Method for producing bar steel

Abstract

To provide a high quality steel product.SOLUTION: A method for producing a steel bar includes a step A of charging a bloom including a pair of wide surfaces and a pair of narrow surfaces into a furnace in a posture in which each of the wide surfaces is in a vertical direction, a step B of heating the bloom in the furnace, a step C of subjecting the bloom to light reduction in a direction perpendicular to the narrow surfaces, a step D of subjecting the bloom to blooming to obtain a steel piece, and a step E of subjecting the steel piece to continuous rolling. The step C can include one or two or more passes. The rolling reduction in each pass is preferably 50mm or more and 30mm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present specification discloses a method for producing long steel bars. In particular, the present specification discloses a method for producing long steel bars, which includes a blooming process for blooming. [Background technology]

[0002] A steel section can be produced by subjecting a steel billet to continuous rolling. This steel billet can be produced by subjecting a bloom to blooming. An example of a method for producing a steel section is disclosed in JP 2009-285698 A. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-285698 A Summary of the Invention [Problem to be solved by the invention]

[0004] Blooming is a hot working process. Prior to blooming, the bloom is heated in a furnace. This heating causes oxygen in the furnace to react with the steel, which can lead to the formation of oxide scale on the bloom's surface. During the initial passes of blooming, the oxide scale is pressed down by the rolling mill. During these passes, defects due to the oxide scale can form on the bloom's surface. These defects impair the quality of the resulting long steel.

[0005] The applicant's intention is to provide a manufacturing method that allows high quality steel products to be obtained. [Means for solving the problem]

[0006] The method for producing long steel bars disclosed in the present specification includes: A: A process of charging a bloom including a pair of wide surfaces and a pair of narrow surfaces into a furnace with each wide surface oriented vertically; B: heating the bloom in the furnace; C: A step of lightly pressing the bloom in a direction perpendicular to the narrow surface; D: A process of subjecting the bloom to blooming to obtain a steel billet. and E: A process of subjecting the above steel billets to continuous rolling Includes.

[0007] Preferably, the step D comprises: D1: A step of applying pressure to the bloom in a direction perpendicular to the broad surface; and D2: A process of applying pressure in a direction perpendicular to the narrow surface using a roll having a caliber into which the narrow surface can fit. Includes.

[0008] The step C may include one or more passes. Preferably, the reduction amount in each pass is 50 mm or more and 30 mm or less.

[0009] The method for producing a steel slab disclosed in the present specification includes the steps of: A: A process of charging a bloom including a pair of wide surfaces and a pair of narrow surfaces into a furnace with each wide surface oriented vertically; B: heating the bloom in the furnace; C: A step of lightly pressing the bloom in a direction perpendicular to the narrow surface; and D: A process of subjecting the bloom to blooming. Includes. [Effects of the Invention]

[0010] This method for producing steel billets can produce billets with few surface defects, and high-quality steel products can be obtained from these billets. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a flowchart showing a method for manufacturing a steel slab according to one embodiment. [Figure 2] FIG. 2 is a perspective view showing a bloom subjected to the manufacturing method of FIG. [Figure 3] FIG. 3 is a cross-sectional view of the bloom of FIG. 2 taken along a direction perpendicular to the length thereof. [Figure 4] FIG. 4 is a front view showing multiple blooms being fed into the furnace. [Figure 5] FIG. 5 is a front view of the bloom of FIG. 2 shown together with the rolls of a blooming mill. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. [Figure 7] FIG. 7 is a front view of the bloom after soft reduction, shown together with the rolls of the blooming mill. [Figure 8] FIG. 8 is a front view of the bloom after reduction, shown together with the rolls of the blooming mill. [Figure 9] FIG. 9 is a front view of the bloom after rotation, shown together with the blooming mill rolls. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, preferred embodiments will be described in detail with reference to the drawings as appropriate.

[0013] A flowchart of a method for producing a steel slab is shown in Figure 1. In this production method, first, a bloom is prepared (STEP 1). This bloom can be obtained through steelmaking, refining, continuous casting, etc.

[0014] The bloom 2 is shown in Fig. 2. The arrow A1 in Fig. 2 indicates the length direction of the bloom 2. The bloom 2 has a pair of end faces 4.

