning occurred. Surface flaws were observed on the surface of the obtained round bar steel.

[Invention Example]
As a square steel material, a square steel material having a cross section of 152.1 mm × 155.8 mm and a difference in distance between two pairs of opposite sides of 3.7 mm was manufactured (step 1).

  About the obtained square steel material, surface flaw detection was performed similarly to the said comparative example 1 (process 2). At this time, as in Comparative Example 1, internal flaw detection was also performed. As a result of internal flaw detection, internal flaws were not recognized, but as a result of surface flaw detection, a plurality of surface flaws were found on the square steel surface at a position near 2 m from the tip of the square steel material. Surface grind was performed by grinding the entire surface in the width direction of the square steel material so as to include all the recognized surface defects (Step 3).

  After surface grinding to remove surface defects, surface flaw detection was performed again. As a result, it was confirmed that the surface defects were completely removed.

  Next, when the distance between two pairs of opposite sides was measured for the cross section of the square steel material after removing the surface flaws, it was 152.1 mm and 155.7 mm, and the difference in the distance between opposite sides was 3.6 mm.

  Then, the surface perpendicular | vertical with respect to the surface ground at the said process 3 was grinded and grind | polished so that the difference of the distance of an opposite side may be below a predetermined value (3.5 mm or less) (process 5).

  After grinding the surface in step 5, when measuring the distance between two pairs of opposite sides of the cross section of the square steel material, they were 152.1 mm and 155.5 mm, and the difference in the distance between opposite sides was 3.4 mm.

  The square steel with the difference in the distance between the opposite sides was subjected to rough rolling with a tandem rolling mill, and then subjected to intermediate rolling and finish rolling to produce round bar steel (φ32.0 mm) (step 6). During rough rolling, no steel return occurred. Even when the obtained round bar steel was hot forged, no surface flaws were observed.

  The above results are summarized in Table 2 below.

Drawing 1 is a mimetic diagram showing a situation when corner steel material is tandem-rolled, and has shown that steel return has not occurred. FIG. 2 is a schematic diagram showing a state in which a square steel material is tandem-rolled, and shows that steel turning has occurred. FIG. 3 is a diagram schematically showing a cross section of a square steel material. FIG. 4 is an enlarged view of the corner portion of the square steel material, and is a schematic diagram illustrating a state when the corner portion of the square steel material is ground.

Claims (2)

A method of roughly manufacturing a square steel material having a substantially square cross-sectional shape by a tandem rolling machine in which stands whose rolling directions are orthogonal to each other are alternately arranged, and then continuing further rolling to produce a bar steel or a wire,
Before rough rolling, the distance between two pairs of opposite sides is measured for the cross section of the square steel material, and when the difference between the distances exceeds a predetermined value, the square steel material is set so that the difference in distance is not more than the predetermined value. A method for producing a steel bar or wire, characterized by grinding the surface of the steel and then tandem rolling. A method of roughly manufacturing a square steel material having a substantially square cross-sectional shape by a tandem rolling machine in which stands whose rolling directions are orthogonal to each other are alternately arranged, and then continuing further rolling to produce a bar steel or a wire,
A step of manufacturing a square steel material having a substantially square cross section (Step 1), a step of performing surface flaw detection on the square steel material (Step 2), and grinding the surface of the square steel material with the surface flaw found in Step 2 above. Step (step 3) to be removed by the step, after the step 3, for the cross section of the square steel material, measuring the distance between two pairs of opposite sides, respectively, calculating the difference between these distances (step 4), the difference in the distance Is greater than a predetermined value, the step of grinding the surface of the square steel material such that the difference in distance is less than or equal to the predetermined value (step 5), and the square steel material in which the difference in distance is less than or equal to the predetermined value is tandem rolled. The manufacturing method of the steel bar or wire characterized by including the process (process 6) to perform.