[0015] As shown in FIG. 3, the cross-sectional shape of the bloom 2 along a direction perpendicular to the longitudinal direction A1 is generally rectangular. The bloom 2 has a pair of broad faces 6 and a pair of narrow faces 8. Each broad face 6 corresponds to a long side of the rectangular cross-section. Each narrow face 8 corresponds to a short side of the rectangle. In FIG. 3, arrow W1 represents the width of the broad face 6, and arrow W2 represents the width of the narrow face 8. Width W1 is greater than width W2. The area of ​​the broad face 6 is greater than the area of ​​the narrow face 8.

[0016] This bloom 2 is loaded into a batch furnace (STEP 2). FIG. 4 shows the bloom 2 in the furnace. FIG. 4 shows a first bloom 2a, a second bloom 2b, and a third bloom 2c. The first bloom 2a is placed on a platform 10. A narrow bottom surface 8ab of the first bloom 2a abuts against the platform 10. The second bloom 2b is placed on the first bloom 2a. A narrow top surface 8at of the first bloom 2a abuts against the second bloom 2b. A narrow bottom surface 8bb of the second bloom 2b abuts against the first bloom 2a. The third bloom 2c is placed on the second bloom 2b. A narrow top surface 8bt of the second bloom 2b abuts against the third bloom 2c. A narrow bottom surface 8cb of the third bloom 2c abuts against the second bloom 2b. The narrow top surface 8ct of the third bloom 2c is exposed to the furnace atmosphere. The wide surface 6 of each bloom 2 does not abut against the base 10 or against other blooms 2. This wide surface 6 is exposed to the furnace atmosphere.

[0017] In this embodiment, three blooms 2 are stacked in the furnace. The number of stacked blooms 2 may be two, or may be four or more.

[0018] This bloom 2 is heated in a furnace (STEP 3). This heating causes the temperature of the bloom 2 to rise. Because the broad surface 6 is exposed to the atmosphere, the bloom 2 comes into contact with the atmosphere over a wide area. Moreover, the distance from the broad surface 6 to the center of the bloom 2 is shorter than the distance from the narrow surface 8 to the center of the bloom 2. Therefore, the temperature of the bloom 2 rises in a relatively short time. Moreover, the temperature distribution in this bloom 2 is small.

[0019] The atmosphere in the furnace is air. When heated, the surface of the bloom 2 reacts with oxygen in the air. This reaction can cause scale to form on the bloom 2.

[0020] The narrow surface 8ab on the bottom side of the first broom 2a abuts against the base 10, so air is unlikely to enter between the base 10 and this narrow surface 8ab. The amount of scale generated on this narrow surface 8ab by heating (STEP 3) is small.

[0021] Since the narrow surface 8at on the top side of the first bloom 2a abuts against the second bloom 2b, air is unlikely to enter between the second bloom 2b and this narrow surface 8at. The amount of scale generated on this narrow surface 8at by heating (STEP 3) is small.

[0022] The narrow surface 8bb on the bottom side of the second bloom 2b abuts against the first bloom 2a, so air is unlikely to enter between the first bloom 2a and this narrow surface 8bb. The amount of scale generated on this narrow surface 8bb by heating (STEP 3) is small.

[0023] The narrow surface 8bt on the top side of the second bloom 2b abuts against the third bloom 2c, so air is unlikely to enter between the third bloom 2c and this narrow surface 8bt. The amount of scalding that occurs on this narrow surface 8bt due to heating (STEP 3) is minimal.

[0024] The narrow surface 8cb on the bottom side of the third bloom 2c abuts against the second bloom 2b, so air is unlikely to enter between the second bloom 2b and this narrow surface 8cb. The amount of scale generated on this narrow surface 8cb by heating (STEP 3) is small.

[0025] As mentioned above, the wide surface 6 is exposed to the atmosphere of the furnace. Air flows through the furnace. On the wide surface 6, the reaction between the steel and oxygen occurs continuously. Scale mainly forms on this wide surface 6.

[0026] After heating (STEP 3), the bloom 2 is removed from the furnace and transported to a blooming mill 12. This blooming mill 12 is shown in FIGS. 5 and 6. The blooming mill 12 has a pair of rolls 14. Each roll 14 has a plain section 16 and a plurality of calibers 18. In the plain section 16 of the blooming mill 12, the bloom 2 is subjected to hot soft reduction (STEP 4). The bloom 2 is subjected to soft reduction with the broad face 6 aligned vertically and the narrow face 8 aligned horizontally. In other words, the reduction direction during soft reduction is perpendicular to the narrow face 8 (the up-down direction in FIGS. 5 and 6). The bloom 2 progresses in the direction indicated by arrow A2 in FIG. 6.

[0027] This soft reduction (STEP 4) generates stress on the broad surface 6. This stress causes the broad surface 6 to distort slightly. Scale is brittle. Therefore, the distortion of the broad surface 6 causes scale to fall off from the bloom 2 on the broad surface 6. The scale that has formed on the narrow surface 8 is pressed by the roll 14. However, the pressure from the roll 14 to the bloom 2 during the soft reduction is small. Therefore, scratches caused by scale are unlikely to occur on the narrow surface 8.

[0028] Since the pressure applied to the bloom 2 by the light reduction (STEP 4) is small, the bloom 2 is unlikely to tilt or bend even though it is reduced at the plain portion 16 (in other words, the portion other than the caliber 18).

[0029] The soft reduction (STEP 4) may be performed in one pass, two passes, or three or more passes. Typically, the soft reduction (STEP 4) is achieved by one pass in which the bloom 2 goes back and forth through the gap between the rolls 14 (i.e., two passes).

[0030] This bloom 2 is then subjected to blooming. In blooming, the bloom 2 is first grasped and rotated by a manipulator or the like (STEP 5). The rotation angle is 90°. After this rotation, the bloom 2 is oriented such that the narrow faces 8 are aligned vertically and the broad faces 6 are aligned horizontally. As shown in FIG. 7, the bloom 2 in this orientation is reduced by the plain section 16 (STEP 6). The direction of this reduction is perpendicular to the broad faces 6. During this reduction, a large pressure is applied to the bloom 2. The bloom 2 after reduction is shown in FIG. 8. Because the scale on the broad faces 6 has been removed by the soft reduction (STEP 4), defects caused by the scale are unlikely to occur during the reduction (STEP 6).

[0031] This bloom 2 is grasped by a manipulator or the like and rotated (STEP 7). The angle of rotation is 90°. After this rotation, the bloom 2 has an orientation in which the wide face 6 is aligned vertically and the narrow face 8 is aligned horizontally. The bloom 2 in this orientation is fitted into a caliber 18, as shown in Figure 9. From a plurality of calibers 18, a caliber 18 having a width corresponding to the width of the narrow face 8 is selected. This caliber 18 presses down the bloom 2 (STEP 8). The direction of this pressing is perpendicular to the narrow face 8. During this pressing, a large pressure is applied to the bloom 2. Because the caliber 18 holds the bloom 2, tilting and bending of the bloom 2 are unlikely to occur during pressing.

[0032] Thereafter, rotation (STEP 5), rolling in the plain section 16 (STEP 6), rotation (STEP 7), and rolling in the caliber 18 (STEP 8) are repeated to obtain a slab of a predetermined size. This blooming process can produce a slab of a dense structure.

[0033] The billet is subjected to continuous rolling to obtain steel products, such as steel bars and steel plates, and steel wires.

[0034] In Figure 6, arrow H1 represents the height of bloom 2 before passing through the gap in roll 14, and arrow H2 represents the height of bloom 2 after passing through this gap. Height H1 is also the length of broad surface 6 before passing through the gap. Height H2 is also the length of broad surface 6 after passing through the gap.

[0035] The reduction amount (H1-H2) per pass in the soft reduction (STEP 4) is preferably 5 mm or more and 30 mm or less. A pass with a reduction amount (H1-H2) of 5 mm or more can sufficiently remove scale from the wide face 6. From this perspective, the reduction amount (H1-H2) is more preferably 10 mm or more. A pass with a reduction amount (H1-H2) of 30 mm or less can suppress defects on the narrow face 8. Furthermore, a pass with a reduction amount (H1-H2) of 30 mm or less can suppress inclination and curvature of the bloom 2. From these perspectives, the reduction amount (H1-H2) is more preferably 25 mm or less, and particularly preferably 20 mm or less.

[0036] The reduction rate Re per pass in the soft reduction (STEP 4) can be calculated by the following formula. Re = (H1 - H2) / H1 100 The rolling reduction Re is preferably 1.0% or more and 6.0% or less. A pass with a rolling reduction Re of 1.0% or more can sufficiently remove scale from the wide face 6. From this perspective, the rolling reduction Re is more preferably 1.5% or more. A pass with a rolling reduction Re of 6.0% or less can suppress defects on the narrow face 8. Furthermore, a pass with a rolling reduction Re of 6.0% or less can suppress inclination and curvature of the bloom 2. From these perspectives, the rolling reduction Re is more preferably 5.0% or less, and particularly preferably 4.0% or less. [Example]

[0037] The effects of the manufacturing method according to the examples will be clarified below, but the scope of the disclosure in this specification should not be construed as being limited based on the description of these examples.

[0038] [Example 1] The bloom shown in Figures 2 and 3 was prepared. The width W1 of the broad face of this bloom was 530 mm, and the width W2 of the narrow face was 380 mm. This bloom was heated in the manner shown in Figure 4. This bloom was soft reduced using the plain section of the roll shown in Figure 5. The direction of the soft reduction was perpendicular to the narrow face. This soft reduction was performed in two passes. The reduction amount in the first pass was 20 mm, and the reduction amount in the second pass was 10 mm. The total reduction amount was 30 mm. This bloom was then subjected to blooming to obtain a steel slab.

[0039] [Example 2-4] Steel slabs were obtained in the same manner as in Example 1, except that the total reduction in soft reduction was set as shown in Table 1 below.

[0040] [Comparative Example 1] A bloom was obtained in the same manner as in Example 1, except that the bloom was subjected to blooming without soft reduction.

[0041] [Tilt and Curve] The degree of inclination and curvature of the bloom under light pressure was visually observed and rated according to the following criteria: A: Very good B: Good C: Slightly poor D: Bad The results are shown in Table 1 below.

[0042] [Scale removal rate] The surface of the bloom after soft reduction was visually inspected and the scale removal rate was calculated, the results of which are shown in Table 1 below.

[0043] [Surface defects] The surface of the bloom after blooming was visually inspected and rated according to the following criteria. A: Very good B: Good C: Slightly poor D: Bad The results are shown in Table 1 below.

[0044] [Table 1]

[0045] As is clear from Table 1, the manufacturing methods of each example produce steel slabs with little scale. These evaluation results clearly show the superiority of this manufacturing method. [Industrial Applicability]

[0046] The method described above is suitable for the manufacture of a variety of steel products. [Explanation of symbols]

[0047] 2. Bloom 6. Wide surface 8. Narrow surface 12...Bulking mill 14 rolls 16 Plain section 18 caliber

Claims

1. A: A step of charging a bloom including a pair of wide surfaces and a pair of narrow surfaces into a furnace with each wide surface oriented vertically; B: Heating the bloom in the furnace; C: A step of lightly pressing the bloom in a direction perpendicular to the narrow surface; D: A step of subjecting the bloom to blooming to obtain a steel billet. and E: A step of subjecting the steel billet to continuous rolling A method for manufacturing long steel comprising the steps of:

2. The step D is D1: A step of applying pressure to the bloom in a direction perpendicular to the broad surface; and D2: A step of applying pressure in a direction perpendicular to the narrow surface using a roll having a caliber into which the narrow surface can fit. The method of claim 1 , comprising:

3. 3. The method according to claim 1, wherein the step C comprises one or more passes, and the rolling reduction in each pass is 50 mm or more and 30 mm or less.

4. A: A step of charging a bloom including a pair of wide surfaces and a pair of narrow surfaces into a furnace with each wide surface oriented vertically; B: Heating the bloom in the furnace; C: A step of lightly pressing the bloom in a direction perpendicular to the narrow surface; and D: A step of subjecting the bloom to blooming. A method for manufacturing steel billets, comprising:

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